Theoretical contributions of tests on animals to the special-mechanisms debate in speech.

Many animal species demonstrate a keen sensitivity very early in life to stimuli that play a role in their survival. Theorists have taken this to mean that species-specific mechanisms evolved in animals that aid in the detection and recognition of important stimuli. Similar arguments have been made about the mechanisms that underlie the perception of speech in humans. Theories of speech perception present convincing arguments that even the phonetic level of language requires specially evolved mechanisms, because of the extreme complexity involved in the mapping between sound and percept. Phenomena such as categorical perception have been attributed to the workings of these mechanisms. This paper lays out an argument concerning the contribution of animal studies on categorical perception to the special-mechanisms debate. Animals provide a model of auditory-level processing in the absence of phonetic-level processing, and test whether the existence of a phenomenon such as categorical perception necessitates specialized mechanisms. A review of the studies shows that animal demonstrate categorical perception of the voicing and place features. These data, as well as some recent findings on young human infants, are considered with regard to their impact on theories of infant speech perception and on the evolution of speech.