Perception of speech is effortless under most circumstances; this may
explain why the complexity of this cognitive process is so often
unappreciated. While most other sounds in the environment are acoustically
very distinctive, the 30 or 40 speech sounds people make are discriminable
only by rapid analysis of rather subtle acoustic cues. Given the
importance of language, it seems plausible not only that our auditory
system evolved a degree of specialization for handling such analyses, but
also that this specialization should assimilate substantial neural
resources. Recent work in comparative physiology and human brain imaging
suggests, in fact, that much of the superior temporal gyrus in humans is
devoted to this perceptual feat.