Atmospheric river

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https://en.wikipedia.org/wiki/Atmospheric_river

An explanation from the National Weather Service on atmospheric rivers

An atmospheric river (AR) is a narrow corridor or filament of concentrated moisture in the atmosphere. Other names for this phenomenon are tropical plume, tropical connection, moisture plume, water vapor surge, and cloud band.

Composite satellite photos of an atmospheric river connecting Asia to North America in October 2017

Atmospheric rivers consist of narrow bands of enhanced water vapor transport, typically along the boundaries between large areas of divergent surface air flow, including some frontal zones in association with extratropical cyclones that form over the oceans. Pineapple Express storms are the most commonly represented and recognized type of atmospheric rivers; the name is due to the warm water vapor plumes originating over the Hawaiian tropics that follow various paths towards western North America, arriving at latitudes from California and the Pacific Northwest to British Columbia and even southeast Alaska.

In some parts of the world, changes in atmospheric humidity and heat caused by climate change are expected to increase the intensity and frequency of extreme weather and flood events caused by atmospheric rivers. This is expected to be especially prominent in the Western United States and Canada.

Description

Layered precipitable water imagery of particularly strong atmospheric rivers on 5 December 2015. The first, caused by Storm Desmond, stretched from the Caribbean to the United Kingdom; the second originated from the Philippines and crossing the Pacific Ocean extended to the west coast of North America.

The term was originally coined by researchers Reginald Newell and Yong Zhu of the Massachusetts Institute of Technology in the early 1990s to reflect the narrowness of the moisture plumes involved. Atmospheric rivers are typically several thousand kilometers long and only a few hundred kilometers wide, and a single one can carry a greater flux of water than Earth's largest river, the Amazon River. There are typically 3–5 of these narrow plumes present within a hemisphere at any given time. These have been increasing in intensity slightly over the past century.

In the current research field of atmospheric rivers, the length and width factors described above in conjunction with an integrated water vapor depth greater than 2.0 cm are used as standards to categorize atmospheric river events.

A January 2019 article in Geophysical Research Letters described them as "long, meandering plumes of water vapor often originating over the tropical oceans that bring sustained, heavy precipitation to the west coasts of North America and northern Europe."

As data modeling techniques progress, integrated water vapor transport (IVT) is becoming a more common data type used to interpret atmospheric rivers. Its strength lies in its ability to show the transportation of water vapor over multiple time steps instead of a stagnant measurement of water vapor depth in a specific air column (integrated water vapor – IWV). In addition, IVT is more directly attributed to orographic precipitation, a key factor in the production of intense rainfall and subsequent flooding.

Scale

Cat	Strength	Impact	Max. IVT	Duration
1	Weak	Primarily beneficial	≥500–750	<24 hours
			≥250–500	24–48 hours
2	Moderate	Mostly beneficial, also hazardous	≥750–1000	<24 hours
			≥500–750	24–48 hours
			≥250–500	>48 hours
3	Strong	Balance of beneficial and hazardous	≥1000–1250	<24 hours
			≥750–1000	24–48 hours
			≥500–750	>48 hours
4	Extreme	Mostly hazardous, also beneficial	≥1250	<24 hours
			≥1000–1250	24-48 hours
			≥750–1000	>48 hours
5	Exceptional	Primarily hazardous	≥1250	24–48 hours
			≥1000	>48 hours
Notes

Maximum vertically integrated water vapor transport, 3-hour average, units of ${\displaystyle \frac{kg}{m^2\cdot s}}$

The Center for Western Weather and Water Extremes (CW3E) at the Scripps Institution of Oceanography released a five-level scale in February 2019 to categorize atmospheric rivers, ranging from "weak" to "exceptional" in strength, or "beneficial" to "hazardous" in impact. The scale was developed by F. Martin Ralph, director of CW3E, who collaborated with Jonathan Rutz from the National Weather Service and other experts. The scale considers both the amount of water vapor transported and the duration of the event. Atmospheric rivers receive a preliminary rank according to the 3-hour average maximum vertically integrated water vapor transport. Those lasting less than 24 hours are demoted by one rank, while those lasting longer than 48 hours are increased by one rank.

Examples of different atmospheric river categories include the following historical storms:

1. February 2, 2017; lasted 24 hours
2. November 19–20, 2016; lasted 42 hours
3. October 14–15, 2016; lasted 36 hours and produced 5–10 inches of rainfall
4. January 8–9, 2017; lasted 36 hours and produced 14 inches of rainfall
5. December 29, 1996 – January 2, 1997; lasted 100 hours and caused >$1 billion in damage

Typically, the Oregon coast averages one Cat 4 atmospheric river (AR) each year; Washington state averages one Cat 4 AR every two years; the San Francisco Bay Area averages one Cat 4 AR every three years; and southern California, which typically experiences one Cat 2 or Cat 3 AR each year, averages one Cat 4 AR every ten years.

Usage: In practice, the AR scale can be used to refer to "conditions" without reference to the word "category", as in this excerpt from the CW3E Scripps Twitter feed: "Late-season atmospheric river to bring precipitation to the high elevations over northern California, western Oregon, and Washington this weekend, with AR 3 conditions forecast over southern Oregon."

Impacts

Atmospheric rivers have a central role in the global water cycle. On any given day, atmospheric rivers account for over 90% of the global meridional (north-south) water vapor transport, yet they cover less than 10% of any given extratropical line of latitude. Atmospheric rivers are also known to contribute to about 22% of total global runoff.

They are also the major cause of extreme precipitation events that cause severe flooding in many mid-latitude, westerly coastal regions of the world, including the west coast of North America, Western Europe, the west coast of North Africa, the Iberian Peninsula, Iran and New Zealand. Equally, the absence of atmospheric rivers has been linked with the occurrence of droughts in several parts of the world, including South Africa, Spain and Portugal.

United States

Water vapor imagery of the eastern Pacific Ocean from the GOES 11 satellite, showing a large atmospheric river aimed across California in December 2010. This particularly intense storm system produced as much as 26 in (660 mm) of precipitation in California and up to 17 ft (5.2 m) of snowfall in the Sierra Nevada during December 17–22, 2010.

The inconsistency of California's rainfall is due to the variability in strength and quantity of these storms, which can produce strenuous effects on California's water budget. The factors described above make California a perfect case study to show the importance of proper water management and prediction of these storms. The significance that atmospheric rivers have for the control of coastal water budgets juxtaposed against their creation of detrimental floods can be constructed and studied by looking at California and the surrounding coastal region of the western United States. In this region atmospheric rivers have contributed 30–50% of total annual rainfall according to a 2013 study. The Fourth National Climate Assessment (NCA) report, released by the U.S. Global Change Research Program (USGCRP) on November 23, 2018 confirmed that along the U.S. western coast, landfalling atmospheric rivers "account for 30%–40% of precipitation and snowpack. These landfalling atmospheric rivers "are associated with severe flooding events in California and other western states."

The USGCRP team of thirteen federal agencies—the DOA, DOC, DOD, DOE, HHS, DOI, DOS, DOT, EPA, NASA, NSF, Smithsonian Institution, and the USAID—with the assistance of "1,000 people, including 300 leading scientists, roughly half from outside the government" reported that, "As the world warms, the "landfalling atmospheric rivers on the West Coast are likely to increase" in "frequency and severity" because of "increasing evaporation and higher atmospheric water vapor levels in the atmosphere."

Based on the North American Regional Reanalysis (NARR) analyses, a team led by National Oceanic and Atmospheric Administration's (NOAA) Paul J. Neiman, concluded in 2011 that landfalling ARs were "responsible for nearly all the annual peak daily flow (APDF)s in western Washington" from 1998 through 2009.

