Question

To what extent is speech production and perception found to correspond to specific cortical loci in the brain? What evidence is there that each process ( production and perception) works independently but also cooperatively?

Answer 1

• Until recently, research in speech perception and speech production has largely focused on the search for psychological and phonetic evidence of discrete, abstract, context-free symbolic units corresponding to phonological segments or phonemes. Despite this common conceptual goal and intimately related objects of study, however, research in these two domains of speech communication has progressed more or less independently for more than 60 years. In this article, we present an overview of the foundational works and current trends in the two fields, specifically discussing the progress made in both lines of inquiry as well as the basic fundamental issues that neither has been able to resolve satisfactorily so far. We then discuss theoretical models and recent experimental evidence that point to the deep, pervasive connections between speech perception and production. We conclude that although research focusing on each domain individually has been vital in increasing our basic understanding of spoken language processing, the human capacity for speech communication is so complex that gaining a full understanding will not be possible until speech perception and production are conceptually reunited in a joint approach to problems shared by both modes.

Historically, language research focusing on the spoken (as opposed to written) word has been split into two distinct fields: speech perception and speech production. Psychologists and psycholinguists worked on problems of phoneme perception, whereas phoneticians examined and modeled articulation and speech acoustics. Despite their common goal of discovering the nature of the human capacity for spoken language communication, the two broad lines of inquiry have experienced limited mutual influence. The division has been partially practical, because methodologies and analysis are necessarily quite different when aimed at direct observation of overt behavior, as in speech production, or examination of hidden cognitive and neurological function, as in speech perception. Academic specialization has also played a part, since there is an overwhelming volume of knowledge available, but single researchers can only learn and use a small portion. In keeping with the goal of this series, however, we argue that the greatest prospects for progress in speech research over the next few years lie at the intersection of insights from research on speech perception and production, and in investigation of the inherent links between these two processes.

In this article, therefore, we will discuss the major theoretical and conceptual issues in research dedicated first to speech perception and then to speech production, as well as the successes and lingering problems in these domains. Then we will turn to several exciting new directions in experimental evidence and theoretical models which begin to close the gap between the two research areas by suggesting ways in which they may work together in everyday speech communication and by highlighting the inherent links between speaking and listening.

  SPEECH PERCEPTION

Before the advent of modern signal processing technology, linguists and psychologists believed that speech perception was a fairly uncomplicated, straightforward process. Theoretical linguistics’ description of spoken language relied on the use of sequential strings of abstract, context-invariant segments, or phonemes, which provided the mechanism of contrast between lexical items (e.g., distinguishing pat from bat).1,2 The immense analytic success and relative ease of approaches using such symbolic structures led language researchers to believe that the physical implementation of speech would adhere to the segmental ‘linearity condition,’ so that the acoustics corresponding to consecutive phonemes would concatenate like an acoustic alphabet or a string of beads stretched out in time. If that were the case, perception of the linguistic message in spoken utterances would be a trivial matching process of acoustics to contrastive phonemes.