A preference for contralateral stimuli in human object- and face-selective cortex

Abstract

Visual input from the left and right visual fields is processed predominantly in the contralateral hemisphere. Here we investigated whether this preference for contralateral over ipsilateral stimuli is also found in high-level visual areas that are important for the recognition of objects and faces. Human subjects were scanned with functional magnetic resonance imaging (fMRI) while they viewed and attended faces, objects, scenes, and scrambled images in the left or right visual field. With our stimulation protocol, primary visual cortex responded only to contralateral stimuli. The contralateral preference was smaller in object- and face-selective regions, and it was smallest in the fusiform gyrus. Nevertheless, each region showed a significant preference for contralateral stimuli. These results indicate that sensitivity to stimulus position is present even in high-level ventral visual cortex.

Figure 1. Illustration of the experimental conditions and the anatomical position of the regions of interest (ROIs).

(A), Illustration of the position of the four stimulus categories (faces, objects, scenes, and scrambled images) left and right of the fixation spot. (B) Illustration of the 5 ROIs for one subject onto a flattened brain. Indicated sulci: CS: calcarine sulcus; ITS: inferior temporal sulcus. Indicated anatomical directions: D: dorsal; V: ventral; P: posterior; A: anterior.

Figure 2. Responses to contralateral and ipsilateral stimuli in the regions of interest.

(A) The response (percent signal change relative to the fixation condition) in each ROI is shown for each stimulus condition (F: faces, O: objects, Se: scenes, Sa: scrambled images). (B) Preference index in each ROI averaged across all stimulus conditions. (C) Preference index in each ROI for the stimulus condition that elicited the strongest responses. Error bars represent the standard error of the mean across subjects.