According to a May 14, 2019 article in San Jose, California's The Mercury News, atmospheric rivers, "giant conveyor belts of water in the sky", cause the moisture-rich "Pineapple Express" storm systems that come from the Pacific Ocean several times annually and account for about 50 percent of California's annual precipitation University of California at San Diego's Center for Western Weather and Water Extremes's director Marty Ralph, who is one of the United States' experts on atmospheric river storms and has been active in AR research for many years, said that, atmospheric rivers are more common in winter. For example, from October 2018 to spring 2019, there were 47 atmospheric rivers, 12 of which were rated strong or extreme, in Washington, Oregon and California. The rare May 2019 atmospheric rivers, classified as Category 1 and Category 2, are beneficial in terms of preventing seasonal wildfires but the "swings between heavy rain and raging wildfires" are raising questions about moving from "understanding that the climate is changing to understanding what to do about it. Atmospheric rivers have caused an average of $1.1 billion in damage annually, much of it occurring in Sonoma County, California, according to a December 2019 study by the Scripps Institution on Oceanography at UC San Diego and the US Army Corps of Engineers, which analyzed data from the National Flood Insurance Program and the National Weather Service. Just twenty counties suffered almost 70% of the damage, the study found, and that one of the main factors in the scale of damage appeared to be the number of properties located in a flood plain. These counties were:

• Snohomish County, WA ($1.2 billion)
• King County, WA ($2 billion)
• Pierce County, WA ($900 million)
• Lewis County, WA ($3 billion)
• Cowlitz County WA ($500 million)
• Columbia County, OR ($700 million)
• Clackamas, County, OR ($900 million)
• Washoe County, NV ($1.3 billion)
• Placer County, CA ($800 million)
• Sacramento County, CA ($1.7 billion)
• Napa County, CA ($1.3 billion)
• Sonoma County, CA ($5.2 billion)
• Marin County, CA ($2.2 billion)
• Santa Clara County, CA ($1 billion)
• Monterey County, CA ($1.3 billion)
• Los Angeles County, CA ($2.7 billion)
• Riverside County, CA ($500 million)
• Orange County, CA ($800 million)
• San Diego County, CA ($800 million)
• Maricopa County, AZ ($600 million)

Canada

According to a January 22, 2019 article in Geophysical Research Letters, the Fraser River Basin (FRB), a "snow-dominated watershed" in British Columbia, is exposed to landfalling ARs, originating over the tropical Pacific Ocean that bring "sustained, heavy precipitation" throughout the winter months. The authors predict that based on their modelling "extreme rainfall events resulting from atmospheric rivers may lead to peak annual floods of historic proportions, and of unprecedented frequency, by the late 21st century in the Fraser River Basin."

In November 2021, massive flooding in the Fraser River Basin near Vancouver was attributed to a series of atmospheric rivers.

Iran

While a large body of research has shown the impacts of the atmospheric rivers on weather-related natural disasters over the western U.S. and Europe, little is known about their mechanisms and contribution to flooding in the Middle East. However, a rare atmospheric river was found responsible for the record floods of March 2019 in Iran that damaged one-third of the country's infrastructures and killed 76 people.

That AR was named Dena, after the peak of the Zagros Mountains, which played a crucial role in precipitation formation. AR Dena started its long, 9000 km journey from the Atlantic Ocean and travelled across North Africa before its final landfall over the Zagros Mountains. Specific synoptic weather conditions, including tropical-extratropical interactions of the atmospheric jets, and anomalously warm sea-surface temperatures in all surrounding basins provided the necessary ingredients for formation of this AR. Water transport by AR Dena was equivalent to more than 150 times the aggregated flow of the four major rivers in the region (Tigris, Euphrates, Karun and Karkheh).

The intense rains made the 2018-2019 rainy season the wettest in the past half century, a sharp contrast with the prior year, which was the driest over the same period. Thus, this event is a compelling example of rapid dry-to-wet transitions and intensification of extremes, potentially resulting from the climate change.

Australia

In Australia, northwest cloud bands are sometimes associated with atmospheric rivers that originate in the Indian Ocean and cause heavy rainfall in northwestern, central, and southeastern parts of the country. They are more frequent when temperatures in the eastern Indian Ocean near Australia are warmer than those in the western Indian Ocean (i.e. a negative Indian Ocean Dipole). Atmospheric rivers also form in the waters to the east and south of Australia and are most common during the warmer months.

Europe

According to an article in Geophysical Research Letters by Lavers and Villarini, 8 of the 10 highest daily precipitation records in the period 1979–2011 have been associated with atmospheric rivers events in areas of Britain, France and Norway.

Satellites and sensors

According to a 2011 Eos magazine article by 1998, the spatiotemporal coverage of water vapor data over oceans had vastly improved through the use of "microwave remote sensing from polar-orbiting satellites", such as the special sensor microwave/imager (SSM/I). This led to greatly increased attention to the "prevalence and role" of atmospheric rivers. Prior to the use of these satellites and sensors, scientists were mainly dependent on weather balloons and other related technologies that did not adequately cover oceans. SSM/I and similar technologies provide "frequent global measurements of integrated water vapor over the Earth's oceans."

Problem of mental causation

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Problem_of_mental_causation

The problem of mental causation is a conceptual issue in the philosophy of mind. That problem, in
short, is how to account for the common sense idea that intentional thoughts or intentional mental states are causes of intentional actions. The problem divides into several distinct sub-problems, including the problem of causal exclusion, the problem of anomalism, and the problem of externalism. However, the sub-problem which has attracted most attention in the philosophical literature is arguably the exclusion problem.

Description

The basic problem of mental causation is an intuitive one: on the face of it, it seems that mental events cause physical events (and vice versa), but how can mental events have any causal effect on physical events? Suppose that a person, John, orders dessert after dinner. It seems that at least one cause for such a physical, behavioral event is that John desired to have dessert and believed that by ordering dessert he would be able to soon have dessert. But, how can such mental events as beliefs and desires cause John's mouth to move in such a way that he orders dessert?

Sub-problems of mental causation

Exclusion problem

What follows is a summary of the causal exclusion problem in its simplest form, and it is merely one of several possible formulations.

To the extent that we do not have to go outside human physiology in order to trace the causal antecedents of any bodily movement, intentional action can be fully causally explained by the existence of these physiological antecedents alone. No mention of mental states need enter into the explanation. This troubles philosophers because intuitively it seems that mental states are crucial in causing a person to act (for example, their beliefs and desires). But, given that physiological facts are sufficient to account for action, mental states appear to be superfluous; they are at risk of being causally and explanatorily irrelevant with respect to human action (Yoo 2006, p. §3b.iii).

Many philosophers consider this apparent irrelevance to be a highly counter-intuitive and undesirable position to take. It ultimately leads to epiphenomenalism—the view that mental events or states are causally irrelevant, they are merely after effects that play no role in any causal chains whatsoever. Thomas Huxley famously noted that epiphenomenalism treats mental states like the steam coming off a train: it plays no causal role in the train's moving forward, it is merely an "emergent property" of the actual causation occurring in the engine (Walter 2003, p. §2).

Problem of anomalism

Another problem with mental causation is that mental events seem anomalous in the sense that there are no scientific laws that mental states can figure into without having exceptions. There are no "strict" laws, and mental events must factor into strict laws in order to fit respectably into the causal order described by current science [see (Davidson 1970)].

In short, one response has been to deny that psychological laws involving mental states require strict, exceptionless laws. Jerry Fodor argues that non-basic (or "special") sciences do not in fact require strict laws (Fodor 1980). In current practice, special sciences (for example, biology and chemistry) have ceteris paribus laws (or laws with "all else being equal" clauses), according to which there are exceptions. However, only in the basic sciences (physics) are there strict, exceptionless laws. Thus, although mental states are anomalous, they can still figure into scientifically respectable laws of psychology.

Problem of externalism

In the latter half of the twentieth century externalism about meanings became espoused by many philosophers. Externalism is roughly the view that certain parts of an individual's environment play a crucial role in the meaning of at least some of an individual's words [see (Putnam 1975) and (Burge 1979)]. A thesis about meaning affects the mind insofar as our thoughts are about things in the world. A common view in the philosophy of mind is that at least certain mental states have intentional content in this sense. For example, one's belief that water is wet has the semantic content of water is wet. The thought is about water and the fact that it is wet. But, if externalism is true—if some of the contents of one's thoughts are constituted at least in part by factors external to one's mind—then there is yet another difficulty in explaining how mental states can cause physical states (Yoo 2006, p. §3b.ii)].

Traditional solutions

Dualist solutions

Main articles: Philosophy of mind and Dualism (philosophy of mind)

Some have claimed that while the mental and the physical are quite different things, they can nonetheless causally interact with one another, a view going back to Descartes [(Descartes & 1642/1986), especially meditations II & VI]. This view is known as interactionist dualism. The major problem that interactionist dualism faces is that of explicating a satisfactory notion of causation according to which non-spatial events, such as mental events, can causally interact with physical events. According to the current mainstream scientific world-view, the physical realm is causally closed, in that causal relationships only hold among physical events in the physical realm. Given these types of considerations, some argue that it is appropriate to say that the main assumptions in interactionist dualism generate the problem of mental causation rather than solve it (see (Yoo 2006, p. §1a).

