Biology subjects

Melcher, D.

Publications and source records attributed to Melcher, D..

12 recordsLinked to original sources

bioRxiv2026

Oscillatory and aperiodic neural dynamics shape temporal perception and weighting of perceptual priors in ADHD profiles

Attention-deficit/hyperactivity disorder (ADHD) is characterized by an atypically compressed sense of time, yet the neural mechanisms underlying this atypical temporal perception remain poorly understood. Temporal perception depends on the brains ability to organize sensory input into coherent experiences, ensuring perceptual stability despite uncertainty. Oscillations in the alpha band (8-13 Hz) and aperiodic 1/f dynamics have been proposed as key neural mechanisms through which the visual system orchestrates sensory information over time. Individuals with ADHD show atypicalities in these neural dynamics, but how these features relate to ADHD differences in temporal processing remains unexplored. Here, we combined a sustained visual temporal integration task with resting-state EEG to test whether oscillatory and aperiodic neural dynamics jointly account for temporal processing performance across neurotypical participants with self-reported ADHD traits (n = 83). Higher ADHD features in both inattentive and hyperactive-impulsive domains were associated with narrower temporal binding windows and reduced serial dependence on prior perception, indicating sharper temporal resolution but diminished perceptual stability. Resting-state EEG revealed systematically faster individual alpha frequency (IAF) and flatter aperiodic spectra in individuals with higher ADHD traits. Mediation analyses showed that faster IAF explained ADHD-related reductions in temporal integration thresholds and serial dependence, whereas increased neural noise selectively amplified perceptual history-dependent biases. These findings reveal distinct oscillatory and aperiodic neural pathways through which ADHD features shape temporal perception, suggesting a multidimensional neural architecture underlying atypical temporal processing in ADHD.

neuroscience↗

bioRxiv2026

Alpha oscillations and aperiodic neural dynamics jointly predict visual temporal resolution, confidence, and dependence on prior experience

Perception requires integrating sensory input over time to construct coherent experiences. Alpha oscillations have been proposed to define the temporal resolution of perception, yet empirical evidence remains inconsistent. Here we combined a sustained visual integration paradigm with resting-state EEG to investigate how oscillatory and aperiodic neural dynamics jointly shape temporal perception. Participants (n=83) viewed alternating gratings that varied in alternation speed, producing the perception of either a fused plaid (integration) or two interchanging gratings (segregation). Faster individual alpha rhythms were associated with narrower temporal integration windows, and a steeper aperiodic spectrum predicted greater perceptual precision. Moreover, individuals with slower alpha frequencies and flatter spectra showed stronger reliance on prior judgments, suggesting reduced sensory precision and increased weighting of recent experience. Subjective confidence increased with faster alpha rhythms, reflecting the clarity of sensory evidence and its consistency with prior responses. Together, these findings show that the perceptual interpretation, confidence and previous experience effects in temporal integration reflect the joint influence of alpha rhythms and aperiodic neural activity. Mechanistically, faster alpha rhythms and lower neural noise may enhance perceptual resolution by generating more precise sampling frames per time unit, leading to finer temporal perception, reduced reliance on prior experience, and greater confidence.

neuroscience↗

bioRxiv2025

Phase-Dependent EEG Decoding of Continuous Visual Stimuli

Neural oscillations support cognition and perception by organizing information across oscillatory cycles, such that different phases correspond to distinct computational states. Although animal studies strongly support this view, evidence in humans is mixed and largely based on brief, flashed stimuli. Here, we tested whether alpha oscillations, the dominant human brain rhythm, rhythmically modulate visual encoding during sustained perception. EEG was recorded while participants viewed long-lasting (2s) Gabor patches. Using a phase-dependent decoding approach, we extracted EEG activity at specific alpha phases and quantified stimulus decoding accuracy. Decoding performance varied systematically with alpha phase, following a smooth unimodal profile that peaked over occipito-parietal electrodes. These effects emerged well after stimulus onset, indicating a sustained modulation of visual processing during continuous input. Our findings demonstrate that visual information is encoded more accurately at specific alpha phases. This provides direct evidence that sensory processing is gated by intrinsic brain activity and introduces a generalizable decoding framework for linking oscillatory phase to neural information processing.

