Pupil Dynamics Research Articles

Pupil Dynamics Induced by Light Reflex After Posterior Chamber Phakic Intraocular Lens Implantation.

To assess the light reflex of the pupil after Implantable Collamer Lens (ICL) (KS-aquaPORT; STAAR Surgical, Nidau, Switzerland) implantation to determine whether the ICL implantation might affect the pupil dynamics. This study examined 28 eyes of 28 consecutive patients who underwent implantation of the posterior phakic ICL for the correction of myopia and astigmatism. Patient age at the time of surgery was 31.1 ± 6.8 years (range: 25 to 42 years). Preoperative refraction was -7.38 ± 2.26 diopters (D) (range: -3.25 to -11.80 D). Light reflex was evaluated using the infrared pupillometer Iriscorder C7364 (Hamamatsu Photonics, Hamamatsu, Japan). Measured parameters included pupil diameter (D1), constriction ratio, maximum constriction velocity, maximum dilation velocity, and the time required to recover 63% of the pupil diameter (T5). At 6 months postoperatively, the authors also investigated the relationship with the amount of vault using the Pentacam (Oculus Optikgeräte, Wetzlar, Germany). Evaluations with the instrument were performed before and at 1, 3, and 6 months after surgery. There was no significant association found between any of the parameters (analysis of variance, D1: P = .99, constriction ratio: P = .59, maximum constriction velocity: P = .87, maximum dilation velocity: P = .13, T5: P =.57). The vault of the ICL at 6 months postoperatively was 382.1 ± 176.5 μm. There were no significant associations between the maximum constriction velocity, maximum dilation velocity, and amount of vaulting (Spearman correlation coefficient maximum constriction velocity: r = 0.07, P = .71, maximum dilation velocity: r = 0.26, P = .28). The light reflex of the pupillary dynamics continued to be maintained at 6 months after ICL implantation. Current findings also verified that ICL implantation had little influence on the postoperative function of the iris. [J Refract Surg. 2017;33(10):704-707.].

Superior Abilities to Focus Visual Attention and Pupil Dynamics are linked with Broader Autism Traits

Superior Abilities to Focus Visual Attention and Pupil Dynamics are linked with Broader Autism Traits

Autonomic Dysfunction after Mild Traumatic Brain Injury.

A mild traumatic brain injury (mTBI) is a complex pathophysiologic process that has a systemic effect on the body aside from solely an impairment in cognitive function. Dysfunction of the autonomic nervous system (ANS) has been found to induce abnormalities in organ systems throughout the body, and may contribute to cardiovascular dysregulation and increased mortality. Autonomic dysfunction, also known as dysautonomia, has been studied in moderate and severe TBI, and has emerged as a major contributing factor in the symptomatology in mTBI as well. Analysis of the ANS has been studied through changes in heart rate variability (HRV), pupillary dynamics, eye pressure, and arterial pulse wave in those with mild TBI. Graded exercise testing has been studied as both a method of diagnosis and as a means of recovery in those with mild TBI, especially in those with persistent symptoms. Given the studies showing persistence of autonomic dysfunction after symptomatic resolution of concussions, further research is needed to establish return to play protocols

Assessing Repeatability of Pupillometric Measurements in the Eyes of Refractive Surgery Candidates Using Infrared Pupillometer.

To assess the repeatability of measuring pupil dynamics using an infrared pupillometer. A total of 124 eyes of 124 patients scheduled for corneal laser refractive surgery were separated into myopic and hyperopic groups and further subdivided based on high or low levels of astigmatism. Measurements were taken using dynamic pupillometry (Topolyzer Vario; Alcon Laboratories, Inc., Sinking Spring, PA). Main outcome measures were pupil diameter size, the distance between the pupil center and the keratoscopic axis, and the spatial shift of the pupil center. Repeatability of measurements was assessed from test-retest repeatability (2.77 Sw), coefficient of variation, and intraclass correlation coefficient (ICC). The 2.77 Sw of all measured parameters was lower than 0.36 and 0.44 mm for myopic and hyperopic eyes, respectively. ICCs of the pupil diameter measurements were higher than 0.963 and 0.926 in myopic and hyperopic eyes, respectively. ICCs of the distance between the pupil center and the corneal vertex along the x-axis were higher than 0.934 and 0.994 in myopic and hyperopic eyes, respectively. Along the y-axis, ICCs of this distance were higher than 0.417 in myopic eyes and higher than 0.504 in hyperopic eyes. The pupil center shift measurement ICCs were lower than 0.482 and 0.526 for myopic and hyperopic eyes, respectively. In all groups, the Topolyzer Vario showed excellent repeatability when measuring pupil dynamic parameters except when measuring pupil center shift and distance between the pupil center and the corneal vertex along the vertical axis. [J Refract Surg. 2017;33(8):552-557.].