Physicalist solutions

Main article: Physicalism

See also: Monism

The other major option is to assert that mental events are either (at least contingently) identical to physical events, or supervene on physical events. Views that fall under this general heading are called physicalism or materialism. But, such views require a particular theory to explain how mental events are physical in nature. One such theory is behaviorism. Behaviorists, in general, argue that mental events are merely dispositions to behave in certain ways. Another theory is the identity theory, according to which mental events are (either type- or token-) identical to physical events. A more recent view, known as functionalism, claims that mental events are individuated (or constituted by) the causal role they play. As such, mental events would fit directly into the causal realm, as they are simply certain causal (or functional) roles.

Idealist solutions

Popper's three-world formulation

Related to dualism above, a more general and somewhat differently posed approach to mental causation is provided by Karl Popper's three worlds. Popper split the world into three categories:

1. The world of physical objects and events, including biological entities
2. The mental or psychological world, the world of our feelings of pain and of pleasure, of our thoughts, of our decisions, of our perceptions and our observations; in other words, the world of mental or psychological states or processes, or of subjective experiences.
3. The world of products of the human mind, including art, science, and religion.

World 3 includes physical theory as a particular case. But World 3 is a creation of the human imagination, and such acts of imagination are a part of World 2. Accordingly, one could argue that the physical notion of causality is a child of the imagination, and although causation has its successes in describing World 1, it may not apply to World 2 or World 3. The subjective aspects of theories contained in World 3 are not readily framed within the third-person perspective of science used to explain World 1.

From this perspective, it is hubris to suppose that the methods successful in describing World 1, in particular to suppose the notions of cause and effect, invented by World 2 in its creation of the theory of World 3 used to explain World 1, have direct application to Worlds 2 and 3 themselves, and control mental agency.

Psychological nativism

A still different approach to mental causation is based upon the philosophies of Kant, Chomsky and Pinker. These philosophers stress the impact of built-in aspects of mind, studied in the field of psychological nativism.

Immanuel Kant (1724–1804) pointed out that we all shape our experience of things through the filter of our mind, a view sometimes called epistemological solipsism. The mind shapes that experience, and among other things, Kant believed the concepts of space and time were programmed into the human brain, as was the notion of cause and effect. We never have direct experience of things, the noumenal world, and what we do experience is the phenomenal world as conveyed by our senses, this conveyance processed by the machinery of the mind and nervous system. Kant focused upon this processing. Kant believed in a priori knowledge arrived at independent of experience, so-called synthetic a priori knowledge. In particular, he thought that by introspection some aspects of the filtering mechanisms of the mind/brain/nervous system could be discovered. The following observations summarize Kant's views upon the subject-object problem, called Kant's Copernican revolution:

"It has hitherto been assumed that our cognition must conform to the objects; but all attempts to ascertain anything about these objects a priori, by means of conceptions, and thus to extend the range of our knowledge, have been rendered abortive by this assumption. Let us then make the experiment whether we may not be more successful in metaphysics, if we assume that the objects must conform to our cognition. This appears, at all events, to accord better with the possibility of our gaining the end we have in view, that is to say, of arriving at the cognition of objects a priori, of determining something with respect to these objects, before they are given to us. We here propose to do just what Copernicus did in attempting to explain the celestial movements. When he found that he could make no progress by assuming that all the heavenly bodies revolved round the spectator, he reversed the process, and tried the experiment of assuming that the spectator revolved, while the stars remained at rest. We may make the same experiment with regard to the intuition of objects."

— Immanuel Kant, English translation by J. M. D. Meiklejohn of The Critique of Pure Reason (1. edition 1781, April 23, 1787 Immanuel Kant, Preface to the 2. edition)

Although Kant has posed the issue of built-in aspects of mind, the particulars that depend upon the science of his day have become outmoded. A more recent approach to these limitations is proposed by Noam Chomsky and Steven Pinker. Like Kant, Noam Chomsky raised the issue of the mind's inherent programming. Chomsky selected as a particular example the acquiring of language by children. Of course, language is indispensable in the formulation and communication of our perceptions of the objective world:

"People do not think in English or Chinese or Apache; they think in a language of thought. This language of thought probably looks a bit like all these languages;...But compared with any given language, mentalese must be richer in some ways and simpler in others."

— Steven Pinker, The Language Instinct, p. 72

Chomsky marshaled evidence that a child's rapid mastery of the complexity of language indicated an innate ability programmed into the development of the human mind from birth that could not be explained by the "blank slate" view of the infant mind. Rather, the mind has a built-in propensity to process symbolic representations. The origins of this ability were sought by Steven Pinker in a Darwinian struggle that established the survival value of the ability to communicate. According to Pinker, Charles Darwin himself "concluded that language ability is 'an instinctive tendency to acquire an art', a design that is not peculiar to humans but seen in other species such as song-learning birds." This observation is strongly supported by research on crows.

This work can be taken to suggest that although a physical theory is an intermediary between our observations and our notions of connections between them, it is an elaborate mental construction that is a meld of the way the mind works and objective observations. Although a physical theory is used to determine connections about objective events, the specific form of the theoretical construct is a product of subjective activities, and this particular form may well involve the workings of the brain. Perhaps some aspects of the universe's operation can be expressed in terms of mental constructs, but this process is analogous with the expression of a computer algorithm in terms of assembly language instructions peculiar to a particular computer, a translation by a compiler of the general statement of an algorithm into specific tiny steps that particular computer can handle.

From this standpoint, as with the philosophy of Kant, the first-person active actions of mental causation may involve innate workings of the brain itself.

Neuroscience of free will

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Neuroscience_of_free_will 

On several different levels, from neurotransmitters through neuron firing rates to overall activity, the brain seems to "ramp up" before movements. This image depicts the readiness potential (RP), a ramping-up activity measured using EEG. The onset of the RP begins before the onset of a conscious intention or urge to act. Some have argued that this indicates the brain unconsciously commits to a decision before consciousness awareness. Others have argued that this activity is due to random fluctuations in brain activity, which drive arbitrary, purposeless movements.

The neuroscience of free will, a part of neurophilosophy, is the study of topics related to free will (volition and sense of agency) using neuroscience and the analysis of how findings from such studies may impact the free will debate.

As medical and scientific technology has advanced, neuroscientists have become able to study the brains of living humans, allowing them to observe the brain's decision-making processes and revealing insights into human agency, moral responsibility, and consciousness. One of the pioneering studies in this field was conducted by Benjamin Libet and his colleagues in 1983 and has been the foundation of many studies in the years since. Other studies have attempted to predict the actions of participants before they happen, explore how we know we are responsible for voluntary movements as opposed to being moved by an external force, or how the role of consciousness in decision-making may differ depending on the type of decision being made.

Some areas of the human brain implicated in mental disorders that might be related to free will. Area 25 refers to Brodmann's area 25, related to major depression.

Philosophers such as Alfred Mele and Daniel Dennett question the language used by researchers, suggesting that "free will" means different things to different people (e.g., some notions of "free will" posit that free will is compatible with determinism, while others do not). Dennett insists that many important and common conceptions of "free will" are compatible with the emerging evidence from neuroscience.

Overview

...the current work is in broad agreement with a general trend in neuroscience of volition: although we may experience that our conscious decisions and thoughts cause our actions, these experiences are in fact based on readouts of brain activity in a network of brain areas that control voluntary action... It is clearly wrong to think of [feeling of willing something] as a prior intention, located at the very earliest moment of decision in an extended action chain. Rather, W seems to mark an intention-in-action, quite closely linked to action execution.

Patrick Haggard discussing an in-depth experiment by Itzhak Fried

The neuroscience of free will encompasses two main fields of study: volition and agency.

Volition, the study of voluntary actions, is difficult to define. If human actions are considered as lying along a spectrum based on conscious involvement in initiating the actions, then reflexes would be on one end, and fully voluntary actions would be on the other. How these actions are initiated and consciousness’ role in producing them is a major area of study in volition.

Agency is the capacity of an actor to act in a given environment. Within the neuroscience of free will, the sense of agency—the subjective awareness of initiating, executing, and controlling one's volitional actions—is usually what is studied.

