Long-term memory in speech perception: Some new findings on talker variability, speaking rate and perceptual learning

This paper summarizes results from recent studies on the role of long-term memory in speech perception and spoken word recognition. Experiments on talker variability, speaking rate and perceptual learning provide strong evidence for implicit memory for very fine perceptual details of speech. Listeners apparently encode specific attributes of the talker's voice and speaking rate into long-term memory. Acoustic-phonetic variability does not appear to be "lost" as a result of phonetic analysis. The process of perceptual normalization in speech perception may therefore entail encoding of specific instances or "episodes" of the stimulus input and the operations used in perceptual analysis. These perceptual operations may reside in a "procedural memory" for a specific talker's voice. Taken together, the present set of findings are consistent with non-analytic accounts of perception, memory and cognition which emphasize the contribution of episodic or exemplar-based encoding in long-term memory. The results from these studies also raise questions about the traditional dissociation in phonetics between the linguistic and indexical properties of speech. Listeners apparently retain non-linguistic information in long-term memory about the speaker's gender, dialect, speaking rate and emotional state, attributes of speech signals that are not traditionally considered part of phonetic or lexical representations of words. These properties influence the initial perceptual encoding and retention of spoken words and therefore should play an important role in theoretical accounts of how the nervous system maps speech signals onto linguistic representations in the mental lexicon.