Biology subjects

Ronconi, L.

Publications and source records attributed to Ronconi, L..

7 recordsLinked to original sources

bioRxiv2025

Spatial grouping modulates the link between individual alpha frequency and temporal integration windows in crowding

Previous research has linked endogenous alpha oscillations ([~]7-13 Hz) to temporal integration windows in visual perception, with higher individual alpha frequency (IAF) predicting improved temporal segregation. Here, we investigated whether alpha-rhythmic temporal integration is a factor in visual crowding and whether this relationship is mediated by spatial grouping mechanisms. 47 participants performed a Vernier discrimination task, in which we manipulated both the stimulus onset asynchrony (SOA) between flankers and targets, and the spatial configuration of the flankers. Specifically, flankers were arranged to either induce crowding or "uncrowding", through the manipulation of good-Gestalt properties. Our results show that crowding has a temporal integration period of around 170 ms but this varies substantially across individuals. Importantly, resting-state IAF predicted individual variance in temporal integration windows: individuals with faster endogenous alpha rhythms could begin to segregate targets from distractors at shorter SOAs. Crucially, this effect was specific for crowding-inducing flankers and disappeared when flankers led to uncrowding. These results suggest that top-down spatial grouping can overwrite the temporal integration constraint imposed by alpha oscillations, highlighting both the relevance of alpha for understanding limits on peripheral visual processing as well as the flexible and context-dependent role of alpha in temporal integration. SIGNIFICANCE STATEMENTThe frequency of alpha-band activity varies across individuals and has previously been linked to temporal integration windows for low-level stimulus properties (e.g., flashes). However, the relevance of individual alpha frequency (IAF) for everyday perception is less clear. We tested whether IAF predicts temporal integration in spatial crowding, a phenomenon that strongly limits perceptual abilities. We found that individuals with higher IAF were better able to spatially segregate targets from flankers at shorter flanker-target offsets, indicating that they spatially integrated the flankers over a smaller temporal window. Interestingly, this effect disappeared when crowding was alleviated by flanker configurations following good-Gestalt principles. Our results suggest that bottom-up mediated spatio-temporal constraints on perception are linked to alpha oscillations but can be overridden by top-down spatial cues.

neuroscience↗

bioRxiv2025

Temporal windows of perceptual organization: Evidence from crowding and uncrowding

Organizing visual input into coherent percepts requires dynamic grouping and segmentation mechanisms that operate across both spatial and temporal domains. While crowding disrupts target perception when nearby elements fall within the same spatial pooling window, specific flanker configurations can alleviate this effect through Gestalt-based grouping, a phenomenon known as uncrowding. Here, we examined the temporal dynamics underlying these spatial organization processes using a Vernier discrimination task. In Experiment 1, we varied stimulus duration and found that uncrowding emerged only after 160 ms, suggesting a time-consuming process. In Experiment 2, we manipulated the stimulus onset asynchrony (SOA) between the target and flankers. We found that presenting good-Gestalt flankers briefly before the target (as little as 32 ms) significantly boosted uncrowding, even in the absence of temporal overlap between the two stimuli. This effect was specific to conditions in which flankers preceded the target, ruling out pure temporal integration and masking accounts. These findings suggest that spatial segmentation can be dynamically facilitated when the temporal order of presentation allows grouping mechanisms to engage prior to target processing. Moreover, the observed time course indicates that segmentation is not purely feedforward, particularly for stimuli that are likely to recruit higher-level visual areas, pointing instead to the involvement of recurrent or feedback processes.

neuroscience↗

bioRxiv2024

Symbolic and Non-Symbolic numbers differently affect centre identification in a number-line bisection task

Numerical and spatial representations are intertwined as in the Mental Number Line, where smaller numbers are on the left and larger numbers on the right. This relationship has been repeatedly demonstrated with various experimental approaches, such as the line bisection task. Spatial accuracy appears to be systematically distorted leftward for smaller digits by elaboration of spatial codes during number processing. Other studies have investigated perceptual and visuo-spatial attention bias using the digit line bisection task, suggesting that these effects may be related to a cognitive illusion in which the reference numbers project their values onto the straight line, creating an illusory lateral disparity. On the other hand, both dot arrays (non-symbolic stimuli) and arabic numbers (symbolic stimuli) demonstrate a privileged relation between spatial and numerical elaboration. The bias toward the larger numerosity flanker was attributed to a length illusion. There is, however, no consensus regarding whether physical features and symbolic and non-symbolic numerical representations exert the same influence over spatial ones. In the present study, we carried out a series of 4 Experiments to provide further evidence for a better understanding of the nature of this differential influence. All experiments presented the numbers in both symbolic and non-symbolic formats. In Experiment 1, the numbers "2-8" were presented in a variety of left-right orientations. In Experiment 2, the flankers were identical, "2-2" or "8-8", and symmetrically displaced with respect to the line. In Experiment 3, we employed asymmetrically distributed eight dots, or font sizes in "8-8" numerals, to create a perceptual imbalance. In Experiment 4, we replicated the manipulation used in Experiment 3, but with two dots and "2-2" numerals. The Non-Symbolic format induced stronger leftward biases, particularly when the larger numerosity (Experiment 1) or the denser stimuli near the line (Experiments 3 and 4) were on the left, while no bias emerged when flankers were numerically equivalent and symmetrical (Experiment 2). The left bias may result from a tendency to estimate the influence of stimulus perception associated with participant scanning direction, similar to the direction of pseudoneglect. Conversely, the Symbolic format induced mostly right bias, possibly due to left-lateralized processing and a tendency to use a common strategy involving scanning from left to right. Altogether our data support the view that abstract numbers and non-symbolic magnitude affect perceptual and attentional biases, yet in distinctive ways.

