1704 Linear and nonlinear color processing in striate cortex of the macaque monkey

Abstract

Objects in our natural environment generate signals in multiple sensory modalities. This fMRI study investigated the influence of prior task-irrelevant auditory information on visually-evoked category-selective activations in the ventral occipito-temporal cortex. Subjects categorized pictures as landmarks or animal faces, while ignoring the preceding congruent or incongruent sound. Behaviorally, subjects responded slower to incongruent than congruent stimuli. At the neural level, the lateral and medial prefrontal cortices showed increased activations for incongruent relative to congruent stimuli consistent with their role in response selection. In contrast, the parahippocampal gyri combined visual and auditory information additively: activation was greater for visual landmarks than animal faces and landmark-related sounds than animal vocalizations resulting in increased parahippocampal selectivity for congruent audiovisual landmarks. Effective connectivity analyses showed that this amplification of visual landmark-selectivity was mediated by increased negative coupling of the parahippocampal gyrus with the superior temporal sulcus for congruent stimuli. Thus, task-irrelevant auditory information influences visual object categorization at two stages. In the ventral occipito-temporal cortex auditory and visual category information are combined additively to sharpen visual category-selective responses. In the left inferior frontal sulcus, as indexed by a significant incongruency effect, visual and auditory category information are integrated interactively for response selection.