Task and contrast effects on performance with parafoval stimulus pairs

The effect on both detection and identification of placing a non-target character to the foveal or peripheral side of the position of a parafoveally presented target character was examined in two experiments. The experiments found more interference with both tasks when the nontarget was peripheral to the target position, but only when the target and nontarget were both darker or brighter than the background. If one character was darker than the background, and the other was brighter, the asymmetry appeared in neither task. In Experiment 2, performance in both tasks was poorer when the two characters had the same features, but this effect was independent of both nontarget position and target-nontarget contrast. While these results are inconsistent with a feature-mixing explanation of the asymmetry, contrast-specific lateral inhibition can account for the phenomena.