Is auditory discrimination mature by middle childhood? A study using time-frequency analysis of mismatch responses from 7 years to adulthood

Abstract

Behavioural and electrophysiological studies give differing impressions of when auditory discrimination is mature. Ability to discriminate frequency and speech contrasts reaches adult levels only around 12 years of age, yet an electrophysiological index of auditory discrimination, the mismatch negativity (MMN), is reported to be as large in children as in adults. Auditory ERPs were measured in 30 children (7 to 12 years), 23 teenagers (13 to 16 years) and 32 adults (35 to 56 years) in an oddball paradigm with tone or syllable stimuli. For each stimulus type, a standard stimulus (1000 Hz tone or syllable [ba]) occurred on 70% of trials, and one of two deviants (1030 or 1200 Hz tone, or syllables [da] or [bi]) equiprobably on the remaining trials. For the traditional MMN interval of 100–250 ms post-onset, size of mismatch responses increased with age, whereas the opposite trend was seen for an interval from 300 to 550 ms post-onset, corresponding to the late discriminative negativity (LDN). Time-frequency analysis of single trials revealed that the MMN resulted from phase-synchronization of oscillations in the theta (4–7 Hz) range, with greater synchronization in adults than children. Furthermore, the amount of synchronization was significantly correlated with frequency discrimination threshold. These results show that neurophysiological processes underlying auditory discrimination continue to develop through childhood and adolescence. Previous reports of adult-like MMN amplitudes in children may be artefactual results of using peak measurements when comparing groups that differ in variance.

Figure 1

Illustration of phase-synchronization account of ERP waveforms. Panel A shows five sine waves in phase, which give an averaged waveform of the same form and amplitude; Panel B shows five sine waves of identical amplitude with random phase; when these are averaged, they will tend to cancel out to give a flatter waveform.

Figure 2

Topographic plots showing averaged weightings of electrodes on first principal component, in relation to age and stimulus type; arbitrary scaling from negative (blue) to positive (red). The average percentage variance accounted for by the principal component is shown beneath each plot.

Figure 3

Mean amplitude of response to standards for principal component in relation to age and stimulus type.

Figure 4

Mean amplitude of difference waves, after subtracting average standard wave, for dummy mismatch (grey lines), large deviants (red lines) and small deviants (blue lines). The same colour coding is used at the bottom of each plot to depict regions where a t-test gave a value below −1.96 when comparing the average amplitude with zero.

Figure 5

Mean amplitude of difference wave in (upper panel) 100–250 ms window, and (lower panel) 350–550 ms window, from dummy mismatch and true mismatch waves for tone and syllable stimuli. Deviant 1 is large deviant and deviant 2 is small deviant.

Figure 6

Power (dB) relative to frequency (Hz) for difference waves in relation to age. The plot shows three lines for each age corresponding to dummy waves and two kinds of mismatch wave, but these are not differentiated by symbols, as they are virtually superimposed.

Figure 7

ITC in the theta range by time for difference waves in relation to age group and deviant type.

Figure 8

ERSP in the theta range by time for difference waves in relation to age group and deviant type.