Human attention: the exclusion of distracting information as a function of real and apparent separation of relevant and irrelevant events

A leading theory suggests that human vision operates by separate and parallel analysis of each of the simple features of the visual scene; but computation of the identity of objects, which needs combination of these features, is undertaken selectively and only for some parts of the incoming information. It is known that the identity of distracting events affects reaction time only for distractors spatially close to the reaction signal. This suggests that the selection is spatially based; perhaps taking place in the projection areas. Experiments on this topic have, however, normally considered events only at a fixed viewing distance; in this study different viewing distances were employed. It was found that, over the range of conditions used, the ability to exclude irrelevant distractors depended upon the true physical separation and not on the angular separation at the eye of the observer. Hence the 'attention' system must operate at a point later than the computation of true physical location, rather than at the very early stage where angular separation only is available.