Estimation of Eye Level: Normal Egocentric Vertical Attentional Biases (P01.002)

OBJECTIVE: The purpose of this study is to learn if egocentric versus allocentric attentional tasks performed in right, center, or left hemispace will differentially influence normal participants9 vertical biases of spatial attention. BACKGROUND: Whereas allocentric (object-based) processing is mediated by the ventral occipito-temporal visual processing stream, egocentric (body-centered) processing is mediated by the dorsal parieto-occipital visual stream. Bilateral lesions of the dorsal stream impair downward attention, and bilateral lesions of the ventral stream impair upward attention. Based on this dichotomy, the finding that neurologically intact adults bisect vertical lines slightly above the midpoint has been has been attributed to activation of the ventral stream during this allocentric task. However, it has not been determined if allocation of egocentric attention will induce a lower spatial bias, and if there are right versus left hemisphere asymmetries in the mediation of allocentric versus egocentric vertical attention. DESIGN/METHODS: Twelve healthy right-handed adults marked their eye level along vertical lines (an egocentric task) or bisected the center of lines (an allocentric task), presented in midline (midsagittal plane) or to the left or right of midline. These lines were either vertically centered at eye level or primarily presented in upper or lower altitudinal space. RESULTS: Participants estimated eye level to be lower than actual eye level when lines were presented in left hemispace, and vertical line bisections deviated upwards the farthest when lines were presented in right hemispace. CONCLUSIONS: Our results suggest right hemisphere dominance for egocentric spatial processing and left hemisphere dominance for allocentric spatial processing in healthy right-handed adults. This finding is consistent with the observations that anosognosia, asomatognosia and egocentric spatial neglect are more commonly observed with right than left hemispheric parietal lesions; however, further studies are needed to elucidate the mechanism for these hemispheric differences in processing of spatial attention. Disclosure: Dr. Falchook has received personal compensation for activities with the University of Florida College of Medicine, the Institute for Advancement of Human Behavior, and PeerView Institute. Dr. Salazar has nothing to disclose. Dr. Johnson has nothing to disclose. Ms. Morales has nothing to disclose. Dr. Williamson has nothing to disclose. Dr. Fischler has nothing to disclose. Dr. Heilman has received personal compensation for activities with law firms as a consultant. Dr. Heilman has received personal compensation in an editorial capacity for Journal Watch.