UC Davis

Clear speech can be more intelligible and better remembered than casual speech. Intelligibility and memory are assumed to be related—under the effortfulness hypothesis, the intelligibility-enhancing properties of clear speech (e.g., slower speech rate) facilitate processing, which frees up working memory resources and confers a memory advantage. However, prior work has only investigated naturally produced clear speech. How does clear speech influence memory for computer voices? The current study examines intelligibility and recognition memory of clear and casual speech for a text-to-speech (TTS) voice and a human voice, and compares older and younger adult listeners. In a speech-perception-in-noise task, clear speech was more intelligible than casual speech for both voices, the human was more intelligible than the TTS voice, and the younger adults performed better than the older adults. In an old-new recognition task, memory was better for the human voice relative to the TTS voice, consistent with the intelligibility results and the effortfulness hypothesis. However, inconsistent with the effortfulness hypothesis, there was no clear speech memory benefit, and the older adults performed better than the younger adults. The current findings are relevant for our understanding of human-computer interaction and theories about the relationship between speaking style and memory.