Bidirectional contrast effects in the perception of VC-CV sequences

The perceived places of articulation of two successive stop consonants are not independent: Given some ambiguity in the formant transition cues and a closure duration between 100 and 200 msec, contrastive perceptual interactions in both directions have been observed in identification tasks. Retroactive contrast declines as the closure interval is lengthened and is strongly influenced by the range of closure durations employed, whereas proactive contrast appears to be less sensitive to these factors (Experiment 1). Reduced contrast and no effects of closure duration are obtained in a discrimination task with selective attention to one stimulus portion; this suggests that the effects in identification arise largely at a higher level of (phonetic) perception (Experiment 2). The contrast effects do not seem to represent a perceptual compensation for coarticulatory dependencies between stops produced in sequence, for there appears to be little coarticulation as far as place of articulation is concerned (Experiment 3). The most plausible hypothesis is that the presumed contrast effects do not result from any direct interaction of spectral cues across the closure interval but are due to perceptual information conveyed by the closure itself: Closure durations of 100–200 msec happen to be most appropriate for sequences of two nonhomorganic stops. Here, it seems, is another case in which listeners’ tacit knowledge of canonical speech patterns determines perception.