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

Altered beta-band oscillations and connectivity underlie detail-oriented visual processing in autism

Sensory and perceptual anomalies have been increasingly recognized as core phenotypic markers for autism spectrum disorders (ASD). A neurophysiological characterization of these anomalies is of utmost importance to understand more complex behavioural manifestations within the spectrum. The present study employed electroencephalography (EEG) to test whether detail-oriented visual perception, a recognized hallmark of ASD, is associated with altered neural oscillations and functional connectivity in beta (and alpha) frequency bands, considering their role in feedback and top-down reentrant signalling in the typical population. A sample of children with diagnosis of ASD (N=18) and typically developing peers (TD; N=20) performed a visual crowding task, where they had to discriminate a peripheral target letter surrounded by flankers at different distances, together with a control condition with no flankers. In TD participants the amplitude of the target-locked N1 component and its cortical sources was significantly modulated as a function of visual crowding, whereas such modulation was absent in the ASD group, suggesting that their visual scene analysis takes place without a flexible neural computation. The comparison between groups showed a decreased activity in the ASD group in occipital, infero-temporal and inferior/middle frontal regions in conditions requiring detail-oriented perception as opposed to conditions requiring the discrimination of target in isolation. Moreover, in TD participants detail-oriented perception was associated with an event-related beta power reduction (15-30 Hz), which was not evident in the ASD group. A data-driven functional connectivity analysis highlighted in the ASD sample an increased connectivity in the beta frequency range between occipital and infero-temporal regions. Notably, individual hyperconnectivity indexes correlated to less severe ASD symptomatology and to a diminished detail-oriented perception, suggesting a potential compensatory mechanism. Overall, these results show that altered communication in the beta frequency band may explain atypical perception in ASD, reflecting aberrant feedback connectivity within the visual system with potential cascade effects in visual scene parsing and higher-order functions.

neuroscience↗

bioRxiv2019

Shared resources between visual attention and visual working memory are allocated through rhythmic sampling

Attention and Visual Working Memory (VWM) are among the most theoretically detailed and empirically tested constructs in human cognition. Nevertheless, the nature of the interrelation between selective attention and VWM still presents a fundamental controversy: do they rely on the same cognitive resources or not? The present study aims at disentangling this issue by capitalizing on recent evidence showing that attention is a rhythmic phenomenon, oscillating over short time windows. Using a dual-task approach, we combined a classic VWM task with a detection task in which we densely sampled detection performance during the time between the memory and the test array. Our results show that an increment in VWM load was related to a worse detection of near threshold visual stimuli and, importantly, to the presence of an oscillatory pattern in detection performance at [~]5 Hz. Furthermore, our findings suggest that the frequency of this sampling rhythm changes according to the strategic allocation of attentional resources to either the VWM or the detection task. This pattern of results is consistent with a central sampling attentional rhythm which allocates shared attentional resources both to the flow of external visual stimulation and also to the internal maintenance of visual information.

neuroscience↗

bioRxiv2019

Anomalous Perception Of Biological Motion In Autism: A Conceptual Review And Meta-Analysis

Despite its popularity, the construct of biological motion (BM) and its putative anomalies in autism spectrum disorder (ASD) are not completely clarified. Here, we propose a new model describing distinct levels of BM processing, and we present a meta-analysis investigating BM perception in ASD. We screened 114 articles testing BM perception in ASD and typical developing peers. A general meta-analysis including all the selected studies (N=27) showed BM processing moderate deficit in ASD, but high heterogeneity. This heterogeneity was explored in different additional meta-analyses where studies were grouped according to different levels of BM processing (first-order/direct/instrumental) and the manipulation of low-level perceptual features (spatial/temporal). Results suggest that the most severe deficit in ASD is evident when perception of BM is serving a secondary purpose (e.g., inferring intentionality/action/emotion) and, interestingly, that temporal dynamics could be an important factor in determining BM processing anomalies in ASD. In conclusion, this work questions the traditional understanding of BM anomalies in ASD and claims for a paradigm shift that deconstructs BM into distinct levels of processing and specific spatio-temporal subcomponents. Public Significance statementSince the seminal study by Johansson (1973), the construct of "biological motion" (BM) has gained a considerable success in a wide range of disciplines. In particular, BM processing has been considered a putative marker for social difficulties in neurodevelopmental conditions such as autism spectrum disorder (ASD). Our work aims to quantitatively test the solidity of this view through a meta-analytic approach and also to better define anomalies in BM perception according to distinct levels of complexity and specific spatio-temporal features. Interestingly, we do it by challenging the traditional approach to the conception of BM. This novel conceptualization has intriguing clinical and theoretical insights.

neuroscience↗