Transition Screen Strongly Enhances Activation in Occipital Ventral Cortex During Perception of Colored Stimuli

Colored Stimuli Loÿs Piettre*, Michel Dojat*, Peggy Gérardin*, Christoph Segebarth*, Kenneth Knoblauch° *INSERM U438, Grenoble, France, °INSERM U371, Lyon, France. Purpose: Recent neuroimaging studies in humans demonstrate that colored patterns preferentially activate a particular area located in the ventral occipital cortex (VO) [1,2,3]. In addition, neural responses in this region appear to be modulated by attentionnal processes [4]. To enhance this response and to facilitate its detection, a commonly used strategy consists in the insertion of a short transition screen inside a sequence of colored stimuli. Understanding the precise effect of such an insertion could provide important information about the mechanisms of color and form perception. Using fMRI, we evaluated the enhancement of the activation during the perception of chromatic versus achromatic patterns with and without the insertion of a transition screen. Materials and methods: Paradigms. Four healthy subjects with normal vision were examined. Two block paradigm experiments were realized (7min.22 each). During stimulation epochs, subjects viewed successively equiluminant (30 cd/m) random color Mondrians with the same geometry (23 rectangles). During control, the achromatic counterparts (grey versions) were displayed with the same geometry and the same mean luminance as the colored versions. During the first experiment, 18 chromatic or achromatic Mondrians were displayed each during 3s (repeated 4 times). During the second experiment, 9 chromatic or achromatic Mondrians were displayed each during 3s and a chromatic or achromatic transition screen was inserted between each Mondrian during 0.5 s (repeated 7 times). The luminance and chromaticity of each transition screen was equal to the mean luminance and chromaticity of its Mondrian predecessor in the sequence (see Fig. 1).