Abstract
Adaptation is a mechanism by which cortical neurons adjust their responses according to recently viewed stimuli. Visual information is processed in a circuit formed by feedforward (FF) and feedback (FB) synaptic connections of neurons in different cortical layers. Here, the functional role of FF-FB streams and their synaptic dynamics in adaptation to natural stimuli is assessed in psychophysics and neural model. We propose a cortical model which predicts psychophysically observed motion adaptation aftereffects (MAE) after exposure to geometrically distorted natural image sequences. The model comprises direction selective neurons in V1 and MT connected by recurrent FF and FB dynamic synapses. Psychophysically plausible model MAEs were obtained from synaptic changes within neurons tuned to salient direction signals of the broadband natural input. It is conceived that, motion disambiguation by FF-FB interactions is critical to encode this salient information. Moreover, only FF-FB dynamic synapses operating at distinct rates predicted psychophysical MAEs at different adaptation time-scales which could not be accounted for by single rate dynamic synapses in either of the streams. Recurrent FF-FB pathways thereby play a role during adaptation in a natural environment, specifically in inducing multilevel cortical plasticity to salient information and in mediating adaptation at different time-scales.
Highlights
Our visual perception is always affected by what we have observed in the past
Natural image sequences were acquired from an open source movie as they are exemplary for everyday visual input
The average motion direction statistics of the skewed and un-skewed image sequences were quantified by correlation based Reichardt motion detectors
Summary
Our visual perception is always affected by what we have observed in the past. For instance, after watching a moving entity after a prolonged amount of time, e.g., sea waves, stationary objects appear to move. Neurons in the visual system decrease their sensitivity after prolonged exposure to a specific type of visual input resulting in such concomitant perceptual modification for subsequently viewed stimulus (Blakemore and Campbell, 1969; Mather et al, 1998; Fang et al, 2005; Clifford et al, 2007). This experience dependent change in the visual system is called adaptation. Adaptation has a key role for optimal and stable perception in a continuously changing natural environment (Clifford et al, 2000; Kohn, 2007; Webster, 2011, 2015).
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