ABSTRACT
Posner and Cohen (1980) demonstrated that a brief noninformative visual cue presented in the periphery speeds the simple detection response to a target if it appears within 100 msec of the cue and in the same location, compared to a target in a different location. This facilitation was attributed to externally controlled covert orienting, that is, the alignment of attention with a location in visual space as the result of an external stimulus event. However, if the target appears more than 300 msec after the cue, the response is slower to a target in the same location (inhibition). Experiments designed to investigate further both the facilitatory and inhibitory components of visual orienting are reported in this chapter. In addition to the facilitation of both simple and choice manual responses, a target from the same location in the periphery as the cue appears to occur earlier than one from a different location, for intervals between the cue and the target of up to 500 msec. Although temporal judgments are unaffected at longer cue-target intervals, both manual and ocular responses are slower to a target appearing between 300 and 1300 msec after a cue in the periphery and in the same location than to one appearing elsewhere. It is argued here that externally controlled orienting is a necessary condition to produce inhibition. However, not every event in the visual periphery results automatically in externally controlled covert orienting. Indeed, such orienting can be reduced or even prevented by additional information present in the visual field, or by the requirements of secondary tasks. The facilitatory and inhibitory components of externally controlled orienting appear to act together to direct the eye-movement system and to maintain selectivity in visual space.
