Environmental engineering applies scientific and engineering
principles to improve and maintain the environment to protect human
health, protect nature's beneficial ecosystems, and improve
environmental-related enhancement of the quality of human life.
Environmental engineers devise solutions for wastewater management, water and air pollution control, recycling, waste disposal, and public health. They design municipal water supply and industrial wastewater treatment systems,and design plans to prevent waterborne diseases and improve sanitation in urban, rural and recreational areas. They evaluate hazardous-waste management
systems to evaluate the severity of such hazards, advise on treatment
and containment, and develop regulations to prevent mishaps. They
implement environmental engineering law, as in assessing the environmental impact of proposed construction projects.
Most jurisdictions impose licensing and registration requirements for qualified environmental engineers.
Etymology
The
word environmental has its root in the late 19th-century French word
environ (verb), meaning to encircle or to encompass. The word
environment was used by Carlyle in 1827 to refer to the aggregate of
conditions in which a person or thing lives. The meaning shifted again
in 1956 when it was used in the ecological sense, where Ecology is the branch of science dealing with the relationship of living things to their environment.
The second part of the phrase environmental engineer originates
from Latin roots and was used in the 14th century French as engignour,
meaning a constructor of military engines such as trebuchets, harquebuses, longbows, cannons, catapults, ballistas, stirrups, armour
as well as other deadly or bellicose contraptions. The word engineer
was not used to reference public works until the 16th century; and it
likely entered the popular vernacular as meaning a contriver of public
works during John Smeaton's time.
Environmental
engineering is a name for work that has been done since early
civilizations, as people learned to modify and control the environmental
conditions to meet needs. As people recognized that their health was related to the quality of their environment, they built systems to improve it. The ancient Indus Valley Civilization (3300 B.C.E. to 1300 B.C.E.) had advanced control over their water resources.
The public work structures found at various sites in the area include
wells, public baths, water storage tanks, a drinking water system, and a
city-wide sewage collection system. They also had an early canal irrigation system enabling large-scale agriculture.
From 4000 to 2000 B.C.E., many civilizations had drainage systems and some had sanitation facilities, including the Mesopotamian Empire, Mohenjo-Daro, Egypt, Crete, and the Orkney Islands in Scotland. The Greeks also had aqueducts and sewer systems that used rain and wastewater to irrigate and fertilize fields.
The first aqueduct in Rome was constructed in 312 B.C.E., and the Romans continued to construct aqueducts for irrigation and safe urban water supply during droughts.
They also built an underground sewer system as early as the 7th century
B.C.E. that fed into the Tiber River, draining marshes to create
farmland as well as removing sewage from the city.
Modern era
Very
little change was seen from the decline of the Roman Empire until the
19th century, where improvements saw increasing efforts focused on
public health. Modern environmental engineering began in London in the mid-19th century when Joseph Bazalgette designed the first major sewerage system following the Great Stink. The city's sewer system conveyed raw sewage to the River Thames, which also supplied the majority of the city's drinking water, leading to an outbreak of cholera. The introduction of drinking water treatment and sewage treatment in industrialized countries reduced waterborne diseases from leading causes of death to rarities.
The field emerged as a separate academic discipline during the
middle of the 20th century in response to widespread public concern
about water and air pollution and other environmental degradation.
As society and technology grew more complex, they increasingly produced
unintended effects on the natural environment. One example is the
widespread application of the pesticide DDT to control agricultural pests in the years following World War II. The story of DDT as vividly told in Rachel Carson's Silent Spring (1962) is considered to be the birth of the modern environmental movement, which led to the modern field of "environmental engineering."
Education
Many universities offer environmental engineering programs through either the department of civil engineering or chemical engineering and also including electronic projects to develop and balance the environmental
conditions. Environmental engineers in a civil engineering program often focus on hydrology, water resources management, bioremediation,
and water and wastewater treatment plant design. Environmental
engineers in a chemical engineering program tend to focus on
environmental chemistry, advanced air and water treatment technologies,
and separation processes. Some subdivisions of environmental engineering include natural resources engineering and agricultural engineering.
Courses for students fall into a few broad classes:
Mechanical engineering courses oriented towards designing machines and mechanical systems for environmental use such as water and wastewater treatment facilities, pumping stations, garbage segregation plants, and other mechanical facilities.
Environmental engineering or environmental systems
courses oriented towards a civil engineering approach in which
structures and the landscape are constructed to blend with or protect
the environment.
Environmental chemistry, sustainable chemistry or environmental chemical engineering
courses oriented towards understanding the effects of chemicals in the
environment, including any mining processes, pollutants, and also
biochemical processes.
Environmental technology
courses oriented towards producing electronic or electrical graduates
capable of developing devices and artifacts able to monitor, measure,
model and control environmental impact, including monitoring and
managing energy generation from renewable sources.
Curriculum
The following topics make up a typical curriculum in environmental engineering:
Environmental engineers evaluate the water balance within a watershed
and determine the available water supply, the water needed for various
needs in that watershed, the seasonal cycles of water movement through
the watershed and they develop systems to store, treat, and convey water
for various uses.
Water is treated to achieve water quality objectives for the end uses. In the case of a potable water supply, water is treated to minimize the risk of infectious disease transmission, the risk of non-infectious illness, and to create a palatable water flavor. Water distribution systems
are designed and built to provide adequate water pressure and flow
rates to meet various end-user needs such as domestic use, fire
suppression, and irrigation.
There are numerous wastewater treatment
technologies. A wastewater treatment train can consist of a primary
clarifier system to remove solid and floating materials, a secondary
treatment system consisting of an aeration basin followed by flocculation and sedimentation or an activated sludge system and a secondary clarifier, a tertiary biological nitrogen removal system, and a final disinfection
process. The aeration basin/activated sludge system removes organic
material by growing bacteria (activated sludge). The secondary
clarifier removes the activated sludge from the water. The tertiary
system, although not always included due to costs, is becoming more
prevalent to remove nitrogen and phosphorus and to disinfect the water before discharge to a surface water stream or ocean outfall.
