Biology subjects

Togoli, I.

Publications and source records attributed to Togoli, I..

5 recordsLinked to original sources

bioRxiv2025

Multifaceted brain representation of numerosity across the senses and presentation formats

Humans can extract numerosity from different senses and a variety of context. How and where the brain abstract numerical information from low-level sensory inputs remains debated. Using multivariate pattern decoding and representational similarity analysis applied to fMRI data, we comprehensively investigate how the brain represents numerical information (range 2-5) across different modalities (auditory, visual) and presentation formats (sequential, simultaneous; symbolic, non-symbolic). We identify a set of brain regions along the dorsal pathway-from early visual cortex to the intraparietal and frontal regions-that encode specific non-symbolic numerical information across formats and modalities. The numerical distance effect, a hallmark of magnitude encoding, was observed in most of these regions. We found aligned representation of numerical information across visual and auditory modalities in intraparietal and frontal regions, but only when they shared a sequential presentation format. Maintaining a distinction between spatial and temporal numerical representations may thus be a fundamental aspect of numerical processing. RSA further revealed a posterior-to-anterior gradient in the intraparietal sulcus (IPS) showing that the dominant factors influencing distributed numerical representations shifted from sensory modality in the posterior parietal regions to presentation format in the anterior parietal areas. Our study reveals a multifaceted brain representation of numerosity across the senses and presentation formats.

neuroscience↗

bioRxiv2024

The mechanisms and neural signature of average numerosity perception

The human brain is endowed with an intuitive sense of number allowing to perceive the approximate quantity of items in a scene, or "numerosity." This ability is not limited to items distributed in space, but also to events unfolding in time and to the average numerosity of dynamic scenes. How the brain computes and represents the average numerosity over time however remains mostly unclear. Here we investigate the mechanisms and electrophysiological (EEG) signature of average numerosity perception. To do so, we used dynamic stimuli composed of 3-12 arrays presented for 50 ms each, and asked participants to judge the average numerosity of the sequence. Our results first show that the weight of different arrays in the sequence in determining the judgement is subject to both primacy and recency effects, depending on the length of the sequence. Moreover, we show systematic perceptual adaptation effects across trials, with the bias on numerical estimates depending on both the average numerosity and length of the preceding stimulus. The EEG results show numerosity-sensitive brain responses starting very early after stimulus onset, and that activity around the offset of the sequence can predict both the accuracy and precision of judgments. Additionally, we show a neural signature of the adaptation effect at around 300 ms, whereby the amplitude of brain responses can predict the strength of the bias. Overall, our findings support the existence of a dedicated, low-level perceptual mechanism involved with the computation of average numerosity, and highlight the processing stages involved with such process.

neuroscience↗

bioRxiv2024

Magnitude processing and integration entail perceptual processes independent from the task

The magnitude dimensions of visual stimuli, such as their numerosity, duration, and size, are intrinsically linked, leading to mutual interactions across them. However, it remains debated whether such interaction across dimensions, or "magnitude integration" effects, arise from low-level perceptual processes that are independent from the task performed, or whether they instead arise from high-level decision-making processes. We address this question with two experiments in which participants watched a series of dot-array stimuli modulated in numerosity, duration, and item size. In experiment 1 (task condition), the task required participants to either judge the numerosity, duration, or size of each stimulus. In experiment 2 (passive condition), instead, a separate group of participants passively watched the stimuli. The behavioral results obtained in the task show robust magnitude integration effects across all three dimensions. Then, we identify a neural signature of magnitude integration by showing that event-related potentials at several latency windows (starting at [~]100-200 ms after stimulus onset) can predict the effect measured behaviorally. In the passive condition, we demonstrate an almost identical modulation of brain responses, occurring at the same processing stages as during the task. Importantly, using a cross-condition multivariate decoding analysis, we demonstrate that brain responses to magnitude in the task condition can predict the response in the passive condition at specific latency windows. These results thus suggest that magnitude processing and integration likely occurs via automatic perceptual processes that are engaged irrespective of the task-relevance of the stimuli, and independently from decision making.

neuroscience↗

bioRxiv2022

The neural signature of magnitude integration between time and numerosity

Magnitude dimensions such as time and numerosity are fundamental components of our visual experience, allowing us to understand the environment and interact with it. Different magnitudes are however not processed independently from each other, but show a relationship whereby the perception of one dimension depends on the others ("magnitude integration"). In this study, we use electroencephalography (EEG) to address whether such integration may arise from a shared brain processing stage where different dimensions are integrated together, or from independent parallel processes interfering with each other. In the experiment, participants judged either the average numerosity or duration of dynamic dot-array stimuli concurrently modulated in both dimensions. First, the behavioural results show a magnitude integration effect in both tasks, with duration affecting the judgement of numerosity and vice versa. The EEG results further show that both numerosity and duration significantly modulate event-related potentials at several distinct latencies. Crucially, however, we identified a significant interaction between numerosity and duration emerging in a specific latency window (360-460 ms) irrespective of the task performed by participants. In this latency window, the modulation of ERPs provided by the interfering magnitude dimension can be predicted by the strength of the behavioural bias. Our results thus support the idea of different magnitude dimensions converging onto a shared perceptual processing stage mediating their integration. Overall, our results demonstrate a clear electrophysiological signature of magnitude integration between numerosity and time, and provide new evidence for a shared representational system encompassing different magnitude dimensions.

neuroscience↗

bioRxiv2022

Different modality-specific mechanisms mediate perceptual history effects in vision and audition

Perceptual history plays an important role in sensory processing and decision making, shaping how we perceive and judge external objects and events. Indeed, past stimuli can bias what we are currently seeing in an attractive fashion, making a current stimulus to appear more similar to its preceding one than it actually is. Such attractive effects across successive stimuli appear to be ubiquitous, affecting almost every aspect of perception - from very basic visual attributes (i.e., orientation) to more complex features (i.e., face identity) - suggesting that they may reflect a fundamental principle of brain processing. However, it is unclear whether the ubiquitous nature of these effects is due to an underlying centralised mechanism mediating all of them, or by the existence of separate mechanisms implemented independently in different perceptual pathways. Here we address this question by assessing the behavioural and neural signature of perceptual history in audition and vision, in the context of time perception. Our results first show a double dissociation between the two modalities, whereby the behavioural effect of perceptual history shows opposite patterns of selectivity for the features and position of the stimuli. Electroencephalography results further support a difference between audition and vision, demonstrating that the signature of perceptual history unfolds according to different dynamics in the two modalities and show different relations with the behavioural effect. Overall, our results suggest that the effect of perceptual history may be mediated by different and at least partially independent mechanisms based on the same computational principle, implemented in different sensory pathways. SIGNIFICANCE STATEMENTThe recent history of stimulation, or perceptual history, plays a fundamental role in perception, shaping what we see according to what we saw in the past. The brain mechanisms mediating the integration of past and present perceptual information are however still unclear. In this study we asked whether perceptual history operates via a centralized mechanism shared across sensory modalities, or via distinct modality-specific mechanisms. Our findings show a double dissociation in attractive perceptual history effects across vision and audition, while EEG data show neural signatures of perceptual history with distinct dynamics and properties. Overall, we thus demonstrate that perceptual history affects sensory processing starting from the earliest level of processing, within distinct modality-specific sensory pathways.

neuroscience↗