Biology subjects

Mathot, S.

Publications and source records attributed to Mathot, S..

At least 19 recordsLinked to original sources

bioRxiv2026

Model-based pupil deconvolution reveals latent attentional dynamics

Changes in pupil size have been widely used as an indirect measure of attention. However, attention engages on a faster timescale than the pupillary response. Therefore, the slow time course of the pupil response makes it difficult to distinguish attentional responses to stimuli presented in close temporal succession. Although signal deconvolution has been used in previous research to estimate latent attentional responses from the pupil signal, existing methods primarily model dilation without considering the visual stimulus evoked constriction phase of the pupil. Here, we introduce a dual-kernel deconvolution model that models constriction and dilation using separate impulse response functions. Using an RSVP paradigm with emotional faces as target stimuli, we demonstrate that the proposed model estimates latent attentional response despite substantial overlap in the measured pupil signal. Importantly, the recovered attentional response resembles the time course of attentional allocation previously predicted by several models of Attentional Blink. Together, these findings demonstrate that the dynamics of latent attentional episodes can be recovered from the pupil response with a temporal resolution previously obscured by the sluggishness of the pupillary response. The proposed method is also provided as a usable software package that serves as a general tool for investigating the temporal dynamics of attention in rapid visual paradigms.

neuroscience↗

bioRxiv2026

Larger Pupils are Associated with Improved Visual, but not Auditory, Near-Threshold Detection

Prestimulus pupil size is associated with near-threshold detection performance in both the visual and auditory domain, a relationship that is commonly attributed to arousal. However, given that larger pupils also let more light into the eye, in the visual domain this relationship is likely also driven by optical effects. To better understand this, we investigated how pupil size, skin conductance, and electroencephalographic (EEG) measures relate to detection performance in both a visual and an auditory task. We found that larger pupils were associated with higher sensitivity in the visual condition but lower sensitivity in the auditory condition. Skin conductance was negatively related to visual sensitivity, but unrelated to auditory sensitivity. EEG power measures were not related to sensitivity in either condition, though pupil size was positively correlated with alpha and beta power. Together, these results suggest that in visual detection the relationship between pupil size and performance is driven by both arousal and optics, whereas in auditory detection the relationship is driven solely by arousal. More broadly, our findings highlight the pupil as an active and functional component of the visual system.

neuroscience↗

bioRxiv2026

Subtle Pupil-Size Changes Associated With Exploration Do Not Affect Visual Sensitivity

When we feel restless and easily distracted, continuously switching tasks (exploration), our pupils tend to be large. In contrast, when we are calmly focused on a single task (exploitation), our pupils tend to be small. According to the Adaptive Gain Theory (AGT), a switch from exploitation to exploration is associated with an increase in norepinephrine in the locus coeruleus, which in turn triggers pupil dilation. However, the AGT does not provide a functional explanation of why exploration triggers pupil dilation. One possibility is that visual sensitivity, which increases with pupil size, is especially important during exploration. We set out to provide evidence consistent with this functional explanation, as well as to replicate two key previous results. Participants performed a four-armed bandit task, which induces both exploration and exploitation behavior. During the task, participants also needed to detect an occasional and unpredictable near-threshold peripheral flash. We replicated two key results: pupils were larger during exploration than during exploitation; and increased pupil size (overall, independent of exploration status) was associated with increased visual sensitivity. However, most importantly, we did not find that visual sensitivity was higher during exploration than during exploitation; probably, the reliable-yet-tiny increase in pupil size during exploration was too small to affect visual sensitivity. We conclude that key previous results are replicable; however, common experimental paradigms, such as the four-armed bandit task, induce only small changes in exploration behavior. Therefore, more powerful paradigms are required in order to test functional explanations of pupil-size changes during exploration and exploitation.

animal behavior and cognition↗

bioRxiv2026

Pupil size reflects the content of covertly attended afterimages

Does attention operate within afterimages? Here we show that it does, using a novel pupillometry-based paradigm. Participants fixated centrally while bright and dark peripheral stimuli were presented, and a central cue directed attention to one of them. Over time, the stimuli perceptually faded due to adaptation and were then removed, leaving strong, negative afterimages. We found that pupil size tracked the brightness of the attended stimulus both during perceptual fading, when stimuli were present but perceptually weakened, and during perception of afterimages, when no physical stimuli were present. In the latter case, pupil size reflected the brightness of the negative afterimage rather than the preceding physical stimulus. This finding shows that covert attention can be directed within afterimages. More broadly, the results suggest that attention to afterimages bridges the gap between external and internal attention, challenging the notion of a strict dichotomy and supporting the view that this distinction is better understood as a continuum.