Environmental engineers apply scientific and engineering principles
to evaluate if there are likely to be any adverse impacts to water
quality, air quality, habitat quality, flora and fauna, agricultural capacity, traffic,
ecology, and noise. If impacts are expected, they then develop
mitigation measures to limit or prevent such impacts. An example of a
mitigation measure would be the creation of wetlands
in a nearby location to mitigate the filling in of wetlands necessary
for a road development if it is not possible to reroute the road.
In the United States, the practice of environmental assessment
was formally initiated on January 1, 1970, the effective date of the National Environmental Policy Act
(NEPA). Since that time, more than 100 developing and developed nations
either have planned specific analogous laws or have adopted procedure
used elsewhere. NEPA is applicable to all federal agencies in the United
States.
Regulatory agencies
Environmental Protection Agency
The U.S. Environmental Protection Agency
(EPA) is one of the many agencies that work with environmental
engineers to solve critical issues. An essential component of EPA's
mission is to protect and improve air, water, and overall environmental
quality to avoid or mitigate the consequences of harmful effects.
Attention or focus, is the concentration of awareness on some phenomenon to the exclusion of other stimuli. It is the selective concentration on discrete information, either subjectively or objectively. William James
(1890) wrote that "Attention is the taking possession by the mind, in
clear and vivid form, of one out of what seem several simultaneously
possible objects or trains of thought. Focalization, concentration, of consciousness are of its essence." Attention has also been described as the allocation of limited cognitive processing resources. Attention is manifested by an attentional bottleneck, in terms of the amount of data the brain can process each second; for example, in human vision, less than 1% of the visual input data stream of 1MByte/sec can enter the bottleneck, leading to inattentional blindness.
Attention remains a crucial area of investigation within education, psychology, neuroscience, cognitive neuroscience, and neuropsychology. Areas of active investigation involve determining the source of the sensory cues and signals that generate attention, the effects of these sensory cues and signals on the tuning properties of sensory neurons, and the relationship between attention and other behavioral and cognitive processes, which may include working memory and psychological vigilance.
A relatively new body of research, which expands upon earlier research
within psychopathology, is investigating the diagnostic symptoms
associated with traumatic brain injury and its effects on attention. Attention also varies across cultures.
The relationships between attention and consciousness are complex
enough that they have warranted philosophical exploration. Such
exploration is both ancient and continually relevant, as it can have
effects in fields ranging from mental health and the study of disorders of consciousness to artificial intelligence and its domains of research.
Contemporary definition and research
Prior to the founding of psychology as a scientific discipline, attention was studied in the field of philosophy. Thus, many of the discoveries in the field of attention were made by philosophers. Psychologist John B. Watson calls Juan Luis Vives the father of modern psychology because, in his book De Anima et Vita (The Soul and Life), he was the first to recognize the importance of empirical investigation. In his work on memory, Vives found that the more closely one attends to stimuli, the better they will be retained.
By the 1990s, psychologists began using positron emission tomography (PET) and later functional magnetic resonance imaging
(fMRI) to image the brain while monitoring tasks involving attention.
Considering this expensive equipment was generally only available in
hospitals, psychologists sought cooperation with neurologists.
Psychologist Michael Posner (then already renowned for his influential work on visual selective attention) and neurologist Marcus Raichle pioneered brain imaging studies of selective attention.
Their results soon sparked interest from the neuroscience community,
which until then had been focused on monkey brains. With the development
of these technological innovations, neuroscientists became interested in this type of research that combines sophisticated experimental paradigms from cognitive psychology with these new brain imaging techniques. Although the older technique of electroencephalography (EEG) had long been used to study the brain activity underlying selective attention by cognitive psychophysiologists,
the ability of the newer techniques to measure precisely localized
activity inside the brain generated renewed interest by a wider
community of researchers. A growing body of such neuroimaging research has identified a frontoparietal attention network which appears to be responsible for control of attention.
A definition of a psychological construct forms a research approach to its study. In scientific works, attention often coincides and substitutes the notion of intentionality
due to the extent of semantic uncertainty in the linguistic
explanations of these notions' definitions. Intentionality has in turn
been defined as "the power of minds to be about something: to represent
or to stand for things, properties and states of affairs".
Although these two psychological constructs (attention and
intentionality) appear to be defined by similar terms, they are
different notions. To clarify the definition of attention, it would be
correct to consider the origin of this notion to review the meaning of
the term given to it when the experimental study on attention was
initiated. It is thought that the experimental approach began with
famous experiments with a 4 x 4 matrix of sixteen randomly chosen
letters – the experimental paradigm that informed Wundt's theory of attention. Wundt
interpreted the experimental outcome introducing the meaning of
attention as "that psychical process, which is operative in the clear
perception of the narrow region of the content of consciousness."
These experiments showed the physical limits of attention threshold,
which were 3-6 letters observing the matrix during 1/10 s of their
exposition.
"We shall call the entrance into the large region of consciousness -
apprehension, and the elevation into the focus of attention -
apperception."
Wundt's theory of attention postulated one of the main features of this
notion that attention is an active, voluntary process realized during a
certain time.
In contrast, neuroscience research shows that intentionality may emerge
instantly, even unconsciously; research reported to register neuronal
correlates of an intentional act that preceded this conscious act (also
see shared intentionality).
Therefore, while intentionality is a mental state (“the power of the
mind to be about something”, arising even unconsciously), the
description of the construct of attention should be understood in the
dynamical sense as the ability to elevate the clear perception of the
narrow region of the content of consciousness and to keep in mind this
state for a time. The attention threshold would be the period of minimum
time needed for employing perception to clearly apprehend the scope of
intention. From this perspective, a scientific approach to attention is
relevant when it considers the difference between these two concepts
(first of all, between their statical and dynamical statuses).
The growing body of literature shows empirical evidence that
attention is conditioned by the number of elements and the duration of
exposition. Decades of research on subitizing have supported Wundt's findings about the limits of a human ability to concentrate awareness on a task.
Latvian prof. Sandra Mihailova and prof. Igor Val Danilov drew an
essential conclusion from the Wundtian approach to the study of
attention: the scope of attention is related to cognitive development.
