Biology subjects

Rideaux, R.

Publications and source records attributed to Rideaux, R..

At least 19 recordsLinked to original sources

bioRxiv2026

Walking Produces Oscillations in Orientation and Direction Perception at the Step Rate

Walking is one of the most stereotyped oscillatory movement able-bodied individuals produce. It is highly consistent within and across individuals, with people taking ~5000 steps a day on average at approximately 2 Hz. This consistency and its ubiquitous role in daily living make walking an ideal behaviour for investigating perception under active conditions. Across two virtual reality experiments, we tested whether stride-based oscillations, as seen in visual detection performance, also occur for visual orientation and motion direction discrimination. Participants followed a simulated screen along a linear path in virtual space while visual stimuli were presented on the screen. Group-level performance in both visual tasks oscillated at approximately two cycles per stride. Peak performance in visual orientation identification aligned with the late swing phase of each step, whereas peak performance in motion direction identification aligned with the late stance or early swing phase. These findings extend recent work showing that visual perception is modulated at the step rate during locomotion.

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bioRxiv2026

Entering and Exiting Awareness are Asymmetrical: Evidence from tracking Continuous Flash Suppression

This study provides a model for obtaining cleaner threshold estimates of entry into and exit from conscious awareness measured with the popular breaking continuous flash suppression (bCFS) and newer tracking CFS (tCFS) paradigms. In both, a suppressed target increases in contrast until it breaks into awareness. tCFS also measures exit thresholds by reversing the contrast change. Both CFS paradigms require a response when the threshold is reached and thus involve a reaction-time component. During this period, target contrast continues to change and threshold estimates are inflated (the "overshoot" problem). Here, we measure reaction-time components for both increasing (entering awareness) and decreasing targets (exiting awareness). We find overshoot is asymmetrical, being greater for stimuli entering (breakthrough thresholds) than for exiting awareness (suppression thresholds). To solve "the overshoot problem", we introduce a mathematical model that quantifies reaction-time components so they can be partialled out to produce clean breakthrough and suppression thresholds. The model can also be applied to previously published CFS studies. The model works for simple target detection and two-alternative target discrimination, even in the continuous tracking paradigm of tCFS. With the timing corrections applied, changes in pupil diameter around transitions in awareness are shown to align with the corrected time points, most clearly when targets exit awareness. Even after correction, the contrast decrease required for a target to exit awareness was greater than the increase required for it to enter awareness.

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bioRxiv2026

A comparison of sharpening and dampening accounts of the role of expectation in shaping the neural fidelity of early visual representations

The natural environment is spatiotemporally structured, and the brain exploits this regularity to predict and prepare for upcoming sensory stimuli. Such predictive processing is thought to increase neural efficiency by reducing metabolic expenditure and altering the fidelity with which newly encountered stimuli are encoded. Competing theoretical frameworks propose this is achieved either through sharpening, whereby expected events are encoded more precisely, or dampening, whereby expected events are suppressed and encoded less precisely. Despite clear, opposing predictions, evidence in humans for each account remains mixed due to methodological and analytical inconsistencies. Here we addressed these issues using probabilistic visual paradigm combined with functional magnetic resonance imaging (fMRI) and electroencephalography (EEG). We used population receptive field (pRF) mapping of fMRI data and inverted encoding of EEG data to compare the fidelity and timecourse of activity in visual areas in response to expected, unexpected, and random stimuli. Both methods produced a consistent pattern of results. Post hoc analysis of EEG data revealed that the apparent effect of expectancy was better explained by local spatiotemporal stimulus properties than the global expectancy manipulation. Although this pattern resembled sensory adaptation, it was more consistent with an expectation of temporal stability combined with dampening, in which both the aggregate response to expected features and their representational fidelity are suppressed. Taken together, our findings suggest that predictive processing may operate through dampening, with ecological advantages for high-fidelity encoding of unexpected sensory events.