neuroscience↗

bioRxiv2025

Atypical weighting of sensory evidence and priors in causality perception along the autism-schizotypy continuum

The brain constructs a perceptual interpretation of the world by integrating sensory input with prior knowledge and expectations. Causality perception, a core example of this inferential process, enables observers to infer cause-effect relationships, such as whether a moving object causes another to move. Traditionally considered a low-level visual computation, causality perception is increasingly recognized as shaped by top-down dynamics, perceptual history, and individual predictive processing styles. Here, we examined how prior experience and cognitive-perceptual traits shape causal inference in 150 neurotypical individuals, using data-driven clustering to stratify participants along the autism-schizotypy (ASD-SSD) spectrum. Participants viewed dynamic collision events in which a moving circle contacted a stationary one, followed by variable temporal lags before the second objects motion, and judged whether the interaction appeared causal or non-causal. Causality judgments were influenced by both physical timing (sensory-driven) and serial dependence on previous perceptual decisions (prior-driven). Hierarchical drift diffusion modeling (HDDM) revealed that SSD-like individuals showed a strong prior bias toward causality, greater serial dependence, and lower decision thresholds, reflecting a prior-dominated perceptual style. Conversely, ASD-like individuals exhibited reduced influence of perceptual history and higher decision thresholds, reflecting a conservative, data-driven style. Crucially, prior bias, serial dependence, and decision-making dynamics were strongly interrelated, revealing a hierarchical structure to perceptual inference across neurocognitive profiles. These findings demonstrate that causality perception emerges from predictive processes operating at multiple timescales and shaped by individual differences in neurocognitive style and perceptual flexibility. Significance StatementAccurate causality perception is a fundamental building block of cognition, supporting our ability to parse the sensory world, guide action, and construct coherent models of the environment. It provides a key example of perceptual inference, and thus how the brain integrates sensory input, prior expectations, and recent experience to shape subjective perception. Here, we show that causality perception is not fixed, but varies systematically across individuals, mirroring broader variability in how different neurocognitive architectures balance sensory evidence and prior expectations along the autism-schizotypy (ASD-SSD) spectrum within the general population. By combining psychophysical data with hierarchical computational modeling, we reveal distinct perceptual inference styles along the autism-schizotypy continuum, ranging from sensory-driven to prior-driven processing. These findings advance predictive processing accounts of individual variability and offer new insights into the mechanisms supporting flexible and adaptive perception in neurodiverse populations.

neuroscience↗

bioRxiv2025

Seeing is Feeling: How Aphantasia Alters Emotional Engagement with Stories

Visual imagery is thought to act as an emotional amplifier, potentially contributing to narrative engagement. To examine this, we conducted two experiments in which participants were presented with emotionally charged audio and video story excerpts. Experiment 1 included 84 online participants from the general population, while Experiment 2 involved 25 individuals with aphantasia (the inability to generate mental images) and 25 controls. In both experiments we assessed narrative engagement behaviorally using the Narrative Engagement Questionnaire (NEQ), while for Experiment 2 we also measured physiological responses. We found a main effect of modality, with video stimuli scoring higher across all NEQ subscales in both experiments. Notably, in experiment 2, a significant group effect on emotional--but not cognitive--engagement emerged, with aphantasics reporting less emotional engagement than controls. Moreover, controls experienced higher heart rate during audio narratives, while aphantasics had a similar heart rate across both modalities. Our results suggest that the enhanced physiological response seen in non-aphantasics during audio narratives is driven by the mental effort required to generate imagery. Furthermore, this capacity for visual imagery appears to enhance emotional engagement with stories. This highlights mental imagerys role in both subjective and physiological responses, emphasizing distinct cognitive processes during narrative engagement.

physiology↗

bioRxiv2025

The Artists' Brain: A Data Fusion Approach to Characterize the Neural Bases of Professional Visual Artists