As the mind grasps more details about an event, it also increases the
number of reasonable combinations within that event, enhancing the
probability of better understanding its features and particularity.
For example, three items in the focal point of consciousness have six
possible combinations (3 factorial), and four items have 24 (4
factorial) combinations. This number of combinations becomes
significantly prominent in the case of a focal point with six items with
720 possible combinations (6 factorial).
Empirical evidence suggests that the scope of attention in young
children develops from two items in the focal point at age up to six
months to five or more items in the focal point at age about five years. As follows from the most recent studies in relation to teaching activities in school, “attention” should be understood as “the state of concentration of an individual’s consciousness
on the process of selecting by his own psyche the information he
requires and on the process of choosing an algorithm for response
actions, which involves the intensification of sensory and intellectual
activities”.
In cognitive psychology
there are at least two models which describe how visual attention
operates. These models may be considered metaphors which are used to
describe internal processes and to generate hypotheses that are falsifiable. Generally speaking, visual attention is thought to operate as a two-stage process.
In the first stage, attention is distributed uniformly over the
external visual scene and processing of information is performed in
parallel. In the second stage, attention is concentrated to a specific
area of the visual scene (i.e., it is focused), and processing is
performed in a serial fashion.
The first of these models to appear in the literature is the spotlight model. The term "spotlight" was inspired by the work of William James, who described attention as having a focus, a margin, and a fringe.
The focus is an area that extracts information from the visual scene
with a high-resolution, the geometric center of which being where visual
attention is directed. Surrounding the focus is the fringe of
attention, which extracts information in a much more crude fashion
(i.e., low-resolution). This fringe extends out to a specified area, and
the cut-off is called the margin.
The second model is called the zoom-lens model and was first introduced in 1986.
This model inherits all properties of the spotlight model (i.e., the
focus, the fringe, and the margin), but it has the added property of
changing in size. This size-change mechanism was inspired by the zoom lens one might find on a camera, and any change in size can be described by a trade-off in the efficiency of processing.
The zoom-lens of attention can be described in terms of an inverse
trade-off between the size of focus and the efficiency of processing:
because attention resources are assumed to be fixed, then it follows
that the larger the focus is, the slower processing will be of that
region of the visual scene, since this fixed resource will be
distributed over a larger area. It is thought that the focus of
attention can subtend a minimum of 1° of visual angle,however the maximum size has not yet been determined.
A significant debate emerged in the last decade of the 20th
century in which Treisman's 1993 Feature Integration Theory (FIT) was
compared to Duncan and Humphrey's 1989 attentional engagement theory
(AET).
FIT posits that "objects are retrieved from scenes by means of
selective spatial attention that picks out objects' features, forms
feature maps, and integrates those features that are found at the same
location into forming objects." Treismans's theory is based on a
two-stage process to help solve the binding problem of attention. These
two stages are the preattentive stage and the focused attention stage.
Preattentive Stage: The unconscious detection and separation of
features of an item (color, shape, size). Treisman suggests that this
happens early in cognitive processing and that individuals are not
aware of the occurrence due to the counter intuitiveness of separating a
whole into its part. Evidence shows that preattentive focuses are
accurate due to illusory conjunctions.
Focused Attention Stage: The combining of all feature identifiers to
perceive all parts as one whole. This is possible through prior
knowledge and cognitive mapping. When an item is seen within a known
location and has features that people have knowledge of, then prior
knowledge will help bring features all together to make sense of what is
perceived. The case of R.M's damage to his parietal lobe, also known as
Balint's syndrome, shows the incorporation of focused attention and combination of features in the role of attention.
Through sequencing these steps, parallel and serial search is better
exhibited through the formation of conjunctions of objects. Conjunctive
searches, according to Treismans, are done through both stages
in order to create selective and focused attention on an object, though
Duncan and Humphrey would disagree. Duncan and Humphrey's AET
understanding of attention maintained that "there is an initial
pre-attentive parallel phase of perceptual segmentation and analysis
that encompasses all of the visual items present in a scene. At this
phase, descriptions of the objects in a visual scene are generated into
structural units; the outcome of this parallel phase is a
multiple-spatial-scale structured representation. Selective attention
intervenes after this stage to select information that will be entered
into visual short-term memory."
The contrast of the two theories placed a new emphasis on the
separation of visual attention tasks alone and those mediated by
supplementary cognitive processes. As Rastophopoulos summarizes the
debate: "Against Treisman's FIT, which posits spatial attention as a
necessary condition for detection of objects, Humphreys argues that
visual elements are encoded and bound together in an initial parallel
phase without focal attention, and that attention serves to select among
the objects that result from this initial grouping."
Neuropsychological model
In
the twentieth century, the pioneering research of Lev Vygotsky and
Alexander Luria led to the three-part model of neuropsychology defining
the working brain as being represented by three co-active processes
listed as Attention, Memory, and Activation. A.R. Luria published his
well-known book The Working Brain in 1973 as a concise adjunct volume to his previous 1962 book Higher Cortical Functions in Man.
In this volume, Luria summarized his three-part global theory of the
working brain as being composed of three constantly co-active processes
which he described as the; (1) Attention system, (2) Mnestic (memory)
system, and (3) Cortical activation system. The two books together are
considered by Homskaya's account as "among Luria's major works in
neuropsychology, most fully reflecting all the aspects (theoretical,
clinical, experimental) of this new discipline."
The product of the combined research of Vygotsky and Luria have
determined a large part of the contemporary understanding and definition
of attention as it is understood at the start of the 21st-century.
Multitasking can be defined as the attempt to perform two or more
tasks simultaneously; however, research shows that when multitasking,
people make more mistakes or perform their tasks more slowly.
Attention must be divided among all of the component tasks to perform
them. In divided attention, individuals attend or give attention to
multiple sources of information at once or perform more than one task at
the same time.
Older research involved looking at the limits of people
performing simultaneous tasks like reading stories, while listening and
writing something else, or listening to two separate messages through different ears (i.e., dichotic listening).
Generally, classical research into attention investigated the ability
of people to learn new information when there were multiple tasks to be
performed, or to probe the limits of our perception (c.f. Donald Broadbent).