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bioRxiv2026

Explicit knowledge gates expectation suppression in the motor system: Evidence from a TMS motor oddball paradigm

Models of predictive processing propose that the brain continuously generates predictions about incoming sensory input, updating an internal model of the environment through prediction errors when those predictions are violated. A foundational assumption of these models is that prediction errors are generated automatically, even in the absence of explicit knowledge of the predictions. Evidence from auditory oddball studies in unconscious patients appears to support this view, though findings are complicated by stimulus-specific adaptation confounds that make it difficult to isolate genuine predictive effects. To investigate whether expectation suppression or prediction-based attenuation extends to the motor system and whether it operates automatically, we developed a novel motor oddball paradigm using brain stimulation. Transcranial magnetic stimulation (TMS) delivered over the primary motor cortex elicits motor-evoked potentials (MEPs) in peripheral muscles, providing an index of corticospinal excitability. By varying stimulation intensity in an oddball-like manner using repeating and deviating sequences, we manipulated the predictability of TMS pulses and compared MEP amplitudes for expected versus unexpected intensity-matched stimulation. Incorporating experimental designs to control for adaptation and an instruction manipulation to test the role of explicit knowledge, expected TMS produced smaller MEPs than unexpected TMS. Critically, this attenuation was observed only in participants explicitly informed about the sequence structure. These findings extend expectation suppression effects to the motor system and support the domain-generality of prediction-based neural attenuation while challenging the assumption that predictive processing operates entirely automatically.

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bioRxiv2025

The Role of Temporal Factors in Processing Rapid Serial Visual Presentations

Sequentially presented visual stimuli are often employed to investigate the temporal limits of our visual perception and attention. Due to the finite nature of the brains processing capacity, experimental designs attempt to increase temporal separation within series to mitigate potential neural interference between stimuli. This is achieved through shortening of stimulus durations and lengthening of interstimulus intervals. Across two experiments, we parametrically varied these parameters for a serially presented checkerboard wedge stimulus and used inverted encoding modelling to assess the fidelity of the neural representation of spatial location. We found longer interstimulus intervals and shorter stimulus durations produced the most reliable decoding. Varying interstimulus interval altered the fidelity of neural representations via inter-item interference. By contrast, the influence of stimulus duration seemed largely analytic; in a fixed duration block, shorter stimulus duration enabled more presentations, which led to increased decoding accuracy. Distinct anticipatory and reactionary neural events were observed for stimuli presented in triplet sequences, which seemed consistent with forwards and backwards visual masking. The absence of an anticipatory event was observed when backward masking was stronger while a reactionary event was present for every stimulus subjected to forward masking.

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bioRxiv2025

Multimodal general expectancy effects elicited without influencing sensory representations

Predictive coding theories posit a reduction in error-signalling neural activity when incoming sensory input matches existing expectations - a phenomenon termed expectation suppression. However, the empirical evidence for expectation suppression, as well as its underlying neural mechanism, is contentious. A further aspect of predictive coding that remains untested is how predictions are integrated across sensorimotor domains. To investigate these two questions, we employed a novel cross-domain probabilistic cueing paradigm, where participants were presented with both visual and motor cues within a single trial. These cues manipulated the orientation and temporal expectancy of target stimuli with 75% validity. Participants completed a reproduction task where they rotated a bar to match the orientation of the target stimulus while their neural and pupil responses were respectively measured via electroencephalography and eye tracking. Our results showed a consistent, feature-unspecific effect of motor expectancy across multiple measures, while evidence for visual expectancy was limited. However, neither motor nor visual expectancy modulated the fidelity of sensory representations. These results indicate that violations of temporal expectancy in the current study may reveal the brains intrinsic sensitivity to temporal regularities in the natural settings, rather than feature-specific predictions. In contrast, the absence of visual expectancy effects in both neural and pupillometry results adds to a growing body of evidence questioning the effectiveness of probabilistic cueing paradigms for establishing expectations capable of altering sensory representations. Due to null findings in the visual and sensory representation analyses, we did not further investigate cross-domain prediction integration.

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bioRxiv2025

Reply to: Model mimicry limits conclusions about neural tuning and can mistakenly imply unlikely priors

In Harrison, Bays, and Rideaux (2023), we presented evidence from electroencephalographical recordings of humans that there is an over representation of horizontal orientations in the visual cortex. Wolf and Rademaker (2024) raise concerns about an analysis used in our study and provide an alternative explanation for our results. Here we address their concerns and provide additional magnetencephalography data supporting the conclusions of our original study.

