Inhibition of concurrent processes in letter and orientation discriminations

Abstract

Two experiments were used to investigate whether two dimensions, viz. letter identity and letter orientation, could be processed concurrently at least up to the level of response selection. To do so each level of one dimension was crossed with a level of the other dimension yielding four unique stimuli that were each mapped to a unique response. One group received a mapping of the faster Letter identity process onto the Hands with orientation specifying the finger (the LH group), while the other (OH) group received the Orientation onto Hands mapping with letter specifying the finger. Varying the speed of the letter identity process through varying the discriminability of the letters should affect the processing time of the LH group more than the OH group. This subadditivity between discriminability of the letter and the mapping group was observed. Further support for concurrent processing was obtained by post hoc analyses of the sequential effects and by an analysis on the type of errors that could have been made. The second experiment showed that when letters were tilted from upright such that subjects had to mentally rotate the letter, the two dimensions were not longer processed concurrently, but in a serial discrete processing mode. The findings support findings of recent studies on strategical effects on information processing.