neuroscience↗

bioRxiv2026

Pupil Constriction Causes Activity in the Human Retina and Visual System

Pupil responses shape the earliest stages of visual perception by regulating the amount of light that enters the eye. How this affects visual processing is still poorly understood. Here we present evidence that pupil constriction causes activity in the human retina and visual system, independently of visual stimulation. Healthy human participants (N=119) viewed brief visual stimuli (light increments or decrements) while pupil size, retinal activity (electroretinogram), and brain activity (electroencephalogram) were recorded. As expected, visual stimulation triggered an initial burst of retinal activity followed by pupil constriction (the pupil light response). Importantly, we used trial-to-trial variability in constriction latency to reveal a previously unknown retinal response that is locked to pupil constriction, rather than to visual stimulation. Presumably, and in line with similar findings in mice, this constriction-locked retinal activity is a response to the sudden decrease in retinal light exposure that accompanies pupil constriction (although contribution of iris muscle activity is not conclusively ruled out). A similar constriction-locked response emerged later over visual cortex. Given these findings, an important open question is how the visual system maintains brightness constancy despite pupil-induced retinal and cortical activity.

neuroscience↗

bioRxiv2026

Pupil size reflects moment-to-moment fluctuations in mental imagery, but not (or hardly) individual differences in imagery

Previous research has shown that the eyes pupils are larger when imaging dark as compared to bright objects or scenes. Based on this, it has been claimed that pupil size is a sensitive marker of mental-imagery vividness. We investigated this claim in three experiments, conducted in two countries (Norway and The Netherlands; Ntotal = 115), in which participants read, listened, or freely imagined stories that evoked a sense of darkness or brightness. In addition, participants rated their imagery vividness after each story, as a measure of moment-to-moment fluctuations in imagery; and their imagery vividness in general, as a measure of individual differences in imagery. Overall, we found that darkness-evoking stories induced larger pupils than brightness-evoking stories, although this effect was highly variable and only statistically reliable for longer (> 1 min) audio stories. Importantly, we consistently found that this pupil-size difference (dark - bright) was largest for vividly imagined stories. Finally, we did not find any relationship between this pupil-size difference and individual differences in general in imagery. We conclude that the strength of pupil-size changes in response to imagined darkness or brightness reflects moment-to-moment fluctuations in imagery vividness within an individual rather than individual differences in imagery vividness as a personal trait.

neuroscience↗

bioRxiv2025

Pupil size correlates with near-threshold detection performance irrespective of stimulus colour, eccentricity, or retinal adaptation-state

In visual near-threshold detection tasks, larger pre-stimulus pupil size is associated with improved accuracy. However, previous studies have used black and white peripherally presented stimuli, leaving open the question of whether the relationship persists when targets differ in their colour or eccentricity. Here we addressed this question with three experiments that systematically varied the lighting conditions and target properties in a visual near-threshold detection task (data collected in 2022-2024). Light conditions ranged from dark to dim to bright, with the dark condition including a period of dark-adaptation. Possible target colours were blue and red on a black background (dark condition), blue and red on a grey background (dim condition), or yellow and cyan on a white background (bright condition). Possible target eccentricities ranged from parafoveal to peripheral, in a continuous manner (experiment 3) or as two predefined near and far eccentricities (experiments 1 & 2). Across all experiments we show that larger pre-stimulus pupil size is associated with improved performance. This large-pupil advantage is not systematically modulated by the colour or eccentricity of the targets, the illumination of the testing room, or retinal adaptation-state. We conclude that the phenomenon is robust, indicating that pupil size affects vision in a behaviourally relevant manner, regardless of the exact conditions. Significance statementBy showing that pupil size is robustly associated with performance in visual near-threshold detection tasks, we provide evidence for the functional role of endogenous pupil size fluctuations in visual perception.

neuroscience↗

bioRxiv2024

The Respiratory-Pupillary Phase Effect: Pupils size is smallest around inhalation onset and largest during exhalation

