VOLUNTARY AND STIMULUS-INDUCED ATTENTION DETECTED AS MOTION SENSATION

Attention may be drawn passively to a visually salient object. We may also actively direct attention to an object of interest. Do the two ki nds of attention, passive and active, interact and jointly influence v isual information processing at some neural level? What happens if the passive and active attentions come into conflict? These questions wer e addressed with the aid of a novel psychophysical technique which rev eals an attentional gradient as a sensation of motion in a line which is presented instantaneously. The subjects were asked to direct attent ion with voluntary effort: to the side opposite to a stimulus change, to an object with a predetermined colour, and to an object moving smoo thly. In every case the same motion sensation was induced in the line from the attended side to the unattended side. This voluntary attentio n, however, can easily and quickly be distracted by a change in the pe riphery, though it can be regained within a period of 200 to 500 ms. T he results suggest that the line motion can be induced in voluntary (t op-down) as well as stimulus-driven (bottom-up) situations, thus indic ating the truly attentional nature of the effect, rather than it being some kind of retinotopic sensory artifact or response bias. The resul ts also suggest that these two kinds of attention have facilitatory ef fects acting together on a relatively early stage of visual informatio n processing.