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bioRxiv2024

Energy efficiency and sensitivity benefits in a motion processing adaptive recurrent neural network

Motion processing is a key function for the survival of many organisms and is initially implemented in the primary visual cortex (V1) and the middle temporal area (V5/MT) of the primate visual cortex. Advances in machine learning approaches have led to the development of motion processing neural networks that have elucidated several aspects of this process. However, it remains unclear how adaptation, a canonical function of sensory processing, influences motion processing. In this study, we developed two recurrent neural networks to study motion processing: MotionNet-R, a baseline model, and AdaptNet, a model that employs adaptive mechanisms inspired by biological systems. Both networks were trained on natural image sequences to estimate motion vectors. We found that both networks developed response properties that resembled those of neurons found in areas V1 and MT, e.g., speed tuning, and AdaptNet recapitulated the motion aftereffect phenomenon (i.e., the waterfall illusion). We show that the emergent computational properties that implement the phenomenon in AdaptNet confirm previous theoretical hypotheses. Further, we compared the performance of the two networks and found that AdaptNet processed motion more efficiently, operationalized as reduced activation. While AdaptNet incurred reduced accuracy in response to prolonged constant input, it was both more accurate and sensitive in response to changes in motion input. These results are consistent with theoretical explanations of adaptation as neural property that supports metabolic efficiency and increased sensitivity to change in the environment. Our findings provide novel insights into the neural mechanisms underlying motion adaptation and highlight the potential advantages of adaptive neural networks in modelling biological processes.

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bioRxiv2024

The influence of temporal context on vision over multiple time scales

Past sensory experiences influence perception of the present. Multiple research subfields have emerged to study this phenomenon at different temporal scales. These phenomena fall into three categories: the influence of immediately preceding sensory events (micro), expectations established by short sequences of events (meso), and regularities over long sequences of events (macro). In a single paradigm, we examined the influence of temporal context on perception at each scale. By integrating behavioural and pupillometry recordings with electroencephalographical recordings from a previous study, we identify two distinct mechanisms that operate across all scales. The first is moderated by attention and supports rapid motor responses to expected events. The second operates independently of task-demands and dampens the feedforward neural responses produced by expected events, leading to unexpected events eliciting earlier and more precise neural representations.

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bioRxiv2024

Investigating orientation adaptation following naturalistic film viewing

Humans display marked changes to their perceptual experience of a stimulus following prolonged or repeated exposure to a preceding stimulus. A well-studied example of such perceptual adaptation is the tilt-aftereffect. Here, prolonged exposure to one orientation leads to a shift in the perception of subsequent orientations. Such a capacity to adapt suggests the visual system is dynamically tuned to our current visual environment. However, it remains unclear to what extent adaptation occurs in response to systematic features in naturalistic scenes. We therefore investigated orientation adaptation in response to natural viewing of filtered live-action film stimuli. Within a session, participants freely viewed 45 minutes of a film which had been filtered to include increased contrast energy within a specified orientation band (0{degrees}, 45{degrees}, 90{degrees}, or 135{degrees}; i.e., the adaptor). To measure adaptation effects, the film was intermittently interrupted to have participants perform a simple orientation judgement task. Having participants complete behavioural trials throughout the testing session, including 45 minutes of total adaptation time, allowed investigation of the accumulation of response biases and changes in such biases over the course of the session. We found participants exhibited stronger adaptation effects in response to cardinal adaptors compared to obliques. However, overall adaptation effects were weaker than those observed under typical tilt-aftereffect paradigms. Further, within a single session, adaptation effects developed inconsistently. The current findings therefore demonstrate a resistance to adaptation in response to naturalistic viewing conditions, suggesting barriers to understanding perceptual adaptation as experienced in nature.

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bioRxiv2024

Violated predictions enhance the representational fidelity of visual features in perception

Predictive coding theories argue that recent experience establishes expectations that generate prediction errors when violated. In humans, brain imaging studies have revealed unique signatures of violated predictions in sensory cortex, but the perceptual consequences of these effects remain unknown. We had observers perform a dual-report task on the orientation of a briefly presented target grating within predictable or random sequences, while we recorded pupil size as an index of surprise. Observers first made a speeded response to categorize the orientation of the target grating (clockwise or counterclockwise from vertical), then reproduced its orientation without time pressure by rotating a bar. This allowed us to separately assess response speed and precision for the same stimuli. Critically, on half the trials, the target orientation deviated from the spatiotemporal structure established by the preceding gratings. Observers responded faster and more accurately to unexpected gratings, and pupillometry provided physiological evidence of observers surprise in response to these events. In a second experiment, we cued the spatial location and timing of the grating and found the same pattern of results, demonstrating that unexpected orientation information is sufficient to produce faster and more precise responses, even when the location and timing of the relevant stimuli are fully expected. These findings indicate that unexpected events are prioritized by the visual system both in terms of processing speed and representational fidelity.