The prevailing view in the study of animal and human pupillary function has been that pupils dilate and are largest during inhalation and constrict and are smallest during exhalation. However, this notion has recently been challenged. Here, we systematically address this question by conducting a study encompassing three experiments (two resting tasks and one visual perception task), with the latter two being pre-registered. Collectively, across nasal and oral breathing, resting, and task conditions, our experiments consistently and robustly demonstrate that pupil size is smallest around inhalation onset and largest around peak exhalation. This phenomenon, which we term the Respiratory-Pupillary Phase Effect (RPPE), directly contradicts the long-held notion that pupils are largest during inhalation and smallest during exhalation. Notably, the dilation and constriction processes overlap with both phases. The observed consistency and significance of the RPPE across various conditions underscore the need for further investigation into its underlying mechanisms and potential impact on human behavior.

physiology↗

bioRxiv2024

The interplay of spontaneous pupil-size fluctuations and EEG power in near-threshold detection

Detection of near-threshold stimuli depends on the properties of the stimulus and the state of the observer. In visual detection tasks, improved sensitivity is associated with larger pre-stimulus pupil size. However, it is still unclear whether this association is due to optical effects (more light entering the eye), correlations with arousal, correlations with cortical excitability (as reflected in alpha power), or a mix of these. To better understand this, we investigated the relative contributions of pupil size and power in the alpha, beta, and theta frequency bands on near-threshold detection. We found that larger pre-stimulus pupil size is associated with improved sensitivity and a more liberal criterion (the likelihood of reporting that a stimulus was detected). Importantly, the relationship between pupil size and sensitivity was not mediated by any of the measured neural variables; the relationship with criterion however was mediated by power in the beta band (12-30 Hz). Pupil size was positively correlated with power in the alpha and beta bands. Additionally, we show that pre-stimulus theta suppression (4 - 8 Hz) is associated with improved sensitivity and a more liberal criterion. Taken together, our results show an independent effect of pupil size on detection sensitivity that is not driven by cortical excitability, but may be driven by optical effects, arousal, or a mix of both.

neuroscience↗

bioRxiv2024

Spontaneous Fluctuations in Pupil Size Shape Retinal Responses to Visual Stimuli

Visual perception is shaped at the earliest stage by the size of the eyes pupil, which determines how much light enters the eye and how well this light is focused. But the exact role of pupil size in visual perception is still poorly understood. We recorded pupil size and electrical activity from the retina and brain while healthy human participants viewed full-screen flashes. We found that early retinal responses, which peaked {+/-}25 ms after stimulus onset and predicted subsequent activity over visual cortex, were strongly affected by stimulus intensity. Importantly, pupil size, at least within the range of naturally occurring fluctuations, did not affect the amplitude of these early retinal responses, despite resulting in substantial changes in retinal light exposure. However, the direction of pupil-size change at the moment of stimulus presentation did modulate the amplitude of early retinal responses, which were enhanced during phases of dilation as compared to constriction. Based on these results, we suggest that fast-acting adaptation processes may normalize early retinal responses with respect to changes in retinal light exposure that result from spontaneous changes in pupil size: an initial form of brightness constancy. These results shed new light on, and raise important and previously unasked questions about, the role of pupil size in visual perception.

neuroscience↗

bioRxiv2024

Effort Drives Saccade Selection

What determines where to move the eyes? We recently showed that pupil size, a well-established marker of effort, also reflects the effort associated with making a saccade (saccade costs). Here we demonstrate saccade costs to critically drive saccade selection: when choosing between any two saccade directions, the least costly direction was consistently preferred. Strikingly, this principle even held during search in natural scenes in two additional experiments. When increasing cognitive demand experimentally through an auditory counting task, participants made fewer saccades and especially cut costly directions. This suggests that the eye-movement system and other cognitive operations consume similar resources that are flexibly allocated among each other as cognitive demand changes. Together, we argue that eye-movement behavior is tuned to adaptively minimize saccade-inherent effort.

neuroscience↗

bioRxiv2023

Non-image forming vision as measured through ipRGC-mediated pupil constriction is not modulated by covert visual attention