One significant finding of modern studies is that a person's brain seems to commit to certain decisions before the person becomes aware of having made them. Researchers have found a delay of about half a second or more (discussed in sections below). With contemporary brain scanning technology, scientists in 2008 were able to predict with 60% accuracy whether 12 subjects would press a button with their left or right hand up to 10 seconds before the subject became aware of having made that choice. These and other findings have led some scientists, like Patrick Haggard, to reject some definitions of "free will".

However, it is very unlikely that a single study could disprove all definitions of free will. Definitions of free will can vary greatly, and each must be considered separately in light of existing empirical evidence. There have also been a number of problems regarding studies of free will. Particularly in earlier studies, research relied on self-reported measures of conscious awareness, but introspective estimates of event timing were found to be biased or inaccurate in some cases. There is no agreed-upon measure of brain activity corresponding to conscious generation of intentions, choices, or decisions, making studying processes related to consciousness difficult. The existing conclusions drawn from measurements are also debatable, as they don't necessarily tell, for example, what a sudden dip in the readings represents. Such a dip might have nothing to do with unconscious decision because many other mental processes are going on while performing the task. Although early studies mainly used electroencephalography, more recent studies have used fMRI, single-neuron recordings, and other measures. Researcher Itzhak Fried says that available studies do at least suggest that consciousness comes in a later stage of decision-making than previously expected – challenging any versions of "free will" where intention occurs at the beginning of the human decision process.

Free will as illusion

It may be possible that our intuitions about the role of our conscious "intentions" have led us astray; it may be the case that we have confused correlation with causation by believing that conscious awareness necessarily causes the body's movement. This possibility is bolstered by findings in neurostimulation, brain damage, but also research into introspection illusions. Such illusions show that humans do not have full access to various internal processes. The discovery that humans possess a determined will would have implications for moral responsibility or lack thereof.

Neuroscientist, philosopher, and author Sam Harris believes that we are mistaken in believing the intuitive idea that intention initiates actions. Harris criticizes the idea that free will is "intuitive": and that careful introspection will cast doubt on free will. Harris argues: "Thoughts simply arise in the brain. What else could they do? The truth about us is even stranger than we may suppose: The illusion of free will is itself an illusion".

In contrast to this claim, neuroscientist Walter Jackson Freeman III, discusses the impact of unconscious systems and actions to change the world according to human intention. Freeman writes: "our intentional actions continually flow into the world, changing the world and the relations of our bodies to it. This dynamic system is the self in each of us, it is the agency in charge, not our awareness, which is constantly trying to keep up with what we do." To Freeman, the power of intention and action can be independent of awareness.

An important distinction to make is the difference between proximal and distal intentions. Proximal intentions are immediate in the sense that they are about acting now. For instance, a decision to raise a hand now or press a button now, as in Libet-style experiments. Distal intentions are delayed in the sense that they are about acting at a later point in time. For instance, deciding to go to the store later. Research has mostly focused on proximal intentions; however, it is unclear to what degree findings will generalize from one sort of intention to the other.

Relevance of scientific research

Some thinkers like neuroscientist and philosopher Adina Roskies think that these studies can still only show, unsurprisingly, that physical factors in the brain are involved before decision-making. In contrast, Haggard believes that "We feel we choose, but we don't". Researcher John-Dylan Haynes adds: "How can I call a will 'mine' if I don't even know when it occurred and what it has decided to do?". Philosophers Walter Glannon and Alfred Mele think that some scientists are getting the science right, but misrepresenting modern philosophers. This is mainly because "free will" can mean many things: it is unclear what someone means when they say "free will does not exist". Mele and Glannon say that the available research is more evidence against any dualistic notions of free will – but that is an "easy target for neuroscientists to knock down". Mele says that most discussions of free will are now in materialistic terms. In these cases, "free will" means something more like "not coerced" or that "the person could have done otherwise at the last moment". The existence of these types of free will is debatable. Mele agrees, however, that science will continue to reveal critical details about what goes on in the brain during decision-making.

[Some senses of free will] are compatible with what we are learning from science... If only that was what scientists were telling people. But scientists, especially in the last few years, have been on a rampage – writing ill-considered public pronouncements about free will which... verge on social irresponsibility.

Daniel Dennett discussing science and free will

This issue may be controversial for good reason: there is evidence to suggest that people normally associate a belief in free will with their ability to affect their lives. Philosopher Daniel Dennett, author of Elbow Room and a supporter of deterministic free will, believes that scientists risk making a serious mistake. He says that there are types of free will that are incompatible with modern science, but those kinds of free will are not worth wanting. Other types of "free will" are pivotal to people's sense of responsibility and purpose (see also: "believing in free will"), and many of these types are actually compatible with modern science.

The other studies described below have only just begun to shed light on the role that consciousness plays in actions, and it is too early to draw very strong conclusions about certain kinds of "free will". It is worth noting that such experiments so far have dealt only with free-will decisions made in short time frames (seconds) and may not have direct bearing on free-will decisions made ("thoughtfully") by the subject over the course of many seconds, minutes, hours or longer. Scientists have also only so far studied extremely simple behaviors (e.g., moving a finger). Adina Roskies points out five areas of neuroscientific research:

1. Action initiation
2. Intention
3. Decision
4. Inhibition and control
5. The phenomenology of agency.

For each of these areas Roskies concludes that the science may be developing our understanding of volition or "will", but it yet offers nothing for developing the "free" part of the "free will" discussion.

There is also the question of the influence of such interpretations in people's behavior. In 2008, psychologists Kathleen Vohs and Jonathan Schooler published a study on how people behave when they are prompted to think that determinism is true. They asked their subjects to read one of two passages: one suggesting that behavior boils down to environmental or genetic factors not under personal control; the other neutral about what influences behavior. The participants then did a few math problems on a computer. But just before the test started, they were informed that because of a glitch in the computer it occasionally displayed the answer by accident; if this happened, they were to click it away without looking. Those who had read the deterministic message were more likely to cheat on the test. "Perhaps, denying free will simply provides the ultimate excuse to behave as one likes", Vohs and Schooler suggested. However, although initial studies suggested that believing in free will is associated with more morally praiseworthy behavior, some recent studies have reported contradictory findings.

Notable experiments

Libet Experiment

A pioneering experiment in this field was conducted by Benjamin Libet in the 1980s, in which he asked each subject to choose a random moment to flick their wrist while he measured the associated activity in their brain (in particular, the build-up of electrical signal called the Bereitschaftspotential (BP), which was discovered by Kornhuber & Deecke in 1965). Although it was well known that the "readiness potential" (German: Bereitschaftspotential) preceded the physical action, Libet asked how it corresponded to the felt intention to move. To determine when the subjects felt the intention to move, he asked them to watch the second hand of a clock and report its position when they felt that they had felt the conscious will to move.

Libet's experiment: (0) repose, until (1) the Bereitschaftspotential is detected, (2-Libet's W) the volunteer memorizes a dot position upon feeling their intention, and then (3) acts.

Libet found that the unconscious brain activity leading up to the conscious decision by the subject to flick their wrist began approximately half a second before the subject consciously felt that they had decided to move. Libet's findings suggest that decisions made by a subject are first being made on an unconscious level and only afterward being translated into a "conscious decision", and that the subject's belief that it occurred at the behest of their will was only due to their retrospective perspective on the event.

The interpretation of these findings has been criticized by Daniel Dennett, who argues that people will have to shift their attention from their intention to the clock, and that this introduces temporal mismatches between the felt experience of will and the perceived position of the clock hand. Consistent with this argument, subsequent studies have shown that the exact numerical value varies depending on attention. Despite the differences in the exact numerical value, however, the main finding has held. Philosopher Alfred Mele criticizes this design for other reasons. Having attempted the experiment himself, Mele explains that "the awareness of the intention to move" is an ambiguous feeling at best. For this reason he remained skeptical of interpreting the subjects' reported times for comparison with their Bereitschaftspotential.

Criticisms

Typical recording of the Bereitschaftspotential that was discovered by Kornhuber and Deecke in 1965). Benjamin Libet investigated whether this neural activity corresponded to the "felt intention" (or will) to move of experimental subjects.

