Biology subjects

Mathot, S.

Publications and source records attributed to Mathot, S..

26 records · Page 2Linked to original sources

bioRxiv2021

Concealed identity information detection with pupillometry in rapid serial visual presentation

The concealed information test (CIT) relies on bodily reactions to stimuli that are hidden in mind. However, people can use countermeasures, such as purposely focusing on irrelevant things, to confound the CIT. A new method designed to prevent countermeasures uses rapid serial visual presentation (RSVP) to present stimuli on the fringe of awareness. Previous studies that used RSVP in combination with electroencephalography (EEG) showed that participants exhibit a clear reaction to their real first name, even when they try to prevent such a reaction (i.e., when their name is concealed information). Since EEG is not easily applicable outside the laboratory, we investigated here whether pupil size, which is easier to measure, can also be used to detect concealed identity information. In our first study, participants adopted a fake name, and searched for this name in an RSVP task, while their pupil sizes were recorded. Apart from this fake name, their real name and a control name also appeared in the task. We found pupil dilation in response to the task-irrelevant real name, as compared to control names. However, while most participants showed this effect qualitatively, it was not statistically significant for most participants individually. In a second study, we preregistered the proof-of-concept methodology and replicated the original findings. Taken together, our results show that the current RSVP task with pupillometry can detect concealed identity information at a group level. Further development of the method is needed to create a valid and reliable concealed identity information detector at the individual level.

physiology↗

bioRxiv2021

Pupil Size Reflects Exploration and Exploitation in Visual Search (and It's Like Object-Based Attention)

The adaptive gain theory (AGT) posits that activity in the locus coeruleus (LC) is linked to two behavioral modes: exploitation, characterized by focused attention on a single task; and exploration, characterized by a lack of focused attention and frequent switching between tasks. Furthermore, pupil size correlates with LC activity, such that large pupils indicate increased LC firing, and by extension also exploration behavior. Most evidence for this correlation in humans comes from complex behavior in game-like tasks. However, predictions of the AGT naturally extend to a very basic form of behavior: eye movements. To test this, we used a visual-search task. Participants searched for a target among many distractors, while we measured their pupil diameter and eye movements. The display was divided into four randomly generated regions of different colors. Although these regions were irrelevant to the task, participants were sensitive to their boundaries, and dwelled within regions for longer than expected by chance. Crucially, pupil size increased before eye movements that carried gaze from one region to another. We propose that eye movements that stay within regions (or objects) correspond to exploitation behavior, whereas eye movements that switch between regions (or objects) correspond to exploration behavior. Public Significance StatementWhen people experience increased arousal, their pupils dilate. The adaptive-gain theory proposes that pupil size reflects neural activity in the locus coeruleus (LC), which in turn is associated with two behavioral modes: a vigilant, distractible mode ("exploration"), and a calm, focused mode ("exploitation"). During exploration, pupils are larger and LC activity is higher than during exploitation. Here we show that the predictions of this theory generalize to eye movements: smaller pupils coincide with eye movements indicative of exploitation, while pupils slightly dilate just before make eye movements that are indicative of exploration.

neuroscience↗

bioRxiv2020

Eye movements in real-life search are guided by task-irrelevant working-memory content

Attention is automatically guided towards stimuli that match the contents of working memory. This has been studied extensively using simplified computer tasks, but it has never been investigated whether (yet often assumed that) memory-driven guidance also affects real-life search. Here we tested this open question in a naturalistic environment that closely resembles real life. In two experiments, participants wore a mobile eye-tracker, and memorized a color, prior to a search task in which they looked for a target word among book covers on a bookshelf. The memory color was irrelevant to the search task. Nevertheless, we found that participants gaze was strongly guided towards book covers that matched the memory color. Crucially, this memory-driven guidance was evident from the very start of the search period. These findings support that attention is guided towards working-memory content in real-world search, and that this is fast and therefore likely reflecting an automatic process. Significance statementA core concept in the field of visual working memory (VWM) is that visual attention is automatically guided towards things that resemble the content of VWM. For example, if you hold the color red in VWM, your attention and gaze would automatically be drawn towards red things in the environment. So far, studies on such memory-driven guidance have only been done with well-controlled computer tasks that used simplified search displays. Here we address the crucial and open question of whether attention is guided by the content of VWM in a naturalistic environment that closely resembles real life. To do so, we conducted two experiments with mobile eye tracking. Crucially, we found strong memory-driven guidance from the very early phase of the search, reflecting that this is a fast, and therefore likely automatic, process that also driven visual search in real life.

neuroscience↗

bioRxiv2019

The effect of semantic brightness on pupil size: A replication with Dutch words

Theories of embodied language hold that word processing is automatically accompanied by sensory and motor simulations. For example, when you read the word sun, a sensory simulation of brightness as well as a motor simulation of pupil constriction would be automatically triggered. Consistent with this notion, Mathot, Grainger, and Strijkers (2017) found that the eyes pupil was slightly smaller after reading single words that were associated with brightness (e.g. sun) as compared to darkness (e.g. night); that is, the pupil light response was modulated by the semantic brightness of words. However, (other) key findings within the field of embodied language have proven difficult to replicate, and we therefore felt that it was crucial to replicate the effect of semantic brightness on pupil size. To this end, we conducted a close-but-non-identical replication of two key experiments from Mathot, Grainger, and Strijkers (2017): one experiment with visually presented words, and one experiment with spoken words. Both experiments were successfully replicated. We propose that cognitive modulations of the pupil light response reflect activity in visual brain areas; therefore, the effect of semantic brightness on pupil size can be used as a marker for the involvement of visual brain areas in language processing, and thus to address a wide variety of key questions within psycholinguistics.

