Task-invoked pupillary response
Task-invoked pupillary response (also known as the "Task-Evoked pupillary response") is a pupillary response caused by a cognitive load imposed on a human and as a result of the decrease in parasympathetic activity in the peripheral nervous system.[1] 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.[2][3] 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 research.[2]
Early history
[edit]Hundreds of years ago, it was said that merchants could read into their customers' thoughts and intentions by paying attention to changes in the customer's pupil diameter.[1]
Biological background
[edit]Pupil size is controlled by the iris dilator muscle, which dilates the pupil, and the iris sphincter muscle, which contracts the pupil. These are affected by the sympathetic and parasympathetic nervous systems, respectively.[4]
Older research suggests this pupillary response is most likely a result of the reticular activating system of the brainstem being linked to the cerebral cortex.[1] The regulation of some functions of the eye, including dilation, is directly affected by the reticular system. Parts of this system are linked to higher nervous structures that are directly involved in cognition aask-related activities, as well as the activation of the cortex. These nervous structures include the:
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 associated with the locus-coeruleus norepinephrine (LC-NE) system[4], and the recent research uses pupil dilations as a biomarker of the LC-NE system activity[5][6]. 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. However, note that a broad range of neural systems influences pupil dilations[7][8][9]. One such system is the basal forebrain-acetylcholine (ACh) pathway[10][11]. Similar to the locus-coeruleus, the basal forebrain projects widely across the brain.
Experimental findings
[edit]Short-term memory
[edit]Beatty and Kahneman (1966) asked participants of an experiment to remember a sequence of digits at a rate of one per second.[1] A pause of 2 seconds followed, and then the participants were asked to repeat the digits at the same rate. They found that 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.[2][12] For this reason, task-evoked pupillary response has the potential to be used as a measure of cognitive load.
Diagnosticity
[edit]Task-evoked pupillary response is not diagnostic when the cognitive load is related to task performance.[1] 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.[1][2] 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
[edit]Some studies suggest that pupillary dilation due to task-evoked pupillary response is associated with greater task performance.[4] For example, when taking part in an experiment involving the n-back 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.[4] When presented with a task measuring the Stroop effect, 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
[edit]Those who are experts in their field experience a lower cognitive load and so a smaller task-evoked pupillary response when compared to novices.[13] This is suggested to be because experts are able to more easily access information.
Intelligence
[edit]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 task.[4] However, tests, targeting fluid intelligence showed that individuals with a higher level of fluid intelligence displayed greater dilation of the pupils than those with lower fluid intelligence.
Surprise and sequential processing
[edit]Sensory information exhibits statistical regularities that humans continuously learn[14]. When these expectations are violated, such as in an oddball paradigm where a deviant stimulus occurs among standards, our perceptual system detects the discrepancy, and the brain responses are generated (mismatch negativity and P300) along with pupil dilations[15][16][17].
More complex violations, such as transitions between structured and random sequences, elicit pupil responses[5][17][6] that scale with the informational change or surprise in the environment [5]. Larger dilations occur for transitions from predictable to unpredictable contexts, highlighting that pupil dynamics reflect not only minor sensory deviations but also the statistical structure of the environment.
Negative results
[edit]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.[1] However, it is argued[by whom?] that during this experiment, the pupil size was recorded 3 seconds after the visual stimulus of the flight simulator display was presented. Since the pupillary response is very rapid, it may be the case that the response has finished by the time the pupil size was measured.
Reliability
[edit]Some external variables, such as light and near reflexes, may cause variance to the task-evoked pupillary response.[1][2] 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.[1] 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.[1]
See also
[edit]References
[edit]- ^ a b c d e f g h i j Kramer AF (1991). "Physiological metrics of mental workload: A review of recent progress.". In Damos DL (ed.). Multiple-task Performance. London: Taylor & Francis Ltd.
- ^ a b c d e Beatty J (March 1982). "Task-evoked pupillary responses, processing load, and the structure of processing resources". Psychological Bulletin. 91 (2): 276–92. doi:10.1037/0033-2909.91.2.276. PMID 7071262.
- ^ Kahneman D (1973). Attention and effort. Englewood Cliffs, N. J.: Prentice-hall.
- ^ a b c d e van der Wel P, van Steenbergen H (December 2018). "Pupil dilation as an index of effort in cognitive control tasks: A review". Psychonomic Bulletin & Review. 25 (6): 2005–2015. doi:10.3758/s13423-018-1432-y. PMC 6267528. PMID 29435963.
