Listener expectations and gender bias in nonsibilant fricative perception.

The nonsibilant English fricatives /f/ and /θ / are known to be acoustically nonrobust. Using /f/ and /θ/ stimuli produced in CV, VCV, and VC syllables in /i α u/ contexts spoken by 10 talkers (5 male), we first replicate previous research suggesting that the most robust cues to this contrast are in the formant transitions in adjacent vowels. We also demonstrate vowel and syllable contextual differences that point to the contrast being most robust in /u/ contexts. In a series of perception experiments we go on to demonstrate effects of bias on perception of /f/ and /θ/ that derive from the uninformative nature of the frication noise, making them vulnerable to misperception in general, and especially in low-saliency contexts where the formant transition information is less robust. In experiment 1, listeners' classification of /f/ and /θ/ demonstrated a general bias to respond /f/ for fricatives produced by females and /θ/ for those produced by males. We hypothesize that the perceived concentrations of spectral energy in the fricative are shifted based on the concentration of energy in the vowel, which depend on a talker's gender. In experiment 2, vowel and frication noise portions were cross-spliced to probe this effect, resulting in the same gender-based bias. In a final experiment the vocalic information was removed and only the frication noise was presented to listeners for classification. In this task there was a general bias for /f/, regardless of the talker gender. Overall we demonstrate topdown gender effects in perception that originate in the strong indexical properties of adjacent vowels rather than being present in the frication noise itself.