Petroc Sumner

The relationship between processing speed and brain network characteristics has been widely studied, yet the results remain inconsistent. While many studies have linked processing speed to the microstructure of white matter, discrepancies arise due to differences in the tasks used, behavioral measures assessed (based on raw reaction time or modelled processing speed), and specific white matter tracts considered. To address these challenges and clarify any relationship between individual differences in speed and white matter brain networks, we present a pre-registered analysis using a large (N=159) dataset, incorporating state-of-the-art MRI data acquired from a high-gradient 3T Connectom scanner. We combine data from three reaction-time tasks to create composite measures of cognitive performance, mitigating the limitations of experiment-specific analyses. Alongside classic behavioral measures of mean reaction time, reaction time variability, and accuracy, we applied the drift-diffusion model to derive the common metric of modelled processing speed, drift rate, as well as accompanying parameters of boundary separation, and non-decision time. Using general linear models, we explored the relationship between these parameters and the whole-brain and task-specific structural networks of the brain, weighted by volume-normalized streamline counts and myelin water fraction. Our results revealed negative associations between the global efficiency of streamline-weighted networks and both mean reaction time and reaction time variability (β=-0.18/-0.21, p=0.025/0.01 for whole-brain and β=-0.18/-0.18, p=0.028/0.022 for the task-specific network). Effect sizes were small, consistent with other pre-registered assessments of brain-behavior correlations. These effects were not captured by decision model parameters signaling a note of caution for the assumed interpretation of these parameters. The significant association with reaction time variability was robust to controlling for age, while age captured significant variance in the association with mean reaction time. This may imply that physiological changes associated with age would be an avenue for research to uncover mechanisms relating structure to reaction time. In sum, we attempted a state-of-the art clarification of whether structural brain organization is associated with speed in common cognitive tasks, and we found a small association with reaction time variability and mean reaction time (and age).

Visual discomfort or visual stress is an uncomfortable subjective experience that occurs in response to specific visual stimuli. It affects a large proportion of the population to various degrees, disproportionately impacting those with heightened sensory sensitivities, particularly neurodivergent individuals. We argue that this might stem from a mismatch between the statistical properties of visual stimuli in human-made environments and those in natural environments that the visual system can process efficiently. We discuss the inefficiency with which images with certain spatial, chromatic and temporal characteristics are processed by the visual system and propose a cerebral mechanism to account for the discomfort they induce. The mechanism offers a potential explanation for the large individual differences in susceptibility to discomfort. We highlight two avenues for intervention: (1) environmental modifications aimed at reducing the prevalence of visually stressing stimuli in urban settings, and (2) individual-level strategies, such as personalised optical treatments. Addressing these challenges requires an interdisciplinary effort bridging neuroscience, vision science, interior and urban design and typography to create visually accessible and inclusive environments.

Mental imagery vividness varies between individuals. Low levels of mental imagery have been associated with high levels of autistic traits, whilst autistic traits are known to positively correlate with sensory sensitivities. This would predict a negative correlation between sensory sensitivity and imagery. However, one recent study has suggested that mental imagery vividness may be positively associated with sensory sensitivities, possibly through the shared mechanism of hyperexcitability of the sensory cortices. The aim of this paper was to explore this contradictory set of associations across two modalities (visual and tactile). We used standardised questionnaires to measure autistic traits, sensory sensitivities, and mental imagery vividness in a sample evenly comprised of autistic and non-autistic adults ( n = 595). Higher autistic traits were significantly associated with lower mental imagery ( r = − 0.20 and r = − 0.17 for visual and tactile imagery respectively), and a higher incidence of aphantasia was observed in the autistic group compared to the non-autistic group. In addition, higher autistic traits were significantly associated with increased sensory sensitivities ( r = 0.76). Importantly, we found negligible evidence of an association between mental imagery and sensory sensitivity, even when controlling for autistic traits. In the first study to directly explore autistic traits, sensory sensitivities and mental imagery, we conclude that there is no clear evidence to suggest that mental imagery and sensory sensitivity are related, challenging the idea of shared mechanisms of hyperexcitability of sensory cortex.

