Perceptual learning and expectations: Cognitive mechanisms in speech recognition

There is substantial plasticity in adult perceptual processing of speech that cannot be accounted for by most theories. Even 1 h of training on low-intelligibility synthetic speech can improve recognition by 20 percentage points for novel words. Whether speech perception is based on auditory properties or articulatory properties, few theories acknowledge the role of cognitive processes, and some explicitly exclude these mechanisms. Evidence will be examined suggesting perceptual learning of phonetic information in adult listeners involves processes such as attention and working memory. In addition, evidence will be examined that speech perception can be influenced, if not typically guided, by listeners’ expectations about speech. In some cases, expectations may be derived by explicit instruction to listeners, and in others, from contextual information. For example, research on talker normalization and perception of sinewave speech has demonstrated that listeners’ expectations about the speech signal change perceptual processing. Evidence will be discussed suggesting mechanisms that mediate this effect of expectations and compare this to mechanisms involved in perceptual learning. Perceptual learning may depend on the same kinds of cognitive mechanisms involved in the top-down guidance of perception by expectations and these mechanisms may be necessary for stable phonetic perception. [Research supported by NIDCD.]