Although everyone has the capacity to draw, only some develop the expertise to produce professional art. Despite extensive creativity research, surprisingly little is known about how years of visual artistic training reshape the neural architecture that distinguishes professional artists from non-artist. To address this gap, we applied joint independent component analysis (jICA) to detect structural (gray matter volume - GM, white matter fractional anisotropy - FA), and functional (resting-state regional homogeneity - ReHo), neuroimaging data from 12 professional visual artists and 12 matched controls. This multimodal approach identified a joint GM-ReHo-FA component (IC2) that significantly distinguished artists from controls (p = .020, d = 1.028). Compared to controls, artists showed coordinated neural adaptations including increased gray matter in parietal, temporal, frontal regions and posterior cingulate cortex; enhanced white matter integrity in anterior thalamic radiations, corticospinal tracts, and association fibers; and increased functional homogeneity in basal ganglia and cerebellar structures. Notably, IC2 expression correlated with higher visual imagery vividness, linking neural adaptations to cognitive abilities fundamental to artistic creation. Taken together, these results highlight the involvement of canonical creativity networks (DMN-ECN) while also extending them to include domain-specific adaptations in cerebellar, sensorimotor, and subcortical systems. Despite these advances, replication with larger samples is necessary.

neuroscience↗

bioRxiv2023

Aperiodic EEG predicts variability of visual temporal processing

The human brain exhibits both oscillatory and aperiodic, or 1/f, activity. Although a large body of research has focused on the relationship between brain rhythms and sensory processes, aperiodic activity has often been dismissed as noise and functionally irrelevant. Prompted by recent findings linking aperiodic activity to the balance between neural excitation and inhibition, we investigated its effects on the temporal resolution of perception. We recorded EEG from participants during resting state and a task in which they detected the presence of two flashes separated by variable inter-stimulus intervals. Two-flash discrimination accuracy typically follows a sigmoid function whose steepness reflects perceptual variability or inconsistent integration/segregation of the stimuli. We found that individual differences in the steepness of the psychometric function correlated with EEG aperiodic exponents over posterior scalp sites. In other words, participants with higher levels of aperiodic activity (i.e., neural excitation) exhibited increased sensory noise, resulting in shallower psychometric curves. Our finding suggest that aperiodic EEG is linked to sensory integration processes usually attributed to the rhythmic inhibition of neural oscillations. Overall, this correspondence between aperiodic neural excitation and behavioral measures of sensory noise provides a more comprehensive explanation of the relationship between brain activity and sensory integration and represents an important extension to theories of how the brain samples sensory input over time.

neuroscience↗

bioRxiv2023

The Extrafoveal Preview Effect is More Pronounced Where Perception is Poor

The pre-saccadic preview of a peripheral target enhances the efficiency of its post-saccadic processing, termed the extrafoveal preview effect. Peripheral visual performance -and thus the quality of the preview- varies around the visual field, even at iso-eccentric locations: it is better along the horizontal than vertical meridian and along the lower than upper vertical meridian. To investigate whether these polar angle asymmetries influence the preview effect, we asked human participants (to preview four tilted gratings at the cardinals, until a central cue indicated to which one to saccade. During the saccade, the target orientation either remained or slightly changed (valid/invalid preview). After saccade landing, participants discriminated the orientation of the (briefly presented) second grating. Stimulus contrast was titrated with adaptive staircases to assess visual performance. Expectedly, valid previews increased participants post-saccadic contrast sensitivity. This preview benefit, however, was inversely related to polar angle perceptual asymmetries; largest at the upper, and smallest at the horizontal meridian. This finding reveals that the visual system compensates for peripheral asymmetries when integrating information across saccades, by selectively assigning higher weights to the less-well perceived preview information. Our study supports the recent line of evidence showing that perceptual dynamics around saccades vary with eye movement direction. Significance StatementWe constantly make saccadic eye movements to bring relevant visual information into the fovea, which has the highest acuity. Before each saccade, we use "previewed" peripheral information to support our post-saccadic vision. Our sensitivity varies around the visual field -at the same eccentricity it is best along the horizontal meridian and worst at the upper vertical meridian. An optimal visual system should rely more on previewed information with higher precision. Our study reveals the opposite: peripheral preview shapes subsequent post-saccadic foveal processing more at locations where peripheral vision is worse. This finding implies that the human visual system compensates for sensitivity differences around the visual field when integrating information across eye movements.

