Processing of complex auditory patterns in musicians and nonmusicians

Abstract

In the present study we investigated the capacity of the memory store underlying the mismatch negativity (MMN) response in musicians and nonmusicians for complex tone patterns. While previous studies have focused either on the kind of information that can be encoded or on the decay of the memory trace over time, we studied capacity in terms of the length of tone sequences, i.e., the number of individual tones that can be fully encoded and maintained. By means of magnetoencephalography (MEG) we recorded MMN responses to deviant tones that could occur at any position of standard tone patterns composed of four, six or eight tones during passive, distracted listening. Whereas there was a reliable MMN response to deviant tones in the four-tone pattern in both musicians and nonmusicians, only some individuals showed MMN responses to the longer patterns. This finding of a reliable capacity of the short-term auditory store underlying the MMN response is in line with estimates of a three to five item capacity of the short-term memory trace from behavioural studies, although pitch and contour complexity covaried with sequence length, which might have led to an understatement of the reported capacity. Whereas there was a tendency for an enhancement of the pattern MMN in musicians compared to nonmusicians, a strong advantage for musicians could be shown in an accompanying behavioural task of detecting the deviants while attending to the stimuli for all pattern lengths, indicating that long-term musical training differentially affects the memory capacity of auditory short-term memory for complex tone patterns with and without attention. Also, a left-hemispheric lateralization of MMN responses in the six-tone pattern suggests that additional networks that help structuring the patterns in the temporal domain might be recruited for demanding auditory processing in the pitch domain.

Figure 1. Examples of tone patterns for the three experimental conditions.

Patterns were constructed individually from four, six or eight different tones, respectively, and the size and direction of intervals was controlled for between subjects. Time and pitch are indicated on arbitrary scales.

Figure 2. Example of three standard sequences and one deviant sequence as they might have occurred during the experiment.

In deviant sequences one note at a random position (large dot) was shifted one tone up or down, unless this would be the same pitch as a neighbouring tone. Time and pitch are indicated on arbitrary scales.

Figure 3. Group data (source waveforms) for the three experimental conditions (four, six and eight tone patterns) and the control condition and for both hemispheres hemisphere in the two groups (musicians  =  black traces, nonmusicians  =  grey traces).

Arrowheads indicate the latency of the mismatch responses in the group averages.

Figure 4. Mean MMN amplitudes for each condition and hemisphere for all subjects.

The analysis of variance indicates a left-lateralized dominance for the six tone condition. Error bars represent standard deviations.

Figure 5. Lower boundaries (black traces) of generated bootstrapped confidence intervals for signal amplitudes (grey traces) for both groups in the three experimental conditions (four, six and eight tones) and the control condition for both hemispheres.

Lower confidence intervals larger than zero indicate that there is significant deflection of source waveform. This is the case in all experimental conditions in both hemispheres for musicians, but only in the control condition, and in the four tone condition (right hemisphere) for non-musicians.