In statistical hypothesis testing, a result has statistical significance when a result at least as "extreme" would be very infrequent if the null hypothesis were true. More precisely, a study's defined significance level, denoted by , is the probability of the study rejecting the null hypothesis, given that the null hypothesis is true; and the p-value of a result, , is the probability of obtaining a result at least as extreme, given that the null hypothesis is true. The result is said to be statistically significant, by the standards of the study, when The significance level for a study is chosen before data collection, and is typically set to 5% or much lower—depending on the field of study.
In any experiment or observation that involves drawing a sample from a population, there is always the possibility that an observed effect would have occurred due to sampling error alone. But if the p-value
of an observed effect is less than (or equal to) the significance
level, an investigator may conclude that the effect reflects the
characteristics of the whole population, thereby rejecting the null hypothesis.
This technique for testing the statistical significance of results was developed in the early 20th century. The term significance does not imply importance here, and the term statistical significance is not the same as research significance, theoretical significance, or practical significance. For example, the term clinical significance refers to the practical importance of a treatment effect.
In 1925, Ronald Fisher advanced the idea of statistical hypothesis testing, which he called "tests of significance", in his publication Statistical Methods for Research Workers. Fisher suggested a probability of one in twenty (0.05) as a convenient cutoff level to reject the null hypothesis. In a 1933 paper, Jerzy Neyman and Egon Pearson called this cutoff the significance level, which they named . They recommended that be set ahead of time, prior to any data collection.
Despite his initial suggestion of 0.05 as a significance level,
Fisher did not intend this cutoff value to be fixed. In his 1956
publication Statistical Methods and Scientific Inference, he recommended that significance levels be set according to specific circumstances.
Related concepts
The significance level is the threshold for
below which the null hypothesis is rejected even though by assumption
it were true, and something else is going on. This means that is also the probability of mistakenly rejecting the null hypothesis, if the null hypothesis is true. This is also called false positive and type I error.
Sometimes researchers talk about the confidence levelγ = (1 − α) instead. This is the probability of not rejecting the null hypothesis given that it is true. Confidence levels and confidence intervals were introduced by Neyman in 1937.
In a two-tailed test, the rejection region for a significance level of α = 0.05 is partitioned to both ends of the sampling distribution and makes up 5% of the area under the curve (white areas).
Statistical significance plays a pivotal role in statistical hypothesis testing. It is used to determine whether the null hypothesis should be rejected or retained. The null hypothesis is the hypothesis that no effect exists in the phenomenon being studied. For the null hypothesis to be rejected, an observed result has to be statistically significant, i.e. the observed p-value is less than the pre-specified significance level .
To determine whether a result is statistically significant, a researcher calculates a p-value,
which is the probability of observing an effect of the same magnitude
or more extreme given that the null hypothesis is true. The null hypothesis is rejected if the p-value is less than (or equal to) a predetermined level, . is also called the significance level, and is the probability of rejecting the null hypothesis given that it is true (a type I error). It is usually set at or below 5%.
For example, when is set to 5%, the conditional probability of a type I error, given that the null hypothesis is true, is 5%, and a statistically significant result is one where the observed p-value is less than (or equal to) 5%. When drawing data from a sample, this means that the rejection region comprises 5% of the sampling distribution. These 5% can be allocated to one side of the sampling distribution, as in a one-tailed test, or partitioned to both sides of the distribution, as in a two-tailed test, with each tail (or rejection region) containing 2.5% of the distribution.
The use of a one-tailed test is dependent on whether the research question or alternative hypothesis specifies a direction such as whether a group of objects is heavier or the performance of students on an assessment is better. A two-tailed test may still be used but it will be less powerful
than a one-tailed test, because the rejection region for a one-tailed
test is concentrated on one end of the null distribution and is twice
the size (5% vs. 2.5%) of each rejection region for a two-tailed test.
As a result, the null hypothesis can be rejected with a less extreme
result if a one-tailed test was used. The one-tailed test is only more powerful than a two-tailed test if the
specified direction of the alternative hypothesis is correct. If it is
wrong, however, then the one-tailed test has no power.
In specific fields such as particle physics and manufacturing, statistical significance is often expressed in multiples of the standard deviation or sigma (σ) of a normal distribution, with significance thresholds set at a much stricter level (for example 5σ).For instance, the certainty of the Higgs boson particle's existence was based on the 5σ criterion, which corresponds to a p-value of about 1 in 3.5 million.
In other fields of scientific research such as genome-wide association studies, significance levels as low as 5×10−8 are not uncommon—as the number of tests performed is extremely large.
Limitations
Researchers
focusing solely on whether their results are statistically significant
might report findings that are not substantive and not replicable. There is also a difference between statistical significance and
practical significance. A study that is found to be statistically
significant may not necessarily be practically significant.
Effect size is a measure of a study's practical significance. A statistically significant result may have a weak effect. To gauge the
research significance of their result, researchers are encouraged to
always report an effect size along with p-values.
An effect size measure quantifies the strength of an effect, such as
the distance between two means in units of standard deviation (cf. Cohen's d), the correlation coefficient between two variables or its square, and other measures.
A statistically significant result may not be easy to reproduce. In particular, some statistically significant results will in fact be
false positives. Each failed attempt to reproduce a result increases the
likelihood that the result was a false positive.
Starting in the 2010s, some journals began questioning whether significance testing, and particularly using a threshold of α=5%, was being relied on too heavily as the primary measure of validity of a hypothesis. Some journals encouraged authors to do more detailed analysis than just
a statistical significance test. In social psychology, the journal Basic and Applied Social Psychology banned the use of significance testing altogether from papers it published, requiring authors to use other measures to evaluate hypotheses and impact.
