Relative frequency effect on choice reaction time.

Subjects gave either vocal (position-naming) or manual (button-press) responses to spatially arrayed lights in a four-alternative choice reaction task. Relative stimulus frequency, stimulus discriminability, and S-R compatibility were each shown to be significant determinants of RT. The effects of discriminability and compatibility on the mean and variance of RT were additive. A significant interaction of frequency X discriminability was taken as evidence that a component of the relative frequency effect arises at the stimulus encoding stage. A second component of the relative frequency effect, presumed to occur at the S-R translation stage, was indicated by a significant interaction of frequency X compatibility. It was proposed that recall of the S-R translation rule takes longer for less frequent stimuli and that this difference increases when S-R pairings are not compatible.