Task-invoked pupillary response (also known as the "Task-''Evoked'' pupillary response") is a

pupillary response Pupillary response is a physiological response that varies the size of the pupil, via the optic and oculomotor cranial nerve. A constriction response (miosis), is the narrowing of the pupil, which may be caused by scleral buckles or drugs such a ...

caused by a

cognitive load In cognitive psychology, cognitive load refers to the amount of working memory resources used. There are three types of cognitive load: ''intrinsic'' cognitive load is the effort associated with a specific topic; ''extraneous'' cognitive load refe ...

imposed on a human and as a result of the decrease in

parasympathetic The parasympathetic nervous system (PSNS) is one of the three divisions of the autonomic nervous system, the others being the sympathetic nervous system and the enteric nervous system. The enteric nervous system is sometimes considered part of t ...

activity in the

peripheral nervous system The peripheral nervous system (PNS) is one of two components that make up the nervous system of bilateral animals, with the other part being the central nervous system (CNS). The PNS consists of nerves and ganglia, which lie outside the brain ...

. It is found to result in a linear increase in pupil dilation as the demand a task places on the working memory increases. Beatty evaluated task-invoked pupillary response in different tasks for short-term memory, language processing, reasoning, perception, sustained attention and selective attention and found that it fulfills Kahneman's three criteria for indicating processing load. That is, it can reflect differences in processing load within a task, between different tasks and between individuals. It is used as an indicator of cognitive load levels in

psychophysiology Psychophysiology (from Ancient Greek, Greek , ''psȳkhē'', "breath, life, soul"; , ''physis'', "nature, origin"; and , ''wiktionary:-logia, -logia'') is the branch of psychology that is concerned with the physiology, physiological bases of psych ...

research.

Early History

Hundreds of years ago, it was said that merchants could read into their customer's thoughts and intentions by paying attention to changes in the customer's pupil diameter.

Biological background

Pupil size is controlled by the

iris dilator muscle The iris dilator muscle (pupil dilator muscle, pupillary dilator, radial muscle of iris, radiating fibers), is a smooth muscle of the eye, running radially in the iris and therefore fit as a dilator. The pupillary dilator consists of a spokelike ...

, which dilate the pupil, and the

iris sphincter muscle The iris sphincter muscle (pupillary sphincter, pupillary constrictor, circular muscle of iris, circular fibers) is a muscle in the part of the eye called the iris. It encircles the pupil of the iris, appropriate to its function as a constrictor ...

, which contract the pupil. These are affected by the sympathetic and parasympathetic nervous systems respectively. Older research suggests this pupillary response is most likely a result of the

reticular activating system The reticular formation is a set of interconnected nuclei that are located throughout the brainstem. It is not anatomically well defined, because it includes neurons located in different parts of the brain. The neurons of the reticular formatio ...

of the brainstem being linked to the

cerebral cortex The cerebral cortex, also known as the cerebral mantle, is the outer layer of neural tissue of the cerebrum of the brain in humans and other mammals. The cerebral cortex mostly consists of the six-layered neocortex, with just 10% consisting of ...

. The regulation of some functions of the eye, including dilation, are directly affected by the reticular system. Parts of this system are linked to higher nervous structures that are directly involved in cognition and task-related activities as well as the activation of the cortex. These nervous structures include the: *

thalamus The thalamus (from Greek θάλαμος, "chamber") is a large mass of gray matter located in the dorsal part of the diencephalon (a division of the forebrain). Nerve fibers project out of the thalamus to the cerebral cortex in all directions, ...

* caudate body *

archicortex The archicortex, or archipallium, is the phylogenetically oldest region of the brain's cerebral cortex. It is often considered contiguous with the olfactory cortex, but its extent varies among species. In older species, such as fish, the archipal ...

neocortex The neocortex, also called the neopallium, isocortex, or the six-layered cortex, is a set of layers of the mammalian cerebral cortex involved in higher-order brain functions such as sensory perception, cognition, generation of motor commands, sp ...

As such, cognitive load can have a direct effect on some functions of the reticular system, like the dilation of the eye, and cause task-evoked pupillary response. More modern work finds that the pupillary response is directly related to the locus-coeruleus

norepinephrine Norepinephrine (NE), also called noradrenaline (NA) or noradrenalin, is an organic chemical in the catecholamine family that functions in the brain and body as both a hormone and neurotransmitter. The name "noradrenaline" (from Latin '' ad'', ...