In brightness the pupil constricts, while in darkness the pupil dilates; this is known as the pupillary light response (PLR). The PLR is driven by all photoreceptors: rods and cones, which contribute to image-forming vision, as well as intrinsically photosensitive retinal ganglion cells (ipRGCs), which contribute to non-image-forming vision. Rods and cones cause immediate pupil constriction upon light exposure, whereas ipRGCs cause sustained constriction for as long as light exposure continues. Recent studies have shown that the initial PLR is modulated by covert attention; however, it remains unclear whether the same holds for the sustained PLR. Here, we investigated the effect of covert attention on sustained, ipRGC-mediated pupil constriction. We leveraged the fact that ipRGCs are predominantly responsive to blue light, causing the most prominent sustained constriction in response to blue light. Replicating previous studies, we found that the pupil constricted more when either directly looking at, or covertly attending to, bright as compared to dim stimuli (with the same color). We also found that the pupil constricted more when directly looking at blue as compared to red stimuli (with the same luminosity); crucially, however, we did not find any difference in pupil size when covertly attending to blue as compared to red stimuli. This suggests that ipRGC-mediated pupil constriction, and possibly non-image-forming vision more generally, is not modulated by covert attention. Significance statementWhen we think of vision, we generally think of image-forming vision, that is, seeing things. However, vision can also be "non-image-forming"; for example, our day-night rhythm and pupil size are regulated by visual input, but not in a way that gives rise to conscious visual awareness. While visual attention shapes image-forming vision, its influence on non-image forming vision remains unclear. We investigated this by using ipRGCs,which contribute to non-image-forming vision and are responsive to blue light. Aside from replicating the effect of covert attention on image-forming vision, we showed that pupil constriction differed between directly looking at blue/ red stimuli, but not during covert attention to these stimuli. This suggests that non-image forming vision is not influenced by covert visual attention.

physiology↗

bioRxiv2023

Baseline Pupil Size Seems Unrelated to Fluid Intelligence, Working Memory Capacity, and Attentional Control

Over the past few years, several studies have explored the relationship between resting-state baseline pupil size and cognitive abilities, including fluid intelligence, working memory capacity, and attentional control. However, the results have been inconsistent. Here we present the findings from two experiments designed to replicate and expand previous research, with the aim of clarifying previous mixed findings. In both experiments, we measured baseline pupil size while participants were not engaged in any tasks, and assessed fluid intelligence using a matrix task. In one experiment we also measured working memory capacity (letter-number-sequencing task) and attentional control (attentional-capture task). We controlled for several personal and demographic variables known to influence pupil size, such as age and nicotine consumption. Our analyses revealed no relationship between resting-state pupil size (average or variability) and any of the measured constructs, neither before nor after controlling for confounding variables. Taken together, our results suggest that any relationship between resting-state pupil size and cognitive abilities is likely to be weak or non-existent.

neuroscience↗

bioRxiv2023

Causal Effects of Pupil Size on Visual Processing

The size of the eyes pupils determines how much light enters the eye and also how well this light is focused. Through this route, pupil size shapes the earliest stages of visual processing. Yet causal effects of pupil size on vision are poorly understood and rarely studied. Here we report the effects of both experimentally induced and spontaneous changes in pupil size on visual processing as measured through EEG. We compare these to the effects of stimulus intensity and covert visual attention, because previous studies have shown that these factors all have comparable effects on some common measures of early visual processing, such as detection performance and steady-state visual evoked potentials; yet it is still unclear whether these are superficial similarities, or rather whether they reflect similar underlying processes. Using a mix of neural-network decoding, ERP analyses, and time-frequency analyses, we find that induced pupil size, spontaneous pupil size, stimulus intensity, and covert visual attention all affect EEG responses, mainly over occipital and parietal electrodes, but--crucially--that they do so in qualitatively different ways. Induced and spontaneous pupil-size changes mainly modulate activity patterns (but not overall power or intertrial coherence) in the high-frequency beta range; this may reflect a causal effect of pupil size on oculomotor activity and/ or visual processing. In addition, spontaneous (but not induced) pupil size tends to correlate positively with intertrial coherence in the alpha band; this may reflect a non-causal relationship, mediated by arousal. Taken together, our findings suggest that pupil size has qualitatively different effects on visual processing from stimulus intensity and covert visual attention. This shows that pupil size causally affects visual processing, and provides concrete starting points for further study of this important yet understudied earliest stage of visual processing.

animal behavior and cognition↗

bioRxiv2022

Covert shifts of attention towards the visual periphery induce pupil dilation

People are best able to detect stimuli in peripheral vision when their pupils are large, and best able to discriminate stimuli in central vision when their pupils are small. However, it is unclear whether our visual system makes use of this by dilating the pupils when attention is directed towards peripheral vision. Therefore, we tested whether pupil size adapts to the breadth of attention. We found that pupils dilate with increasing attentional breadth, both when attention is diffusely spread and when attention is directed at specific locations in peripheral vision. We further found a correlation with performance, suggesting a functional benefit of this effect. Based on our results and others, we propose that cognitively driven pupil dilation is not an epiphenomenal marker of Locus Coeruleus activity, as is often assumed, but rather is an adaptive response that reflects an emphasis on peripheral vision.

