two tones always differed, and the subject’s task was to indicate if the second tone was
higher or lower than the first. The tones themselves were identical across the two tasks. The
idea here is that whereas the simple pitch discrimination task merely requires that a differ-
ence be noted, the second, pitch-direction task requires that the tones be discriminated and
ordered along some underlying pitch scale.
The findings (Figure 16.3) indicated several interesting dissociations. First, the patients with
lesions within the left temporal lobe were quite unimpaired as compared to control partici-
pants on either task, regardless of the extent of excision with HG. Second, the patients with
damage to the right temporal lobe but excluding HG also had normal thresholds. The group
of subjects with right HG damage, however, showed a fourfold increase in their pitch thresh-
olds, but only for the pitch-direction task; they were normal on the simple pitch discrimina-
tion task. The findings are thus quite specific in indicating that only a certain restricted lesion
in the right temporal lobe has an effect, and then only on a particular task. Thus, one may con-
clude that the right primary auditory area plays a special role not simply in discriminating one
pitch from another, but in some aspect of organizing the sounds according to their pitch. This
aspect of pitch organization, it is argued, is essential for any musical use of pitch information.
Interestingly, all but one of the patients in question were able to perform the task itself; it was
only the threshold that was abnormally high. This aspect of the result suggests that a much
coarser level of pitch organization still exists in these patients, which may be mediated by left
auditory cortex, a point to which we shall return below.
These results are consistent with those of a much earlier study^6 in which patients
with right temporal lobe excisions with encroachment onto Heschl’s gyri had significant
difficulties with a missing-fundamental pitch discrimination task but not with the identical
235Figure 16.3Mean frequency difference discrimination thresholds observed in two pitch discrimination tasks in
patients with right or left (RT or LT) temporal-lobe excision, extending into the region of HG (A) or sparing this
area (a). The simple discrimination thresholds were not different across the groups. Thresholds in the direction-
of-pitch-change task were significantly higher in the RTA group than in any of the other groups. (Reproduced
with permission from Ref. 4).
150100Pitch difference
Direction of pitch change500Frequency discriminationthreshold (Hz)Group NC LTa LTA RTa R TA
N14 12 5 6 8