Biology subjects

Cass, J.

Publications and source records attributed to Cass, J..

7 recordsLinked to original sources

bioRxiv2026

Perceptual repulsion and decisional attraction in male body serial dependence: a dimensional dissociation in channel architecture

Our judgments of the world are shaped by what we have just seen. This serial dependence is often treated as one bias, but it can constitute opposing influences: an attractive pull toward recent input and a repulsive push away from it. These have been linked to different stages, decisional and perceptual, but separated only for simple visual features. We asked whether the same separation holds for a socially significant category, the human body. Observers categorised images of male bodies as low or high on body fat and muscularity (binary choice, N = 74); a trial-level analysis estimated the perceptual and decisional contribution to each judgment. For body fat, the perceptual contribution was repulsive and clearly tuned, following a derivative-of-Gaussian profile peaking at a moderate difference between successive bodies ({sigma} {approx} 5.6 standardised units), while the decisional contribution was attractive; the dissociation held in most observers. Muscularity showed the same attractive decisional bias, but its perceptual tuning emerged only at longer viewing times, where its width approached that for body fat, indicating a difference in resolvability rather than an absence of tuning. To our knowledge, this is the first estimate of the tuning of the perceptual repulsion channels from binary categorisation of continuously varying stimuli, the first separation of perceptual and decisional components in body perception, and the first evidence of serial dependence for male bodies. Perception emphasises how a body differs from the previous one while the decision favours continuity, a division of labour spanning low-level features to high-level body judgments.

neuroscience↗

bioRxiv2026

Crowding distorts features, not objects: structured target confusions in a 4AFC conjunction task

Visual crowding is the disruption of peripheral object identification by nearby flanking clutter. It remains unclear whether crowding disrupts the bound representation of an object or degrades the object's component features separately. We addressed this with a 4AFC conjunction-report task in which observers reported both the orientation and the brightness of every target. Target Gabors at 6 degrees eccentricity were presented alone or flanked at 1, 3, or 5 degrees separation by Gabors varying independently in colour and/or orientation similarity to the target. We analysed the data three ways: joint accuracy, accuracy on each feature alone, and the statistical coupling between the two report channels. Orientation reports were principally impaired by orientation-similar flankers within the smallest target-flanker separations, whereas luminance reports were impaired by target-colour-similar flankers across a broader spatial range. Observed joint accuracy was closely predicted by the product of the two marginal accuracies in every condition. A complementary chi-square analysis of the full 4x4 stimulus-response matrices agreed with this conclusion at the most-crowded conditions, while revealing structured response biases that the ratio test could not detect. These biases were present at baseline and were not amplified by crowding. The conjunction errors observed under crowding therefore arose from two largely independent feature-specific failures, rather than from disruption of a representation in which the two features are bound. These results indicate that object-level crowding errors in this paradigm are the downstream signature of two independent feature-level processes rather than the breakdown of an object-level mechanism.

neuroscience↗

bioRxiv2026

Two components of rapid temporal recalibration: a stimulus-driven shift and a decisional carryover dissociate across the senses

Multisensory synchrony judgments depend on recent history: the point of subjective simultaneity (PSS) shifts toward recently experienced timing relationships. This shift, known as rapid temporal recalibration, is almost always interpreted as perceptual, a change in when events appear simultaneous. Yet serial dependence in such judgments can arise from two mechanistically distinct sources that a raw PSS shift cannot separate: a genuine perceptual realignment, which slides the psychometric function sideways along the multisensory asynchrony axis (an odd effect), and a decisional carryover, a bias to repeat the previous verdict, which lifts the function vertically without moving the PSS (an even effect). We re-analysed eight published datasets investigating rapid recalibration spanning audiovisual, audiotactile, and visuotactile pairings and audiovisual speech, decomposing serial dependence into these two components within a single mixed-effects model. The components dissociated by modality: perceptual recalibration was robust for audiovisual pairs but weak for audiotactile and absent for visuotactile pairings, whereas the decisional carryover was largest for the tactile pairings and weak for audiovisual pairings, so that the two traded off across the senses. In audiovisual speech, the decisional carryover was gated by the spoken syllable but not by the talkers identity and did not persist beyond one trial, identifying it as a content-specific, one-step decision memory rather than a motor habit or a multi-trial store. Separating the perceptual and decisional contributions to a timing judgment thus re-draws the map of temporal recalibration and revises several conclusions drawn from the undecomposed PSS.

