Both fast and slow speech can increase listening effort and impair speech comprehension in young listeners

Speech rate can vary under different communicative circumstances (e.g., listener demands, speaking style), and such variation can affect the cognitive effort required to process speech. The present study examined how different speech rates, including both fast and slow rates, affect listening effort and speech comprehension in normal-hearing young listeners using a dual-task paradigm. The results showed that the recognition accuracy of key content words decreased under fast conditions for both the single-task and dual-task groups. In contrast, the number of comprehension errors increased under both the fast and slow speech conditions in the dual-task group. This was found using an additional method of evaluating speech comprehension, demonstrating that linguistic and mnemonic processes required for successful speech comprehension can be impaired when listening to slow speech, especially under high cognitive load. The subjective effort ratings similarly increased for fast and slow speech, but this was shown only in the control group, whereas the dual-task group showed no changes in the ratings by speech rates. This suggests that the subjective awareness of listening difficulty was reduced in dual-tasking situations. This study highlights the importance of multi-level assessment of speech perception, especially in cognitively challenging situations.