Other editors, commenting on this ban have noted: "Banning the reporting of p-values,
as Basic and Applied Social Psychology recently did, is not going to
solve the problem because it is merely treating a symptom of the
problem. There is nothing wrong with hypothesis testing and p-values per se as long as authors, reviewers, and action editors use them correctly." Some statisticians prefer to use alternative measures of evidence, such as likelihood ratios or Bayes factors. Using Bayesian statistics can avoid confidence levels, but also requires making additional assumptions, and may not necessarily improve practice regarding statistical testing.
The widespread abuse of statistical significance represents an important topic of research in metascience.
Redefining significance
In 2016, the American Statistical Association (ASA) published a statement on p-values, saying that "the widespread use of 'statistical significance' (generally interpreted as 'p ≤
0.05') as a license for making a claim of a scientific finding (or
implied truth) leads to considerable distortion of the scientific
process". In 2017, a group of 72 authors proposed to enhance reproducibility by changing the p-value threshold for statistical significance from 0.05 to 0.005. Other researchers responded that imposing a more stringent significance threshold would aggravate problems such as data dredging; alternative propositions are thus to select and justify flexible p-value thresholds before collecting data, or to interpret p-values as continuous indices, thereby discarding thresholds and statistical significance. Additionally, the change to 0.005 would increase the likelihood of
false negatives, whereby the effect being studied is real, but the test
fails to show it.
In 2019, over 800 statisticians and scientists signed a message calling
for the abandonment of the term "statistical significance" in science, and the ASA published a further official statement declaring:
We
conclude, based on our review of the articles in this special issue and
the broader literature, that it is time to stop using the term
"statistically significant" entirely. Nor should variants such as
"significantly different," "," and "nonsignificant" survive, whether expressed in words, by asterisks in a table, or in some other way.
In philosophy of mind, qualia (/ˈkwɑːliə,ˈkweɪ-/; singular: quale/-li,-leɪ/) are defined as instances of subjective, conscious experience. The term qualia derives from the Latin neuter plural form (qualia) of the Latin adjective quālis (Latin pronunciation:[ˈkʷaːlɪs]) meaning "of what sort" or "of what kind" in relation to a specific instance, such as "what it is like to taste a specific apple — this particular apple now".
Examples of qualia include the perceived sensation of pain of a headache, the taste of wine, and the redness of an evening sky. As qualitative characteristics of sensations, qualia stand in contrast to propositional attitudes, where the focus is on beliefs about experience rather than what it is directly like to be experiencing.
C.S. Peirce introduced the term quale in philosophy in 1866, and in 1929 C. I. Lewis was the first to use the term "qualia" in its generally agreed-upon modern sense. Frank Jackson
later defined qualia as "...certain features of the bodily sensations
especially, but also of certain perceptual experiences, which no amount
of purely physical information includes". Philosopher and cognitive scientistDaniel Dennett suggested that qualia was "an unfamiliar term for something that could not be more familiar to each of us: the ways things seem to us".
The nature and existence of qualia under various definitions
remain controversial. Much of the debate over the importance of qualia
hinges on the definition of the term, and various philosophers emphasize
or deny the existence of certain features of qualia. Some philosophers
of mind, like Daniel Dennett,
argue that qualia do not exist. Other philosophers, as well as
neuroscientists and neurologists, believe qualia exist and that the
desire by some philosophers to disregard qualia is based on an erroneous
interpretation of what constitutes science.
Definitions
Many
definitions of qualia have been proposed. One of the simpler, broader
definitions is: "The 'what it is like' character of mental states. The
way it feels to have mental states such as pain, seeing red, smelling a
rose, etc."
It
must be confessed, moreover, that perception, and that which depends on
it, are inexplicable by mechanical causes, that is, by figures and
motions. And, supposing that there were a mechanism so constructed as to
think, feel and have perception, we might enter it as into a mill. And
this granted, we should only find on visiting it, pieces which push one
against another, but never anything by which to explain a perception.
This must be sought, therefore, in the simple substance, and not in the
composite or in the machine.
Charles Sanders Peirce introduced the term quale in philosophy in 1866, and in 1929 C.I. Lewis was the first to use the term "qualia" in its generally agreed upon modern sense.
There are recognizable qualitative
characters of the given, which may be repeated in different experiences,
and are thus a sort of universals; I call these "qualia." But although
such qualia are universals, in the sense of being recognized from one to
another experience, they must be distinguished from the properties of
objects. Confusion of these two is characteristic of many historical
conceptions, as well as of current essence-theories. The quale is
directly intuited, given, and is not the subject of any possible error
because it is purely subjective.
Frank Jackson later defined qualia as "...certain
features of the bodily sensations especially, but also of certain
perceptual experiences, which no amount of purely physical information
includes".
Daniel Dennett suggested that qualia was "an unfamiliar term for something that could not be more familiar to each of us: the ways things seem to us". He identifies four properties that are commonly ascribed to qualia. According to these, qualia are:
ineffable – they cannot be communicated, or apprehended by any means other than direct experience.
intrinsic – they are non-relational properties, which do not change depending on the experience's relation to other things.
private – all interpersonal comparisons of qualia are systematically impossible.
directly or immediately apprehensible by consciousness – to experience a quale is to know one experiences a quale, and to know all there is to know about that quale.
If qualia of this sort exist, then a normally sighted person who sees red would be unable to describe the experience of this perception
in such a way that a listener who has never experienced color will be
able to know everything there is to know about that experience. Though
it is possible to make an analogy,
such as "red looks hot", or to provide a description of the conditions
under which the experience occurs, such as "it's the color you see when
light of 700-nm
wavelength is directed at you", supporters of this definition of qualia
contend that such descriptions cannot provide a complete description of
the experience.