There is also older literature on people's performance on multiple
tasks performed simultaneously, such as driving a car while tuning a
radio or driving while being on the phone.
The vast majority of current research on human multitasking is based on performance of doing two tasks simultaneously,
usually that involves driving while performing another task, such as
texting, eating, or even speaking to passengers in the vehicle, or with a
friend over a cellphone. This research reveals that the human
attentional system has limits for what it can process: driving
performance is worse while engaged in other tasks; drivers make more
mistakes, brake harder and later, get into more accidents, veer into
other lanes, and/or are less aware of their surroundings when engaged in
the previously discussed tasks.
There has been little difference found between speaking on a hands-free cell phone or a hand-held cell phone,
which suggests that it is the strain of attentional system that causes
problems, rather than what the driver is doing with his or her hands.
While speaking with a passenger is as cognitively demanding as speaking
with a friend over the phone,
passengers are able to change the conversation based upon the needs of
the driver. For example, if traffic intensifies, a passenger may stop
talking to allow the driver to navigate the increasingly difficult
roadway; a conversation partner over a phone would not be aware of the
change in environment.
There have been multiple theories regarding divided attention. One, conceived by cognitive scientist Daniel Kahneman,
explains that there is a single pool of attentional resources that can
be freely divided among multiple tasks. This model seems oversimplified,
however, due to the different modalities (e.g., visual, auditory,
verbal) that are perceived.
When the two simultaneous tasks use the same modality, such as
listening to a radio station and writing a paper, it is much more
difficult to concentrate on both because the tasks are likely to
interfere with each other. The specific modality model was theorized by
Cognitive Psychologists David Navon and Daniel Gopher in 1979. However, more recent research using well controlled dual-task paradigms points at the importance of tasks.
As an alternative, resource theory has been proposed as a more
accurate metaphor for explaining divided attention on complex tasks.
Resource theory states that as each complex task is automatized,
performing that task requires less of the individual's limited-capacity
attentional resources.
Other variables play a part in our ability to pay attention to and
concentrate on many tasks at once. These include, but are not limited
to, anxiety, arousal, task difficulty, and skills.
Simultaneous
Simultaneous
attention is a type of attention, classified by attending to multiple
events at the same time. Simultaneous attention is demonstrated by
children in Indigenous communities, who learn through this type of attention to their surroundings.
Simultaneous attention is present in the ways in which children of
indigenous backgrounds interact both with their surroundings and with
other individuals. Simultaneous attention requires focus on multiple
simultaneous activities or occurrences. This differs from multitasking,
which is characterized by alternating attention and focus between
multiple activities, or halting one activity before switching to the
next.
Simultaneous attention involves uninterrupted attention to
several activities occurring at the same time. Another cultural practice
that may relate to simultaneous attention strategies is coordination
within a group. Indigenous heritage toddlers and caregivers in San Pedro
were observed to frequently coordinate their activities with other
members of a group in ways parallel to a model of simultaneous
attention, whereas middle-class European-descent families in the U.S.
would move back and forth between events.
Research concludes that children with close ties to Indigenous American
roots have a high tendency to be especially wide, keen observers. This points to a strong cultural difference in attention management.
Alternative topics and discussions
Overt and covert orienting
Attention may be differentiated into "overt" versus "covert" orienting.
Overt orienting is the act of selectively attending to an item or location over others by moving the eyes to point in that direction.
Overt orienting can be directly observed in the form of eye movements.
Although overt eye movements are quite common, there is a distinction
that can be made between two types of eye movements; reflexive and
controlled. Reflexive movements are commanded by the superior colliculus of the midbrain.
These movements are fast and are activated by the sudden appearance of
stimuli. In contrast, controlled eye movements are commanded by areas in
the frontal lobe. These movements are slow and voluntary.
Covert orienting is the act of mentally shifting one's focus without moving one's eyes.Simply, it is changes in attention that are not attributable to overt
eye movements. Covert orienting has the potential to affect the output
of perceptual processes by governing attention to particular items or
locations (for example, the activity of a V4 neuron whose receptive
field lies on an attended stimuli will be enhanced by covert attention)
but does not influence the information that is processed by the senses.
Researchers often use "filtering" tasks to study the role of covert
attention of selecting information. These tasks often require
participants to observe a number of stimuli, but attend to only one.
The current view is that visual covert attention is a mechanism for
quickly scanning the field of view for interesting locations. This shift
in covert attention is linked to eye movement circuitry that sets up a
slower saccade to that location.
There are studies that suggest the mechanisms of overt and covert
orienting may not be controlled separately and independently as
previously believed. Central mechanisms that may control covert
orienting, such as the parietal lobe, also receive input from subcortical centres involved in overt orienting.
In support of this, general theories of attention actively assume
bottom-up (reflexive) processes and top-down (voluntary) processes
converge on a common neural architecture, in that they control both
covert and overt attentional systems.
For example, if individuals attend to the right hand corner field of
view, movement of the eyes in that direction may have to be actively
suppressed.
Covert attention has been argued to reflect the existence of processes "programming explicit ocular movement". However, this has been questioned on the grounds that N2, "a neural measure of covert attentional allocation—does not always precede eye movements".
However, the researchers acknowledge, "it may be impossible to
definitively rule out the possibility that some kind of shift of covert
attention precedes every shift of overt attention".
Exogenous and endogenous orienting
Orienting
attention is vital and can be controlled through external (exogenous)
or internal (endogenous) processes. However, comparing these two
processes is challenging because external signals do not operate
completely exogenously, but will only summon attention and eye movements
if they are important to the subject.
Exogenous (from Greekexo, meaning "outside", and genein, meaning "to produce") orienting is frequently described as being under control of a stimulus.
Exogenous orienting is considered to be reflexive and automatic and is
caused by a sudden change in the periphery. This often results in a
reflexive saccade. Since exogenous cues are typically presented in the
periphery, they are referred to as peripheral cues. Exogenous
orienting can even be observed when individuals are aware that the cue
will not relay reliable, accurate information about where a target is
going to occur. This means that the mere presence of an exogenous cue
will affect the response to other stimuli that are subsequently
presented in the cue's previous location.
