Effects of flash luminance and positional expectancies on visual response latency

It is well established that human observers respond more quickly to visual targets that appear in expected locations than they do to ones in unexpected locations. These variations in simple reaction time have been attributed to a covert alignment of an attentional mechanism to the expected target location. The present experiments investigated the influence of strength of signal and strength of subject’s positional expectancy on the magnitude of this attentional effect. In the first experiment, target luminance was varied over a range of three log units, and it was found that the effects of luminance were essentially additive with the effect of the positional expectancy (i.e., the attention effect). The second experiment found that the magnitude of visual attention interacts with the information value of the precue used to create the spatial expectancy, although, once again, luminance had additive effects. The resuls are interpreted as indicating that, rather than influencing early visual processing, the act of attending to a spatial location operates fairly late in the detection process.