Blending into the Crowd: Electrophysiological Evidence of Gestalt Perception of a Human Dyad

Adaptation of Ocular Opponency Neurons Mediates Attention-Induced Ocular Dominance Plasticity

Previous research has shown that ocular dominance can be biased by prolonged attention to one eye. The ocular-opponency-neuron model of binocular rivalry has been proposed as a candidate account for this phenomenon. Yet direct neural evidence is still lacking. By manipulating the contrast of dichoptic testing gratings, here we measured the steady-state visually evoked potentials (SSVEPs) at the intermodulation frequencies to selectively track the activities of ocular-opponency-neurons before and after the "dichoptic-backward-movie" adaptation. One hour of adaptation caused a shift of perceptual and neural ocular dominance towards the unattended eye. More importantly, we found a decrease in the intermodulation SSVEP response after adaptation, which was significantly greater when high-contrast gratings were presented to the attended eye than when they were presented to the unattended eye. These results strongly support the view that the adaptation of ocular-opponency-neurons contributes to the ocular dominance plasticity induced by prolonged eye-based attention.

Negligible contribution of adaptation of ocular opponency neurons to the effect of short-term monocular deprivation

Introduction

Modeling work on binocular rivalry has described how ocular opponency neurons represent interocular conflict. These neurons have recently been considered to mediate an ocular dominance shift to the eye that has viewed a backward movie for long during which time the other eye is presented with a regular movie. Unlike typical short-term monocular deprivation, the visual inputs are comparable across eyes in that "dichoptic-backward-movie" paradigm. Therefore, it remains unclear whether the ocular opponency neurons are also responsible for the short-term monocular deprivation effect which is prevalently explained by the homeostatic compensation theory. We designed two experiments from distinct perspectives to investigate this question.

Methods

In Experiment 1, we mitigated the imbalance in the activity of opponency neurons between the two eyes during monocular deprivation by presenting video stimuli alternately. In Experiment 2, we directly evaluated the response of opponency neurons before and after monocular deprivation using SSVEP techniques.

Results

Consistent with each other, both experiments failed to provide reliable evidence supporting the involvement of ocular opponency neurons in the short-term monocular deprivation effect.

Discussion

Our results suggest that ocular opponency neurons may not play an essential role in the short-term monocular deprivation effect, potentially due to interference from the homeostatic plasticity mechanism.

Intermodulation responses show integration of interacting bodies in a new whole

People are often seen among other people, relating to and interacting with one another. Recent studies suggest that socially relevant spatial relations between bodies, such as the face-to-face positioning, or facingness, change the visual representation of those bodies, relative to when the same items appear unrelated (e.g., back-to-back) or in isolation. The current study addresses the hypothesis that face-to-face bodies give rise to a new whole, an integrated representation of individual bodies in a new perceptual unit. Using frequency-tagging EEG, we targeted, as a measure of integration, an EEG correlate of the non-linear combination of the neural responses to each of two individual bodies presented either face-to-face as if interacting, or back-to-back. During EEG recording, participants (N = 32) viewed two bodies, either face-to-face or back-to-back, flickering at two different frequencies (F1 and F2), yielding two distinctive responses in the EEG signal. Spectral analysis examined the responses at the intermodulation frequencies (nF1±mF2), signaling integration of individual responses. An anterior intermodulation response was observed for face-to-face bodies, but not for back-to-back bodies, nor for face-to-face chairs and machines. These results show that interacting bodies are integrated into a representation that is more than the sum of its parts. This effect, specific to body dyads, may mark an early step in the transformation towards an integrated representation of a social event, from the visual representation of individual participants in that event.