Variability and Invariance in Speech and Lexical Processing: Evidence from Aphasia and Functional Neuroimaging
The processes underlying both speaking and understanding appear to be easy and seamless. And yet, speech input is highly variable, the lexical form of a word shares its sound shape with many other words in the lexicon, and often a given word has multiple meanings. The goal of this research is to examine how and in what ways the neural system is, on the one hand, sensitive to the variability in the speech and lexical processing system, and, on the other, how it is able to resolve this variability. To this end, we will review recent research investigating how the perceptual system resolves variability in selecting the appropriate word from its competitors and determining what category a sound belongs to, e.g. [d] or [t], and how different acoustic features of sounds, e.g. [d-t] vs. [s-z], map on to a common abstract feature, e.g. voicing. We will then examine how higher level information sources such as semantic and conceptual information are used in perceiving degraded speech. The implications of these findings will be considered for models of the functional and neural architecture of language.