Effects of repetition on the facilitatory and inhibitory components of orienting in visual space.

Three experiments are reported which investigate the possibility of habituation of externally-controlled covert orienting with repetition. A brief event in the visual field (for example, a luminance change) can speed the detection response to a target if it occurs in the same location within approx. 100 msec and can bias temporal order judgments in the absence of eye movements. This early facilitatory component is seen as the result of an externally-controlled covert orienting response, that is, the realignment of attention, but not the eyes, with the location of the initial event. However, after approx. 300 msec, the response to a target appearing in the same location is slower than to one appearing elsewhere (the inhibitory component). Experiment 1 employed a cue-target procedure, the subject's task being to ignore each non-informative cue but to respond as quickly as possible to the onset of each target. Three conditions were investigated which differed according to the number of consecutive cues presented in the same location [1, 5, 30]. Facilitatory and inhibitory components were present in all three, indicating that under these conditions, externally-controlled covert orienting does not habituate with repetition and occurs to non-random as well as random sequences of cues. In addition, there was evidence that the inhibitory component is larger for a response to a target appearing in the same location as the cue and the previous target than in the same location as the cue only. In order to investigate this further, a continuous target-target procedure was used in experiments 2 and 3 (simple and choice reaction time, with 3 and 1 response-stimulus intervals respectively), which demonstrated that inhibition does not build up over successive repetitions of targets appearing in the same location, but actually decreases. The results are discussed in relation to the possible functions of the facilitatory and inhibitory components in maintaining selectivity in visual space.