In a variation of this task, Haggard and Eimer (1999) asked subjects to decide not only when to move their hands, but also to decide which hand to move. In this case, the felt intention correlated much more closely with the "lateralized readiness potential" (LRP), an event-related potential (ERP) component that measures the difference between left and right hemisphere brain activity. Haggard and Eimer argue that the feeling of conscious will must therefore follow the decision of which hand to move, since the LRP reflects the decision to lift a particular hand.

A more direct test of the relationship between the Bereitschaftspotential and the "awareness of the intention to move" was conducted by Banks and Isham (2009). In their study, participants performed a variant of the Libet's paradigm in which a delayed tone followed the button press. Subsequently, research participants reported the time of their intention to act (e.g., Libet's W). If W were time-locked to the Bereitschaftspotential, W would remain uninfluenced by any post-action information. However, findings from this study show that W in fact shifts systematically with the time of the tone presentation, implicating that W is, at least in part, retrospectively reconstructed rather than pre-determined by the Bereitschaftspotential.

A study conducted by Jeff Miller and Judy Trevena (2010) suggests that the Bereitschaftspotential (BP) signal in Libet's experiments doesn't represent a decision to move, but that it's merely a sign that the brain is paying attention. In this experiment the classical Libet experiment was modified by playing an audio tone indicating to volunteers to decide whether to tap a key or not. The researchers found that there was the same RP signal in both cases, regardless of whether or not volunteers actually elected to tap, which suggests that the RP signal doesn't indicate that a decision has been made.

In a second experiment, researchers asked volunteers to decide on the spot whether to use left hand or right to tap the key while monitoring their brain signals, and they found no correlation among the signals and the chosen hand. This criticism has itself been criticized by free-will researcher Patrick Haggard, who mentions literature that distinguishes two different circuits in the brain that lead to action: a "stimulus-response" circuit and a "voluntary" circuit. According to Haggard, researchers applying external stimuli may not be testing the proposed voluntary circuit, nor Libet's hypothesis about internally triggered actions.

Libet's interpretation of the ramping up of brain activity prior to the report of conscious "will" continues to draw heavy criticism. Studies have questioned participants' ability to report the timing of their "will". Authors have found that preSMA activity is modulated by attention (attention precedes the movement signal by 100 ms), and the prior activity reported could therefore have been product of paying attention to the movement. They also found that the perceived onset of intention depends on neural activity that takes place after the execution of action. Transcranial magnetic stimulation (TMS) applied over the preSMA after a participant performed an action shifted the perceived onset of the motor intention backward in time, and the perceived time of action execution forward in time.

Others have speculated that the preceding neural activity reported by Libet may be an artefact of averaging the time of "will", wherein neural activity does not always precede reported "will". In a similar replication they also reported no difference in electrophysiological signs before a decision not to move and before a decision to move.

Benjamin Libet himself did not interpret his experiment as evidence of the inefficacy of conscious free will — he points out that although the tendency to press a button may be building up for 500 milliseconds, the conscious will retain a right to veto any action at the last moment. According to this model, unconscious impulses to perform a volitional act are open to suppression by the conscious efforts of the subject (sometimes referred to as "free won't"). A comparison is made with a golfer, who may swing a club several times before striking the ball. The action simply gets a rubber stamp of approval at the last millisecond.

Some studies have replicated Libet's findings, whilst addressing some of the original criticisms. A 2011 study conducted by Itzhak Fried found with a greater than 80% accuracy that individual neurons fire 700 ms before a reported "will" to act (long before EEG activity predicted such a response). This was accomplished with the help of volunteer epilepsy patients, who needed electrodes implanted deep in their brain for evaluation and treatment anyway. Now able to monitor awake and moving patients, the researchers replicated the timing anomalies that were discovered by Libet. Similarly to these tests, Chun Siong Soon, Anna Hanxi He, Stefan Bode and John-Dylan Haynes have conducted a study in 2013 claiming to be able to predict by 4 s the choice to sum or subtract before the subject reports it.

William R. Klemm pointed out the inconclusiveness of these tests due to design limitations and data interpretations and proposed less ambiguous experiments, while affirming a stand on the existence of free will like Roy F. Baumeister or Catholic neuroscientists such as Tadeusz Pacholczyk. Adrian G. Guggisberg and Annaïs Mottaz have also challenged Libet and Fried's findings, stating that "the instantaneous appearance of conscious intentions might be an artifact of the method used for assessing the contents of consciousness" and that "studies using alternatives to the Libet clock have suggested that intention consciousness is a multistage process just as the neural mechanisms of motor decisions", concluding that "the time of conscious intentions reported by the participants therefore might be only the culmination of preceding conscious deliberations, not a unique and instantaneous event" and "if this is true, the delay between the onset of neural predictors of motor decisions and conscious intentions reported with the Libet clock is not due to unconscious neural processes but due to conscious evaluations which are not final yet".

Another criticism stems from the fact that, despite being treated as the same by Libet, an urge, a wish and a desire are not the same thing as an intention, a decision, and a choice.

In an empirical study in 2019, researchers found that readiness potentials were absent for deliberate decisions, and preceded arbitrary decisions only.

In a study published in 2012, Aaron Schurger, Jacobo D. Sitt, and Stanislas Dehaene published in PNAS proposed that the occurrence of the readiness potentials observed in Libet-type experiments is stochastically occasioned by ongoing spontaneous subthreshold fluctuations in neural activity, rather than an unconscious goal-directed operation, and challenged assumptions about the causal nature of the Bereitschaftspotential itself (and the "pre-movement buildup" of neural activity in general when faced with a choice), thus denying the conclusions drawn from studies such as Libet's and Fried's. See The Information Philosopher, New Scientist, and The Atlantic, for commentary on this study.

Unconscious actions

Timing intentions compared to actions

A study by Masao Matsuhashi and Mark Hallett, published in 2008, claims to have replicated Libet's findings without relying on subjective report or clock memorization on the part of participants. The authors believe that their method can identify the time (T) at which a subject becomes aware of his own movement. Matsuhashi and Hallet argue that T not only varies, but often occurs after early phases of movement genesis have already begun (as measured by the readiness potential). They conclude that a person's awareness cannot be the cause of movement, and may instead only notice the movement.

The experiment

Matsuhashi and Hallett's study can be summarized thus. The researchers hypothesized that, if our conscious intentions are what causes movement genesis (i.e. the start of an action), then naturally, our conscious intentions should always occur before any movement has begun. Otherwise, if we ever become aware of a movement only after it has already been started, our awareness could not have been the cause of that particular movement. Simply put, conscious intention must precede action if it is its cause.

To test this hypothesis, Matsuhashi and Hallet had volunteers perform brisk finger movements at random intervals, while not counting or planning when to make such (future) movements, but rather immediately making a movement as soon as they thought about it. An externally controlled "stop-signal" sound was played at pseudo-random intervals, and the volunteers had to cancel their intent to move if they heard a signal while being aware of their own immediate intention to move. Whenever there was an action (finger movement), the authors documented (and graphed) any tones that occurred before that action. The graph of tones before actions therefore only shows tones (a) before the subject is even aware of his "movement genesis" (or else they would have stopped or "vetoed" the movement), and (b) after it is too late to veto the action. This second set of graphed tones is of little importance here.

In this work, "movement genesis" is defined as the brain process of making movement, of which physiological observations have been made (via electrodes) indicating that it may occur before conscious awareness of intent to move (see Benjamin Libet).

By looking to see when tones started preventing actions, the researchers supposedly know the length of time (in seconds) that exists between when a subject holds a conscious intention to move and performs the action of movement. This moment of awareness is called T (the mean time of conscious intention to move). It can be found by looking at the border between tones and no tones. This enables the researchers to estimate the timing of the conscious intention to move without relying on the subject's knowledge or demanding them to focus on a clock. The last step of the experiment is to compare time T for each subject with their event-related potential (ERP) measures (e.g., seen in this page's lead image), which reveal when their finger movement genesis first begins.

The researchers found that the time of the conscious intention to move T normally occurred too late to be the cause of movement genesis. See the example of a subject's graph below on the right. Although it is not shown on the graph, the subject's readiness potentials (ERP) tells us that his actions start at −2.8 seconds, and yet this is substantially earlier than his conscious intention to move, time T (−1.8 seconds). Matsuhashi and Hallet concluded that the feeling of the conscious intention to move does not cause movement genesis; both the feeling of intention and the movement itself are the result of unconscious processing.

