There are several theories of spoken word recognition, three of which will be discussed here. The first theory (motor theory of speech perception) is of historical importance, and merits inclusion for that reason. The other two theories (cohort theory and the TRACE model) have been very influential in recent years.
A key issue is to explain how it is that listeners perceive words accurately even though the speech signal provides variable information. Liberman et al. (1967) argued in their motor theory of speech perception that listeners mimic the articulatory movements of the speaker, but this need not involve measurable articulatory responses. The motor signal thus produced was claimed to provide much less variable and inconsistent information about what the speaker is saying than the speech signal itself. Our reliance on the motor signal allows spoken word recognition to be reasonably accurate.
Evidence consistent with the motor theory was reported by Dorman, Raphael, and Liberman (1979). A tape was made of the sentence, "Please say shop", and a 50-millisecond period of silence was inserted between "say" and "shop". As a result, the sentence was misheard as "Please say chop". Our speech musculature forces us to pause between "say" and "chop", but not between "say" and "shop", and so the evidence from internal articulation would favour the wrong interpretation of the last word in the sentence.
The assumption that the motor signal provides invariant information about speech segments is incorrect. There are, for example, as many different motor manifestations of a given consonant as there are acoustic manifestations (MacNeilage, 1972). Such findings rather undermine the main reason for proposing the motor theory in the first place.
It follows from the motor theory that infants with limited expertise in articulation of speech should be very poor at speech perception. In fact, infants perform very well on many tests of speech perception (e.g., Eimas et al., 1987). Thus, the ability to produce and make use of the motor signal is not necessary for good levels of speech perception. Simultaneous translators can listen to speech in one language while producing fluent speech in another language at the same time, and it is hard to see how this could happen on the motor theory.
In spite of experimental disconfirmations, motor theory has influenced contemporary thinking. For example, one of the attractive features of motor theory was that it drew a clear distinction between the
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