Abrupt changes in visual stimulation enhance processing of form and location information

Two experiments investigated the role that abrupt changes in stimulation play in the processing of visual information. In both experiments, the prestimulus field contained a linear array of alternating characters and the target field contained a single target character in one of the positions of the prestimulus array. The target character was either identical to the character in the prestimulus array in that position (no-form change) or was a different character (form change). In the first experiment, the duration of the prestimulus array was 500 msec, and judgments about both the target’s form and location were found to be more accurate in the form-change condition. In the second experiment, the duration of the prestimulus array was varied from 10 to 320 msec. A general decrease was found in performance (in both form and location judgments) as the duration of the prestimulus array was increased. The detrimental effect of increasing the duration of the prestimulus array was larger for no-form-change than for form-change trials. These results are accounted for by a quantitative model that assumes that a stimulus onset initiates a brief period of rapid information processing, followed by a period with reduced rate of processing.