Combination rule for redundant information in reaction time tasks with divided attention

Abstract

Five choice reaction time experiments were conducted to investigate the redundant-signals effect in letter identification. In two experiments, displays were large letters formed by small letters. Three experiments used simple two-letter displays with different spatial arrangements. Data were analyzed by the measurement model of variable criterion theory. In all experiments, throughout the RT distributions, the strength of the redundant signals condition was an extremely precise linear function of the sum of the strengths of the separate components. Each stimulus component contributed about one-half of its strength. The form of the distribution was entirely determined by this additive relation. However, the superiority of the redundant-signals condition is not produced by this summation, but by an additive constant present throughout the distribution. It is suggested that this represents a decrement produced by a distractor in a relevant location in single-target conditions. The results strongly favor strength theory as opposed to separate activation models that account for the redundant-signals effect by statistical facilitation. Additional information provided concerns the global precedence effect and S-R compatibility.