Visual motion sensation yielded by non-visually driven attention.

When a visual stimulus (the "cue") is presented and followed by a line, the line is perceived to grow rapidly from the cued side even when it is presented physically simultaneously (the "line-motion effect"). We now report that the same line motion can be observed when the cue is presented in a non-visual modality, such as auditory or somatosensory. A beep sound was presented either from the left or the right speaker as an auditory cue, or an electric pulse was applied to a finger put on the left or the right side of a CRT display as a somatosensory cue. A line probe was then presented between the two possible cue positions. Both the auditory and the somatosensory cues led to line motion, thus the line motion could not be interpreted as a variation of within-modality effects, such as visual apparent motion. When the cue lead time was manipulated, the obtained time courses of the effects were similar across the three cue modalities (Experiment 1). The minor differences could be explained simply in terms of latency of detection, according to results of another experiment (Experiment 2). Finally, the line-motion task was compared with a task of temporal order judgment, where two targets were presented simultaneously at the cued and the uncued sides, and the subject was asked to judge which of the targets had appeared first. As a result, similar dependencies on cue lead time were obtained between the two tasks within subjects (Experiment 3). Thus, the non-visual cue seems to facilitate "prior entry" of a visual stimulus nearby in the spatial representation, much the same way as a visual cue does. These effects should be attributed to modality non-specific spatial attention, i.e., a "gradient" of information processing efficiency across various locations.