Cognition Seen Through the Eyes of Hearing Aid Users : Working Memory Resource Allocation for Speech Perception and Recall

Sammanfattning: This thesis investigates how hearing aid users allocate working (WM) memory resources under various task demands when listening to and storing speech in memory for later recall. This was done by combining an auditory recall task, the Sentence-final Word Identification and Recall (SWIR) test, with pupillometry. Different pupillary responses were used to obtain insights into momentary WM resource allocation and overall WM resource allocation over time. The task demands were manipulated by varying hearing aid noise reduction settings, as well as by varying the task difficulty of the SWIR test and the task difficulty predictability.The findings from the first two studies showed that recall performance in competing speech was better, and baseline pupillary responses were higher when noise reduction was activated compared to when it was not. This indicates that attenuating background noise frees up WM resources to be used for storing speech in memory rather than speech processing. While unpredictable task difficulty elicited higher baseline pupillary responses than predictable task difficulty, it did not have any effect on recall performance. This finding suggests that task difficulty predictability does not affect WM resource allocation. Instead, unpredictable task difficulty may lead to increased alertness in anticipation of the end of the SWIR test list. The findings of the third study showed that increased transient task-evoked pupillary responses, which reflect the momentary intensity of attention during encoding, were associated with a higher likelihood of subsequent recall. Moreover, higher WM capacity was also linked to higher likelihood of subsequent recall, presumably due to the ability to allocate more attentional resources during encoding. Lastly, the findings from the fourth study indicated that the combination of the SWIR test and pupillometry is suitable for capturing WM resource allocation. Although arousal decreased over time, recall performance remained stable, suggesting that participants did not reach the point of disengagement.Overall, a novel learning from this thesis is that increased pupillary responses may be a marker of “successful effort” when additional WM resources are allocated to achieve a better recall performance in the SWIR test. Furthermore, this thesis gives insights into which factors affect WM resource allocation and how to reduce the amount of processing resources required to understand speech, which may contribute to optimizing auditory rehabilitation in the future.