Processing of spatial locations: hemispace effects during encoding but not recall.

Abstract

Traditionally, functional differences in the visual modality between the two hemispheres are investigated by tachistoscopic procedures. In these experiments, the stimuli reach the contralateral hemisphere first, and results are commonly interpreted on the basis of neuroanatomical access models. However, numerous studies demonstrated that the hemispace where the stimulus is perceived also plays a critical role in producing laterality effects ("hemispace effects"). In the present experiment, subjects were instructed to memorize the relative spatial positions of six figures horizontally aligned on a presentation board. The presentation board was located either to the left, to the right or in front of the subjects (left, right and central learning positions). During a recall phase, each figure was presented in the center of a computer screen and subjects were required to indicate by keypress whether a figure had been located in the left or right half of the presentation board. As in the learning phase, the computer screen was located to the left, the right or in front of the subjects (left, right and central recall positions). We found that the positions of the figures initially memorized in the left hemispace were recalled faster than figures initially memorized in the right hemispace. Hemispatial position during recall had no effect on performance. These results are discussed with respect to hemispheric specialization and theories of hemispace effects.