Dependence of target redundancy effects on noise conditions and number of targets.

Abstract

In a letter identification task using a four-position array, reaction time (RT) decreased as a negatively accelerated function of the number of targets, both with and without noise letters in nontarget positions. The effect was much greater in the noise condition, in which each redundant target replaced a noise letter. In such situations, the redundant-targets effect should probably be attributed to noise reduction rather than to redundancy. Scaling analysis of the RT distributions indicated that neither noise nor redundancy affects the rate of growth of excitatory strength, but that both affect the time at which growth begins. Excitatory strength grew as a function of the number of redundant targets according to a principle of decreasing gain, with much greater growth in the noise conditions. Further experiments indicated that whether noise is manipulated between or within subjects is important. Unless all stimuli present are reliabl targets, redundancy effects are eliminated or reduced in no-noise conditions.