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Abstract
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.