Another way of defining qualia is as "raw feels". A raw feel
is a perception in and of itself, considered entirely in isolation from
any effect it might have on behavior and behavioral disposition. In contrast, a cooked feel
is that perception seen in terms of its effects. For example, the
perception of the taste of wine is an ineffable, raw feel, while the
behavioral reaction one has to the warmth or bitterness caused by that
taste of wine would be a cooked feel. Cooked feels are not qualia.
Arguably, the idea of hedonistic utilitarianism,
where the ethical value of things is determined from the amount of
subjective pleasure or pain they cause, is dependent on the existence of
qualia.
Arguments regarding the existence of qualia
Since,
by definition, qualia cannot be fully conveyed verbally, they also
cannot be demonstrated directly in an argument – a more nuanced approach
is needed. Arguments for qualia generally come in the form of thought experiments designed to lead one to the conclusion that qualia exist.
The inverted spectrum thought experiment, originally developed by John Locke, invites us to imagine two individuals who perceive colors differently:
where one person sees red, the other sees green, and vice versa.
Despite this difference in their subjective experiences, they behave and
communicate as if their perceptions are the same, and no physical or
behavioral test can reveal the inversion. Critics of functionalism, and of physicalism
more broadly, argue that if we can imagine this happening without
contradiction, it follows that we are imagining a change in a property
that determines the way things look to us, but that has no physical
basis.
The idea that an inverted spectrum would be undetectable in
practice is also open to criticism on more scientific grounds, by C. L.
Hardin, among others.As Alex Byrne puts it:
...there are more perceptually
distinguishable shades between red and blue than there are between green
and yellow, which would make red-green inversion behaviorally
detectable. And there are yet further asymmetries. Dark yellow is brown
(qualitatively different from yellow), whereas dark blue is blue[...]
Similarly, desaturated bluish-red is pink (qualitatively different from
saturated bluish-red), whereas desaturated greenish-yellow is similar to
saturated greenish-yellow. Again, red is a "warm" color, whereas blue
is "cool"—and perhaps this is not a matter of learned associations with
temperature.
In
the "fading qualia" and "dancing qualia" brain replacement thought
experiments, Chalmers starts by supposing that qualia depend on the
substrate (e.g. that the silicon-based equivalent experiences different
qualia or no qualia). He then argues that the subject's inability to
notice any change creates a contradiction.
According to David Chalmers, all "functionally isomorphic"
systems (those with the same "fine-grained functional organization",
i.e., the same information processing) will have qualitatively identical
conscious experiences. He calls this the principle of organizational invariance. For example, it implies that a silicon chip
that is functionally isomorphic to a brain will have the same
perception of the color red, given the same sensory inputs. He proposed
the thought experiment of the "dancing qualia" to demonstrate this. It
is a reductio ad absurdum
argument that starts by supposing that two such systems can have
different qualia in the same situation. It involves a switch that
enables connecting the main part of the brain with either of these two
subsystems. For example, one subsystem could be a chunk of brain that
causes an object to appear red, and the other could be a silicon chip
that causes the object to appear blue. Since both perform the same
function within the brain, the subject would be unable to notice any
change during the switch. Chalmers argues that this would be highly
implausible if the qualia were truly switching between red and blue,
hence the contradiction. Therefore, he concludes that the dancing qualia
is impossible in practice, and the functionally isomorphic digital
system would not only experience qualia, but it would have conscious
experiences that are qualitatively identical to those of the biological
system (e.g., seeing the same color). He also proposed a similar thought
experiment, named the fading qualia, that argues that it is not
possible for the qualia to fade when each biological neuron is replaced
by a functional equivalent.
Thomas Nagel argues that while a human might be able to imagine what it is like to be a bat by taking "the bat's point of view", it would still be impossible "to know what it is like for a bat to be a bat." (Townsend's big-eared bat pictured).
American philosopher Thomas Nagel's paper What Is it Like to Be a Bat? is often cited in debates about qualia, though it does not use the word
"qualia". Nagel argues that consciousness has an essentially subjective
character, a what-it-is-like aspect. He states that "an organism has
conscious mental states if and only if there is something that it is
like to be that organism – something it is like for the organism." Nagel suggests that this subjective aspect may never be sufficiently accounted for by the objective methods of reductionistic
science. He claims that "if we acknowledge that a physical theory of
mind must account for the subjective character of experience, we must
admit that no presently available conception gives us a clue about how
this could be done." Furthermore, "it seems unlikely that any physical theory of mind can be
contemplated until more thought has been given to the general problem
of subjective and objective."
Saul Kripke
argues that one key consequence of the claim that such things as raw
feels, or qualia, can be meaningfully discussed is that it leads to the
logical possibility of two entities exhibiting identical behavior in all
ways despite one of them entirely lacking qualia. While few claim that such an entity, called a philosophical zombie, actually exists, the possibility is raised as a refutation of physicalism, and in defense of the hard problem of consciousness (the problem of accounting for, in physical terms, subjective, intrinsic, first-person experiences).
The argument holds that it is conceivable for a person to have a
duplicate, identical in every physical way, but lacking consciousness,
called a "philosophical zombie." It would appear exactly the same as the
original person, in both behavior and speech, just without subjective phenomenology.
For these zombies to exist, qualia must not arise from any specific
part or parts of the brain, for if it did there would be no difference
between "normal humans" and philosophical zombies: The
zombie/normal-human distinction can only be valid if subjective
consciousness is separate from the physical brain.
According to Chalmers, the simplest form of the argument goes as follows:
It is conceivable that there be zombies.
If it is conceivable that there be zombies, it is metaphysically possible that there be zombies.
If it is metaphysically possible that there be zombies, then consciousness is non-physical.
Consciousness is nonphysical.