Several studies have investigated the influence of valid and invalid cues.
They concluded that valid peripheral cues benefit performance, for
instance when the peripheral cues are brief flashes at the relevant
location before the onset of a visual stimulus. Psychologists Michael
Posner and Yoav Cohen (1984) noted a reversal of this benefit takes
place when the interval between the onset of the cue and the onset of
the target is longer than about 300 ms. The phenomenon of valid cues producing longer reaction times than invalid cues is called inhibition of return.
Endogenous (from Greekendo,
meaning "within" or "internally") orienting is the intentional
allocation of attentional resources to a predetermined location or
space. Simply stated, endogenous orienting occurs when attention is
oriented according to an observer's goals or desires, allowing the focus
of attention to be manipulated by the demands of a task. In order to
have an effect, endogenous cues must be processed by the observer and
acted upon purposefully. These cues are frequently referred to as central cues.
This is because they are typically presented at the center of a
display, where an observer's eyes are likely to be fixated. Central
cues, such as an arrow or digit presented at fixation, tell observers to
attend to a specific location.
When examining differences between exogenous and endogenous
orienting, some researchers suggest that there are four differences
between the two kinds of cues:
exogenous orienting is less affected by cognitive load than endogenous orienting;
observers are able to ignore endogenous cues but not exogenous cues;
exogenous cues have bigger effects than endogenous cues; and
expectancies about cue validity and predictive value affects endogenous orienting more than exogenous orienting.
There exist both overlaps and differences in the areas of the brain
that are responsible for endogenous and exogenous orientating.
Another approach to this discussion has been covered under the topic
heading of "bottom-up" versus "top-down" orientations to attention.
Researchers of this school have described two different aspects of how
the mind focuses attention to items present in the environment. The
first aspect is called bottom-up processing, also known as
stimulus-driven attention or exogenous
attention. These describe attentional processing which is driven by the
properties of the objects themselves. Some processes, such as motion or
a sudden loud noise, can attract our attention in a pre-conscious, or
non-volitional way. We attend to them whether we want to or not. These aspects of attention are thought to involve parietal and temporal cortices, as well as the brainstem. More recent experimental evidence support the idea that the primary visual cortex creates a bottom-up saliency map, which is received by the superior colliculus in the midbrain area to guide attention or gaze shifts.
The second aspect is called top-down processing, also known as goal-driven, endogenous attention, attentional control or executive
attention. This aspect of our attentional orienting is under the
control of the person who is attending. It is mediated primarily by the frontal cortex and basal ganglia as one of the executive functions. Research has shown that it is related to other aspects of the executive functions, such as working memory, and conflict resolution and inhibition.
Influence of processing load
A "hugely influential" theory regarding selective attention is the perceptual load theory,
which states that there are two mechanisms that affect attention:
cognitive and perceptual. The perceptual mechanism considers the
subject's ability to perceive or ignore stimuli, both task-related and
non task-related. Studies show that if there are many stimuli present
(especially if they are task-related), it is much easier to ignore the
non-task related stimuli, but if there are few stimuli the mind will
perceive the irrelevant stimuli as well as the relevant. The cognitive
mechanism refers to the actual processing of the stimuli. Studies
regarding this showed that the ability to process stimuli decreased with
age, meaning that younger people were able to perceive more stimuli and
fully process them, but were likely to process both relevant and
irrelevant information, while older people could process fewer stimuli,
but usually processed only relevant information.
Some people can process multiple stimuli, e.g. trained Morse code
operators have been able to copy 100% of a message while carrying on a
meaningful conversation. This relies on the reflexive response due to
"overlearning" the skill of morse code reception/detection/transcription
so that it is an autonomous function requiring no specific attention to
perform. This overtraining of the brain comes as the "practice of a
skill [surpasses] 100% accuracy," allowing the activity to become
autonomic, while your mind has room to process other actions
simultaneously.
Based on the primary role of the perceptual load theory,
assumptions regarding its functionality surrounding that attentional
resources are that of limited capacity which signify the need for all of
the attentional resources to be used.
This performance, however, is halted when put hand in hand with
accuracy and reaction time (RT). This limitation arises through the
measurement of literature when obtaining outcomes for scores. This
affects both cognitive and perceptual attention because there is a lack
of measurement surrounding distributions of temporal and spatial
attention. Only a concentrated amount of attention on how effective one
is completing the task and how long they take is being analyzed making a
more redundant analysis on overall cognition of being able to process
multiple stimuli through perception.
Clinical model
Attention
is best described as the sustained focus of cognitive resources on
information while filtering or ignoring extraneous information.
Attention is a very basic function that often is a precursor to all
other neurological/cognitive functions. As is frequently the case,
clinical models of attention differ from investigation models. One of
the most used models for the evaluation of attention in patients with
very different neurologic pathologies is the model of Sohlberg and Mateer. This hierarchic model is based in the recovering of attention processes of brain damage patients after coma.
Five different kinds of activities of growing difficulty are described
in the model; connecting with the activities those patients could do as
their recovering process advanced.
Focused attention: The ability to respond discretely to specific sensory stimuli.
Sustained attention (vigilance and concentration): The ability to maintain a consistent behavioral response during continuous and repetitive activity.
Selective attention: The ability to maintain a behavioral or
cognitive set in the face of distracting or competing stimuli.
Therefore, it incorporates the notion of "freedom from distractibility."
Alternating attention: The ability of mental flexibility that
allows individuals to shift their focus of attention and move between
tasks having different cognitive requirements.
Divided attention: This refers to the ability to respond simultaneously to multiple tasks or multiple task demands.
This model has been shown to be very useful in evaluating attention
in very different pathologies, correlates strongly with daily
difficulties and is especially helpful in designing stimulation programs
such as attention process training, a rehabilitation program for
neurological patients of the same authors.
Other descriptors for types of attention
Mindfulness: Mindfulness has been conceptualized as a clinical model of attention. Mindfulness practices are clinical interventions that emphasize training attention functions.
