Dependent spatial channels in visual processing

The present experiments were designed to test whether or not processing in visual information channels defined by spatial position is independent in the visual search paradigm. In Experiment 1 subjects were asked to judge whether or not a red square was present in a display of two colored geometric figures. Their mean reaction time (RT) to respond no to a “divided target” display in which one figure was red and the other was a square was about 100 msec longer than to control displays containing either two red circles or two green squares. This result is inconsistent with a spatially serial independent-channel model and with many spatially parallel independent-channel models. The relatively slow responding to divided target displays was replicated in Experiments 2 and 3, when subjects judged whether or not an “A” was present in a display of two alphanumeric characters, and a divided target display was one which contained two features of “A.” Experiments 4 and 5 demonstrated that the dependence observed in the first three experiments was probably the result of two mechanisms: crosstalk integration, whereby the target features are integrated across the two spatial channels, and repetition facilitation, whereby processing is facilitated (in some cases) when the two figures in the display are physically identical. Experiment 6 suggested that subjects organized the display in terms of spatial channels even when the task allowed subjects to ignore spatial location.