neuroscience↗

bioRxiv2022

Distinct cortical networks subserve spatio-temporal sampling in vision through different oscillatory rhythms

Although visual input arrives continuously, sensory information is segmented into discrete events. Here, the neural correlates of spatiotemporal binding in male/female human subjects were investigated with MEG using two tasks where separate flashes were presented on each trial but were perceived, in a bi-stable way, as either a single, or two separate, events. The first task (two-flash fusion: TFF) involved judging one versus two flashes while in the second task (apparent motion: AM) participants judged coherent motion versus two stationary flashes. Results indicate two different functional networks underlying two unique aspects of visual temporal binding. In the TFF task, involving an integration window of {approx}50 ms, evoked responses differed as a function of perceptual interpretation by {approx}25 ms after stimuli presentation. Multivariate decoding of subjective perception based on prestimulus oscillatory phase was significant for alpha-band activity in the right medial temporal (MT) area, with the strength of pre-stimulus connectivity between early visual areas and MT being predictive of performance. In contrast, the longer integration window ({approx}130 ms) for AM showed evoked field differences only {approx}250 ms after stimuli onset. Phase decoding of the perceptual outcome in the AM task was strongest for theta-band activity, localized to a right intra-parietal sulcus (IPS) source. Pre-stimulus connectivity between MT and IPS seeds in the theta band best predicted perceptual outcome. Overall, these results show a strong relationship between specific spatiotemporal binding windows and specific oscillations, linked to the information flow between different areas of the "where" and "when" visual processing pathways. Significance StatementMultiple neural rhythms seem relevant for sampling visual information across space and time, but the cortical networks underlying these fundamental computational principles of the visual system remain unexplored. We filled this gap by employing source-level multivariate decoding and connectivity analyses of magnetoencephalographic data recorded during an integration/segregation task of temporal and spatio-temporal events. We identified a first and faster network involving early visual areas (V2 to MT/V5) that determines the basic temporal resolution of visual perception at the speed of the alpha rhythm, and a second slower network involving parietal regions (IPS) that had a key role in the integration of more complex spatiotemporal events at a theta speed. These findings elucidate the neural mechanisms that transfer sensory information into temporal sequences.

neuroscience↗

bioRxiv2020

Individual Resting-state alpha peak frequency and within-trial changes in alpha peak frequency both predict visual flash segregation performance

Although sensory input is continuous, information must be combined over time to guide action and cognition, leading to the proposal of temporal sampling windows. A number of studies have suggested that a 10Hz sampling window might be involved in the "frame rate" of visual processing. To investigate this, we tested the ability of participants to localize and enumerate 1 or 2 visual flashes presented either at near-threshold (NT) or full contrast intensities, while recording magnetoencephalography (MEG). Performance was linked to the alpha frequency both at the individual level and trial-by-trial. Participants with a higher resting state alpha peak frequency showed the greatest improvement in performance as a function of ISI within the 100ms time window, while those with slower alpha improved more when ISI exceeded 100ms. On each trial, correct enumeration (1 vs. 2) performance was paired with faster pre-stimulus instantaneous alpha frequency. The effect of the timing of the NT stimulus on the perception was consistent with visual temporal integration windows being embedded in a sampling rhythm. Our results suggest that visual sampling/processing speed, linked to peak alpha frequency, is both an individual trait and varies in a state-dependent manner. Significance StatementA fundamental question in sensory and cognitive neuroscience is how the brain makes sense of the continuous flow of sensory input, parsing it into meaningful objects and events. The speed of cortical alpha rhythms is hypothesized to predict the temporal resolution of visual perception. We present a magnetoencephalography study investigating whether this temporal resolution is an individual trait or, in contrast, depends on fluctuations in brain state. Our results show that both individual resting state alpha frequency, a relatively stable trait, and trial-by-trial fluctuations of the instantaneous alpha frequency determine temporal segregation performance. These results have important implications for how our moment-by-moment perceptual experience is shaped as well as future intervention strategies to improve visual processing for specific tasks.