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bioRxiv2024

Inverted encoding of neural responses to audiovisual stimuli reveals super-additive multisensory enhancement

A central challenge for the brain is how to combine separate sources of information from different sensory modalities to optimally represent objects and events in the external world, such as combining someones speech and lip movements to better understand them in a noisy environment. At the level of individual neurons, audiovisual stimuli often elicit super-additive interactions, where the neural response is greater than the sum of auditory and visual responses. However, investigations using electroencephalography (EEG) to record brain activity have revealed inconsistent interactions, with studies reporting a mix of super- and sub-additive effects. A possible explanation for this inconsistency is that standard univariate analyses obscure multisensory interactions present in EEG responses by overlooking multivariate changes in activity across the scalp. To address this shortcoming, we investigated EEG responses to audiovisual stimuli using inverted encoding, a population tuning approach that uses multivariate information to characterise feature-specific neural activity. Participants (n = 41) completed a spatial localisation task for both unisensory stimuli (auditory clicks, visual flashes) and combined audiovisual stimuli (spatiotemporally congruent clicks and flashes). To assess multivariate changes in EEG activity, we used inverted encoding to recover stimulus location information from event-related potentials (ERPs). Participants localised audiovisual stimuli more accurately than unisensory stimuli alone. For univariate ERP analyses we found an additive multisensory interaction. By contrast, multivariate analyses revealed a super-additive interaction [~]180 ms following stimulus onset, such that the location of audiovisual stimuli was decoded more accurately than that predicted by maximum likelihood estimation. Our results suggest that super-additive integration of audiovisual information is reflected within multivariate patterns of activity rather than univariate evoked responses.

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bioRxiv2024

Task-related modulation of event-related potentials does not reflect changes to sensory representations

Attention supports efficient perception by increasing the neural signals of targets while supressing those of distractors. Decades of work studying the event-related potentials of electroencephalography (EEG) recordings have established our understanding of attention in the human brain, but many aspects of this phenomenon remain unknown. Several recent studies suggest that multivariate analyses may provide new insights into how attention shapes the neural representations of stimuli; however, it is unclear whether the increased multivariate decoding accuracy associated with task relevance represents a change in the stimulus representation or an additional cognitive process. To understand what the change in multivariate information that is associated with task relevance reflects, here we used inverted encoding to characterize how task relevance shapes the neural representation of space and colour. For both spatial and feature-based tasks, we found that the change in the EEG recordings associated with task relevance is not related to the stimulus representation. Rather, our findings indicate that this phenomenon reflects an additional cognitive process, such as target recognition.

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bioRxiv2023

Neural tuning instantiates prior expectations in the human visual system

Perception is often modelled as a process of active inference, whereby prior expectations are combined with noisy sensory measurements to estimate the structure of the world. This mathematical framework has proven critical to understanding perception, cognition, motor control, and social interaction. While theoretical work has shown how priors can be computed from environmental statistics, their neural instantiation could be realised through multiple competing encoding schemes. Using a data-driven approach, here we extract the brains representation of visual orientation and compare this with simulations from different sensory coding schemes. We found that the tuning of the human visual system is highly conditional on stimulus-specific variations in a way that is not predicted by previous proposals. We further show that the adopted encoding scheme effectively embeds an environmental prior for natural image statistics within the sensory measurement, providing the functional architecture necessary for optimal inference in the earliest stages of cortical processing.

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bioRxiv2021

Comparison of seven modelling algorithms for GABA-edited 1H-MRS

Edited MRS sequences are widely used for studying GABA in the human brain. Several algorithms are available for modelling these data, deriving metabolite concentration estimates through peak fitting or a linear combination of basis spectra. The present study compares seven such algorithms, using data obtained in a large multi-site study. GABA-edited (GABA+, TE = 68 ms MEGA-PRESS) data from 222 subjects at 20 sites were processed via a standardised pipeline, before modelling with FSL-MRS, Gannet, AMARES, QUEST, LCModel, Osprey and Tarquin, using standardised vendor-specific basis sets (for GE, Philips and Siemens) where appropriate. After referencing metabolite estimates (to water or creatine), systematic differences in scale were observed between datasets acquired on different vendors hardware, presenting across algorithms. Scale differences across algorithms were also observed. Using the correlation between metabolite estimates and voxel tissue fraction as a benchmark, most algorithms were found to be similarly effective in detecting differences in GABA+. An inter-class correlation across all algorithms showed single-rater consistency for GABA+ estimates of around 0.38, indicating moderate agreement. Upon inclusion of a basis set component explicitly modelling the macromolecule signal underlying the observed 3.0 ppm GABA peaks, single-rater consistency improved to 0.44. Correlation between discrete pairs of algorithms varied, and was concerningly weak in some cases. Our findings highlight the need for consensus on appropriate modelling parameters across different algorithms, and for detailed reporting of the parameters adopted in individual studies to ensure reproducibility and meaningful comparison of outcomes between different studies. HighlightsO_LIGABA-edited MRS data from 222 healthy adults across 20 research sites were analyzed C_LIO_LIData were modelled using seven different algorithms, yielding GABA+ and Glx estimates C_LIO_LIModerate agreement was seen across all the tested algorithms C_LIO_LIAdding a component to represent co-edited macromolecule signals improved concordance C_LIO_LIBaseline modelling emerged as major factor differentiating outcomes C_LI