(LC-NE) system. The LC-NE system is linked to areas of the brain related to the detection, cognition and attention of task demands. It is also very likely that the reason the LC is linked to pupillary activity is due to the shared interactions with the gigantocellularis nucleus of the ventral medulla.

Experimental findings

Short term memory

Beatty and

Kahneman Daniel Kahneman (; he, דניאל כהנמן; born March 5, 1934) is an Israeli-American psychologist and economist notable for his work on the psychology of judgment and decision-making, as well as behavioral economics, for which he was awarde ...

(1966) asked participants of an experiment to remember a sequence of digits at a rate of one per second. A pause of 2 seconds followed and then the participants were asked to repeat the digits at the same rate. They found pupillary diameter increased with each digit the participants heard and then decreased as they repeated the digits back in order. The maximum size depended on how many digits were to be remembered and repeated. As such, the extent of dilation is directly related to the level of difficulty of the task, thus the amount of cognitive load, or "mental effort" that was experienced by participants. For this reason, task-evoked pupillary response has potential to be used as a measure of cognitive load.

Diagnosticity

Task-evoked pupillary response is not diagnostic when the cognitive load is related to task performance. This is because the pupillary response is the same for a large array of activities that require mental effort including perceptual, cognitive and response related tasks. Instead, task-evoked pupillary response can be observed as a measure of cognitive load. However, task-evoked pupillary response appears to be diagnostic when it comes to data-limited processing. For example, if presented with changes to weak auditory stimuli, the pupil will not demonstrate any changes in diameter but will instead be affected by changes to experimental conditions.

Task Performance

Some studies suggest pupillary dilation due to task-evoked pupillary response is associated with greater task performance. For example, when taking part in an experiment involving the

n-back The n-back task is a continuous performance task that is commonly used as an assessment in psychology and cognitive neuroscience to measure a part of working memory and working memory capacity.Gazzaniga, Michael S.; Ivry, Richard B.; Mangun, George ...

task, a correlation was observed between those with higher dilation, due to pupillary response, and improved performance. Conversely, other studies show the opposite relationship, where higher pupillary dilation is associated with lower task performance. When presented with a task measuring the

Stroop effect ---- ---- Naming the font color of a printed word is an easier and quicker task if word meaning and font color are congruent. If two words are both printed in red, the average time to say "red" in response to the written word "green" is ...

, higher pupil dilation positively correlated with the size of the Stroop effect. This is suggested to be because those who are poor at a test regarding incongruencies must put in more mental effort than those more skilled at stopping themselves when faced with incongruency. However, the same correlation could be explained through the potential ease with which information is accessed by those who have good inhibitory control.

Expertise

Those who are experts in their field experience a lower cognitive load and so a smaller task-evoked pupillary response when compared to novices. This is suggested to be because experts are able to more easily access information.

Intelligence

A study showed that the pupils of more intelligent individuals show a smaller increase in diameter when compared to less intelligent individuals completing the same

arithmetic Arithmetic () is an elementary part of mathematics that consists of the study of the properties of the traditional operations on numbers— addition, subtraction, multiplication, division, exponentiation, and extraction of roots. In the 19th ...

task. However, tests, targeting

fluid intelligence The concepts of fluid intelligence (''g''f) and crystallized intelligence (''g''c) were introduced in 1963 by the psychologist Raymond Cattell. According to Cattell's psychometrically-based theory, general intelligence (''g'') is subdivided into ' ...

showed that individuals with a higher level of fluid intelligence displayed greater dilation of the pupils than those with lower fluid intelligence.

Negative results

Wierwille and colleagues found that task-evoked pupillary response provided negative results when pilots were asked to run a flight simulator while solving navigational problems. However, it is argued that during this experiment, the pupil size was recorded 3 seconds after the visual stimulant of the

flight simulator A flight simulator is a device that artificially re-creates aircraft flight and the environment in which it flies, for pilot training, design, or other purposes. It includes replicating the equations that govern how aircraft fly, how they rea ...

display was presented. Due to the fact that the pupillary response is very rapid, it may be the case that the response may have finished by the time the pupil size was measured.

Reliability

Some external variables such as light and near reflexes may cause variance to the task-evoked pupillary response. It is for this reason, that Kramer argues that the use of this pupillary response as a scientific measure of cognitive load should be kept to the laboratory, and not for use in the field. This is shown further by Hess who found that when participants move their view across a non-uniform field, such as a photograph, the task-evoked pupillary response may be affected.

References

{{DEFAULTSORT:Task-Invoked Pupillary Response Eye