Biology subjects

Vilotijevic, A.

Publications and source records attributed to Vilotijevic, A..

7 recordsLinked to original sources

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↗

bioRxiv2025

A confound-free method to manipulate pupil size in psychological experiments

Those who study visual perception and visuo-spatial attention are increasingly paying interest to the ways in which these processes are influenced by the size of the pupil. However, this realm of research is complicated by the pupils notorious susceptibility to confounders and difficulties in disentangling cause and effect. Recent studies have sought a solution in the exploitation of intrinsically photosensitive retinal ganglion cells (ipRGCs), which trigger pupil constrictions upon detecting blue light. Experiments typically present stimuli against blue versus red backgrounds of equal perceived luminance, to effectuate systematically smaller pupils in the former than in the latter condition. Here we provide a further validation of this method, by testing a scenario of potential concern. Via retino-hypothalamic pathways, ipRGC activation modulates alertness and arousal. Blue and red backgrounds may therefore differentially impact behavior in addition to the pupil, potentially confounding inferences about the pupils impact on cognition. This was investigated with an auditory task in which participants responded as quickly as possible to sequences of randomly timed beeps while looking at blue versus red displays. Each participant was tested with an easy and a difficult version of the auditory task. Results suggest that the ipRGC method is good to go: in the presence of effects of task difficulty on both pupil size and task performance, the display color exclusively influenced pupil size without affecting task performance.

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

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

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↗