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bioRxiv2021

Spatial structure, phase, and the contrast of natural images

The sensitivity of the human visual system is thought to be shaped by environmental statistics. A major endeavour in vision science, therefore, is to uncover the image statistics that predict perceptual and cognitive function. When searching for targets in natural images, for example, it has recently been proposed that target detection is inversely related to the spatial similarity of the target to its local background. We tested this hypothesis by measuring observers sensitivity to targets that were blended with natural image backgrounds. Targets were designed to have a spatial structure that was either similar or dissimilar to the background. Contrary to masking from similarity, we found that observers were most sensitive to targets that were most similar to their backgrounds. We hypothesised that a coincidence of phase-alignment between target and background results in a local contrast signal that facilitates detection when target-background similarity is high. We confirmed this prediction in a second experiment. Indeed, we show that, by solely manipulating the phase of a target relative to its background, the target can be rendered easily visible or undetectable. Our study thus reveals that, in addition to its structural similarity, the phase of the target relative to the background must be considered when predicting detection sensitivity in natural images.

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bioRxiv2021

No balance between glutamate+glutamine and GABA+ in visual and motor cortices of the human brain

Theoretical work, supported by electrophysiological evidence, asserts that a balance between excitation and inhibition (E/I) is critical for healthy brain function. In magnetic resonance spectroscopy (MRS) studies, the ratio of excitatory (glutamate) and inhibitory ({gamma}-aminobutyric acid, GABA) neurotransmitters is often used as a proxy for this E/I balance. Recent MRS work found a positive correlation between GABA+ and Glx (glutamate+glutamine) in medial parietal cortex, providing validation for this proxy and supporting the link between the E/I balance observed in electrophysiology and that detected with MRS. Here we assess the same relationship, between GABA+ and Glx, in primary visual and motor cortices of resting male and female human participants. We find moderate to strong evidence that there is no positive correlation between these neurotransmitters in either location. We show this holds true when controlling for a range of other factors (i.e., demographics, signal quality, tissue composition, other neurochemicals) and regardless of the state of neural activity (i.e., resting/active). These results show that there is no brain-wide balance between excitatory and inhibitory neurotransmitters and indicates a dissociation between the E/I balance observed in electrophysiological work and the ratio of MRS-detected neurotransmitters.

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bioRxiv2020

Exploring and explaining properties of motion processing in biological brains using a neural network

Visual motion perception underpins behaviours ranging from navigation to depth perception and grasping. Our limited access to biological systems constrain our understanding of how motion is processed within the brain. Here we explore properties of motion perception in biological systems by training a neural network ( MotionNetxy) to estimate the velocity image sequences. The network recapitulates key characteristics of motion processing in biological brains, and we use our complete access to its structure explore and understand motion (mis)perception at the computational-, neural-, and perceptual-levels. First, we find that the network recapitulates the biological response to reverse-phi motion in terms of direction. We further find that it overestimates the speed of slow reverse-phi motion while underestimating the speed of fast reverse-phi motion because of the correlation between reverse-phi motion and the spatiotemporal receptive fields tuned to motion in opposite directions. Second, we find that the distribution of spatiotemporal tuning properties in the V1 and MT layers of the network are similar to those observed in biological systems. We then show that compared to MT units tuned to fast speeds, those tuned to slow speeds primarily receive input from V1 units tuned to high spatial frequency and low temporal frequency. Third, we find that there is a positive correlation between the pattern-motion and speed selectivity of MT units. Finally, we show that the network captures human underestimation of low coherence motion stimuli, and that this is due to pooling of noise and signal motion. These findings provide biologically plausible explanations for well-known phenomena, and produce concrete predictions for future psychophysical and neurophysiological experiments.

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