Biology subjects

Barbot, A.

Publications and source records attributed to Barbot, A..

5 recordsLinked to original sources

bioRxiv2025

System-Level Computations Underlie Visual Field Heterogeneity

Human visual perception for basic dimensions varies with eccentricity and polar angle, influencing daily activities such as reading, searching and scene perception. We investigated whether and how system-level computations that transform visual input into perception underlie these heterogeneities. Using the equivalent noise method and perceptual template model, we estimated gain, internal noise, and nonlinearity for orientation discrimination across eccentricity (fovea, parafovea and perifovea) and around polar angle. Participants discriminated the orientation of Gabors embedded in dynamic white noise and showed the expected variations across eccentricity and around polar angle. Importantly, visual performance declined with eccentricity due to decreased gain and nonlinearity and increased internal noise. Observers with stronger eccentricity effects showed greater gain decrease. Only gain varied with polar angle--higher along the horizontal than vertical meridian, and lower than upper vertical meridian--paralleling performance asymmetries. This dissociation aligns with known variations in neuronal count and tuning, suggesting that neural correlations and neural noise contribute to these system-level computations. By revealing distinct system-level computations underlying the eccentricity effect and polar angle asymmetries, our findings link perceptual heterogeneity across the visual field and neural architecture and provide insights into how the human brain encodes information under neural constraints. Significance StatementHuman visual performance varies across eccentricity-distance from gaze-and around polar angle -circular dimension. Retinal factors and cortical surface area account for eccentricity, but only partially for polar angle variations. Here, we show that system-level computations--how signal are amplified and how noisy the system is--distinctly underlie these perceptual variations. Decline across eccentricity stems from both reduced gain and nonlinearity and elevated internal noise, whereas variation around polar angle arises solely from gain difference. This dissociation implies fundamental differences in information processing along two axes of the visual field. Our results provide a computational link between behavior and its neural bases and highlight the importance of considering both eccentricity and polar angle in modeling and understanding human perception.

neuroscience↗

bioRxiv2024

Neural Adaptation to the Eye's Optics Through Phase Compensation

How does the brain achieve a seemingly veridical and in-focus perception of the world, knowing how severely corrupted visual information is by the eyes optics? Optical blur degrades retinal image quality by reducing the contrast and disrupting the phase of transmitted signals. Neural adaptation can attenuate the impact of blur on image contrast, yet vision rather relies on perceptually-relevant information contained within the phase structure of natural images. Here we show that neural adaptation can compensate for the impact of optical aberrations on phase congruency. We used adaptive optics to fully control optical factors and test the impact of specific optical aberrations on the perceived phase of compound gratings. We assessed blur-induced changes in perceived phase over three distinct exposure spans. Under brief blur exposure, perceived phase shifts matched optical theory predictions. During short-term ([~]1h) exposure, we found a reduction in blur-induced phase shifts over time, followed by after-effects in the opposite direction-a hallmark of adaptation. Finally, patients with chronic exposure to poor optical quality showed altered phase perception when tested under fully-corrected optical quality, suggesting long-term neural compensatory adjustments to phase spectra. These findings reveal that neural adaptation to optical aberrations compensates for alterations in phase congruency, helping restore perceptual quality over time.

neuroscience↗

bioRxiv2020

Cortical Magnification in Human Visual Cortex Parallels Task Performance around the Visual Field

Human vision has striking radial asymmetries, with performance on many tasks varying sharply with stimulus polar angle. Performance is generally better on the horizontal than vertical meridian, and on the lower than upper vertical meridian, and these asymmetries decrease gradually with deviation from the vertical meridian. Here we report cortical magnification at a fine angular resolution around the visual field. This precision enables comparisons between cortical magnification and behavior, between cortical magnification and retinal cell densities, and between cortical magnification in twin pairs. We show that cortical magnification in human primary visual cortex, measured in 163 subjects, varies substantially around the visual field, with a pattern similar to behavior. These radial asymmetries in cortex are larger than those found in the retina, and they are correlated between monozygotic twin pairs. These findings indicate a tight link between cortical topography and behavior, and suggest that visual field asymmetries are partly heritable.

neuroscience↗

bioRxiv2020

Changes in perilesional V1 underlie training-induced recovery in cortically-blind patients

Damage to the primary visual cortex (V1) causes profound, homonymous visual-field loss termed cortical blindness (CB). Though long considered intractable, multiple studies now show that perceptual training can recover visual functions in chronic CB. A popular hypothesis is that training recruits intact extrageniculostriate pathways. Alternatively, training may induce plastic changes within spared regions of the damaged V1. Here, we linked changes in luminance detection sensitivity with retinotopic fMRI activity in eleven chronic CB patients, before and after extensive visual discrimination training. Our results show that the strength of spared V1 activity representing perimetrically blind-field locations before training predicts the amount of training-induced recovery of luminance detection sensitivity. Additionally, training caused an enlargement of population receptive fields in perilesional V1 cortex, which increased blind-field coverage. These findings uncover fundamental changes in perilesional V1 cortex underlying training-induced restoration of conscious luminance detection sensitivity in cortically-blind patients.

neuroscience↗

bioRxiv2020

Functional reorganization of visual processing following long-term adaptation to optical defects

How we see is fundamentally limited by the eyes optics, which determine retinal image quality and constrain neural processing. Elucidating how long-term exposure to optical defects alters visual processing is vital for understanding the human brains capacity for and limits of sensory plasticity. Using adaptive optics to bypass the eyes optical aberrations, we assessed changes in visual processing in neurotypically-developed adults with keratoconus (KC)--a corneal disease causing severe optical aberrations during adulthood that cannot be fully corrected using conventional methods. As a result, KC patients are chronically exposed to degraded retinal images in their everyday life, making them an ideal model to understand how prolonged exposure to poor optical quality alters visual processing. Here, we show that when tested under similar fully-corrected optical conditions as neurotypical observers, KC patients exhibited altered contrast sensitivity, with impaired sensitivity for fine spatial details and better sensitivity for coarse spatial details. Both gains and losses in contrast sensitivity were more pronounced in patients with poorer habitual optical quality. Moreover, using an equivalent noise paradigm and a computational model of visual processing, we show that these alterations in visual processing are mediated by changes in signal enhancement of spatial frequency selective mechanisms. The present findings uncover fundamental properties of neural compensation mechanisms in response to long-term exposure to optical defects, which alter sensory processing and limit the benefits of improved optics. The outcome is a large-scale functional reorganization favoring the processing of sensory information less affected by the eyes optics. Significance statementThe eyes optics represent an intrinsic limit to human visual perception, determining the quality of retinal images. Neural adaptation optimizes the brains limited sensory processing capacity to the structure of the degraded retinal inputs, providing an exceptional quality of vision given these optical limitations. Here, we show that prolonged exposure to poor optical quality results in a functional reorganization of visual processing that favors sensory information less affected by the eyes optics. The present study helps elucidate how optical factors shape the way the brain processes visual information. Notably, the resulting adaptive neural plasticity limits the immediate perceptual benefits of optical interventions, a factor that must be taken into consideration when treating the increasing human population affected by optical defects.

neuroscience↗