Biology subjects

Rouw, R.

Publications and source records attributed to Rouw, R..

5 recordsLinked to original sources

bioRxiv2025

Pupil size reveals the perceptual quality and effortless nature of synesthesia

Synesthesia describes cross-over processes that can generate extra conscious percepts, such as seeing additional color when reading numbers. While existing research focuses on the mechanisms and effects of synesthetic associations, it often overlooks its most distinctive feature: unique sensory phenomenology. Here, we introduce pupillometry as an objective physiological measure of synesthetic color phenomenology. Across 16 grapheme-color synesthetes and two matched control groups, pupil responses tracked the brightness of synesthetic colors under constant physical visual input, scaling with self-reported strength. Synesthetic colors elicited pupil dynamics comparable to real colors, dissociating synesthetes from non-synesthetes. These responses emerged too rapidly to reflect imagery and scaled with reported color brightness, revealing cross-over caused genuine perceptual processing. Controls required to generate color associations showed greater effort-linked pupil dilation than synesthetes or controls who did not report colors, providing evidence for the effortless nature of synesthesia. Synesthesia thus provides a tractable human model for studying physiologically measurable phenomenology. Significance statementHow can we measure what someone actually experiences? Synesthesia, in which stimuli such as numbers can evoke cross-over sensations like seeing colors, provides a rare test case. Here we make this extraordinary sensation objectively measurable and show that it has a distinct sensory signature. We find that pupil size reflects the brightness of synesthetic colors even when physical light remains constant. Pupils constrict for bright colors and dilate for dark ones, revealing the quality and strength of the percept. These responses emerge rapidly and differ from those of non-synesthetes. Together, synesthesia provides a tractable model for studying internally generated sensations, with pupillometry offering a direct, measurable window into conscious perception.

neuroscience↗

bioRxiv2024

Decoupling Coldness and Softness in Tactile Wetness Perception Using Tunable Hydrogels

This study investigates the perception of tactile wetness, a complex sensation experienced by humans. Previous research has primarily focused on either thermal or mechanical cues separately, or has used textiles as stimuli whose parameters are difficult to control. Here, we employed polyacrylamide hydrogels with varying stiffness levels soaked in liquids of distinct thermal conductivities. By psychophysically evaluating participants perception of wetness, we showed that the wetness judgments for the samples exhibit a transitive relationship based on the mechanical and thermal cues from an intrinsically tunable organic material. We developed a prediction model of human wetness judgment with an accuracy of 90% and found that the best metrics for the most accurate model were those that were the most human-adjacent: change in temperature at the skin-sample interface (thermal) and compressive force from 2 mm indentation of the sample (mechanical). Given these parameters, we developed a perceptual space capable of recreating 7 distinct levels of wetness perception with the physical parameters used in this study. The results provide insights into the relative contributions of mechanical and thermal stimulus properties in wetness perception. Most notably, this work highlights that the physical characteristics of the skin-stimulus interface can provide ample information for creating a wetness perceptual space, as opposed to the chemical composition of the hydrogels.

neuroscience↗

bioRxiv2023

Use of dye sensitizers for increased photoacoustic mechanosensation

The photoacoustic effect refers to the generation of pressure waves in matter stimulated by light[1]. In the context of radiology (i.e., photoacoustic imaging) waves generated by pulsed laser light are detected by an ultrasound transducer[2-4]. It has been shown that photoacoustic waves produce a mechanical, tactile sensation in humans on bare skin[5]. In a series of psychophysical experiments, performed with both medical grade and off-the-shelf pulsed light systems, participants could detect, categorically describe, and discern the direction of travel of pulsed optical stimuli with the use of a dye as an optical absorber on the skin. To a large extent, the sensations were perceived as localized vibration on the glabrous surface of the fingers, when sensitized with the thin film of dye. This form of sensory stimulation demonstrates an enhanced non-contact, non-optogenetic, in situ activation of the mechanosensory system. This modality of sensation may provide a tool that leads to new insights in psychology, neuroscience, mechanobiology, and the health sciences. Finally, it has many advantageous characteristics for human interaction with artificial environments, as optical signals can be projected onto the skin across distances.

neuroscience↗

bioRxiv2020

Increased orbitofrontal connectivity in misophonia

For individuals with misophonia, specific innocuous sensory stimuli - such as hearing another person chewing or breathing - evoke strong negative emotional and physiological responses, such as extreme anger, disgust, stress and anxiety. Instead people with misophonia do not experience or display atypical reactions to generic aversive sounds such as screams or nails scratching on a blackboard. Misophonia appears to be unrelated to neurological trauma or hearing deficit, and features a characteristic developmental pattern. Its aetiology is currently unknown. The few previous fMRI studies on misophonia showed that sufferers feature increased dorsal anterior insula activity during trigger vs. generic aversive sounds. While this effect likely reflects the saliency associated with the perception of trigger sounds in people with misophonia, in the present fMRI study we investigate the neural mechanisms underlying the emotional reaction to trigger stimuli. To this aim, we probe the task-dependent connectivity of mid-cingulate, medial premotor and ventrolateral premotor cortex. We observe that only in participants with misophonia the presentation of trigger audio-visuals prompts an increased interaction of these three brain regions with the lateral orbitofrontal cortex. This brain region is crucial for behavioural inhibition mediated by cognitive and emotional content (such as in reward-reversal learning) and is part of the temporo-amygdala-orbitofrontal network, which integrates visceral and emotional states with cognition and behaviour. We also observe that in people with misophonia trigger sounds prompt a significant increase in the interaction between mid-cingulate and the primary auditory cortex. Our study replicates previous results and expands the network of brain regions involved in misophonia. The involvement of the orbitofrontal cortex suggests a defective functioning of high-order integrative processes allowing the reappraisal of experience-dependent negative emotional association with harmless sensory stimuli, and sheds light on the mechanisms underlying the compulsive nature of the misophonic reaction. The increased interaction, rather than the overall activity, of the primary auditory cortex with the mid-cingulate supports the hypothesis that the emotional response in misophonia is subserved by an indirect auditory-limbic pathway processing the subjective valence of specific sounds, rather than their physical properties alone.

neuroscience↗

bioRxiv2020

Context influences how individuals with misophonia respond to sounds

Misophonia is a newly researched condition in which specific sounds cause an intense, aversive response in individuals, characterized by negative emotions and autonomic arousal. Although virtually any sound can become a misophonic "trigger," the most common sounds appear to be bodily sounds related to chewing and eating as well as other repetitive sounds. An intriguing aspect of misophonia is the fact that many misophonic individuals report that they are triggered more, or even only, by sounds produced by specific individuals, and less, or not at all, by sounds produced by animals (although there are always exceptions). In general, anecdotal evidence suggests that misophonic triggers involve a combination of sound stimuli and contextual cues. The aversive stimulus is more than just a sound and can be thought of as a Gestalt of features which includes sound as a necessary component as well as additional contextual information. In this study, we explore how contextual information influences misophonic responses to human chewing, as well as sonically similar sounds produced by non-human sources. The current study revealed that the exact same sound can be perceived as being much more or less aversive depending on the contextual information presented alongside the auditory information. The results of this study provide a foundation for potential cognitive based therapies.

neuroscience↗