Cortical processing of complex tone stimuli: mismatch negativity at the end of a period of rapid pitch modulation

Abstract

In this study, synthesised instrumental tones were used to examine human auditory cortical processes engaged at the end of a period of w rapid pitch modulation. It was previously S.J. Jones, O. Longe, M. Vaz Pato, Auditory evoked potentials to abrupt pitch and timbre Ž . x change of complex tones: electrophysiological evidence of 'streaming'?, Electroencephalogr. Clin. Neurophysiol., 108 1998 131-142 suggested that the 'change-N1' produced by infrequent changes in pitch or timbre of a continuous complex tone represents the activity of a neuronal population topographically distinct from that responsible for the 'onset-N1' at the beginning of the tone. In the present study a Ž . superficially similar negativity was produced when the tone came to rest on a steady pitch after a period of rapid 8-16 changesrs modulation; its scalp maximum was anterior to that of the two previously identified potentials but similar to that of the mismatch negativity elicited by discontinuous tones. By varying the modulation rate the latency was shown to be relatively constant with respect to the time the next pitch change was expected but failed to occur. The largest responses averaging c. 7 mV were evoked at the end of modulation sequences which were both rhythmic and repetitive, but a potential was still produced when there was no rhythmic pattern or repetition of individual notes. This response to non-occurrence of an expected but not necessarily specified change implies an automatic process for comparing the incoming sound with an extrapolated template of the preceding pattern in which timing as well as pitch information is accurately represented. We suggest this technique offers a robust method for eliciting the mismatch negativity, which may extend the opportunities for electrophysiological investigation of higher auditory processes. q

Spectro-temporal analysis of complex tones: two cortical processes dependent on retention of sounds in the long auditory store

“…As in the previous study (Vaz Pato and Jones, 1999), the MN1 and MP2 at the end of the period of pitch oscillation appeared to be more anteriorly distributed on the scalp than the CP1, CN1 and CP2 at the beginning of the oscillatory period. Whereas the CN1 was of comparable amplitude at Fz and Cz, MN1 was more evidently larger at Fz for all stimulus durations except the shortest (Fig.…”

“…When pitch changes are made at rates greater than about 10/s the associated N1 and P2 potentials are markedly attenuated or absent, but on resumption of a steady pitch a large (up to 10 mV) negative potential with a more anterior distribution is evoked (Vaz Pato and Jones, 1999). We have argued that this is probably an MMN in a relatively pure form, undistorted by overlapping N1 components.…”

“…We have also previously argued (Vaz Pato and Jones, 1999) that the MN1 at the end of a period of rapid pitch oscillation must represent a different process from the CN1 at the beginning. Since the CN1 is almost completely abolished when pitch changes occur at a rate of 16/s, it would not be logically plausible for a large CN1 to be generated by the last change.…”

The N1 complex to gaps in noise: Effects of preceding noise duration and intensity

“…The results indicated that the primary auditory cortex responds immediately to stimulus changes and integrates stimulus features over a period of about 200 ms. In another series of studies on fusion of rapid stimulus alternations (Vaz Pato and Jones, 1999;Jones et al, 2000a,b), continuous synthesized musical instrument notes oscillated between two pitches at a rapid rate (8-16 notes/s, i.e., every 63-125 ms) and the 'changetype' N 1 and P 2 potentials associated with each individual change were abolished ('fused oscillations'), indicating an integration time of around 100 ms. Thus, different approaches to determine the time span of stimulus constancy or temporal integration resulted in quite different results (between 30 and 300 ms), depending on possible confounding factors such as spectral changes, adaptation rates, refractory periods and on/off effects.…”

“…Previous studies on temporal integration, change and constancy (Alain et al, 1997;Vaz Pato and Jones, 1999;Jones et al, 2000a,b;Gage and Roberts, 2000;Roß et al, 2002;Alain et al, 2004;Heinrich et al, 2004) used stimuli that included spectral changes due to stimulus onset and offset that may have interacted with duration. Consequently, depending on the procedures employed, different values ranging between 30 and 300 ms were obtained.…”