- ^ a b c Basgol, Hamit; Dayan, Peter; Franz, Volker H. (2025-02-01). "Violation of auditory regularities is reflected in pupil dynamics". Cortex. 183: 66–86. doi:10.1016/j.cortex.2024.10.023. ISSN 0010-9452. PMID 39616966.
- ^ a b Zhao, Sijia; Chait, Maria; Dick, Fred; Dayan, Peter; Furukawa, Shigeto; Liao, Hsin-I. (2019-09-06). "Pupil-linked phasic arousal evoked by violation but not emergence of regularity within rapid sound sequences". Nature Communications. 10 (1): 4030. doi:10.1038/s41467-019-12048-1. ISSN 2041-1723. PMC 6731273. PMID 31492881.
- ^ Joshi, Siddhartha; Li, Yin; Kalwani, Rishi M.; Gold, Joshua I. (2016-01-06). "Relationships between pupil diameter and neuronal activity in the locus coeruleus, colliculi, and cingulate cortex". Neuron. 89 (1): 221–234. doi:10.1016/j.neuron.2015.11.028. ISSN 0896-6273. PMC 4707070. PMID 26711118.
- ^ Joshi, Siddhartha; Gold, Joshua I. (2020-06-01). "Pupil size as a window on neural substrates of cognition". Trends in Cognitive Sciences. 24 (6): 466–480. doi:10.1016/j.tics.2020.03.005. ISSN 1364-6613. PMC 7271902. PMID 32331857.
- ^ Strauch, Christoph; Wang, Chin-An; Einhäuser, Wolfgang; Stigchel, Stefan Van der; Naber, Marnix (2022-08-01). "Pupillometry as an integrated readout of distinct attentional networks". Trends in Neurosciences. 45 (8): 635–647. doi:10.1016/j.tins.2022.05.003. ISSN 0166-2236. PMID 35662511.
- ^ Larsen, Rylan S.; Waters, Jack (2018-03-09). "Neuromodulatory correlates of pupil dilation". Frontiers in Neural Circuits. 12 21. doi:10.3389/fncir.2018.00021. ISSN 1662-5110. PMC 5854659. PMID 29593504.
- ^ Lloyd, Beth; de Voogd, Lycia D; Mäki-Marttunen, Verónica; Nieuwenhuis, Sander (2023-06-27). "Pupil size reflects activation of subcortical ascending arousal system nuclei during rest". eLife. 12 e84822. doi:10.7554/eLife.84822. hdl:1887/3672318. ISSN 2050-084X.
- ^ Hess EH, Polt JM (March 1964). "Pupil size in relation to mental activity during simple problem-solving". Science. 143 (3611): 1190–2. Bibcode:1964Sci...143.1190H. doi:10.1126/science.143.3611.1190. PMID 17833905. S2CID 27169110.
- ^ Szulewski A, Roth N, Howes D (July 2015). "The use of task-evoked pupillary response as an objective measure of cognitive load in novices and trained physicians: a new tool for the assessment of expertise". Academic Medicine. 90 (7): 981–7. doi:10.1097/ACM.0000000000000677. PMID 25738386.
- ^ Barascud, Nicolas; Pearce, Marcus T.; Griffiths, Timothy D.; Friston, Karl J.; Chait, Maria (2016-02-02). "Brain responses in humans reveal ideal observer-like sensitivity to complex acoustic patterns". Proceedings of the National Academy of Sciences. 113 (5): E616-25. doi:10.1073/pnas.1508523113. ISSN 0027-8424. PMC 4747708. PMID 26787854.
- ^ Alamia, Andrea; VanRullen, Rufin; Pasqualotto, Emanuele; Mouraux, André; Zenon, Alexandre (2019-07-03). "Pupil-linked arousal responds to unconscious surprisal". Journal of Neuroscience. 39 (27): 5369–5376. doi:10.1523/JNEUROSCI.3010-18.2019. ISSN 0270-6474. PMC 6607748. PMID 31061089.
- ^ Liao, Hsin-I.; Yoneya, Makoto; Kidani, Shunsuke; Kashino, Makio; Furukawa, Shigeto (2016-02-17). "Human pupillary dilation response to deviant auditory stimuli: effects of stimulus properties and voluntary attention". Frontiers in Neuroscience. 10: 43. doi:10.3389/fnins.2016.00043. ISSN 1662-453X. PMC 4756168. PMID 26924959.
- ^ a b Başgöl, Hamit; Raab, Florian; Dayan, Peter; Franz, Volker H (2025-10-02). "Modality-general sensitivity of pupil responses to regularity violations". osf.io. doi:10.31234/osf.io/um9fe_v1. Retrieved 2025-10-21.