Beyond sensory images: Object-based representation in the human ventral pathway

Abstract

We investigated whether the topographically organized, category-related patterns of neural response in the ventral visual pathway are a representation of sensory images or a more abstract representation of object form that is not dependent on sensory modality. We used functional MRI to measure patterns of response evoked during visual and tactile recognition of faces and manmade objects in sighted subjects and during tactile recognition in blind subjects. Results showed that visual and tactile recognition evoked category-related patterns of response in a ventral extrastriate visual area in the inferior temporal gyrus that were correlated across modality for manmade objects. Blind subjects also demonstrated category-related patterns of response in this "visual" area, and in more ventral cortical regions in the fusiform gyrus, indicating that these patterns are not due to visual imagery and, furthermore, that visual experience is not necessary for category-related representations to develop in these cortices. These results demonstrate that the representation of objects in the ventral visual pathway is not simply a representation of visual images but, rather, is a representation of more abstract features of object form.

Fig. 1.

Brain areas that responded during tactile and/or visual object perception in sighted subjects and during tactile perception in blind subjects. Sagittal and axial images from group Z-score maps of activated areas are shown for the sighted and blind subjects. The inferior temporal (IT) and ventral temporal (VT) regions activated by tactile and visual object perception are indicated. The tactile/visual overlap map shows the areas activated by both tactile and visual perception (shown in yellow), as well as the areas activated only by tactile (red) and visual (green) perception. The white lines in the sagittal images correspond to the locations of the axial slices and, similarly, the white line in the axial slice indicates the location of the sagittal section.

Fig. 2.

Mean time series, averaging across subjects, voxels, and blocks, for the response in inferior temporal cortex during the one-back repetition detection and simple tactile exploration tasks in sighted and blind subjects.

Fig. 3.

Correlations between patterns of neural response evoked by two tactile recognition tasks (one-back repetition task and simple exploration) in sighted and blind subjects. Each bar represents the mean correlation across subjects ± SE. Blue and red bars depict the mean within-category correlations, separating correlations for manmade objects (shoes and bottles) from correlations for faces. Green and yellow bars depict the mean between-category correlations, separating correlations between patterns of response to faces as compared to manmade objects for correlations between patterns to the two categories of manmade objects.

Fig. 4.

Proportion of visually responsive cortex with maximal responses to faces, bottles, or shoes that was also activated by tactile recognition of objects.

Fig. 5.

Crossmodal correlations between category-related patterns of response during visual and tactile recognition. Each bar represents the mean correlation across subjects ± SE. Blue and red bars depict the mean within-category correlations, separating correlations for manmade objects (shoes and bottles) from correlations for faces. Green and yellow bars depict the mean between-category correlations, separating correlations between patterns of response to faces as compared to manmade objects from correlations between patterns to the two categories of manmade objects.