Orienting a spatial attention--its reflexive, compensatory, and voluntary mechanisms.

Attention is a mechanism to select sensory information. It is a modulatory process which normally cannot be observed as overt responses. We have studied spatial attention using a new visual illusion of motion--line-motion effect: a line, which was presented physically at once, was perceived to be drawn from one side when attention was captured to that side of the line by a preceding visual cue stimulus. This effect was due to acceleration of visual information processing at the locus of attention. The motion illusion was produced by both stimulus-induced (bottom-up) and voluntary (top-down) attention, which suggested that the two kinds of attention act on relatively early stages of visual processing. The objective of this study was to examine how various modes of spatial attention might be represented and reorganized in the brain. Using the induction of illusory line motion as a measure we found that: (1) once attention is captured by a moving object, it follows the object as it moves; and (2) attention moves with a saccade in the retinal coordinates such that its focus remains fixed in space. We then asked whether attention acts across different sensory modalities. We found that both auditory and somatosensory cues induced focal visual attention in space where the cue was presented. Based on these findings we propose a model which would allow (1) matching of visual spatial information obtained across saccades, and (2) matching of spatial information obtained in different sensory modalities.