Former AI researcher Marvin Minsky sees the argument as circular. He says the proposition of something physically identical to a human but without subjective experience
assumes that the physical characteristics of humans cannot produce
consciousness, which is exactly what the argument claims to prove. In
other words, it tries to prove consciousness is nonphysical by assuming
consciousness is nonphysical.
Joseph Levine's paper Conceivability, Identity, and the Explanatory Gap
takes up where the criticisms of conceivability arguments (such as the
inverted spectrum argument and the zombie argument) leave off. Levine
agrees that conceivability is a flawed means of establishing
metaphysical realities, but points out that even if we come to the metaphysical conclusion that qualia are physical, there is still an explanatory problem.
While I think this materialist response is right in the end, it does not suffice to put the mind-body problem
to rest. Even if conceivability considerations do not establish that
the mind is in fact distinct from the body, or that mental properties
are metaphysically irreducible to physical properties, still they do
demonstrate that we lack an explanation of the mental in terms of the
physical.
However, such an epistemological
or explanatory problem might indicate an underlying metaphysical issue,
as even if not proven by conceivability arguments, the non-physicality
of qualia is far from ruled out.
In the end, we are right back where
we started. The explanatory gap argument doesn't demonstrate a gap in
nature, but a gap in our understanding of nature. Of course a plausible
explanation for there being a gap in our understanding of nature is that
there is a genuine gap in nature. But so long as we have countervailing
reasons for doubting the latter, we have to look elsewhere for an
explanation of the former.
In 1982, F. C. Jackson offered what he calls the "knowledge argument" for qualia. It goes as follows:
Mary is a brilliant scientist who
is, for whatever reason, forced to investigate the world from a
black-and-white room via a black-and-white television monitor. She
specializes in the neurophysiology of vision and acquires all the
physical information there is to obtain about what goes on when we see
ripe tomatoes or the sky and use terms like "red", "blue", and so on.
She discovers, for example, just which wavelength combinations from the
sky stimulate the retina, and exactly how this produces via the central
nervous system the contraction of the vocal cords and expulsion of air
from the lungs that results in the uttering of the sentence "The sky is
blue." What happens when Mary is released from her black-and-white room
or is given a color television monitor? Does she learn anything new or
not?
Jackson claimed that she does.
This thought experiment
has two purposes. First, it is intended to show that qualia exist. If
we accept the thought experiment, we believe that upon leaving the room
Mary gains something: the knowledge of a particular thing that she did
not possess before. That knowledge, Jackson argues, is knowledge of the
quale that corresponds to the experience of seeing red, and it must thus
be conceded that qualia are real properties, since there is a
difference between a person who has access to a particular quale and one
who does not.
The second purpose of this argument is to refute the physicalist
account of the mind. Specifically, the knowledge argument is an attack
on the physicalist claim about the completeness of physical truths. The
challenge posed to physicalism by the knowledge argument runs as follows:
While in the room, Mary has acquired all the physical facts
there are about color sensations, including the sensation of seeing red.
When Mary exits the room and sees a ripe red tomato, she learns a
new fact about the sensation of seeing red, namely its subjective
character.
Therefore, there are non-physical facts about color sensations. [From 1, 2]
If there are non-physical facts about color sensations, then color sensations are non-physical events.
Therefore, color sensations are non-physical events. [From 3, 4]
If color sensations are non-physical events, then physicalism is false.
Therefore, physicalism is false. [From 5, 6]
Some critics argue that Mary's confinement to a monochromatic
environment wouldn't prevent her from forming color experiences or that
she might deduce what colors look like from her complete physical
knowledge. Others suggest that the thought experiment's conceivability
might conflict with current or future scientific understanding of
vision, but defenders maintain that its purpose is to challenge
materialism conceptually, not scientifically.
Early in his career Jackson argued that qualia are epiphenomenal, meaning they have no causal influence on the physical world. The issue with this view is that if qualia are non-physical, it becomes
unclear how they can have any effect on the brain or behavior. Jackson
later rejected epiphenomenalism, arguing that knowledge about qualia is
impossible if they are epiphenomenal. He concluded that there must be an
issue with the knowledge argument, eventually embracing a representationalist account, arguing that sensory experiences can be understood in physical terms.
Proponents of qualia
Analytic philosophy
David Chalmers
David Chalmers formulated the hard problem of consciousness, which raised the issue of qualia to a new level of importance and acceptance in the field of the philosophy of mind. In 1995 Chalmers argued for what he called "the principle of
organizational invariance": if a system such as one of appropriately
configured computer hardware reproduces the functional organization of
the brain, it will also reproduce the qualia associated with the brain.
Christian List
Philosopher Christian List
has argued that mental phenomena are non-reducible to physical
phenomena on the basis of first-person perspectives and the
unanswerability of the vertiginous question. List has also argued that the problem of other minds
creates a "quadrilemma" for theories of consciousness, and that the
four metaphysical claims of first-person realism, non-solipsism,
non-fragmentation, and one-world cannot all be simultaneously true and
at least one must be rejected, but any combination of three is
internally consistent. List has proposed a model he calls the "many-worlds theory of consciousness" as a possible alternative to solipsism.
E. J. Lowe
E. J. Lowe
denies that indirect realism, wherein which we have access only to
sensory features internal to the brain, necessarily implies a Cartesian dualism. He agrees with Bertrand Russell
that the way images are received by our retinas, our "retinal images",
are connected to "patterns of neural activity in the cortex". He defends a version of the causal theory of perception
in which a causal path can be traced between the external object and
the perception of it. He is careful to deny that we do any inferring
from the sensory field; he believes this allows us to build an access to knowledge on that causal connection. In a later work he moves closer to the non-epistemic argument in that he postulates "a wholly non-conceptual component of perceptual experience".
