Clear speech promotes speaking rate normalization

Abstract

When speaking in noisy conditions or to a hearing-impaired listener, talkers often use clear speech which is slower, louder, and hyperarticulated relative to conversational speech. In other research, changes in speaking rate are known to affect speech perception (called temporal contrast effects, or speaking rate normalization). For example, when a sentence is spoken quickly, the voice onset time (VOT) in the next word sounds longer by comparison (e.g., more like the /t/ of “tier”); a sentence spoken slowly makes the VOT in the next word sound shorter (e.g., like the /d/ of “deer”). Typically, one sentence is manipulated to produce fast and slow versions. We tested whether naturally produced clear and conversational speaking styles would also produce these temporal contrast effects. On each trial, listeners heard either a clear (slow) sentence or a conversational (fast) sentence followed by a target word to be categorized as “deer” or “tier.” Temporal contrast effects were observed both for conversational relative to clear speech and for conversational relative to a slowed version of the conversational speech. Changing speaking styles aids speech intelligibility but may produce other consequences such as contrast effects that alter sound/word recognition.