Short-and medium-term plasticity for speaker adaptation seem to be independent

Abstract

In a classic paper, Ladefoged and Broadbent [1] showed that listeners adapt to speakers based on short-term exposure of a single phrase. Recently, Norris, McQueen, and Cutler [2] presented evidence for a lexically conditioned medium-term adaptation to a particular speaker based on an exposure of 40 critical words among 200 items. In two experiments, I investigated whether there is a connection between the two findings. To this end, a vowel-normalization paradigm (similar to [1]) was used with a carrier phrase that consisted of either words or nonwords. The range of the second formant was manipulated and this affected the perception of a target vowel in a compensatory fashion: A low F2-range made it more likely that a target vowel was perceived as a front vowel, that is, with an inherently high F2. Manipulation of the lexical status of the carrier phrase, however, did not affect vowel normalization. In contrast, the range of vowels in the carrier phrase did influence vowel normalization. If the carrier phrase consisted of high-front vowels only, vowel categories shifted only for high-front vowels. This may indicate that the short-term and medium-term adaptations are brought about by different mechanisms.