neuroscience↗

bioRxiv2019

Post-saccadic face processing is modulated by pre-saccadic preview: Evidence from fixation-related potentials

Humans actively sample their environment with saccadic eye movements to bring relevant information into high-acuity foveal vision. Despite being lower in resolution, peripheral information is also available prior to each saccade. How pre-saccadic extrafoveal preview of a visual object influences its post-saccadic processing is still an unanswered question. Here, we investigated this question by simultaneously recording behavior and fixation-related brain potentials while human subjects made saccades to face stimuli. We manipulated the relationship between pre-saccadic \"previews\" and post-saccadic images to explicitly isolate the influences of the former. Subjects performed a gender discrimination task on a newly foveated face under three preview conditions: phase-scrambled face, incongruent face (different identity from the foveated face), and congruent face (same identity). As expected, reaction times were faster after a congruent-face preview compared to the phase-scrambled and incongruent conditions. Importantly, a face preview (either incongruent or congruent) resulted in a strong reduction of post-saccadic neural responses. Specifically, we analyzed the classic face-selective N170 component at occipito-temporal EEG electrodes, which was still present in our experiments with active looking. We found that this component was strongly attenuated for face preview conditions compared to scrambled conditions. This large and long-lasting decrease in evoked activity is consistent with an active prediction mechanism influencing category-specific neural processing at the start of a new fixation. These findings constrain theories of visual stability and show that the extrafoveal preview methodology can be a useful tool to investigate its underlying mechanisms.\n\nSignificance StatementNeural correlates of object recognition have traditionally been studied by flashing stimuli to the central visual field. This procedure differs in fundamental ways from natural vision, where viewers actively sample the environment with eye movements and also obtain a low-resolution preview of soon-to-be-fixated objects. Here we show that the N170, a classic electrophysiological marker of the structural processing of faces, also occurs during a more natural viewing condition but is massively reduced due to extrafoveal preprocessing (preview benefit). Our results therefore highlight the importance of peripheral vision during trans-saccadic processing in building a coherent and stable representation of the world around us.

neuroscience↗

bioRxiv2018

Previewing a face in the periphery reduces the fN170: Combined EEG and eye-tracking suggests two stages of trans-saccadic predictive processes

The world appears stable despite saccadic eye-movements. One possible explanation for this phenomenon is that the visual system predicts upcoming input across saccadic eye-movements, based on peripheral preview of the saccadic target. We tested this idea using concurrent electroencephalography (EEG) and eye-tracking. Participants made cued saccades to peripheral upright or inverted face stimuli that could change (invalid preview) or keep their orientation (valid preview) across the saccade. Experiment 1 demonstrated better discrimination performance and a reduced fixation-locked N170 (fN170) with valid than with invalid preview demonstrating integration of pre- and post-saccadic information. Moreover, the early fixation-locked EEG showed a preview face inversion effect suggesting that we perceive pre-saccadic input up to about 170 ms post fixation-onset, at least for face orientation. Experiment 2 replicated Experiment 1 and manipulated the proportion of valid and invalid trials (mostly valid versus mostly invalid, 66.6% to 33.3%) to test whether the preview effect reflected active expectations. A whole-scalp Bayes factor analysis provided evidence for no influence of proportion on the fN170 preview effect. Instead, before the saccade the preview face orientation effect declined earlier in the mostly invalid than in the mostly valid block suggesting some form of pre-saccadic expectations. We conclude that visual stability is achieved by two trans-saccadic integration processes: pre-saccadic prediction, reflected in the pre-saccadic proportion modulation, and early post-saccadic change-detection reflected in the fN170 preview effect.

neuroscience↗