J. B. Maund
John
Barry Maund, an Australian philosopher of perception, argues that
qualia can be described on two levels, a fact that he refers to as "dual
coding".
Maund extended his argument with reference to color. Color he sees as a dispositional property, not an objective one. Colors are "virtual properties", which means they are as if
things possessed them. Although the naïve view attributes them to
objects, they are intrinsic, non-relational, inner experiences. This
allows for the different perceptions between person and person, and also
leaves aside the claim that external objects are colored.
Moreland Perkins
In his book Sensing the World, Moreland Perkins argues that qualia need not be identified as their
objective sources: a smell, for instance, bears no direct resemblance to
the molecular shape that gives rise to it, nor is a toothache actually
in the tooth. Like Hobbes
he views the process of sensing as complete in itself; as he puts it,
it is not like "kicking a football" where an external object is
required – it is more like "kicking a kick". This explanation evades the
Homunculus Objection, as adhered to by Gilbert Ryle,
among others. Ryle was unable to entertain this possibility, protesting
that "in effect it explained the having of sensations as the not having
of sensations". However, A. J. Ayer
called this objection "very weak" as it betrayed an inability to detach
the notion of eyes, or indeed any sensory organ, from the neural
sensory experience.
Howard Robinson and William Robinson
Philosopher Howard Robinson argued against reducing sensory experiences to physical explanations. He defended the theory of sense data,
maintaining that sensory experiences involve qualia. As a dualist,
Robinson held that mind and matter have distinct metaphysical natures.
He maintained that the knowledge argument shows that physicalism fails
to account for the qualitative nature of qualia.
Similarly, William Robinson, in Understanding Phenomenal Consciousness, advocates for dualism and rejects the idea of reducing phenomenal
experience to neural processes. His theory of Qualitative Event Realism
proposes that phenomenal consciousness consists of immaterial events
caused by brain activity but not reducible to it. He seeks to conciliate
dualism with scientific methodology, aiming for a future unified theory
that respects both phenomenal qualities and scientific explanations.
Neuroscience
Gerald Edelman
In his book Bright Air, Brilliant Fire, neuroscientist and Nobel laureate in Physiology / Medicine Gerald Edelman
says "that [it] definitely does not seem feasible [...] to ignore
completely the reality of qualia". As he sees it, it is impossible to
explain color, sensations, and similar experiences "to a 'qualia-free'
observer" by description alone. Edelman argues that proposing such a
theory of consciousness is proposing "a theory based on a kind of
God's-eye view of consciousness" and that any scientific theory requires
the assumption "that observers have sensation as well as perception."
He concludes by stating that assuming a theory that requires neither
could exist "is to indulge the errors of theories that attempt
syntactical formulations mapped onto objectivist interpretations –
theories that ignore embodiment as a source of meaning. There is no
qualia-free scientific observer."
Antonio Damasio
Neurologist Antonio Damasio, in his book The Feeling Of What Happens,
defines qualia as "the simple sensory qualities to be found in the
blueness of the sky or the tone of sound produced by a cello, and the
fundamental components of the images in the movie metaphor are thus made
of qualia."
Damasio points out that "in all likelihood, I will never know
your thoughts unless you tell me, and you will never know mine until I
tell you." The reason he gives for this is that "the mind and its
consciousness are first and foremost private phenomena" that are
personal, private experiences that should be investigated as such. While
he believes that trying to study these experiences "by the study of
their behavioral correlates is wrong," he does think they can be studied
as "the idea that subjective experiences are not scientifically
accessible is nonsense." In his view the way to do this is for "enough
observers [to] undertake rigorous observations according to the same
experimental design; and [...] that those observations be checked for
consistency across observers and that they yield some form of
measurement." He also thinks that "subjective observations [...] can
inspire objective experiments" and "be explained in terms of the
available scientific knowledge".
In his mind:
The resistance found in some
scientific quarters to the use of subjective observations is a
revisitation of an old argument between behaviorists, who believed that only behaviors, not mental experiences, could be studied objectively, and cognitivists, who believed that studying only behavior did not do justice to human complexity.
Rodolfo Llinás
Neurologist Rodolfo Llinás states in his book I of the Vortex
that qualia, from a neurological perspective, are essential for an
organism's survival and played a key role in the evolution of nervous systems, including in simple creatures like ants or cockroaches.
Llinás contends that qualia are a product of neuronal oscillation and cites anesthesia experiments, showing that qualia can be "turned off" by altering brain oscillations while other connections remain intact.
Vilayanur Ramachandran
Vilayanur S. Ramachandran
Vilayanur S. Ramachandran and William Hirstein proposed three laws of qualia (with a fourth later added), which are
"functional criteria that need to be fulfilled in order for certain
neural events to be associated with qualia" by philosophers of the mind:
Qualia are irrevocable and indubitable. You don't say 'maybe it
is red but I can visualize it as green if I want to'. An explicit neural
representation of red is created that invariably and automatically
'reports' this to higher brain centres.
Once the representation is created, what can be done with it is
open-ended. You have the luxury of choice, e.g., if you have the percept
of an apple you can use it to tempt Adam, to keep the doctor away, bake
a pie, or just to eat. Even though the representation at the input
level is immutable and automatic, the output is potentially infinite.
This isn't true for, say, a spinal reflex arc where the output is also
inevitable and automatic. Indeed, a paraplegic can even have an erection
and ejaculate without an orgasm.
Short-term memory. The input invariably creates a representation
that persists in short-term memory – long enough to allow time for
choice of output. Without this component, again, you get just a reflex
arc.
Attention. Qualia and attention are closely linked. You need
attention to fulfill criterion number two; to choose. A study of
circuits involved in attention, therefore, will shed much light on the
riddle of qualia.
