Multiple sources of acoustic variation affect speech processing efficiency.

Phonetic variability across talkers imposes additional processing costs during speech perception, evident in performance decrements when listening to speech from multiple talkers. However, within-talker phonetic variation is a less well-understood source of variability in speech, and it is unknown how processing costs from within-talker variation compare to those from between-talker variation. Here, listeners performed a speeded word identification task in which three dimensions of variability were factorially manipulated: between-talker variability (single vs multiple talkers), within-talker variability (single vs multiple acoustically distinct recordings per word), and word-choice variability (two- vs six-word choices). All three sources of variability led to reduced speech processing efficiency. Between-talker variability affected both word-identification accuracy and response time, but within-talker variability affected only response time. Furthermore, between-talker variability, but not within-talker variability, had a greater impact when the target phonological contrasts were more similar. Together, these results suggest that natural between- and within-talker variability reflect two distinct magnitudes of common acoustic-phonetic variability: Both affect speech processing efficiency, but they appear to have qualitatively and quantitatively unique effects due to differences in their potential to obscure acoustic-phonemic correspondences across utterances.