Analysis and interpretation

This study is similar to Libet's in some ways: volunteers were again asked to perform finger extensions in short, self-paced intervals. In this version of the experiment, researchers introduced randomly timed "stop tones" during the self-paced movements. If participants were not conscious of any intention to move, they simply ignored the tone. On the other hand, if they were aware of their intention to move at the time of the tone, they had to try to veto the action, then relax for a bit before continuing self-paced movements. This experimental design allowed Matsuhashi and Hallet to see when, once the subject moved his finger, any tones occurred. The goal was to identify their own equivalent of Libet's W, their own estimation of the timing of the conscious intention to move, which they would call T (time).

Testing the hypothesis that "conscious intention occurs after movement genesis has already begun" required the researchers to analyse the distribution of responses to tones before actions. The idea is that, after time T, tones will lead to vetoing and thus a reduced representation in the data. There would also be a point of no return P where a tone was too close to the movement onset for the movement to be vetoed. In other words, the researchers were expecting to see the following on the graph: many unsuppressed responses to tones while the subjects are not yet aware of their movement genesis, followed by a drop in the number of unsuppressed responses to tones during a certain period of time during which the subjects are conscious of their intentions and are stopping any movements, and finally a brief increase again in unsuppressed responses to tones when the subjects do not have the time to process the tone and prevent an action – they have passed the action's "point of no return". That is exactly what the researchers found (see the graph on the right, below).

Graphing tones as they appeared (or didn't) in the time before any action. In this case, researchers believe that the subject becomes aware of his actions at about 1.8 seconds (this is time T). A typical subject's ERP recordings suggest movement preparation as early as −2.8 seconds.

The graph shows the times at which unsuppressed responses to tones occurred when the volunteer moved. He showed many unsuppressed responses to tones (called "tone events" on the graph) on average up until 1.8 seconds before movement onset, but a significant decrease in tone events immediately after that time. Presumably this is because the subject usually became aware of his intention to move at about −1.8 seconds, which is then labelled point T. Since most actions are vetoed if a tone occurs after point T, there are very few tone events represented during that range. Finally, there is a sudden increase in the number of tone events at 0.1 seconds, meaning that this subject has passed point P. Matsuhashi and Hallet were thus able to establish an average time T (−1.8 seconds) without subjective report. This, they compared to ERP measurements of movement, which had detected movement beginning at about −2.8 seconds on average for this participant. Since T, like Libet's original W, was often found after movement genesis had already begun, the authors concluded that the generation of awareness occurred afterwards or in parallel to action, but most importantly, that it was probably not the cause of the movement.

Criticisms

Haggard describes other studies at the neuronal levels as providing "a reassuring confirmation of previous studies that recorded neural populations" such as the one just described. Note that these results were gathered using finger movements and may not necessarily generalize to other actions such as thinking, or even other motor actions in different situations. Indeed, the human act of planning has implications for free will, and so this ability must also be explained by any theories of unconscious decision-making. Philosopher Alfred Mele also doubts the conclusions of these studies. He explains that simply because a movement may have been initiated before our "conscious self" has become aware of it does not mean that our consciousness does not still get to approve, modify, and perhaps cancel (called vetoing) the action.

Unconsciously cancelling actions

Retrospective judgement of free choice

Recent research by Simone Kühn and Marcel Brass suggests that consciousness may not be what causes some actions to be vetoed at the last moment. First of all, their experiment relies on the simple idea that we ought to know when we consciously cancel an action (i.e. we should have access to that information). Secondly, they suggest that access to this information means humans should find it easy to tell, just after completing an action, whether it was "impulsive" (there being no time to decide) and when there was time to "deliberate" (the participant decided to allow/not to veto the action). The study found evidence that subjects could not tell this important difference. This again leaves some conceptions of free will vulnerable to the introspection illusion. The researchers interpret their results to mean that the decision to "veto" an action is determined unconsciously, just as the initiation of the action may have been unconscious in the first place.

The experiment

The experiment involved asking volunteers to respond to a go-signal by pressing an electronic "go" button as quickly as possible. In this experiment the go-signal was represented as a visual stimulus shown on a monitor. The participants' reaction times (RT) were gathered at this stage, in what was described as the "primary response trials".

The primary response trials were then modified, in which 25% of the go-signals were subsequently followed by an additional signal – either a "stop" or "decide" signal. The additional signals occurred after a "signal delay" (SD), a random amount of time up to 2 seconds after the initial go-signal. They also occurred equally, each representing 12.5% of experimental cases. These additional signals were represented by the initial stimulus changing colour (e.g., to either a red or orange light). The other 75% of go-signals were not followed by an additional signal, and therefore considered the "default" mode of the experiment. The participants' task of responding as quickly as possible to the initial signal (i.e. pressing the "go" button) remained.

Upon seeing the initial go-signal, the participant would immediately intend to press the "go" button. The participant was instructed to cancel their immediate intention to press the "go" button if they saw a stop signal. The participant was instructed to select randomly (at their leisure) between either pressing the "go" button or not pressing it, if they saw a decide signal. Those trials in which the decide signal was shown after the initial go-signal ("decide trials"), for example, required that the participants prevent themselves from acting impulsively on the initial go-signal and then decide what to do. Due to the varying delays, this was sometimes impossible (e.g., some decide signals simply appeared too late in the process of them both intending to and pressing the go button for them to be obeyed).

Those trials in which the subject reacted to the go-signal impulsively without seeing a subsequent signal show a quick RT of about 600 ms. Those trials in which the decide signal was shown too late, and the participant had already enacted their impulse to press the go-button (i.e. had not decided to do so), also show a quick RT of about 600 ms. Those trials in which a stop signal was shown and the participant successfully responded to it, do not show a response time. Those trials in which a decide signal was shown, and the participant decided not to press the go-button, also do not show a response time. Those trials in which a decide signal was shown, and the participant had not already enacted their impulse to press the go-button, but (in which it was theorised that they) had had the opportunity to decide what to do, show a comparatively slow RT, in this case closer to 1400 ms.

The participant was asked at the end of those "decide trials" in which they had actually pressed the go-button whether they had acted impulsively (without enough time to register the decide signal before enacting their intent to press the go-button in response to the initial go-signal stimulus) or based upon a conscious decision made after seeing the decide signal. Based upon the response time data, however, it appears that there was discrepancy between when the user thought that they had had the opportunity to decide (and had therefore not acted on their impulses) – in this case deciding to press the go-button, and when they thought that they had acted impulsively (based upon the initial go-signal) – where the decide signal came too late to be obeyed.

The rationale

Kühn and Brass wanted to test participant self-knowledge. The first step was that after every decide trial, participants were next asked whether they actually had time to decide. Specifically, the volunteers were asked to label each decide trial as either failed-to-decide (the action was the result of acting impulsively on the initial go-signal) or successful decide (the result of a deliberated decision). See the diagram on the right for this decide trial split: failed-to-decide and successful decide; the next split in this diagram (participant correct or incorrect) will be explained at the end of this experiment. Note also that the researchers sorted the participants’ successful decide trials into "decide go" and "decide no-go", but were not concerned with the no-go trials, since they did not yield any RT data (and are not featured anywhere in the diagram on the right). Note that successful stop trials did not yield RT data either.

The different types of trials and their different possible outcomes

Kühn and Brass now knew what to expect: primary response trials, any failed stop trials, and the "failed-to-decide" trials were all instances where the participant obviously acted impulsively – they would show the same quick RT. In contrast, the "successful decide" trials (where the decision was a "go" and the subject moved) should show a slower RT. Presumably, if deciding whether to veto is a conscious process, volunteers should have no trouble distinguishing impulsivity from instances of true deliberate continuation of a movement. Again, this is important, since decide trials require that participants rely on self-knowledge. Note that stop trials cannot test self-knowledge because if the subject does act, it is obvious to them that they reacted impulsively.

Results and implications

The general distribution of reaction times for the different trials. Notice the timing of the two peaks for trials labelled "successful decide".

Unsurprisingly, the recorded RTs for the primary response trials, failed stop trials, and "failed-to-decide" trials all showed similar RTs: 600 ms seems to indicate an impulsive action made without time to truly deliberate. What the two researchers found next was not as easy to explain: while some "successful decide" trials did show the tell-tale slow RT of deliberation (averaging around 1400 ms), participants had also labelled many impulsive actions as "successful decide". This result is startling because participants should have had no trouble identifying which actions were the results of a conscious "I will not veto", and which actions were un-deliberated, impulsive reactions to the initial go-signal. As the authors explain:

[The results of the experiment] clearly argue against Libet's assumption that a veto process can be consciously initiated. He used the veto in order to reintroduce the possibility to control the unconsciously initiated actions. But since the subjects are not very accurate in observing when they have [acted impulsively instead of deliberately], the act of vetoing cannot be consciously initiated.

