Differential Processing of Objects under Various Viewing Conditions in the Human Lateral Occipital Complex

Abstract

The invariant properties of human cortical neurons cannot be studied directly by fMRI due to its limited spatial resolution. Here, we circumvented this limitation by using fMR adaptation, namely, reduction of the fMR signal due to repeated presentation of identical images. Object-selective regions (lateral occipital complex [LOC]) showed a monotonic signal decrease as repetition frequency increased. The invariant properties of fMR adaptation were studied by presenting the same object in different viewing conditions. LOC exhibited stronger fMR adaptation to changes in size and position (more invariance) compared to illumination and viewpoint. The effect revealed two putative subdivisions within LOC: caudal-dorsal (LO), which exhibited substantial recovery from adaptation under all transformations, and posterior fusiform (PF/LOa), which displayed stronger adaptation. This study demonstrates the utility of fMR adaptation for revealing functional characteristics of neurons in fMRI studies.

Autism and the development of face processing

“…In contrast, activations of face-selective regions in the STS do not correlate with recognition performance [11]. Sixth, the FFA rapidly habituates to repeated presentation of a face, suggesting that it is involved in fine-grain processing of faces, not just category detection [12,134]. Seventh, the FFA is activated more by face identity than variations in eye gaze or expression [9,12], while the STS showed the opposite effects [9].…”

“…Here, we focus on a face selective region in the fusiform gyrus, namely the ''fusiform face area'' (FFA) [7] which has received particular attention for its role in face recognition in adults for several reasons. First, some patients who have suffered focal injury to the temporal cortex are selectively impaired in face recognition (prosopagnosia), while others are selectively impaired in the recognition of non-face objects (object agnosia) [133][134][135]. Second, neuroimaging methods have revealedspecific face-selective regions in the fusiform gyrus, namely the ''FFA'' [7].…”

Interpreting fMRI data: maps, modules and dimensions

“…Studies using fMRI adaptation 5,20 have indicated that the FFA discriminates between different individual faces 36 and the LOC discriminates between individual object exemplars 37,38 . Adaptation studies have also shown that these regions are partly insensitive to size, position and spatial scale 39,40 but more sensitive to viewpoint and direction of illumination 37,41,42 .…”

“…In addition, fMRI adaptation has revealed sensitivity to a range of within-category differences 37,38,44 . In addition, category membership seems to be the main determinant of the population response in the IT.…”

“…Studies using fMRI adaptation 5,20 have indicated that the FFA discriminates between different individual faces 36 and the LOC discriminates between individual object exemplars 37,38 . Adaptation studies have also shown that these regions are partly insensitive to size, position and spatial scale 39,40 but more sensitive to viewpoint and direction of illumination 37,41,42 . However, fMRI adaptation is an indirect measure of selectivity that might be linked only partially to neuronal selectivity 43 ; moreover, the extent to which the sensitivity of the ventral visual cortex to object exemplars can be explained through sensitivity for low-level stimulus properties such as luminance, contrast, line orientation or texture has not been systematically explored.…”