Effects of noise on visual orienting
Eleven experiments are reported which examine the effects of 90 dB (A) white noise on the processes which govern orienting of attention in visual space. The selectivity hypothesis argues that noise alters the priorities which govern stimulus selection so that subjectively dominant aspects of the environment are attended to more fully than those which are non-dominant. The applicability of this hypothesis is examined with regard to attentional orienting. Three experimental paradigms are used. The first involves a central cue presented immediately prior to target onset. In the absence of eye movements reaction times to expected targets are faster than to unexpected targets, but noise has no effects on performance. It is concluded that the power of the central alerting cue is focussing attention in a maximal fashion and noise has no further effect on policies of allocation. A second task design involves the presentation of positional information prior to a block of trials. Under such conditions subjects fail to maintain orienting as trials continue. Noise enhances the ability to maintain orienting over time. This effect is discussed in the light of the selectivity hypothesis. It is argued that the inability to maintain orienting is not due to the inhibition which arises as a result of successive responding. Rather it is due to the difficulty involved in maintaining an active orientation. The third paradigm involves orienting to specific locations on the basis of information stored in short-term memory. When recall of this information is aided by a visual warning signal occurring prior to target onset noise has no effect on performance. Without this signal, noise alters performance and these data are compared to predictions based upon the selectivity hypothesis. These effects are discussed in terms of a noise-induced change in the strategy of performance, rather than an effect which is mechanistic.