The Task-Evoked Pupil Response in Divided Auditory Attention Tasks

Successful processing of complex auditory information relies on the interplay between low-level sensory processing and higher-level cognitive processing. However, the extent to which specific auditory processing tasks rely on cognitive processing as opposed to lower-level sensory processing is unclear. The task-evoked pupil response (TEPR) can quantify the cognitive load that complex listening tasks elicit. Previous research by Koelewijn et al (2014) indicated that dividing attention across two sentences presented dichotically resulted in larger pupil dilation (indicative of greater cognitive load) compared with selectively attending to one. However, it was unclear whether the larger pupil dilation measured during the divided attention task were the result of dividing attention or were due to the increased memory demand inherent to that task.

The first aim of the current study was to address the above issue of memory demand by comparing pupil dilation between divided and selective auditory attention tasks, while keeping memory and response load constant. The second aim was to further clarify the influence of memory demands on TEPRs in these auditory tasks by comparing the pupil dilation recorded to measures of participants' digit memory capacity.

A repeated measures design was used. Each participant undertook two selective and three divided auditory attention tasks, generated by varying the specific instructions before each condition of the dichotic digits test (DDT). In addition, participants completed forward and reverse digit span (DS) tasks.

Thirty-one otologically healthy adults (aged 18-40 years) participated in this study.

A repeated measures analysis of variance was used to compare mean and peak pupil dilation between the selective and divided attention tasks. Spearman correlation analyses were used to examine potential relationships between DS scores and mean and peak pupil dilation elicited by the DDT conditions.

Participants demonstrated larger mean and peak pupil dilation (indicative of greater cognitive load) when they were required to divide their attention across both ears than when they were required to selectively attend to input in one ear. DS scores were not significantly correlated with mean or peak pupil dilation measures.

Auditory divided attention tasks involve significantly greater cognitive load than auditory selective attention tasks, even when memory demands are equal. In addition, mean and peak pupil dilation generated during the DDT are not significantly associated with digit memory capacity. The findings indicate that poor performance on tasks involving divided attention may be due to a cognitive deficit as opposed to an auditory processing deficit. Clinicians should consider this when using divided attention tasks in auditory processing assessments.