(see Chapter 9, this volume). One of the salient features of the auditory nervous system, in
fact, is that a tonotopic organization exists from the earliest level of the periphery, at the
basilar membrane, to many fields within the auditory cortex. This topographic organiza-
tion along the frequency axis points to the importance of pitch information in auditory
processing generally. However, does the cortex carry out some essential function in the rep-
resentation of pitch information? Several classic studies in experimental animals with bilat-
eral destruction of auditory cortical areas have suggested that simple pitch discrimination
remains unaffected, indicating that earlier levels of processing, in the midbrain or thala-
mus, for example, may be sufficient.1–3However, the nature of the pitch processing task
appears to be critical in answering this question.
In a recent study from my lab, Johnsrude et al.^4 explored the specificity of pitch dis-
crimination using a behavioural-lesion technique. We tested patients who had undergone
surgical excision in the auditory cortex in the right or left temporal lobe; the patients’
lesions were classified according to magnetic resonance imaging (MRI) as extending or not
into Heschl’s gyrus (HG), which contains the primary auditory cortex (see Ref. 5 for
description of a lesion quantification procedure, and Figures 16.1 and 16.2). A simple psy-
chophysical ‘staircase’ discrimination task was used, with pairs of pure tones to determine
the threshold or minimal frequency separation needed to achieve a certain level of per-
formance. Two separate tasks were administered. In the first, the two tones were either
identical or different in pitch, and the subject answered accordingly. In the second task, the
233Figure 16.1Magnetic resonance image of a normal human brain showing a horizontal section through the region
of Heschl’s gyrus, marked HG. The orientation and level of the horizontal section is indicated by the dashed line
in the inset.