neuroscience↗

bioRxiv2022

Categorical bias as a crucial parameter in visual working memory: the effect of memory load and retention interval

Visual information can be stored as continuous as well as categorical representations in visual working memory (VWM) to guide subsequent behavior. Yet it is still unclear what determines whether VWM is represented as continuous or categorical information, or as a mix of both. Recent studies have shown that color VWM representations adjust flexibly depending on the number of memory items as well as the duration that these items need to be maintained for. The current study aims to extend and replicate these crucial effects. In a delayed estimation task, participants memorized one to four colored objects presented at different spatial locations, followed by a delay of 100, 500, 1,000, or 2,000 ms. Next, a probe indicated the location of the color that participants needed to report. We measured the extent to which responses were biased in the direction of prototypical colors. Crucially, we implemented this categorical bias in an extension to the classic mixture model (Zhang & Luck 2008) in which the center of the error distribution is a crucial parameter that characterizes the extent to which VWM is biased by color categories. We found that VWM shows a strong categorical bias in all cases, and that this bias increases with increasing memory load; strikingly, this effect of memory load on categorical bias is stronger at longer intervals (1,000 ms or longer), as compared to shorter intervals, yet it peaks for intermediate memory loads as opposed to the highest memory load. Overall, our results suggest that when visual information needs to be maintained for one second or longer, VWM becomes more reliant on categorical representations as memory load increases.

neuroscience↗

bioRxiv2022

Methods in Cognitive Pupillometry: Design, Preprocessing, and Statistical Analysis

Cognitive pupillometry is the measurement of pupil size to investigate cognitive processes such as attention, mental effort, working memory, and many others. Currently, there is no commonly agreed-upon methodology for conducting cognitive-pupillometry experiments, and approaches vary widely between research groups and even between different experiments from the same group. This lack of consensus makes it difficult to know which factors to consider when conducting a cognitive-pupillometry experiment. Here we provide a comprehensive, hands-on guide to methods in cognitive pupillometry, with a focus on trial-based experiments in which the measure of interest is the task-evoked pupil response to a stimulus. We cover all methodological aspects of cognitive pupillometry: experimental design; preprocessing of pupil-size data; and statistical techniques to deal with multiple comparisons when testing pupil-size data. In addition, we provide code and toolboxes (in Python) for preprocessing and statistical analysis, and we illustrate all aspects of the proposed workflow through an example experiment and example scripts.

animal behavior and cognition↗

bioRxiv2021

Is categorization in visual working memory a way to reduce mental effort? A pupillometry study

Recent studies on visual working memory (VWM) have shown that visual information can be stored in VWM as continuous (e.g., a specific shade of red) as well as categorical representations (e.g., the general category red). It has been widely assumed, yet never directly tested, that continuous representations require more VWM mental effort than categorical representations; given limited VWM capacity, this would mean that fewer continuous, as compared to categorical, representations can be maintained simultaneously. We tested this assumption by measuring pupil size, as a proxy for mental effort, in a delayed estimation task. Participants memorized one to four ambiguous (boundaries between adjacent color categories) or prototypical colors to encourage continuous or categorical representations, respectively; after a delay, a probe indicated the location of the to-be-reported color. We found that, for set size 1, pupil size was larger while maintaining ambiguous as compared to prototypical colors, but without any difference in memory precision; this suggests that participants relied on an effortful continuous representation to maintain a single ambiguous color, thus resulting in pupil dilation while preserving precision. In contrast, for set size 2 and higher, pupil size was equally large while maintaining ambiguous and prototypical colors, but memory precision was now substantially reduced for ambiguous colors; this suggests that participants now also relied on categorical representations for ambiguous colors (which are by definition a poor fit to any category), thus reducing memory precision but not resulting in pupil dilation. Taken together, our results suggest that continuous representations are more effortful than categorical representations, and that very few continuous representations (perhaps only one) can be maintained simultaneously. Significance statementVisual working memory (VWM) can store visual information in two more-or-less distinct formats: continuous and categorical representations. It is widely assumed that VWM capacity for continuous representations is more limited than for categorical representations, yet this assumption has never been explicitly tested. Here we address this crucial question of whether continuous representations cost more resources, and as a consequence limits VWM capacity, as compared to categorical representations. To do so, we measured pupil size (as a proxy for mental effort) and memory performance in a delayed estimation task. Crucially, our results suggest that continuous representations are more effortful than categorical representations, and that only one continuous representation can be maintained in VWM at one time.

neuroscience↗