In decide trials, the participants, it seems, were not able to reliably identify whether they had really had time to decide;– at least, not based on internal signals. The authors explain that this result is difficult to reconcile with the idea of a conscious veto, but is simple to understand if the veto is considered an unconscious process. Thus it seems that the intention to move might not only arise from the unconscious mind, but it may only be inhibited if the unconscious mind says so.

Criticisms

After the above experiments, the authors concluded that subjects sometimes could not distinguish between "producing an action without stopping and stopping an action before voluntarily resuming", or in other words, they could not distinguish between actions that are immediate and impulsive as opposed to delayed by deliberation. To be clear, one assumption of the authors is that all the early (600 ms) actions are unconscious, and all the later actions are conscious. These conclusions and assumptions have yet to be debated within the scientific literature or even replicated (it is a very early study).

The results of the trial in which the so-called "successful decide" data (with its respective longer time measured) was observed may have possible implications for our understanding of the role of consciousness as the modulator of a given action or response, and these possible implications cannot merely be omitted or ignored without valid reasons, especially when the authors of the experiment suggest that the late decide trials were actually deliberated.

It is worth noting that Libet consistently referred to a veto of an action that was initiated endogenously. That is, a veto that occurs in the absence of external cues, instead relying on only internal cues (if any at all). This veto may be a different type of veto than the one explored by Kühn and Brass using their decide signal.

Daniel Dennett also argues that no clear conclusion about volition can be derived from Benjamin Libet's experiments supposedly demonstrating the irrelevance of conscious volition. According to Dennett, ambiguities in the timings of the different events are involved. Libet tells when the readiness potential occurs objectively, using electrodes, but relies on the subject reporting the position of the hand of a clock to determine when the conscious decision was made. As Dennett points out, this is only a report of where it seems to the subject that various things come together, not of the objective time at which they actually occur:

Suppose Libet knows that your readiness potential peaked at millisecond 6,810 of the experimental trial, and the clock dot was straight down (which is what you reported you saw) at millisecond 7,005. How many milliseconds should he have to add to this number to get the time you were conscious of it? The light gets from your clock face to your eyeball almost instantaneously, but the path of the signals from retina through lateral geniculate nucleus to striate cortex takes 5 to 10 milliseconds — a paltry fraction of the 300 milliseconds offset, but how much longer does it take them to get to you. (Or are you located in the striate cortex?) The visual signals have to be processed before they arrive at wherever they need to arrive for you to make a conscious decision of simultaneity. Libet's method presupposes, in short, that we can locate the intersection of two trajectories:

• the rising-to-consciousness of signals representing the decision to flick
• the rising to consciousness of signals representing successive clock-face orientations

so that these events occur side-by-side as it were in place where their simultaneity can be noted.

The point of no return

In early 2016, PNAS published an article by researchers in Berlin, Germany, The point of no return in vetoing self-initiated movements, in which the authors set out to investigate whether human subjects had the ability to veto an action (in this study, a movement of the foot) after the detection of its Bereitschaftspotential (BP). The Bereitschaftspotential, which was discovered by Kornhuber & Deecke in 1965, is an instance of unconscious electrical activity within the motor cortex, quantified by the use of EEG, that occurs moments before a motion is performed by a person: it is considered a signal that the brain is "getting ready" to perform the motion. The study found evidence that these actions can be vetoed even after the BP is detected (i. e. after it can be seen that the brain has started preparing for the action). The researchers maintain that this is evidence for the existence of at least some degree of free will in humans: previously, it had been argued that, given the unconscious nature of the BP and its usefulness in predicting a person's movement, these are movements that are initiated by the brain without the involvement of the conscious will of the person. The study showed that subjects were able to "override" these signals and stop short of performing the movement that was being anticipated by the BP. Furthermore, researchers identified what was termed a "point of no return": once the BP is detected for a movement, the person could refrain from performing the movement only if they attempted to cancel it at least 200 milliseconds before the onset of the movement. After this point, the person was unable to avoid performing the movement. Previously, Kornhuber and Deecke underlined that absence of conscious will during the early Bereitschaftspotential (termed BP1) is not a proof of the non-existence of free will, as also unconscious agendas may be free and non-deterministic. According to their suggestion, man has relative freedom, i.e. freedom in degrees, that can be increased or decreased through deliberate choices that involve both conscious and unconscious (panencephalic) processes.

Neuronal prediction of free will

Despite criticisms, experimenters are still trying to gather data that may support the case that conscious "will" can be predicted from brain activity. fMRI machine learning of brain activity (multivariate pattern analysis) has been used to predict the user choice of a button (left/right) up to 7 seconds before their reported will of having done so. Brain regions successfully trained for prediction included the frontopolar cortex (anterior medial prefrontal cortex) and precuneus/posterior cingulate cortex (medial parietal cortex). In order to ensure report timing of conscious "will" to act, they showed the participant a series of frames with single letters (500 ms apart), and upon pressing the chosen button (left or right) they were required to indicate which letter they had seen at the moment of decision. This study reported a statistically significant 60% accuracy rate, which may be limited by experimental setup; machine-learning data limitations (time spent in fMRI) and instrument precision.

Another version of the fMRI multivariate pattern analysis experiment was conducted using an abstract decision problem, in an attempt to rule out the possibility of the prediction capabilities being product of capturing a built-up motor urge. Each frame contained a central letter like before, but also a central number, and 4 surrounding possible "answers numbers". The participant first chose in their mind whether they wished to perform an addition or subtraction operation, and noted the central letter on the screen at the time of this decision. The participant then performed the mathematical operation based on the central numbers shown in the next two frames. In the following frame the participant then chose the "answer number" corresponding to the result of the operation. They were further presented with a frame that allowed them to indicate the central letter appearing on the screen at the time of their original decision. This version of the experiment discovered a brain prediction capacity of up to 4 seconds before the conscious will to act.

Multivariate pattern analysis using EEG has suggested that an evidence-based perceptual decision model may be applicable to free-will decisions. It was found that decisions could be predicted by neural activity immediately after stimulus perception. Furthermore, when the participant was unable to determine the nature of the stimulus, the recent decision history predicted the neural activity (decision). The starting point of evidence accumulation was in effect shifted towards a previous choice (suggesting a priming bias). Another study has found that subliminally priming a participant for a particular decision outcome (showing a cue for 13 ms) could be used to influence free decision outcomes. Likewise, it has been found that decision history alone can be used to predict future decisions. The prediction capacities of the Chun Siong Soon et al. (2008) experiment were successfully replicated using a linear SVM model based on participant decision history alone (without any brain activity data). Despite this, a recent study has sought to confirm the applicability of a perceptual decision model to free will decisions. When shown a masked and therefore invisible stimulus, participants were asked to either guess between a category or make a free decision for a particular category. Multivariate pattern analysis using fMRI could be trained on "free-decision" data to successfully predict "guess decisions", and trained on "guess data" in order to predict "free decisions" (in the precuneus and cuneus region).

Criticisms

Contemporary voluntary decision prediction tasks have been criticised based on the possibility the neuronal signatures for pre-conscious decisions could actually correspond to lower-conscious processing rather than unconscious processing. People may be aware of their decisions before making their report, yet need to wait several seconds to be certain. However, such a model does not explain what is left unconscious if everything can be conscious at some level (and the purpose of defining separate systems). Yet limitations remain in free-will prediction research to date. In particular, the prediction of considered judgements from brain activity involving thought processes beginning minutes rather than seconds before a conscious will to act, including the rejection of a conflicting desire. Such are generally seen to be the product of sequences of evidence accumulating judgements.

Other related phenomena

Retrospective construction

It has been suggested that sense authorship is an illusion. Unconscious causes of thought and action might facilitate thought and action, while the agent experiences the thoughts and actions as being dependent on conscious will. The idea behind retrospective construction is that, while part of the "yes, I did it" feeling of agency seems to occur during action, there also seems to be processing performed after the fact – after the action is performed – to establish the full feeling of agency. However, to assign agency, one does not have to believe that agency is free.

