The contribution of auditory attention to processing load in normal hearing and hearing impaired adult listeners

A major complaint of people with hearing impairment is the high level of processing load they experience (listening effort) when having a conversation in a noisy environment. From previous studies we know that the pupil dilation response, an objective measure of listening effort, is affected by working memory capacity and linguistic abilities. These studies also suggested the involvement of attention-related processes, but it is unclear how these processes work.

In this project we investigate the effect of auditory attention on processing load in normally hearing and hearing-impaired listeners. Research shows that knowledge about where, when, and whom is going to talk benefits speech perception. We suggest that this knowledge allows a listener to better focus attention, resulting in better filtering of irrelevant information. This should lead to less use of working memory capacity and linguistic resources, and therefore, less processing load.

In the first study we investigated the effect of focused versus divided attention on processing load. In this study 12 normal hearing young adults (21 to 26 years) had to focus on either one or both of two sentences that were presented dichotically and masked by fluctuating noise. They showed a larger pupil dilation response, indicating higher processing load or listening effort, when processing two sentences simultaneously instead of one.

In the second study 56 normal hearing young adults (18 to 28 years) participated in three experiments. Dichotic tasks similar to those in the first study were used. In these experiments target location (left or right ear), speech onset, and talker variability were manipulated by keeping these features either fixed during an entire block of sentences or by randomizing these over trials. The results showed a performance benefit when they were able to focus on the target location. Additionally, a decrease in pupil dilation response was observed when they were able to focus on location or talker.

In a third study we examined the effect of focused attention and location information on processing load in adults with a moderate sensorineural hearing impairment. Preliminary results will be presented.

Based on the results of all studies we conclude that communicating in a cocktail party like environment requires substantial processing load because of the demands placed on attentional processes.