Of house and men: The functional organization of face and place representations in the ventral visual stream using fMRI techniques

Abstract

The ventral part of the visual cortex has been proven to be highly selective to objects. Certain areas seem to be specifically tuned to certain categories of objects, such as faces, body parts, and houses. Even though the ventral visual stream has been studied extensively in the past, not much is known about its precise organization. Do the object-selective areas operate as separate clusters, or are they part of a larger topographic map, where continuous changes in stimuli lead to continuous shifts in activations across the cortex? Such topographic maps have been found in the primary visual cortex and surrounding areas when looking at the retinotopic organization of visual information, but few studies have focused on the extent of topographic maps and to what extent they are applicable to other aspects of perception. As the face-selective areas of the ventral visual stream have received special attention in the ongoing discussions about functional organization, a series of studies were set up with the face-and place-selective areas of high-level visual cortex as the main focus. Study 1 investigated whether the category-selective regions are embedded in a topographic map, adapting the continuous mapping techniques used in retinotopic mapping research to suit the object-selective areas of the human brain. A morph-series was created between a face and a house, to try and establish whether the morph-stimuli were represented in the intermediate area between the face-and house-selective areas, forming a continuous map of object category. While the phase-encoding technique was proven to be successful in detecting the presented stimulus information (face and house information), no large-scale maps were found in the ventral visual stream. Study 2 tested the potential of the phase-encoding technique by performing the same tests as in Study 1, this time on participants suffering from specific retinal defects. It highlighted the differences in responses in lower and higher visual cortex and it illustrated the risks involved in using relative comparison techniques: deactivations in the primary visual cortex and the foveal confluence caused patterns of ‘activations’ in areas that should not be responsive due to a lack of retinal input. Finally, Study 3 focused on the functional organization of the face-selective areas, using a multivariate technique to try and gain more insight into the representations of these areas by manipulating perceptual (featural information such as eye color and mouth shape, and configural information such as spacing between eyes and the position of the mouth) and contextual information linked to faces. As the contextual information dealt with the location a face was associated with, the place-selective areas were also taken into account. Results show that mainly perceptual information was represented in the face-selective regions. Contextual information linked to location was only distinguishable in the place-selective areas, while effects of familiarity (whether or not a face was associated with background information) were found in some of the face-selective areas. Together, these studies reveal more about the functional organization and the representations in high-level cortex.nrpages: 120status: publishe