Vigilant attention: Remaining focused on a non-arousing
stimulus or uninteresting task for a sustained period is far more
difficult than attending to arousing stimuli and interesting tasks, and
requires a specific type of attention called 'vigilant attention'.
Thereby, vigilant attention is the ability to give sustained attention
to a stimulus or task that might ordinarily be insufficiently engaging
to prevent our attention being distracted by other stimuli or tasks.
Neural correlates
Most experiments show that one neural correlate
of attention is enhanced firing. If a neuron has a different response
to a stimulus when an animal is not attending to a stimulus, versus when
the animal does attend to the stimulus, then the neuron's response will
be enhanced even if the physical characteristics of the stimulus remain
the same.
In a 2007 review, Professor Eric Knudsen describes a more general model which identifies four core processes of attention, with working memory at the center:
Working memory temporarily stores information for detailed analysis.
Competitive selection is the process that determines which information gains access to working memory.
Through top-down sensitivity control, higher cognitive processes can
regulate signal intensity in information channels that compete for
access to working memory, and thus give them an advantage in the process
of competitive selection. Through top-down sensitivity control, the
momentary content of working memory can influence the selection of new
information, and thus mediate voluntary control of attention in a
recurrent loop (endogenous attention).
Bottom-up saliency filters automatically enhance the response to
infrequent stimuli, or stimuli of instinctive or learned biological
relevance (exogenous attention).
Neurally, at different hierarchical levels spatial maps can enhance
or inhibit activity in sensory areas, and induce orienting behaviors
like eye movement.
At the top of the hierarchy, the frontal eye fields (FEF) and the dorsolateral prefrontal cortex contain a retinocentric spatial map. Microstimulation in the FEF induces monkeys to make a saccade
to the relevant location. Stimulation at levels too low to induce a
saccade will nonetheless enhance cortical responses to stimuli located
in the relevant area.
At the next lower level, a variety of spatial maps are found in the parietal cortex. In particular, the lateral intraparietal area (LIP) contains a saliency map and is interconnected both with the FEF and with sensory areas.
Exogenous attentional guidance in humans and monkeys is by a bottom-up saliency map in the primary visual cortex. In lower vertebrates, this saliency map is more likely in the superior colliculus (optic tectum).
Certain automatic responses that influence attention, like orienting
to a highly salient stimulus, are mediated subcortically by the superior colliculi.
At the neural network level, it is thought that processes like lateral inhibition mediate the process of competitive selection.
In many cases attention produces changes in the EEG. Many animals, including humans, produce gamma waves (40–60 Hz) when focusing attention on a particular object or activity.
Another commonly used model for the attention system has been put forth by researchers such as Michael Posner. He divides attention into three functional components: alerting, orienting, and executive attention that can also interact and influence each other.
Alerting is the process involved in becoming and staying attentive toward the surroundings. It appears to exist in the frontal and parietal lobes of the right hemisphere, and is modulated by norepinephrine.
Orienting is the directing of attention to a specific stimulus.
Children
appear to develop patterns of attention related to the cultural
practices of their families, communities, and the institutions in which
they participate.
In 1955, Jules Henry
suggested that there are societal differences in sensitivity to signals
from many ongoing sources that call for the awareness of several levels
of attention simultaneously. He tied his speculation to ethnographic
observations of communities in which children are involved in a complex
social community with multiple relationships.
Many Indigenous children in the Americas predominantly learn by observing
and pitching in. There are several studies to support that the use of
keen attention towards learning is much more common in Indigenous
Communities of North and Central America than in a middle-class
European-American setting. This is a direct result of the Learning by Observing and Pitching In model.
Keen attention is both a requirement and result of learning by
observing and pitching-in. Incorporating the children in the community
gives them the opportunity to keenly observe and contribute to
activities that were not directed towards them. It can be seen from
different Indigenous communities and cultures, such as the Mayans of San Pedro, that children can simultaneously attend to multiple events. Most Maya children have learned to pay attention to several events at once in order to make useful observations.
One example is simultaneous attention which involves
uninterrupted attention to several activities occurring at the same
time. Another cultural practice that may relate to simultaneous
attention strategies is coordination within a group. San Pedro toddlers
and caregivers frequently coordinated their activities with other
members of a group in multiway engagements rather than in a dyadic
fashion.
Research concludes that children with close ties to Indigenous American
roots have a high tendency to be especially keen observers.
This learning by observing and pitching-in model requires active
levels of attention management. The child is present while caretakers
engage in daily activities and responsibilities such as: weaving,
farming, and other skills necessary for survival. Being present allows
the child to focus their attention on the actions being performed by
their parents, elders, and/or older siblings. In order to learn in this
way, keen attention and focus is required. Eventually the child is
expected to be able to perform these skills themselves.
Modelling
In the domain of computer vision, efforts have been made to model the mechanism of human attention, especially the bottom-up intentional mechanism and its semantic significance in classification of video contents. Both spatial attention and temporal attention have been incorporated in such classification efforts.
Generally speaking, there are two kinds of models to mimic the
bottom-up salience mechanism in static images. One is based on the
spatial contrast analysis. For example, a center–surround mechanism has
been used to define salience across scales, inspired by the putative
neural mechanism.
It has also been hypothesized that some visual inputs are intrinsically
salient in certain background contexts and that these are actually
task-independent. This model has established itself as the exemplar for
salience detection and consistently used for comparison in the
literature; the other kind of model is based on the frequency domain analysis. This method was first proposed by Hou et al.. This method was called SR. Then, the PQFT method was also introduced. Both SR and PQFT only use the phase information. In 2012, the HFT method was introduced, and both the amplitude and the phase information are made use of. The Neural Abstraction Pyramid
is a hierarchical recurrent convolutional model, which incorporates
bottom-up and top-down flow of information to iteratively interpret
images.
Hemispatial neglect, also called unilateral neglect, often occurs when people have damage to the right hemisphere of their brain.
This damage often leads to a tendency to ignore the left side of one's
body or even the left side of an object that can be seen. Damage to the
left side of the brain (the left hemisphere) rarely yields significant
neglect of the right side of the body or object in the person's local
environments.