neuroscience↗

bioRxiv2019

Behavioral and Computational Evidence for Simultaneous Guidance of Attention by Multiple Working Memory Items

During visual search, task-relevant representations in visual working memory (VWM), known as attentional templates, are assumed to guide attention. A current debate concerns whether only one (Single-Item-Template hypothesis, or SIT) or multiple (Multiple-Item-Template hypothesis, or MIT) items can serve as attentional templates simultaneously. The current study was designed to test these two hypotheses. Participants memorized two colors, prior to a visual-search task in which the target and the distractor could match or not match the colors held in VWM. Robust attentional guidance was observed when one of the memory colors was presented as the target (reduced response times [RTs] on target-match trials) or the distractor (increased RTs on distractor-match trials). We constructed two drift-diffusion models that implemented the MIT and SIT hypotheses, which are similar in their predictions about overall RTs, but differ in their predictions about RTs on individual trials. Critically, simulated RT distributions and error rates revealed a better match of the MIT hypothesis to the observed data than the SIT hypothesis. Taken together, our findings provide behavioral and computational evidence for the concurrent guidance of attention by multiple items in VWM. Significance statementTheories differ in how many items within visual working memory can guide attention at the same time. This question is difficult to address, because multiple- and single-item-template theories make very similar predictions about average response times. Here we use drift-diffusion modeling in addition to behavioral data, to model response times at an individual level. Crucially, we find that our model of the multiple-item-template theory predicts human behavior much better than our model of the single-item-template theory; that is, modeling of behavioral data provides compelling evidence for multiple attentional templates that are simultaneously active.

neuroscience↗

bioRxiv2019

The effect of pupil size and peripheral brightness on detection and discrimination performance

It is easier to read dark text on a bright background (positive polarity) than to read bright text on a dark background (negative polarity). This positive-polarity advantage is often linked to pupil size: A bright background induces small pupils, which in turn increases visual acuity. Here we report that pupil size, when manipulated through peripheral brightness, has qualitatively different effects on discrimination of fine stimuli in central vision and detection of faint stimuli in peripheral vision. Small pupils lead to improved discrimination performance, consistent with the positive-polarity advantage, but only for very small stimuli that are at the threshold of visual acuity. In contrast, large pupils lead to improved detection performance. These results are likely due to two pupil-size related factors: Small pupils increase visual acuity, which improves discrimination of fine stimuli; and large pupils increase light influx, which improves detection of faint stimuli. Light scatter is likely also a contributing factor: When a display is bright, light scatter creates a diffuse veil of retinal illumination that reduces image contrast, thus impairing detection performance. We further found that pupil size was larger during the detection task than during the discrimination task, even though both tasks were equally difficult and similar in visual input; this suggests that the pupil may automatically assume an optimal size for the current task. Our results may explain why pupils dilate in response to arousal: This may reflect an increased emphasis on detection of unpredictable danger, which is crucially important in many situations that are characterized by high levels of arousal. Finally, we discuss the implications of our results for the ergonomics of display design.

neuroscience↗

bioRxiv2018

The Pupillary Light Response Reflects Visual Working Memory Content

Recent studies have shown that the pupillary light response (PLR) is modulated by higher cognitive functions, presumably through activity in visual sensory brain areas. Here we use the PLR to test the involvement of sensory areas in visual working memory (VWM). In two experiments, participants memorized either bright or dark stimuli. We found that pupils were smaller when a pre-stimulus cue indicated that a bright stimulus should be memorized; this reflects a covert shift of attention during encoding of items into VWM. Crucially, we obtained the same result with a post-stimulus cue, which shows that internal shifts of attention within VWM affect pupil size as well. Strikingly, pupil size reflected VWM content only briefly. This suggests that a shift of attention within VWM momentarily activates an \"active\" memory representation, but that this representation quickly transforms into a \"hidden\" state that does not rely on sensory areas.

neuroscience↗

bioRxiv2018

Can you have multiple attentional templates? Large-scale replications of Van Moorselaar, Theeuwes and Olivers (2014) and Hollingworth and Beck (2016)

Stimuli that resemble the content of visual working memory (VWM) capture attention. However, theories disagree on how many VWM items can bias attention simultaneously. The multiple-state account posits a distinction between template and accessory VWM items, such that only a single template item biases attention. In contrast, homogenous-state accounts posit that all VWM items bias attention. Recently, Van Moorselaar et al. (2014) and Hollingworth and Beck (2016) tested these accounts, but obtained seemingly contradictory results. Van Moorselaar et al. (2014) found that a distractor in a visual-search task captured attention more when it matched the content of VWM (memory-driven capture). Crucially, memory-driven capture disappeared when more than one item was held in VWM, in line with the multiple-state account. In contrast, Hollingworth and Beck (2016) found memory-driven capture even when multiple items were kept in VWM, in line with a homogenous-state account. Considering these mixed results, we replicated both studies with a larger sample, and found that all key results are reliable. It is unclear to what extent these divergent results are due to paradigm differences between the studies. We conclude that is crucial to our understanding of VWM to determine the boundary conditions under which memory-driven capture occurs.

neuroscience↗