297In the first study, the subjects were presented with pitch changes of 2.5, 5, and 10 per cent
at 500 Hz sounds, first, during reading a book and, second, during a target-detection task.^41
It was found that they detected more accurately the sounds which consisted of three low-
est partials than pure sinusoidal tones. Correspondingly, the frequency-MMN amplitude
was larger and latency shorter in spectrally rich tones than in pure tones. This result sug-
gests that pitch discrimination, under attentional control as well as prior to that, is facili-
tated by the presence of the harmonic partials.
Subsequently it was determined whether adding harmonic partials or prolonging the
sound would further facilitate pitch discrimination.^42 To this aim, the frequency-MMN
was recorded to a 2.5 per cent pitch change in pure tones with only one sinusoidal fre-
quency component (500 Hz) and in spectrally rich tones with three (500...1500 Hz) and
five (500...2500 Hz harmonic partials. Stimuli were 100 and 250 ms in duration (in sep-
arate blocks). During these recordings, subjects concentrated on watching a silent movie.
The data show that the MMN amplitude was enhanced with spectrally rich sounds when
compared with pure tones, with no difference between spectrally rich tones having three or
five partials. Moreover, the prolonged sound duration did not significantly enhance the
MMN. This suggests, first of all, that relatively few harmonic partials (at least when they
Figure 19.1The MMN elicited by 2.5, 5, 10, and 20 per cent pitch changes in pure sinusoidal tones (left) and in
spectrally rich sounds (right) at 250 Hz (top) and 4000 Hz (bottom). The lines denote difference waves in which
the event-related potential elicited by the standard tone has been subtracted from the deviant-tone ERP. The
MMN was consistently larger when the pitch change was presented among spectrally rich sounds. Its amplitude
also systematically reflected the magnitude of the pitch change. Adapted from Ref. 43.
Pure tones Complex soundsMMNP3a400 ms- 5 μV
20%
10%2.5%250 Hz4000 HzMagnitude of the pitch change5%Pitch MMN