Serial recall performance of visually presented items is impaired by task-irrelevant speech that the participants are instructed to ignore. This so-called Irrelevant Speech Effect (ISE) has been attributed to attentional capture, interference with the efficiency of serial rehearsal, or interference with phonological representations.
Here, we used a task that required constant counting to learn more about the task characteristics that are responsible for evoking the ISE. In the continuous counting task, participants counted the number of two symbols (rectangles and triangles) that appear consecutively on a computer screen. Participants (N=83) were assigned to one of three "switch-rate" conditions that varied in cognitive load based on the frequency with which symbols changed within one trial (25%, 50%, or 75%). Performance was measured in silence, and with foreign speech and environmental sounds, that the participants were instructed to ignore.
Counting accuracy and reaction times were negatively affected by the task-irrelevant speech, but not by the environmental sounds. Furthermore, the ISE did not interact with cognitive load. These findings suggest that it is not necessarily the serial order component nor attentional capture that is sufficient for ISE evocation. The general implications for the role of ISE evocation will be discussed.