Pupillometry as a Screening Tool to Detect Pseudoexfoliation Syndrome

Our objective was to evaluate the diagnostic value of a handheld pupillometer in differentiating eyes with pseudoexfoliation syndrome (PXS) from healthy controls. This population-based, cross-sectional study was conducted in the province of Eskisehir, Turkey. Subjects 40 years of age and older were randomly recruited using stratified two-stage cluster sampling from the database of the Turkish Statistical Institute office in Eskisehir. Recruitment took place between June and October 2014. The inclusion criteria were healthy subjects who did not have a previous diagnosis of glaucoma or other issues affecting pupil dynamics. After an extensive ophthalmic examination, pupillometry was performed under standard photopic room lighting conditions. After pupillometry, the pupil was dilated and digital images of the anterior segment were taken for confirmation of PXS. An inter-eye pupil diameter difference of ≥0.4 mm was defined as pupil asymmetry. Of the 2356 invited subjects, 2017 agreed to participate (85.6%), and 1559 subjects were eligible for the study. An age-matched subgroup consisting of 529 healthy controls was randomly selected to compare with the 60 subjects who were diagnosed with PXS. The mean pupil diameters of subjects with PXS and healthy controls were 3.57 ± 0.68 mm and 3.68 ± 0.63 mm, respectively (P = .652). In the ROC analysis, the precision of pupil diameter in discriminating PXS was low (AUC 0.56, sensitivity 14%, specificity 94%). Pupil asymmetry increased the chances of having PXS by 3.46-fold. Pupillometry performed poorly in the detection of PXS scoring a positive predictive value of 26%.

Influence of refractive error on pupillary dynamics in the normal and mild traumatic brain injury (mTBI) populations

PurposeThere have been several studies investigating static, baseline pupil diameter in visually-normal individuals across refractive error. However, none have assessed the dynamic pupillary light reflex (PLR). In the present study, both static and dynamic pupillary parameters of the PLR were assessed in both the visually-normal (VN) and the mild traumatic brain injury (mTBI) populations and compared as a function of refractive error. MethodsThe VN population comprised 40 adults (22–56 years of age), while the mTBI population comprised 32 adults (21–60 years of age) over a range of refractive errors (−9.00D to +1.25D). Seven pupillary parameters (baseline static diameter, latency, amplitude, and peak and average constriction and dilation velocities) were assessed and compared under four white-light stimulus conditions (dim pulse, dim step, bright pulse, and bright step). The Neuroptics, infrared, DP-2000 binocular pupillometer (30Hz sampling rate; 0.05mm resolution) was used in the monocular (right eye) stimulation mode. ResultsFor the majority of pupillary parameters and stimulus conditions, a Gaussian distribution best fit the data, with the apex centered in the low myopic range (−2.3 to −4.9D). Responsivity was reduced to either side of the apex. ConclusionsOver a range of dynamic and static pupillary parameters, the PLR was influenced by refractive error in both populations. In cases of high refractive error, the PLR parameters may need to be compensated for this factor for proper categorization and diagnosis.

High-intensity Focused Ultrasound Cycloplasty: Analysis of Pupil Dynamics.

