Structure in talker variability: How much is there and how much can it help?

One of the persistent puzzles in understanding human speech perception is how listeners cope with talker variability. One thing that might help listeners is structure in talker variability: rather than varying randomly, talkers of the same gender, dialect, age, etc. tend to produce language in similar ways. Sociolinguistic research has shown that listeners are sensitive to this covariation between linguistic variation and socio-indexical variables. In this paper I present new techniques based on ideal observer models to quantify 1) the amount and type of structure in talker variation, and 2) how useful such structure can be for robust speech recognition in the face of talker variability. I demonstrate these techniques in two phonetic domains---word-initial stop voicing and vowel identity---and show that these domains have different amounts and types of talker variability, consistent with previous, impressionistic findings. An `R` package accompanies this paper, enabling researchers to apply these techniques to their own data.