In the moment, unconscious agency processing can alter how we perceive the timing of sensations or actions. Kühn and Brass apply retrospective construction to explain the two peaks in "successful decide" RTs. They suggest that the late decide trials were actually deliberated, but that the impulsive early decide trials that should have been labelled "failed-to-decide" were mistaken during unconscious agency processing. They say that people "persist in believing that they have access to their own cognitive processes" when in fact we do a great deal of automatic unconscious processing before conscious perception occurs.

Criticisms

Criticism to Daniel Wegner's claims regarding the significance of introspection illusion for the notion of free will has been published.

Manipulating choice

Transcranial magnetic stimulation uses magnetism to safely stimulate or inhibit parts of the brain.

Some research suggests that TMS can be used to manipulate the perception of authorship of a specific choice. Experiments showed that neurostimulation could affect which hands people move, even though the subjective experience of will was intact. An early TMS study revealed that activation of one side of the neocortex could be used to bias the selection of one's opposite side hand in a forced-choice decision task. K. Ammon and S. C. Gandevia found that it was possible to influence which hand people move by stimulating frontal regions that are involved in movement planning using transcranial magnetic stimulation in the left or right hemisphere of the brain.

Right-handed people would normally choose to move their right hand 60% of the time, but when the right hemisphere was stimulated, they would instead choose their left hand 80% of the time (recall that the right hemisphere of the brain is responsible for the left side of the body, and the left hemisphere for the right). Despite the external influence on their decision-making, the subjects were apparently unaware of any influence, as when questioned they felt that their decisions appeared to be made in an entirely natural way. In a follow-up experiment, Alvaro Pascual-Leone and colleagues found similar results, but also noted that the transcranial magnetic stimulation must occur within the motor area and within 200 milliseconds, consistent with the time-course derived from the Libet experiments: with longer response times (between 200 and 1100 ms), magnetic stimulation had no effect on hand preference regardless of the site stimulated.

In late 2015, following a previous 2010 study, both based on earlier investigations on both monkeys and humans, a team of researchers from the UK and the US published an article demonstrating similar findings. The researchers concluded that "motor responses and the choice of hand can be modulated using tDCS". However, a different attempt by Y. H. Sohn et al. failed to replicate such results.

Manipulating the perceived intention to move

Various studies indicate that the perceived intention to move (have moved) can be manipulated. Studies have focused on the pre-supplementary motor area (pre-SMA) of the brain, in which readiness potential indicating the beginning of a movement genesis has been recorded by EEG. In one study, directly stimulating the pre-SMA caused volunteers to report a feeling of intention, and sufficient stimulation of that same area caused physical movement. In a similar study, it was found that people with no visual awareness of their body can have their limbs be made to move without having any awareness of this movement, by stimulating premotor brain regions. When their parietal cortices were stimulated, they reported an urge (intention) to move a specific limb (that they wanted to do so). Furthermore, stronger stimulation of the parietal cortex resulted in the illusion of having moved without having done so.

This suggests that awareness of an intention to move may literally be the "sensation" of the body's early movement, but certainly not the cause. Other studies have at least suggested that "The greater activation of the SMA, SACC, and parietal areas during and after execution of internally generated actions suggests that an important feature of internal decisions is specific neural processing taking place during and after the corresponding action. Therefore, awareness of intention timing seems to be fully established only after execution of the corresponding action, in agreement with the time course of neural activity observed here."

Another experiment involved an electronic ouija board where the device's movements were manipulated by the experimenter, while the participant was led to believe that they were entirely self-conducted. The experimenter stopped the device on occasions and asked the participant how much they themselves felt like they wanted to stop. The participant also listened to words in headphones, and it was found that if experimenter stopped next to an object that came through the headphones, they were more likely to say that they wanted to stop there. If the participant perceived having the thought at the time of the action, then it was assigned as intentional. It was concluded that a strong illusion of perception of causality requires: priority (we assume the thought must precede the action), consistency (the thought is about the action), and exclusivity (no other apparent causes or alternative hypotheses).

Hakwan C. Lau et al. set up an experiment where subjects would look at an analog-style clock, and a red dot would move around the screen. Subjects were told to click the mouse button whenever they felt the intention to do so. One group was given a transcranial magnetic stimulation (TMS) pulse, and the other was given a sham TMS. Subjects in the perceived intention condition were told to move the cursor to where it was when they felt the inclination to press the button. In the movement condition, subjects moved their cursor to where it was when they physically pressed the button. TMS applied over the pre-SMA after a participant performed an action shifted the perceived onset of the motor intention backward in time, and the perceived time of action execution forward in time. Results showed that the TMS was able to shift the perceived intention condition forward by 16 ms, and shifted back by 14 ms for the movement condition. Perceived intention could be manipulated up to 200 ms after the execution of the spontaneous action, indicating that the perception of intention occurred after the executive motor movements. The results of three control studies suggest that this effect is time-limited, specific to modality, and also specific to the anatomical site of stimulation. The investigators conclude that the perceived onset of intention depends, at least in part, on neural activity that takes place after the execution of action. Often it is thought that if free will were to exist, it would require intention to be the causal source of behavior. These results show that intention may not be the causal source of all behavior.

Related models

The idea that intention co-occurs with (rather than causes) movement is reminiscent of "forward models of motor control" (FMMC), which have been used to try to explain inner speech. FMMCs describe parallel circuits: movement is processed in parallel with other predictions of movement; if the movement matches the prediction, the feeling of agency occurs. FMMCs have been applied in other related experiments. Janet Metcalfe and her colleagues used an FMMC to explain how volunteers determine whether they are in control of a computer game task. On the other hand, they acknowledge other factors as well. The authors attribute feelings of agency to desirability of the results (see self-serving biases) and top-down processing (reasoning and inferences about the situation).

There is also a model, called epiphenomenalism, that argues that conscious will is an illusion, and that consciousness is a by-product of physical states of the world. Others have argued that data such as the Bereitschaftspotential undermine epiphenomenalism for the same reason, that such experiments rely on a subject reporting the point in time at which a conscious experience and a conscious decision occurs, thus relying on the subject to be able to consciously perform an action. That ability would seem to be at odds with epiphenomenalism, which, according to Thomas Henry Huxley, is the broad claim that consciousness is "completely without any power… as the steam-whistle which accompanies the work of a locomotive engine is without influence upon its machinery".

Related brain disorders

Various brain disorders implicate the role of unconscious brain processes in decision-making tasks. Auditory hallucinations produced by schizophrenia seem to suggest a divergence of will and behaviour. The left brain of people whose hemispheres have been disconnected has been observed to invent explanations for body movement initiated by the opposing (right) hemisphere, perhaps based on the assumption that their actions are consciously willed. Likewise, people with "alien hand syndrome" are known to conduct complex motor movements against their will.

Neural models of voluntary action

A neural model for voluntary action proposed by Haggard comprises two major circuits. The first involving early preparatory signals (basal ganglia substantia nigra and striatum), prior intention and deliberation (medial prefrontal cortex), motor preparation/readiness potential (preSMA and SMA), and motor execution (primary motor cortex, spinal cord and muscles). The second involving the parietal-pre-motor circuit for object-guided actions, for example grasping (premotor cortex, primary motor cortex, primary somatosensory cortex, parietal cortex, and back to the premotor cortex). He proposed that voluntary action involves external environment input ("when decision"), motivations/reasons for actions (early "whether decision"), task and action selection ("what decision"), a final predictive check (late "whether decision") and action execution.

Another neural model for voluntary action also involves what, when, and whether (WWW) based decisions. The "what" component of decisions is considered a function of the anterior cingulate cortex, which is involved in conflict monitoring. The timing ("when") of the decisions are considered a function of the preSMA and SMA, which is involved in motor preparation. Finally, the "whether" component is considered a function of the dorsal medial prefrontal cortex.

Prospection

Main article: Prospection

Martin Seligman and others criticize the classical approach in science that views animals and humans as "driven by the past" and suggest instead that people and animals draw on experience to evaluate prospects they face and act accordingly. The claim is made that this purposive action includes evaluation of possibilities that have never occurred before and is experimentally verifiable.

Seligman and others argue that free will and the role of subjectivity in consciousness can be better understood by taking such a "prospective" stance on cognition and that "accumulating evidence in a wide range of research suggests [this] shift in framework".