hide
Free keywords:
-
Abstract:
Motion processing is a fundamental property of the visual system. Classical electrophysiology studies in the macaque as well as fMRI studies in the human have revealed an extensive network of visual areas that contain neurons selective for direction of motion. Recent evidence from macaque fMRI (Tolias et al., J Neurosci 2001) and electrophysiology (Tolias et al. Nat Neurosci 2005) suggests that the direction-of-motion selectivity of macaque visual areas is not a fixed property but can change dynamically as a function of the state of adaptation to a moving stimulus.
Here we used a visual motion adaptation paradigm to study the direction-of-motion selectivity of human visual areas with functional magnetic resonance imaging (fMRI). The visual stimuli we used consisted of expanding/contracting dot kinematograms at 100 coherence. These were presented passively while the subject performed an attentionally demanding task at the fovea. After moving unidirectionally (expanding or contracting) for about 160 sec the kinematogram abruptly reversed direction of motion. By measuring the blood oxygen level dependent (BOLD) signal response elicited by the direction of motion reversal and comparing it to the initial response elicited when the adapting stimulus turns on, we were able to assess the degree of direction-of-motion selectivity in the various visual areas.
We found that an extensive network of visual areas shows BOLD rebound when the direction of motion reverses after adaptation, including areas that according to classical electrophysiology do not show strong direction-of-motion selectivity (for example area V4). Our results agree qualitatively with the findings in the macaque (Tolias et al., J Neurosci 2001), and together underscore the dynamic nature of functional cortical architecture.