These authors approach qualia from an empirical perspective and not
as a logical or philosophical problem. They wonder how qualia evolved,
and in doing so consider a skeptical point of view in which, since the
objective scientific description of the world is complete without
qualia, it is nonsense to ask why they evolved or what they are for.
However they decide against this skeptical view.
Based on the parsimony principle of Occam's razor, one could accept epiphenomenalism
and deny qualia, since they are not necessary for a description of the
functioning of the brain. However, they argue that Occam's razor is not
useful for scientific discovery. For example, the discovery of relativity in physics was not the product
of accepting Occam's razor but rather of rejecting it and asking the
question of whether a deeper generalization, not required by the
currently available data, was true and would allow for unexpected
predictions. Most scientific discoveries arise, these authors argue,
from ontologically promiscuous conjectures that do not come from current data.
The authors then point out that skepticism might be justified in
the philosophical field, but that science is the wrong place for
skepticism, such as asking if "your red is not my green" or if we can be
logically certain that we are not dreaming. Science, these authors
assert, deals with what is probably true, beyond reasonable doubt, not
with what can be known with complete and absolute certainty. The authors
say that most neuroscientists and even most psychologists dispute the
very existence of the problem of qualia.
Critics of qualia
Daniel Dennett
Daniel Dennett
In Consciousness Explained and Quining Qualia,Daniel Dennett
argues against qualia by claiming that the "knowledge argument" breaks
down if one tries to apply it practically. In a series of thought
experiments, which he calls intuition pumps, he brings qualia into the world of neurosurgery, clinical psychology, and psychological experimentation.
He argues that, once the concept of qualia is so imported, we can
either make no use of it, or the questions introduced by it are
unanswerable precisely because of the special properties defining
qualia.
In Dennett's updated version of the inverted spectrum thought experiment, which he calls alternative neurosurgery,
you again awake to find that your qualia have been inverted – grass
appears red, the sky appears orange, etc. According to the original
account, you should be immediately aware that something has gone
horribly wrong. Dennett argues, however, that it is impossible to know
whether the diabolical neurosurgeons have indeed inverted your qualia
(e.g. by tampering with your optic nerve), or have simply inverted your
connection to memories of past qualia. Since both operations would
produce the same result, you would have no means on your own to tell
which operation has actually been conducted, and you are thus in the odd
position of not knowing whether there has been a change in your
"immediately apprehensible" qualia.
Dennett argues that for qualia to be taken seriously as a
component of experience – for them to make sense as a discrete concept –
it must be possible to show that:
it is possible to know that a change in qualia has occurred, as opposed to a change in something else; or that
there is a difference between having a change in qualia and not having one.
Dennett attempts to show that we cannot satisfy (a) either through
introspection or through observation, and that qualia's very definition
undermines its chances of satisfying (b).
Supporters of qualia point out that in order for you to notice a
change in qualia, you must compare your current qualia with your
memories of past qualia. Arguably, such a comparison would involve
immediate assessment of your current qualia and your memories of past
qualia, but not of the past qualia themselves. Furthermore, modern functional brain imaging
has increasingly suggested that the memory of an experience is
processed in similar ways, and in similar zones of the brain, as the
original perception.
This may mean that there would be asymmetric outcomes between
altering the mechanism of perception of qualia and altering the memory
of that qualia. If the diabolical neurosurgery altered the immediate
perception of qualia, the inversion might not be noticed directly, since
the brain zones which re-process the memories would invert the
remembered qualia. On the other hand, alteration of the qualia memories
themselves would be processed without inversion, and thus you would
perceive them as an inversion. Thus, you might know immediately if
memory of your qualia had been altered, but might not know if immediate
qualia were inverted or whether the diabolical neurosurgeons had done a
sham procedure.
Dennett responds to the Mary the color scientist
thought experiment by arguing that Mary would not, in fact, learn
something new if she stepped out of her black and white room to see the
color red. Dennett asserts that if she already truly knew "everything
about color", that knowledge would include a deep understanding of why
and how human neurology causes us to sense the quale of color. Mary
would therefore already know exactly what to expect upon seeing red,
before ever leaving the room.
Dennett argues that the misleading aspect of the story is that
Mary is supposed to not merely be knowledgeable about color but to
actually know all the physical facts about it, which would be a
knowledge so deep that it exceeds what can be imagined, and twists our
intuitions. If Mary really does know everything physical there is to
know about the experience of color, then this effectively grants her
almost omniscient powers of knowledge. Using this, she will be able to
deduce her own reaction, and figure out exactly what the experience of
seeing red will feel like.[55]: 15–16
Dennett finds that many people find it difficult to see this, so
he uses the case of RoboMary to further illustrate what it would be like
for Mary to possess such a vast knowledge of the physical workings of
the human brain and color vision. RoboMary is an intelligent robot who,
instead of having color cameras as eyes, has a software lock such that
they are only able to perceive black and white and shades in-between.[55]: 27–28
RoboMary can examine the computer brain of similar
non-color-locked robots when they see red, and see exactly how they
react and what kinds of impulses occur. RoboMary can also construct a
simulation of her own brain, unlock the simulation's color-lock and,
with reference to the other robots, simulate exactly how this simulation
of herself reacts to seeing red. RoboMary naturally has control over
all of her internal states except for the color-lock. With the knowledge
of her simulation's internal states upon seeing red, RoboMary can put
her own internal states directly into the states they would be in upon
seeing red. In this way, without ever actually seeing red through her
cameras, she will know exactly what it is like to see red.[55]: 28
Dennett uses this example as an attempt to show us that Mary's
all-encompassing physical knowledge makes her own internal states as
transparent as those of a robot or computer, and it is as
straightforward for her to figure out exactly how it feels to see red.[55]: 16–17
Perhaps Mary's failure to learn exactly what seeing red feels
like is simply a failure of language, or a failure of our ability to
describe experiences. An alien race with a different method of
communication or description might be perfectly able to teach their
version of Mary exactly how seeing the color red would feel. Perhaps it
is simply a uniquely human failing to communicate first-person
experiences from a third-person perspective. Dennett suggests that the
description might even be possible using English. He uses a simpler
version of the Mary thought experiment to show how this might work. What
if Mary was in a room without triangles and was prevented from seeing
or making any triangles? An English-language description of just a few
words would be sufficient for her to imagine what it is like to see a
triangle – she can simply and directly visualize a triangle in her mind.