The effects of spatial neglect, however, may vary and differ
depending on what area of the brain was damaged. Damage to different
neural substrates can result in different types of neglect. Attention
disorders (lateralized and nonlaterized) may also contribute to the
symptoms and effects. Much research has asserted that damage to gray matter within the brain results in spatial neglect.
New technology has yielded more information, such that there is a
large, distributed network of frontal, parietal, temporal, and
subcortical brain areas that have been tied to neglect. This network can be related to other research as well; the dorsal attention network is tied to spatial orienting.
The effect of damage to this network may result in patients neglecting
their left side when distracted about their right side or an object on
their right side.
Attention in social contexts
Social attention
is one special form of attention that involves the allocation of
limited processing resources in a social context. Previous studies on
social attention often regard how attention is directed toward socially
relevant stimuli such as faces and gaze directions of other individuals.
In contrast to attending-to-others, a different line of researches has
shown that self-related information such as own face and name
automatically captures attention and is preferentially processed
comparing to other-related information. These contrasting effects between attending-to-others and attending-to-self prompt a synthetic view in a recent Opinion article
proposing that social attention operates at two polarizing states: In
one extreme, individual tends to attend to the self and prioritize
self-related information over others', and, in the other extreme,
attention is allocated to other individuals to infer their intentions
and desires. Attending-to-self and attending-to-others mark the two ends
of an otherwise continuum spectrum of social attention. For a given
behavioral context, the mechanisms underlying these two polarities might
interact and compete with each other in order to determine a saliency
map of social attention that guides our behaviors.
An imbalanced competition between these two behavioral and cognitive
processes will cause cognitive disorders and neurological symptoms such
as autism spectrum disorders and Williams syndrome.
Distracting factors
According to Daniel Goleman's book, Focus: The Hidden Driver of Excellence, there are two types of distracting factors affecting focus – sensory and emotional.
A sensory distracting factor would be, for example, while a
person is reading this article, they are neglecting the white field
surrounding the text.
An emotional distracting factor would be when someone is focused
on answering an email, and somebody shouts their name. It would be
almost impossible to neglect the voice speaking it. Attention is
immediately directed toward the source. Positive emotions have also been
found to affect attention. Induction of happiness has led to increased
response times and an increase in inaccurate responses in the face of
irrelevant stimuli. Two possible theories as to why emotions might make
one more susceptible to distracting stimuli is that emotions take up too
much of one's cognitive resources and make it harder to control your
focus of attention. The other theory is that emotions make it harder to
filter out distractions, specifically with positive emotions due to a
feeling of security.
Another distracting factor to attention processes is insufficient
sleep. Sleep deprivation is found to impair cognition, specifically
performance in divided attention. Divided attention is possibly linked
with the circadian processes.
Failure to attend
Inattentional blindness
was first introduced in 1998 by Arien Mack and Irvic Rock. Their
studies show that when people are focused on specific stimuli, they
often miss other stimuli that are clearly present. Though actual
blindness is not occurring here, the blindness that happens is due to
the perceptual load of what is being attended to.
Based on the experiment performed by Mack and Rock, Ula Finch and Nilli
Lavie tested participants with a perceptual task. They presented
subjects with a cross, one arm being longer than the other, for 5
trials. On the sixth trial, a white square was added to the top left of
the screen. The results conclude that out of 10 participants, only 2
(20%) actually saw the square. This would suggest that when a higher
focus was attended to the length of the crossed arms, the more likely
someone would altogether miss an object that was in plain sight.
Change blindness
was first tested by Rensink and coworkers in 1997. Their studies show
that people have difficulty detecting changes from scene to scene due to
the intense focus on one thing, or lack of attention overall. This was
tested by Rensink through a presentation of a picture, and then a blank
field, and then the same picture but with an item missing. The results
showed that the pictures had to be alternated back and forth a good
number of times for participants to notice the difference. This idea is
greatly portrayed in films that have continuity errors. Many people do
not pick up on differences when in reality, the changes tend to be
significant.
History of the study
Philosophical period
Psychologist Daniel E. Berlyne credits the first extended treatment of attention to philosopher Nicolas Malebranche
in his work "The Search After Truth". "Malebranche held that we have
access to ideas, or mental representations of the external world, but
not direct access to the world itself." Thus in order to keep these ideas organized, attention is necessary.
Otherwise we will confuse these ideas. Malebranche writes in "The
Search After Truth", "because it often happens that the understanding
has only confused and imperfect perceptions of things, it is truly a
cause of our errors.... It is therefore necessary to look for means to
keep our perceptions from being confused and imperfect. And, because,
as everyone knows, there is nothing that makes them clearer and more
distinct than attentiveness, we must try to find the means to become
more attentive than we are". According to Malebranche, attention is crucial to understanding and keeping thoughts organized.
Philosopher Gottfried Wilhelm Leibniz introduced the concept of apperception
to this philosophical approach to attention. Apperception refers to
"the process by which new experience is assimilated to and transformed
by the residuum of past experience of an individual to form a new
whole."
Apperception is required for a perceived event to become a conscious
event. Leibniz emphasized a reflexive involuntary view of attention
known as exogenous orienting. However, there is also endogenous
orienting which is voluntary and directed attention. Philosopher Johann Friedrich Herbart
agreed with Leibniz's view of apperception; however, he expounded on it
in by saying that new experiences had to be tied to ones already
existing in the mind. Herbart was also the first person to stress the
importance of applying mathematical modeling to the study of psychology.
Throughout the philosophical era, various thinkers made
significant contributions to the field of attention studies, beginning
with research on the extent of attention and how attention is directed.
In the beginning of the 19th century, it was thought that people were
not able to attend to more than one stimulus at a time. However, with
research contributions by Sir William Hamilton, 9th Baronet
this view was changed. Hamilton proposed a view of attention that
likened its capacity to holding marbles. You can only hold a certain
number of marbles at a time before it starts to spill over. His view
states that we can attend to more than one stimulus at once. William Stanley Jevons later expanded this view and stated that we can attend to up to four items at a time.