ABSTRACTAimHigh-intensity focused ultrasound cystoplasty (UCP) aims to noninvasively and selectively target the ciliary body, thus lowering intraocular pressure (IOP). To be used on a large scale, the safety of the UCP procedure should be studied. Therefore, its effect on pupil behavior is important to better inform patients and to help physicians predict possible treatment side effects. This study aimed to evaluate to what extent UCP procedure (EyeOP-1®) affects pupil dynamics.Materials and methodsConsecutive glaucoma patients with uncontrolled IOP despite optimal medication scheduled for UCP treatment were recruited and followed for 6 months. Pupillometry (PlusoptiX® S04) was performed at baseline, and 1, 3 and 6 months after UCP procedure at scotopic and mesopic conditions. The difference between pupil diameter (PD) in both lighting conditions was calculated at the three follow-up visits. Demographic, clinical characteristics and specific ocular parameters (anterior chamber depth and volume, white-to-white measurement, axial length, phakic status) were registered. Statistical analysis was performed using STATA 14.1.ResultsSixteen eyes of 16 patients with a mean age of 69 ± 11 years were included. Mean preoperative IOP and number of medications were 23.6 ± 3.0 mm Hg and 2.4 ± 1.3, respectively. Mean baseline scotopic and mesopic PD were 4.8 ± 0.8 mm and 4.4 ± 0.9 mm, respectively (difference = 0.38 ± 0.30 mm; range 0.1 to 1.2 mm). At month-1, the pupil diameter (PD) change between scotopic (4.6 ± 0.7 mm) and mesopic (4.5 ± 0.8 mm) conditions decreased to 0.03 ± 0.34 mm, p = 0.01. On the longer follow-up periods, however, the amplitude difference in PD compared to baseline was no longer significant (month-3: 0.28 ± 0.49 mm; month 6: 0.23 ± 0.41 mm; p >0.05). At the end of follow-up, mean scotopic and mesopic PD were 4.7 ± 1.0 mm and 4.4 ± 0.9 mm, respectively.Conclusion and clinical significanceIn the early postoperative period after UCP treatment, most patients present with a less light-reactive pupil, which seems to normalize with time.How to cite this articleSousa DC, Ferreira NP, Marques-Neves C, Somers A, Vandewalle E, Stalmans I, Pinto LA. High-intensity Focused Ultrasound Cycloplasty: Analysis of Pupil Dynamics. J Curr Glaucoma Pract 2018;12(3):102-106.

When does an easy task become hard? A systematic review of human task-evoked pupillary dynamics versus cognitive efforts

The amount of working memory recourses available (or required) to process a cognitive task (easy or hard) represents human cognitive effort. Working memory resources (visual or auditory) and cognitive efforts are interconnected with visual or auditory pathways. In this review, various facets of pupillary dynamics literature are compared in order to determine an optimal method of cognitive effort assessment. Some key categorical areas of interest are identified including the presented stimulus, observed response, comparisons and different methods of analysis. In details review, a set of predetermined evaluation criteria were used and a decision matrix is developed to outline the best practice in papillary dynamics. Based on the summery table in the form of the decision matrix, a quantitative model with artificial neural network (ANN) is selected for a best practice of cognitive effort estimation. The mental multiplication task is found an effective stimulus (cognitive task) to evoke the pupillary response for various level of task difficulty. In most cases, aural and visual are considered as two presentation modes, two sensory inputs, and two mental resources and greatly imparts in cognitive workload. Through this review, it is also explored that, linking together by transfer and error functions, a combination of an ANN and a multinomial processing tree can used in cognitive effort analysis. This research direction can further explored to estimate the relationship between cognitive task and cognitive effort, to facilitate in technology development for neurological disorders, such as narcolepsy, on the neural pathways involved in cognitive processing.

Pupil Dynamics Reflect Behavioral Choice and Learning in a Go/NoGo Tactile Decision-Making Task in Mice.

The eye’s pupil undergoes dynamic changes in diameter associated with cognitive effort, motor activity and emotional state, and can be used to index brain state across mammalian species. Recent studies in head-fixed mice have linked arousal-related pupil dynamics with global neural activity as well as the activity of specific neuronal populations. However, it has remained unclear how pupil dynamics in mice report trial-by-trial performance of behavioral tasks, and change on a longer time scale with learning. We measured pupil dynamics longitudinally as mice learned to perform a Go/NoGo tactile decision-making task. Mice learned to discriminate between two textures presented to the whiskers by licking in response to the Go texture (Hit trial) or withholding licking in response to the NoGo texture (Correct Reject trial, CR). Characteristic pupil dynamics were associated with behavioral choices: large-amplitude pupil dilation prior to and during licking accompanied Hit and False Alarm (FA) responses, while smaller amplitude dilation followed by constriction accompanied CR responses. With learning, the choice-dependent pupil dynamics became more pronounced, including larger amplitude dilations in both Hit and FA trials and earlier onset dilations in Hit and CR trials. A more pronounced constriction was also present in CR trials. Furthermore, pupil dynamics predicted behavioral choice increasingly with learning to greater than 80% accuracy. Our results indicate that pupil dynamics reflect behavioral choice and learning in head-fixed mice, and have implications for understanding decision- and learning-related neuronal activity in pupil-linked neural circuits.