Similarly, Dennett proposes, it is perfectly, logically, possible that
the quale of what it is like to see red could eventually be described in
an English-language description of millions or billions of words.[53]
In Are we explaining consciousness yet?,[56]
Dennett approves of an account of qualia defined as the deep, rich
collection of individual neural responses that are too fine-grained for
language to capture. For instance, a person might have an alarming
reaction to yellow because of a yellow car that hit her previously, and
someone else might have a nostalgic reaction to a comfort food. These
effects are too individual-specific to be captured by English words. "If
one dubs this inevitable residue qualia, then qualia are
guaranteed to exist, but they are just more of the same, dispositional
properties that have not yet been entered in the catalog".[56]
Paul Churchland
According to Paul Churchland, Mary might be considered akin to a feral child
who suffered extreme isolation during childhood. Technically when Mary
leaves the room, she would not have the ability to see or know what the
color red is, as a brain has to learn and develop how to see colors.
Patterns need to form in the V4 section of the visual cortex, which occurs via exposure to wavelengths of light. This exposure needs to occur during the early stages of brain development. In Mary's case, the identifications and categorizations of color will only be in respect to representations of black and white.[57]
Gary Drescher
In his book Good and Real,[58]Gary Drescher compares qualia with "gensyms" (generated symbols) in Common Lisp.
These are objects that Lisp treats as having no properties or
components, which can only be identified as equal or not equal to other
objects. Drescher explains, "we have no introspective access to whatever
internal properties make the red gensym recognizably distinct from the green [...] even though we know the sensation when we experience it."[58]
Under this interpretation of qualia, Drescher responds to the Mary
thought experiment by noting that "knowing about red-related cognitive
structures and the dispositions they engender –
even if that knowledge were implausibly detailed and exhaustive – would
not necessarily give someone who lacks prior color-experience the
slightest clue whether the card now being shown is of the color called
red." However, this does not imply that our experience of red is
non-mechanical, as "gensyms are a routine feature of
computer-programming languages".[23]: 82
David Lewis
David K. Lewis
introduced a hypothesis about types of knowledge and their transmission
in qualia cases. Lewis agrees that Mary cannot learn what red looks
like through her monochrome physicalist studies, but he proposes that
this does not matter. Learning transmits information, but experiencing
qualia does not transmit information: it communicates abilities. When
Mary sees red, she does not acquire any new information; she instead
gains new abilities. Now she can remember what red looks like, imagine
what other red things might look like and recognize further instances of
redness.
Lewis states that Jackson's thought experiment uses the phenomenal information hypothesis – that is, that the new knowledge that Mary gains upon seeing red is phenomenal information. Lewis then proposes a different ability hypothesis that differentiates between two types of knowledge: knowledge "that" (information) and knowledge "how" (abilities).
Normally the two are entangled; ordinary learning is also an experience
of the subject concerned, and people learn both information (for
instance, that Freud was a psychologist) and gain ability (to recognize
images of Freud). However, in the thought experiment, Mary can use
ordinary learning only to gain "that" knowledge. She is prevented from
using experience to gain the "how" knowledge that would allow her to
remember, imagine and recognize the color red.
We have the intuition that Mary has been deprived of some vital
data to do with the experience of redness. It is also uncontroversial
that some things cannot be learned inside the room; for example, Mary
cannot learn how to ski within the room. Lewis has articulated that
information and ability are potentially different things. In this way, physicalism
is still compatible with the conclusion that Mary gains new knowledge.
It is also useful for considering other instances of qualia – "being a
bat" is an ability, so it is "how" knowledge.[59]
Marvin Minsky
Marvin Minsky
Artificial intelligence researcher Marvin Minsky thinks the problems posed by qualia are essentially issues of complexity, or rather of mistaking complexity for simplicity.
Now, a philosophical dualist might then complain: "You've described how hurting affects your mind – but you still can't express how hurting feels." This, I maintain, is a huge mistake – that attempt to reify "feeling"
as an independent entity, with an essence that's indescribable. As I
see it, feelings are not strange alien things. It is precisely those
cognitive changes themselves that constitute what "hurting" is –
and this also includes all those clumsy attempts to represent and
summarize those changes. The big mistake comes from looking for some
single, simple, "essence" of hurting, rather than recognizing that this is the word we use for complex rearrangement of our disposition of resources.[60]
David Papineau
David Papineau is a defender of the a posteriori physicalist solution to the mind–body problem. He is one of the originators of the teleosemantic theory of mental representation, a solution to the problem of intentionality which derives the intentional content of our beliefs from their biological purpose. In the book Thinking about Consciousness, he offers the causal argument as what he considers the best argument for physicalism:
Conscious mental occurrences have physical effects
All physical effects are fully caused by purely physical prior histories
The physical effects of conscious states are not always overdetermined by distinct causes.
Physicalism follows. Although Papineau recognises that it is possible
to reject these premisses, he claims that to do so leads to empirically
implausible conclusions.
