Evidence for precategorical extrinsic vowel normalization.

Three experiments investigated whether extrinsic vowel normalization takes place largely at a categorical or a precategorical level of processing. Traditional vowel normalization effects in categorization were replicated in Experiment 1: Vowels taken from an [I]-[ε] continuum were more often interpreted as /I/ (which has a low first formant, F(1)) when the vowels were heard in contexts that had a raised F(1) than when the contexts had a lowered F(1). This was established with contexts that consisted of only two syllables. These short contexts were necessary for Experiment 2, a discrimination task that encouraged listeners to focus on the perceptual properties of vowels at a precategorical level. Vowel normalization was again found: Ambiguous vowels were more easily discriminated from an endpoint [ε] than from an endpoint [I] in a high-F(1) context, whereas the opposite was true in a low-F(1) context. Experiment 3 measured discriminability between pairs of steps along the [I]-[ε] continuum. Contextual influences were again found, but without discrimination peaks, contrary to what was predicted from the same participants' categorization behavior. Extrinsic vowel normalization therefore appears to be a process that takes place at least in part at a precategorical processing level.