Many people experience aversive hypersensitivity (discomfort/visual stress) to stimuli such as bright lights, striped patterns, strobing, motion, or complex visual scenes such as supermarkets. Such sensory hypersensitivity is often associated with one or more of a range of neurological, psychiatric, and neurodevelopmental conditions or neurodivergence. The cortical mechanisms of sensory hypersensitivity, and reasons why it occurs with such a range of conditions, remain unknown. For three decades, theories have focused on excitation/inhibition balance, where visual discomfort reflects over-excitation relative to inhibition. Visual gamma oscillations induced by viewing stripes are an accepted index of excitation/inhibition, and are successfully modeled by a cortical circuit. Visual gamma is, therefore, predicted to be altered in people with high visual discomfort. We tested this in two studies. The first used circular moving gratings to evoke visual gamma, alongside self-reported scales for sensory sensitivity and for discomfort induced by viewing images (N = 166). We found no correlation of subjective sensitivity or discomfort with gamma frequency or amplitude (all r<0.1), or with the modeled excitation/inhibition parameters. In study 2, we recruited two groups of participants with high and low sensitivity to visual stripes (N = 23,27), and induced gamma with gratings of four different spatial frequencies. We found no group differences in gamma frequency, amplitude or modeled parameters. We conclude that visual discomfort is not simply explained by higher excitation/inhibition ratio in the visual cortex, despite the dominance of this assumed explanation.

Measuring vestibular rehabilitation progress with questionnaires can be difficult in time-limited clinical settings. We developed and tested a new brief tool: Client Oriented Scale of Improvement for Dizziness and Imbalance (COSIDI), based on validated client-oriented scales for hearing aids (COSI) and for tinnitus (COSIT), and on wider evidence for involving patients in specifying the goals for rehabilitation. We developed the COSIDI with patient and clinician feedback and validated it through comparison with Dizziness Handicap Inventory (DHI) and Vestibular Rehabilitation Benefit Questionnaire (VRBQ) during normal clinical appointments. 91 outpatients in three clinical settings in Cardiff, Swansea and Southampton. COSIDI improvement scores showed comparable effect size with DHI and VRBQ (Cohen's d = 1.1 vs 1.2 and 0.64) and correlated highly with the existing measures (r = 0.73). Clinicians found COSIDI to be useful and appropriate for rehabilitation measurement, due to its patient-focus, brevity and support for goal-setting. COSIDI is a valid tool for assessing vestibular rehabilitation, used alone or as complementary to other tools, which clinicians indicated provide useful prompts for patients to consider.

Individuals who experience subjective sensory sensitivities can experience aversion, discomfort or distraction in the presence of sensory stimuli such as loud noises, bright lights, or strong smells. This qualitative analysis took a diagnosis-independent approach to understand the lived experience of sensory sensitivities in 713 individuals. Participants’ descriptions of the effect of their sensitivities on their daily lives were multi-faceted. Themes derived using template thematic analysis centred on sensitivities as limiting social and functional capabilities, creating challenges in personal relationships, and being described as effortful and exhausting. Diverse coping mechanisms were explained, including limiting sensory input, sensory stimulation, self-regulation and the role of others. Participants also described exacerbating factors that were both situational (e.g. focused tasks and crowds) and internal (e.g. stress and fatigue). Physical locations described as challenging were also identified to provide targets for sensory accommodations; these included schools, workplaces and shops. This work underscores the diverse and clear impact subjective sensitivities can have and highlights a need to acknowledge sensory differences outside of diagnostic silos to support wellbeing. Lay Many people feel overwhelmed by things like loud noises, bright lights, or strong smells; this is known as sensory sensitivity. It is common but we know relatively little about how much these experiences can affect daily life. In this study, 713 people shared their personal experiences with sensory sensitivities. By analysing their answers, we found that sensory sensitivities can make it harder for people to socialise, study, work or do everyday tasks like shopping or cooking. People described how these sensitivities often lead to them feeling exhausted or needing time alone to recover. People also told us that their reactions to sensory input could cause tension in their relationships. Some situations made these experiences worse. For example, being tired, stressed or in busy, unpredictable environments. People used different strategies to cope, such as wearing earplugs or sunglasses, avoiding certain places, using calming techniques like deep breathing, or seeking support from people around them. People said that places like schools, workplaces and shops could be particularly difficult for them to be in. Importantly, this study showed that sensory sensitivities can be experienced by many different people, including those without any diagnoses or areas of neurodivergence. By listening to their voices, we can better understand what makes environments difficult and how we might make public spaces more comfortable and inclusive for everyone.