Papineau’s book The Metaphysics of Sensory Experience has
been critiqued by philosopher Benj Hellie. Hellie instead argues in
favor of a theory with the existence of qualia, and that all
alternatives to qualia fail.[61]
In attempting to answer the question "why is the phenomenal
immaterial?", he notes that there is nothing to suggest that the
phenomenal and the physical are anything more than two different ways of
talking about the states or properties of people.[62]: 29
Even if the appearance/reality distinction does not exist for
phenomenal properties, the fact that self-attributions of such
properties are typically considered incorrigible could simply reflect an
epistemic distinction or a linguistic convention.[62]: 29, 32 If this is the case, then Rorty claims that the problem of consciousness is not actually a real metaphysical problem:
"[T]he purportedly metaphysical "problem of consciousness" is no more
and no less than the epistemological "problem of privileged access,"
and that once this is seen questions about dualism versus materialism
lose their interest."[62]: 69
Rorty suggests that the only answer that one can give as to why
qualia are ontologically distinct from physical processes is that the
lack of an appearance/reality distinction is an essential feature of
their being (i.e. it is an essential feature of a quale that it be
incorrigibly known), but he notes that in making this move, qualia have
been hypostatized such that they can take on the property of being pure
appearances. In other words, they have been turned into non-physical,
property-bearing particulars, meaning they are no longer properties of
the person who has them, but rather particulars that exist in addition to
that person. Thus, the intuition that the physical facts do not entail
the phenomenal facts is simply the intuition that the universal pain
quale does not exist anywhere in a world of particular pains which
instantiate it:
"The neo-dualist who identifies a pain with how it feels to be in
pain is hypostatizing a property—painfulness—into a special sort of
particular, a particular of that sort whose esse is percipi and
whose reality is exhausted in our initial acquaintance with it. The
neo-dualist is no longer talking about how people feel but about
feelings as little self-subsistent entities, floating free of people in
the way in which universals float free of the instantiations."[62]: 30
He thus criticizes philosophers who accuse materialists of not taking
qualia seriously when they talk about the neural workings of the brain:
"Thus when neo-dualists say that how pains feel are essential to what pains are, and then criticize Smart
for thinking of the causal role of certain neurons as what is essential
to pain, they are changing the subject. Smart is talking about what is
essential to people being in pain, whereas neo-dualists like Kripke are talking about what is essential for something's being a pain."[62]: 31
The belief that these essentially
private features of mental states exist, and that they form the
introspectible essence of whatever possesses them, is grounded in a
confusion, one that Wittgenstein tried to sweep away in his arguments
against the possibility of a private language. When you judge that I am
in pain, it is on the basis of my circumstances and behavior, and you
could be wrong. When I ascribe a pain to myself, I don't use any such
evidence. I don't find out that I am in pain by observation, nor can I
be wrong. But that is not because there is some other fact about my
pain, accessible only to me, which I consult in order to establish what I
am feeling. For if there were this inner private quality, I could
misperceive it; I could get it wrong, and I would have to find out
whether I am in pain. To describe my inner state, I would also have to
invent a language, intelligible only to me – and that, Wittgenstein
plausibly argues, is impossible. The conclusion to draw is that I
ascribe pain to myself not on the basis of some inner quale but on no
basis at all.[63]
In his book On Human Nature,[64]
Scruton poses a potential line of criticism to this, which is that
while Wittgenstein's private language argument does disprove the concept
of reference to qualia, or the idea that we can talk, even to
ourselves, of their nature; it does not disprove their existence
altogether. Scruton believes that this is a valid criticism, and this is
why he stops short of actually saying that qualia do not exist, and
instead merely suggests that we should abandon the concept. However, he
quotes Wittgenstein in response: "Whereof one cannot speak, thereof one
must be silent."[64]
Michael Tye
Michael Tye
Michael Tye
believes there are no qualia, no "veils of perception" between us and
the referents of our thought. He describes our experience of an object
in the world as "transparent", meaning that no matter what private
understandings and/or misunderstandings we may have of something, it is
still there before us in reality. The idea that qualia intervene between
ourselves and their origins he regards as a "massive error. That is
just not credible. It seems totally implausible [...] that visual
experience is systematically misleading in this way." He continues: "the
only objects of which you are aware are the external ones making up the
scene before your eyes."[23]: 46-47
From this he concludes "that there are no such qualities of
experiences. They are qualities of external surfaces (and volumes and
films), if they are qualities of anything." Thus he believes we can take
our experiences at face value since there is no fear of losing contact
with the realness of physical objects.[23]: 49
In Tye's thought there is no question of qualia without
information being contained within them; it is always "an awareness
that" and always "representational". He characterizes the perception of
children as a misperception of referents that are undoubtedly as present
for them as they are for grown-ups. As he puts it, they may not know
that "the house is dilapidated", but there is no doubt about their
seeing the house. After-images are dismissed as presenting no problem
for the transparency theory because, as he puts it, after-images being illusory, there is nothing that one sees.[23]: 58–59
Tye proposes that phenomenal experience has five basic elements,
for which he has coined the acronym PANIC – Poised, Abstract,
Nonconceptual, Intentional Content.[23]: 63
"Poised" - the phenomenal experience is always present to the understanding, whether or not the agent is able to apply a concept to it.
"Abstract" - it is unclear whether you are in touch with a concrete object (for example, someone may feel a pain in an amputated limb).
"Nonconceptual" - phenomenon can exist although one does not have the concept by which to recognize it.
"Intentional (Content)" - it represents something, whether or not the observer is taking advantage of that fact.
Tye adds that the experience is like a map in that, in most cases, it
goes beyond the shapes, edges, volumes, etc. in the world – you may not
be reading the a map but, as with an actual map there is a reliable
match with what it is mapping. This is why Tye calls his theory representationalism,
makes it plain that Tye believes that he has retained a direct contact
with what produces the phenomena and is therefore not hampered by any
trace of a "veil of perception".
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