Shifting attention between visual dimensions as a source of the task switch cost

Abstract

“Task-switching” experiments have documented a puzzling phenomenon: advance warning of the switch reduces but does not eliminate the “switch cost”. Theoretical accounts have posited that the “residual” switch cost arises whilst selecting the relevant stimulus-response mapping, leaving earlier perceptual processes unaffected. We put the latter assumption to the test by seeking electrophysiological markers of encoding a perceptual dimension. Participants categorized a colored letter as vowel/consonant or its color as “warm”/“cold”. Orthogonally to these classifications, some colors were eight times more frequent than others, and the letters were in upper or lower case. Color frequency modulated the EEG amplitude at around 150 ms when participants repeated the color classification task. When participants switched from the letter task to the color task this effect was significantly delayed. Thus, even when prepared for, a task switch delays or prolongs encoding of the relevant perceptual dimension.