Cross-modal and other effects in selective perception
On the whole the psychophysics experiments imply that often two dimensions of a stimulus, or two stimuli, may be better than one. Whether the dimensions are completely independent, or whether two modalities are used, there are a number of experiments which show that increasing dimensionality leads to increasing information transmission. Extensive reviews of this work are available in Attneave (1959) and Gamer (1962). The addition of an extra dimension to the stimulus once the limit of information transmission has been reached frequently results in at least a slight increase in performance. This is the opposite to what one might expect from the work on selective attention which we have already discussed in the previous chapters. How it can happen is not well understood at present. But there seem to be at least two pointers to an explanation. Firstly most of the experiments which show that adding a dimension or a channel can increase information transmission are 'one shot' experiments, while most of the experiments which show only competition are continuous tasks; and secondly there is often some way in which the dimensions are correlated when they improve performance.