Anatomic and functional asymmetries interactively shape human early visual cortex responses

Abstract

Early visual processing is surprisingly flexible even in the adult brain. This flexibility involves both long-term structural plasticity and online adaptations conveyed by top-down feedback. Although this view is supported by rich evidence from both human behavioral studies and invasive electrophysiology in nonhuman models, it has proven difficult to close the gap between species. In particular, it remains debated whether noninvasive measures of neural activity can capture top-down modulations of the earliest stages of processing in the human visual cortex. We previously reported modulations of retinotopic C1, the earliest component of the human visual evoked potential. However, these effects were selectively observed in the upper visual field (UVF). Here we test whether this asymmetry is linked to an interaction between differences in spatial resolution across the visual field and the specific stimuli used in previous studies. We measured visual evoked potentials in response to task-irrelevant, high-contrast textures of different densities in a comparatively large sample of healthy volunteers (N = 31) using high-density electroencephalogram. Our results show differential response profiles for upper and lower hemifields, with UVF responses saturating at higher stimulus densities. In contrast, lower visual field responses did not increase, and even showed a tendency toward a decrease at the highest density tested. We propose that these findings reflect feature-and task-specific pooling of signals from retinotopic regions with different sensitivity profiles. Such complex interactions between anatomic and functional asymmetries need to be considered to resolve whether human early visual cortex activity is modulated by top-down factors.

Sleep does not aid the generalisation of binocular disparity‐based learning to the other visual hemifield

“…Recent evidence suggests that learning on the TDT largely relates to improved temporal learning (Wang et al, 2013) and that appropriate training procedures can induce transfer of texture discrimination learning. This could explain why a growing number of studies report substantial amounts of ocular and retinotopic transfer (Wang et al, 2012;Xiong et al, 2016;Zhang et al, 2010), in contrast to findings based on the classical paradigm (Karni & Sagi, 1991 The main rationale behind the present follow-up study was to account for the potentially confounding effects of numerous visualfield anisotropies (Abrams et al, 2012;Karim & Kojima, 2010), particularly those between the vertical hemifields (Herde et al, 2020;Previc et al, 1995;Rauss et al, 2009;Skrandies, 1987). For example, differences in spatial and temporal resolution between the upper and lower visual field could have masked high-level transfer of learning as well as sleep benefits in our previous study.…”

“…In our previous study, we investigated transfer from the lower to the upper hemifield (Klinzing et al., 2020). The lack of generalisation observed there could at least partly have been the result of anatomical and functional anisotropies between the upper and lower visual hemifields (Herde et al., 2020; Skrandies, 1987). In the present study, we addressed this potential confound by assessing transfer between horizontal hemifields and observed qualitatively and quantitatively similar effects.…”

“…The main rationale behind the present follow‐up study was to account for the potentially confounding effects of numerous visual‐field anisotropies (Abrams et al., 2012; Karim & Kojima, 2010), particularly those between the vertical hemifields (Herde et al., 2020; Previc et al., 1995; Rauss et al., 2009; Skrandies, 1987). For example, differences in spatial and temporal resolution between the upper and lower visual field could have masked high‐level transfer of learning as well as sleep benefits in our previous study.…”

Binocular disparity-based learning does not generalize to the other visual hemifield

“…In our previous study, we investigated transfer from the lower to the upper hemifield 19 . The lack of generalization observed there could have been partly the result of anatomic and functional anisotropies between the upper and lower visual hemifields 21,22,29,30 . Here, we addressed this potential confound by assessing transfer between horizontal hemifields and observe qualitatively and quantitatively similar effects.…”

“…The main reason for conducting this follow-up study was to account for the potentially confounding effects of numerous visual-field anisotropies 30,43,44 , particularly those between the vertical hemifields 21,22,29,45,46 . For example, differences in spatial and temporal resolution between upper and lower visual fields could have masked high-level transfer of learning, as well as sleep benefits, given that participants were always trained in the lower visual field.…”