Pupillometry reveals changes in physiological arousal during a sustained listening task.

Hearing loss is associated with anecdotal reports of fatigue during periods of sustained listening. However, few studies have attempted to measure changes in arousal, as a potential marker of fatigue, over the course of a sustained listening task. The present study aimed to examine subjective, behavioral, and physiological indices of listening-related fatigue. Twenty-four normal-hearing young adults performed a speech-picture verification task in different signal-to-noise ratios (SNRs) while their pupil size was monitored and response times recorded. Growth curve analysis revealed a significantly steeper linear decrease in pupil size in the more challenging SNR, but only in the second half of the trial block. Changes in pupil dynamics over the course of the more challenging listening condition block suggest a reduction in physiological arousal. Behavioral and self-report measures did not reveal any differences between listening conditions. This is the first study to show reduced physiological arousal during a sustained listening task, with changes over time consistent with the onset of fatigue.

Pupillary responses and memory-guided visual search reveal age-related and Alzheimer’s-related memory decline

Episodic memory – composed of memory for unique spatiotemporal experiences – is known to decline with aging, and even more severely in Alzheimer ’s disease (AD). Memory for trial-unique objects in spatial scenes depends on the integrity of the hippocampus and interconnected structures that are among the first areas affected in AD. We reasoned that memory for objects-in-scenes would be impaired with aging, and that further impairments would be observed in AD. We asked younger adults, healthy older adults, older adults at-risk for developing cognitive impairments, and older adults with probable early AD to find changing items (‘targets’) within images of natural scenes, measuring repeated-trial changes in search efficiency and pupil diameter. Compared to younger adults, older adults took longer to detect target objects in repeated scenes, they required more fixations and those fixations were more dispersed. Whereas individuals with AD showed some benefit of memory in this task, they had substantially longer detection times, and more numerous, dispersed fixations on repeated scenes compared to age-matched older adults. Correspondingly, pupillary responses to novel and repeated scenes were diminished with aging and further in AD, and the memory-related changes were weaker with aging and absent in AD. Our results suggest that several nonverbal measures from memory-guided visual search tasks can index aging and Alzheimer’s disease status, including pupillary dynamics. The task measurements are sensitive to the integrity of brain structures that are associated with Alzheimer’s-related neurodegeneration, the task is well tolerated across a range of abilities, and thus, it may prove useful in early diagnostics and longitudinal tracking of memory decline.

Comparison of pupillary dynamics to light in the mild traumatic brain injury (mTBI) and normal populations

Purpose: To determine if mTBI adversely affects the pupillary light reflex (PLR).Methods: The PLR was evaluated in mTBI and compared to normal individuals under a range of test conditions. Nine pupil parameters (maximum, minimum and final pupil diameter, latency, amplitude and peak and average constriction and dilation velocities) and six stimulus conditions (dim pulse, dim step, bright pulse, bright step, bright red step and bright blue step) were assessed in 32 adults with mTBI (21–60 years of age) and compared to 40 normal (22–56 years of age). The Neuroptics, infrared, DP-2000 binocular pupillometer was used (30 Hz sampling rate; 0.05 mm resolution) with binocular stimulation and recording.Results: Different test conditions allowed for discrimination of different parameters. For any of the given six test conditions, five-to-eight of the nine pupillary parameters were statistically different (p < 0.05) between the two diagnostic groups. The most promising parameters for diagnostic differentiation were constriction latency, all pupillary diameters, average constriction velocity and peak dilation velocity.Conclusions: MTBI adversely affects the PLR. This suggests an impairment of the autonomic nervous system. The findings suggest the potential for quantitative pupillary dynamics to serve as an objective mTBI biomarker.

Pupil dynamics with periodic flashes: effect of age on mesopic adaptation.

The purpose of this study is to determine the pupillary dynamics with periodical flashes from a peripheral glare source, in similar conditions to night driving, while focusing on dependence with age. We measured two groups of people: youth and adults. Maximum pupil size decreases due to periodic flashes. Latency does not present significant differences. The reduction of pupil size is greater for older adults. The presence of a peripheral and periodic glare source modifies the pupil size. This leads to a reduction of retinal illuminance, which is greater for older adults.