neuroscience↗

bioRxiv2025

Effects of shock on perceptual learning in a virtual reality environment

This study investigates two aspects of visual processing and perceptual learning: the impact of training on the human visual systems ability to integrate information across the visual field and the influence of aversive electrodermal stimulation on perceptual performance in an orientation averaging task. Through a ten-day training regimen that manipulated the set-size of Gabor element arrays, we observe consistent degradation in orientation averaging performance with increasing set-size, with training leading to overall improvements in accuracy and response times, but only a marginal interaction with set-size (for response times). This suggests that training-related enhancements likely operate at a post-integration and/or decisional stage of processing rather than at an early encoding stage. The second inquiry explores the effects of aversive stimuli on perceptual learning-based orientation averaging performance, with participants exposed to no shock, performance-contingent shock or random shock conditions. Our results show that while performance improved across training there was no discernible effect of the shock condition on task accuracy or response times and no evidence of an interaction with set size. State anxiety levels, measured by the State-Trait Anxiety Inventory, indicated that whilst anxiety was elevated in both shock conditions, this was not associated with variations on orientation averaging performance. We also find that visual performance feedback, represented by a health bar, significantly influenced accuracy, but not response times, regardless of the presence or absence of shock. This unexpected impact of visual feedback suggests potential roles for attention and motivation in perceptual performance. Public significance statementThis study enhances our understanding of how training and stress influence visual processing and perceptual learning, revealing critical insights into the mechanisms that govern how we integrate visual information. By exploring the effects of acute stress and visual feedback, our findings suggest potential applications for improving learning outcomes in various contexts, from virtual to real-world environments.

neuroscience↗

bioRxiv2025

Reciprocal roles of crowding and serial dependence on visual perception

Visual perception arises from the interplay between current and prior sensory inputs. Two perceptual phenomena-serial dependence and visual crowding-result from the mandatory integration of retinal information across time and space, respectively. This study investigated, for the first time, their functional relationship for orientation and brightness discrimination tasks. Participants performed orientation and brightness discrimination tasks (blocked) on peripheral targets surrounded by distractors of varying color, orientation, and proximity. Both serial dependence (the influence of prior stimuli on current judgments) and visual crowding (impaired peripheral recognition caused by nearby distractors) were observed. Similar double dissociations in task and stimulus specificity emerged for both phenomena, suggesting functional links mediated by distinct processing mechanisms for brightness and orientation judgments. Additionally, the two effects interacted: crowding reduced serial dependence on subsequent trials, indicating that spatial information is prioritized over temporal information when spatial redundancy is high. Conversely, serial dependence increased crowding for orientation judgments, while for brightness judgments, serial dependence operated additively without affecting crowding. These interactions were spatially specific, occurring only when targets appeared in the same location across consecutive trials. Notably, a positive correlation between crowding and serial dependence was found exclusively for orientation judgments and only when targets appeared at the same location across trials. The reciprocal interaction and positive correlation between serial dependence and crowding observed for orientation judgments indicate that that these processes are intrinsically linked, possibly via a common neural mechanism. In contrast, for brightness judgments, the unilateral effect of crowding on serial dependence--along with the absence of correlation-indicates distinct neural mechanisms. Here, brightness crowding likely precedes serial dependence, reflecting a prioritization of spatial redundancy minimization over temporal stabilization. These findings suggest that the brain strategically integrates spatial and temporal information through distinct yet overlapping mechanisms, balancing spatial precision with temporal stability based on task demands and stimulus characteristics.

neuroscience↗

bioRxiv2023

PhysiCell Studio: a graphical tool to make agent-based modeling more accessible

Defining a multicellular model can be challenging. There may be hundreds of parameters that specify the attributes and behaviors of objects. Hopefully the model will be defined using some format specification, e.g., a markup language, that will provide easy model sharing (and a minimal step toward reproducibility). PhysiCell is an open source, physics-based multicellular simulation framework with an active and growing user community. It uses XML to define a model and, traditionally, users needed to manually edit the XML to modify the model. PhysiCell Studio is a tool to make this task easier. It provides a graphical user interface that allows editing the XML model definition, including the creation and deletion of fundamental objects, e.g., cell types and substrates in the microenvironment. It also lets users build their model by defining initial conditions and biological rules, run simulations, and view results interactively. PhysiCell Studio has evolved over multiple workshops and academic courses in recent years which has led to many improvements. Its design and development has benefited from an active undergraduate and graduate research program. Like PhysiCell, the Studio is open source software and contributions from the community are encouraged.

bioinformatics↗

bioRxiv2019

A Bayesian framework for the detection of diffusive heterogeneity

Cells are crowded and spatially heterogeneous, complicating the transport of organelles, proteins and other substrates. One aspect of this complex physical environment, the mobility of passively transported substrates, can be quantitatively characterized by the diffusion coefficient: a descriptor of how rapidly substrates will diffuse in the cell, dependent on their size and effective local viscosity. The spatial dependence of diffusivity is challenging to quantitatively characterize, because temporally and spatially finite observations offer limited information about a spatially varying stochastic process. We present a Bayesian framework that estimates diffusion coefficients from single particle trajectories, and predicts our ability to distinguish differences in diffusion coefficient estimates, conditional on how much they differ and the amount of data collected. This framework is packaged into a public software repository, including a tutorial Jupyter notebook demonstrating implementation of our method for diffusivity estimation, analysis of sources of uncertainty estimation, and visualization of all results. This estimation and uncertainty analysis allows our framework to be used as a guide in experimental design of diffusivity assays.

biophysics↗