1860–1909
This
period of attention research took the focus from conceptual findings to
experimental testing. It also involved psychophysical methods that
allowed measurement of the relation between physical stimulus properties
and the psychological perceptions of them. This period covers the
development of attentional research from the founding of psychology to
1909.
Wilhelm Wundt
introduced the study of attention to the field of psychology. Wundt
measured mental processing speed by likening it to differences in
stargazing measurements. Astronomers in this time would measure the time
it took for stars to travel. Among these measurements when astronomers
recorded the times, there were personal differences in calculation.
These different readings resulted in different reports from each
astronomer. To correct for this, a personal equation
was developed. Wundt applied this to mental processing speed. Wundt
realized that the time it takes to see the stimulus of the star and
write down the time was being called an "observation error" but actually
was the time it takes to switch voluntarily one's attention from one
stimulus to another. Wundt called his school of psychology voluntarism. It was his belief that psychological processes can only be understood in terms of goals and consequences.
Franciscus Donders used mental chronometry to study attention and it was considered a major field of intellectual inquiry by authors such as Sigmund Freud.
Donders and his students conducted the first detailed investigations of
the speed of mental processes. Donders measured the time required to
identify a stimulus and to select a motor response. This was the time
difference between stimulus discrimination and response initiation.
Donders also formalized the subtractive method which states that the
time for a particular process can be estimated by adding that process to
a task and taking the difference in reaction time between the two
tasks. He also differentiated between three types of reactions: simple reaction, choice reaction, and go/no-go reaction.
Hermann von Helmholtz
also contributed to the field of attention relating to the extent of
attention. Von Helmholtz stated that it is possible to focus on one
stimulus and still perceive or ignore others. An example of this is
being able to focus on the letter u in the word house and still
perceiving the letters h, o, s, and e.
One major debate in this period was whether it was possible to attend to two things at once (split attention). Walter Benjamin described this experience as "reception in a state of distraction." This disagreement could only be resolved through experimentation.
Everyone knows what attention
is. It is the taking possession by the mind, in clear and vivid form, of
one out of what seem several simultaneously possible objects or trains
of thought. Focalization, concentration, of consciousness are of its
essence. It implies withdrawal from some things in order to deal
effectively with others, and is a condition which has a real opposite in
the confused, dazed, scatterbrained state which in French is called
distraction, and Zerstreutheit in German.
James differentiated between sensorial attention and intellectual
attention. Sensorial attention is when attention is directed to objects
of sense, stimuli that are physically present. Intellectual attention is
attention directed to ideal or represented objects; stimuli that are
not physically present. James also distinguished between immediate or
derived attention: attention to the present versus to something not
physically present. According to James, attention has five major
effects. Attention works to make us perceive, conceive, distinguish,
remember, and shorten reactions time.
1910–1949
During this period, research in attention waned and interest in behaviorism flourished, leading some to believe, like Ulric Neisser,
that in this period, "There was no research on attention". However,
Jersild published very important work on "Mental Set and Shift" in 1927.
He stated, "The fact of mental set is primary in all conscious
activity. The same stimulus may evoke any one of a large number of
responses depending upon the contextual setting in which it is placed".
This research found that the time to complete a list was longer for
mixed lists than for pure lists. For example, if a list was names of
animals versus a list of the same size with names of animals, books,
makes and models of cars, and types of fruits, it takes longer to
process the second list. This is task switching.
In 1931, Telford discovered the psychological refractory period. The stimulation of neurons is followed by a refractory phase during which neurons are less sensitive to stimulation. In 1935 John Ridley Stroop developed the Stroop Task which elicited the Stroop Effect.
Stroop's task showed that irrelevant stimulus information can have a
major impact on performance. In this task, subjects were to look at a
list of colors. This list of colors had each color typed in a color
different from the actual text. For example, the word Blue would be
typed in Orange, Pink in Black, and so on.
Example: BluePurpleRedGreenPurpleGreen
Subjects were then instructed to say the name of the ink color
and ignore the text. It took 110 seconds to complete a list of this type
compared to 63 seconds to name the colors when presented in the form of
solid squares. The naming time nearly doubled in the presence of conflicting color words, an effect known as the Stroop Effect.
1950–1974
In the 1950s, research psychologists renewed their interest in attention when the dominant epistemology shifted from positivism (i.e., behaviorism) to realism during what has come to be known as the "cognitive revolution". The cognitive revolution admitted unobservable cognitive processes like attention as legitimate objects of scientific study.
Modern research on attention began with the analysis of the "cocktail party problem" by Colin Cherry
in 1953. At a cocktail party how do people select the conversation that
they are listening to and ignore the rest? This problem is at times
called "focused attention", as opposed to "divided attention". Cherry
performed a number of experiments which became known as dichotic listening and were extended by Donald Broadbent and others. In a typical experiment, subjects would use a set of headphones to listen to two streams of words in different ears
and selectively attend to one stream. After the task, the experimenter
would question the subjects about the content of the unattended stream.
Broadbent's Filter Model of Attention
states that information is held in a pre-attentive temporary store, and
only sensory events that have some physical feature in common are
selected to pass into the limited capacity processing system. This
implies that the meaning of unattended messages is not identified. Also,
a significant amount of time is required to shift the filter from one
channel to another. Experiments by Gray and Wedderburn and later Anne Treisman
pointed out various problems in Broadbent's early model and eventually
led to the Deutsch–Norman model in 1968. In this model, no signal is
filtered out, but all are processed to the point of activating their
stored representations in memory. The point at which attention becomes
"selective" is when one of the memory representations is selected for
further processing. At any time, only one can be selected, resulting in
the attentional bottleneck.
This debate became known as the early-selection vs. late-selection models. In the early selection models (first proposed by Donald Broadbent), attention shuts down (in Broadbent's model) or attenuates (in Treisman's refinement)
processing in the unattended ear before the mind can analyze its
semantic content. In the late selection models (first proposed by J.
Anthony Deutsch and Diana Deutsch), the content in both ears is analyzed semantically, but the words in the unattended ear cannot access consciousness. Lavie's perceptual load theory, however, "provided elegant solution to" what had once been a "heated debate".