Pupil diameter changes reflect difficulty and diagnostic accuracy during medical image interpretation.

BackgroundNo automated methods exist to objectively monitor and evaluate the diagnostic process while physicians review computerized medical images. The present study tested whether using eye tracking to monitor tonic and phasic pupil dynamics may prove valuable in tracking interpretive difficulty and predicting diagnostic accuracy.MethodsPathologists interpreted digitized breast biopsies varying in diagnosis and rated difficulty, while pupil diameter was monitored. Tonic diameter was recorded during the entire duration of interpretation, and phasic diameter was examined when the eyes fixated on a pre-determined diagnostic region during inspection.ResultsTonic pupil diameter was higher with increasing rated difficulty levels of cases. Phasic diameter was interactively influenced by case difficulty and the eventual agreement with consensus diagnosis. More difficult cases produced increases in pupil diameter, but only when the pathologists’ diagnoses were ultimately correct. All results were robust after adjusting for the potential impact of screen brightness on pupil diameter.ConclusionsResults contribute new understandings of the diagnostic process, theoretical positions regarding locus coeruleus-norepinephrine system function, and suggest novel approaches to monitoring, evaluating, and guiding medical image interpretation.

Effects of Ripasudil Hydrochloride Hydrate Instillation on Pupil Dynamics

ABSTRACTPurpose: We investigated the effects of instillation of ripasudil hydrochloride hydrate (GLANATEC®) on pupil dynamics.Materials and Methods: Fourteen healthy participants (mean age: 30 years), who had no ophthalmic diseases other than refractive error, were enrolled in this study. A single dose of GLANATEC® was instilled into the left eye only. The pupillary response was measured before and 30 and 120 min after instillation; we also measured intraocular pressure (IOP) at the same time points.Results: The IOP in the left eye was significantly lower at both 30 (p < 0.05) and 120 (p < 0.01) min after instillation than at baseline, whereas that in the right eye was not significantly different from baseline at either of the measured post-instillation time points. In contrast, the pupillary response did not significantly differ between the three time points.Conclusions: A single instillation of low concentration GLANATEC® may have no effect on pupil diameter and pupillary response.

Pupil Size Changes as an Active Information Channel for Biofeedback Applications.

Pupil size is usually regarded as a passive information channel that provides insight into cognitive and affective states but defies any further control. However, in a recent study (Ehlers et al. 2015) we demonstrate that sympathetic activity indexed by pupil dynamics allows strategic interference by means of simple cognitive techniques. Utilizing positive/negative imaginings, subjects were able to expand pupil diameter beyond baseline variations; albeit with varying degrees of success and only over brief periods. The current study provides a comprehensive replication on the basis of considerable changes to the experimental set-up. Results show that stricter methodological conditions (controlled baseline settings and specified user instructions) strengthen the reported effect, whereas overall performance increases by one standard deviation. Effects are thereby not restricted to pupillary level. Parallel recordings of skin conductance changes prove a general enhancement of induced autonomic arousal. Considering the stability of the results across studies, we conclude that pupil size information exceeds affective monitoring and may constitute an active input channel in human-computer interaction. Furthermore, since variations in pupil diameter reliably display self-induced changes in sympathetic arousal, the relevance of this parameter is strongly indicated for future approaches in clinical biofeedback.

Determinants of pupil diameters and pupil dynamics in an adult Chinese population.

To investigate the determinants of pupil diameter (PD), amplitude of pupil diameter change (PD-change) and speed of pupil constriction (SPC) using video anterior segment optical coherence tomography (AS-OCT) in a population-based sample of Chinese adults. Chinese adults aged 40 to 80years who were free from glaucoma were consecutively recruited from the population-based Singapore Chinese Eye Study. The SPC was measured by AS-OCT videography. Univariate and multivariate analyses were performed to examine the effects of demographic and ocular biometric factors (e.g., axial length [AL], anterior chamber depth [ACD], baseline PD, iris thickness at the area of the dilator muscle [ITDMR], iris area [IA], and iris bowing [IB]) on SPC, PD, and PD-change. A total of 266/302 (89.5%) AS-OCT videos of eligible eyes were available for analysis. Among these subjects, 64.3% were women, and the mean age (± standard deviation [SD]) was 56 ± 8.3years. SPC was not associated with sex. In multiple regression analyses, SPC was independently associated with baseline PD (β = 0.116, p = 0.006). Baseline PD was independently associated with ACD (β = 0.341, p < 0.001), TISA 500 (β = -4.513, p < 0.001), IA (β = -2.796, p < 0.001), and ITDMR (β = 6.573, p < 0.001). PD-change was independently associated with ACD (β = 0.256, p < 0.001), IA (β = -1.507, p < 0.001), IB (β = 0.630, p = 0.011), and ITDMR (β = 3.124, p < 0.001). Among normal eyes in an adult Chinese population, SPC was associated with larger baseline PD. Larger baseline PD and greater PD change form dark to light were associated with greater ACD, with smaller IA and thicker ITDMR.

