Biology subjects

Zamboni, E.

Publications and source records attributed to Zamboni, E..

4 recordsLinked to original sources

bioRxiv2023

The role of task on the human brain's responses to, and representation of, visual regularity defined by reflection and rotation

Identifying and segmenting objects in an image is generally achieved effortlessly and is facilitated by the presence of symmetry: a principle of perceptual organisation used to interpret sensory inputs from the retina into meaningful representations. However, while imaging studies show evidence of symmetry selective responses across extrastriate visual areas in the human brain, whether symmetry is processed automatically is still under debate. We used functional Magnetic Resonance Imaging (fMRI) to study the response to and representation of two types of symmetry: reflection and rotation. Dot pattern stimuli were presented to 15 human participants (10 female) under stimulus-relevant (symmetry) and stimulus-irrelevant (luminance) task conditions. Our results show that symmetry-selective responses emerge from area V3 and extend throughout extrastriate visual areas. This response is largely maintained when participants engage in the stimulus irrelevant task, suggesting an automaticity to processing visual symmetry. Our multi-voxel pattern analysis (MVPA) results extend these findings by suggesting that not only spatial organisation of responses to symmetrical patterns can be distinguished from that of non-symmetrical (random) patterns, but also that representation of reflection and rotation symmetry can be differentiated in extrastriate and object-selective visual areas. Moreover, task demands did not affect the neural representation of the symmetry information. Intriguingly, our MVPA results show an interesting dissociation: representation of luminance (stimulus irrelevant feature) is maintained in visual cortex only when task relevant, while information of the spatial configuration of the stimuli is available across task conditions. This speaks in favour of the automaticity for processing perceptual organisation: extrastriate visual areas compute and represent global, spatial properties irrespective of the task at hand. Key PointsO_LISymmetry selective responses observed in extrastriate visual cortex but not V1 whether stimulus spatial configuration is task relevant or irrelevant. C_LIO_LIRepresentation for reflection and rotation differ in extrastriate and object-selective areas, during both stimulus relevant and irrelevant tasks. C_LIO_LIRepresentation of luminance information is available only when task relevant. C_LI

neuroscience↗

bioRxiv2023

The emergence of tuning to global shape properties of radial frequency patterns in the ventral visual pathway

Radial frequency patterns - created by sinusoidal modulations of a circles radius - are processed globally when radial frequency is low. These closed shapes therefore offer a useful way to interrogate the human visual system for global processing of curvature. Radial frequency patterns elicit greater responses than those to radial gratings in V4 and more anterior face selective regions of the ventral visual pathway. This is largely consistent with work on non-human primates showing curvature processing emerges in V4, but is evident also higher up the ventral visual stream. Rather than contrasting radial frequency patterns with other stimuli, we presented them at varied frequencies in a regimen that allowed tunings to radial frequency to be derived from 8 human participants (3 female). We found tuning to low radial frequency in lateral occipital areas and to some extent in V4. In a control experiment we added a high frequency ripple to the stimuli disrupting the local contour. Low frequency tuning to these stimuli remained in the ventral visual stream underscoring its role in global processing of shape curvature. We then used representational similarity analysis to show that in lateral occipital areas the neural representation was related to stimulus similarity, when it was computed with a model that captured how stimuli are perceived. We show therefore that global processing of shape curvature emerges in the ventral visual stream as early as V4, but is found more strongly in lateral occipital regions, which exhibit responses and representations that relate well to perception.

neuroscience↗

bioRxiv2020

Recurrent plasticity mechanisms for perceptual decisions in the human brain

Learning and experience are critical for translating ambiguous sensory information from our environments to perceptual decisions. Yet, evidence on how training molds the adult human brain remains controversial, as fMRI at standard resolution does not allow us to discern the finer-scale mechanisms that underlie sensory plasticity. Here, we combine ultra-high field (7T) functional imaging at sub-millimetre resolution with orientation discrimination training to interrogate experience-dependent plasticity across cortical depths. Our results provide evidence for recurrent plasticity, by contrast to sensory encoding vs. feedback mechanisms. We demonstrate that learning alters orientation-specific representations in superficial rather than middle V1 layers, suggesting changes in read-out rather than input signals. Further, learning increases feedforward rather than feedback layer-to-layer connectivity in occipito-parietal regions, suggesting that sensory plasticity gates perceptual decisions. Our findings propose finer-scale plasticity mechanisms that re-weight sensory signals to inform improved decisions, bridging the gap between micro- and macro-circuits of experience-dependent plasticity.

neuroscience↗

bioRxiv2020

Suppressive recurrent and feedback computations for adaptive processing in the human brain

Adapting to the environment statistics by reducing brain responses to repetitive sensory information is key for efficient information processing. Yet, the fine-scale computations that support this adaptive processing in the human brain remain largely unknown. Here, we capitalize on the sub-millimetre resolution afforded by ultra-high field imaging to examine BOLD-fMRI signals across cortical depth and discern competing hypotheses about the brain mechanisms (feedforward vs. feedback) that mediate adaptive visual processing. We demonstrate suppressive recurrent processing within visual cortex, as indicated by stronger BOLD decrease in superficial than middle and deeper layers for gratings that were repeatedly presented at the same orientation. Further, we show dissociable connectivity mechanisms for adaptive processing: enhanced feedforward connectivity within visual cortex, while feedback occipito-parietal connectivity, reflecting top-down influences on visual processing. Our findings provide evidence for a circuit of local recurrent and feedback interactions that mediate rapid brain plasticity for adaptive information processing.

neuroscience↗