Evidence for distinct levels of neural adaptation to both coherent and incoherently moving visual surfaces in visual area hMT+

Abstract

Visual adaptation describes the processes by which the visual system alters its operating properties in response to changes in the environment. It is one of the mechanisms controlling visual perceptual bistability - when two perceptual solutions are available - by controlling the duration of each percept. Moving plaids are an example of such ambiguity. They can be perceived as two surfaces sliding incoherently over each other or as a single coherent surface. Here, we investigated, using fMRI, whether activity in the human motion complex (hMT+), a region tightly related to the perceptual integration of visual motion, is modulated by distinct forms of visual adaptation to coherent or incoherent perception of moving plaids. Our hypothesis is that exposure to global coherent or incoherent moving stimuli leads to different levels of measurable adaptation, reflected in hMT+ activity. We found that the strength of the measured visual adaptation effect depended on whether subjects integrated (coherent percept) or segregated (incoherent percept) surface motion signals. Visual motion adaptation was significant both for coherent motion and globally incoherent surface motion. Although not as strong as to the coherent percept, visual adaptation due to the incoherent percept also affects hMT+. This shows that adaptation can contribute to regulate percept duration during visual bistability, with distinct weights, depending on the type of percept. Our findings suggest a link between bistability and adaptation mechanisms, both due to coherent and incoherent motion percepts, but in an asymmetric manner. These asymmetric adaptation weights have strong implications in models of perceptual decision and may explain asymmetry of perceptual interpretation periods.

The dual nature of the BOLD signal: Responses in visual area hMT+ reflect both input properties and perceptual decision

“…In line with previous reports, we found that the incoherent percept induced higher hMT+ activity than the coherent percept (Castelo-Branco et al, 2002;Duarte et al, 2017;Sousa et al, 2018).…”

“…In line with previous reports, we found that the incoherent percept induced higher hMT+ activity than the coherent percept (Castelo‐Branco et al, 2002; Duarte et al, 2017; Sousa et al, 2018). This possibly reflects a larger number or size of functional units responding to the component motion.…”

“…In order to investigate to which extent fMRI signals reflect input processing versus perceptual output, a paradigm of bistable visual perception of ambiguous motion was used here. Ambiguous moving stimuli can be constructed from superimposed gratings, such as the moving plaids (Adelson & Movshon, 1982; Castelo‐Branco et al, 2002; Rust et al, 2006; Sousa et al, 2018). Observers' perception spontaneously switches between an incoherent percept (component motion), segregating the visual cues in two moving surfaces, and a coherent percept (pattern motion), integrating the visual cues as one single moving surface.…”

A human cortical adaptive mutual inhibition circuit underlying competition for perceptual decision and repetition suppression reversal

“…It does therefore provide a critical opportunity to study mechanisms of interaction between the neuronal pools in human motion complex representing different perceptual domains and define, based on adaptation, how they influence the final percept. Previously, we have found evidence for distinct levels of adaptation during both percepts of this type of stimulus (45) and that adaptation competes with short-term visual memory mechanisms for perceptual interpretation (46). Here, we tested for evidence of an adapting reciprocal inhibition mechanism in the same brain region.…”

Alterations in white matter integrity and network topological properties are associated with a decrease in global motion perception in older adults

“…The aim of the present study was to investigate the effects of age-related reduction in WM integrity and connectivity on GMP at WM microscopic and macroscopic levels using RDK and DTI. Previous studies have revealed that GMP mainly depends on regions of the dorsal visual stream and the parietal lobe ( Biehl et al, 2017 ; Chaplin et al, 2017 ; Sousa et al, 2018 ; Ward et al, 2018 ). Our hypotheses were as follows: (1) Changes in the integrity of WM fiber tracts connecting the visual cortex to other cortical regions would be significantly correlated with changes in GMP in older adults.…”