The presentation of self in the classical ballet class: dancing with Erving Goffman

This article analyses the social interactions and behaviours evident within an adult, amateur ballet class in one of Scotland’s cities. Using an ethnographic empirical approach, the study utilises Erving Goffman’s model of dramaturgy to explore the impression management of participants from the ballet class. Evidence (data) was generated through a triangulation of methods enabling the following themes to be explored: vocabulary of ballet; ballet body idiom; and teacher–pupil dynamics. The creation of a grounded coding framework saw evidence emerge to suggest that the nature of the dominant ‘realities’ being presented and maintained are ones that reinforce and authenticate the dancers as embodied ballet students. Much ballet-related behaviour involves staged presentations of self, felt to be necessary for conveying the ‘correct’ impression or demeanour expected of a ballet dancer. This article explores the techniques adopted to foster, present and maintain these fronts, seeking to theoretically explain their contextual aspects.

Nonlinear analysis of pupillary dynamics.

Pupil size reflects autonomic response to different environmental and behavioral stimuli, and its dynamics have been linked to other autonomic correlates such as cardiac and respiratory rhythms. The aim of this study is to assess the nonlinear characteristics of pupil size of 25 normal subjects who participated in a psychophysiological experimental protocol with four experimental conditions, namely “baseline”, “anger”, “joy”, and “sadness”. Nonlinear measures, such as sample entropy, correlation dimension, and largest Lyapunov exponent, were computed on reconstructed signals of spontaneous fluctuations of pupil dilation. Nonparametric statistical tests were performed on surrogate data to verify that the nonlinear measures are an intrinsic characteristic of the signals. We then developed and applied a piecewise linear regression model to detrended fluctuation analysis (DFA). Two joinpoints and three scaling intervals were identified: slope α0, at slow time scales, represents a persistent nonstationary long-range correlation, whereas α1 and α2, at middle and fast time scales, respectively, represent long-range power-law correlations, similarly to DFA applied to heart rate variability signals. Of the computed complexity measures, α0 showed statistically significant differences among experimental conditions (p<0.001). Our results suggest that (a) pupil size at constant light condition is characterized by nonlinear dynamics, (b) three well-defined and distinct long-memory processes exist at different time scales, and (c) autonomic stimulation is partially reflected in nonlinear dynamics.

The window of my eyes: Task disengagement and mental fatigue covary with pupil dynamics

Although mental fatigue is a complex, multi-facetted state that involves changes in motivation, cognition, and mood, one of its main characteristics is reduced task engagement. Despite its relevance for performance and safety, knowledge about the underlying neurocognitive processes in mental fatigue is still limited. Inspired by the idea that central norepinephrine plays an important role in regulating task engagement, we test a set of predictions that have been derived from recent studies that relate pupil dynamics to the levels of norepinephrine in the brain. Participants worked on a 2-back task for 2h while we used pupil measures to further explore the link between task engagement and the effects of mental fatigue. We hypothesized that baseline pupil diameter and stimulus-evoked pupil dilations decrease with increasing fatigue. Also, because previous studies have shown that the effects of fatigue are reversible by increasing the task rewards, we hypothesized that increasing the task rewards after 2h on the task would restore these pupil measures to pre-fatigue levels. While we did not find a decrease in baseline pupil diameter, we found that increasing mental fatigue coincided with diminished stimulus-evoked pupil dilation. Also, we confirmed that when sufficient rewards were presented to a fatigued individual, the pupil dilations could be restored. This supports the view that motivational factors are important in predicting engagement versus disengagement during fatigue.