It has been hypothesized that the brain computes two different kinds of spatial-relation representations: one used to assign a spatial relation to a category and the other used to specify metric distance with precision, The present visual half-field experiment offers support for this distinction by showing that the left and right cerebral hemispheres make more effective use of the categorization and metric distance representations, respectively. Furthermore, the inclusion of a bilateral stimulus presentation condition permits the computation of a reversed association that offers additional support for the distinction between two types of spatial-relation representation. Kosslyn (1987) has hypothesized that the human brain computes two different kinds of spatial-relation representations. One type of representation is used to assign a spatial relation to a category, such as "outside of' or "above," whereas the other type of representation preserves location information using a metric coordinate system in which distances are specified effectively. One way to obtain converging information about the plausibility of the distinction between these two processing subsystems is to show that they have different neurological substrata. With this in mind, Kosslyn has suggested that the left cerebral hemisphere makes more effective use of the categorization processing subsystem and that the right cerebral hemisphere makes more effective use of the metric distance processing subsystem. The present experiment was designed to provide tests of this lateralization hypothesis.On each trial of the present experiment, the subjects were shown a stimulus consisting of a horizontal line and a small dot in one of 12 possible locations (6 above the line and 6 below the line). During different experimental sessions, each subject performed a categorization task and a distance judgment task using these stimuli. Stimuli on different trials were presented to the right visual field-left hemisphere (RVF-LH) or the left visual field-right hemisphere (LVF -RH). It was of particular interest to determine whether or not there would be a task x visual field interaction (a processing dissociation, as discussed by Hellige, 1983, and Zaidel, 1983) and whether the interaction would be of the form predicted by Kosslyn's (1987) hypothesis. Because the stimuli and responses are identical for the categorization and distance-judgment tasks of the present experiment, any such interaction must The research reported here was supported in part by Research Grant BNS-8608893 from the National Science Foundation. The authors thank Alice Healy, Stephen Kosslyn, and two anonymous reviewers for helpful comments on an earlier draft of this manuscript. Correspondence may be sent to Joseph B. Hellige, Department of Psychology, University of Southern California, Los Angeles, CA 90089-1061. reflect differences in the processing subsystems required rather than other differences related to stimulus input (cf. .During the categorization task, the subjects were required to ind...

Abacus experts exhibit superior short-term memory for digits, but the underlying neurophysiological mechanism remains unknown. Using event-related fMRI, we examined the brain activity of abacus experts and non-experts during the memory retention period of a delayed match-to-sample task using digits as stimuli. In controls, activity was greater in cortical areas related to verbal working memory, including Broca's area. In contrast, in experts, activity was greater in cortical areas related to visuo-spatial working memory, including the bilateral superior frontal sulcus and superior parietal lobule. This provides neurophysiological evidence that abacus experts utilize a visuo-spatial representation for digit memory.

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Recent studies have shown that (1) the global precedence effects in processing the hierarchically organized stimulus can be attenuated by eliminating the low spatial frequencies contained in the stimulus and (2) the human magnocellular pathway is responsible for processing low spatial frequencies and the pathway can be attenuated by imposing a red background on the stimulus. In the present study, a reaction-time experiment was conducted to examine the effect of background color of the stimulus to the processing of the hierarchically organized stimulus. The result showed that although the control condition (a green background) produced a prototypical asymmetric global interference, a red background that was equiluminant to the green background produced a symmetrical interference. It was concluded that the human magnocellular pathway is at least partially responsible in producing the global precedence effects.