Audio-tactile integration and the influence of musical training

Abstract

Perception of our environment is a multisensory experience; information from different sensory systems like the auditory, visual and tactile is constantly integrated. Complex tasks that require high temporal and spatial precision of multisensory integration put strong demands on the underlying networks but it is largely unknown how task experience shapes multisensory processing. Long-term musical training is an excellent model for brain plasticity because it shapes the human brain at functional and structural levels, affecting a network of brain areas. In the present study we used magnetoencephalography (MEG) to investigate how audio-tactile perception is integrated in the human brain and if musicians show enhancement of the corresponding activation compared to non-musicians. Using a paradigm that allowed the investigation of combined and separate auditory and tactile processing, we found a multisensory incongruency response, generated in frontal, cingulate and cerebellar regions, an auditory mismatch response generated mainly in the auditory cortex and a tactile mismatch response generated in frontal and cerebellar regions. The influence of musical training was seen in the audio-tactile as well as in the auditory condition, indicating enhanced higher-order processing in musicians, while the sources of the tactile MMN were not influenced by long-term musical training. Consistent with the predictive coding model, more basic, bottom-up sensory processing was relatively stable and less affected by expertise, whereas areas for top-down models of multisensory expectancies were modulated by training.

Figure 1. Outline of the multisensory matching rule that defined the audio-tactile correspondence of fingers to pitches.

Figure 2. Outline of the four different conditions (A congruent = standard, B incongruent, C tactile deviant and D auditory deviant).

The upper part of each image represents the melody played and the lower part shows the exact location of the simultaneous tactile stimulation of one finger of the left hand per tone. Tones in ovals represent sinusoidal timbres and the tone in a rectangle represents a sawtooth timbre. A: In a congruent trial the match of tone and stimulated finger is always correct. B: In an incongruent trial the match of one tone and finger pair is not correct (with regard to the multisensory matching rule). C: In a tactile-deviant trial one time the location of the finger stimulation is shifted from the fingertip to the second phalanx. D: In an auditory-deviant trial one of the tones is presented in sawtooth timbre instead of sinusoidal timbre.

Figure 3. Statistical parametric maps and grand averaged global field power of the audio-tactile incongruency response.

A: Right: Statistical parametric maps of the audio-tactile incongruency response and the musicians versus non-musicians comparison as revealed by the flexible factorial model for the time window of 125 to 165 ms. Threshold: AlphaSim corrected at p<0.001 by taking into account peak voxel significance (threshold p<0.001 uncorrected) and cluster size (threshold size,>259 voxels). Left: Grand average global field power for standard (black line) and deviant (grey line) response. The gray bar indicates the time interval where the analysis was performed. B: Right: Statistical parametric maps of the audio-tactile incongruency response and the musicians versus non-musicians comparison as revealed by the flexible factorial model for the time window of 190 to 240 ms. Threshold: AlphaSim corrected at p<0.001 by taking into account peak voxel significance (threshold p<0.001 uncorrected) and cluster size (threshold size,>161 voxels). Left: Grand average global field power for standard (black line) and deviant (gray line) response. The gray bar indicates the time interval where the analysis was performed.

Figure 4. Statistical parametric maps and grand averaged global field power of the tactile MMN response.

A: Right: Statistical parametric maps of the tactile MMN response and the musicians versus non-musicians comparison as revealed by the flexible factorial model for the time window of 125 to 165 ms. Threshold: AlphaSim corrected at p<0.001 by taking into account peak voxel significance (threshold p<0.001 uncorrected) and cluster size (threshold size,>198 voxels). Left: Grand average global field power for standard (black line) and deviant (gray line) response. The gray bar indicates the time interval where the analysis was performed. B: Right: Statistical parametric maps of the tactile MMN response and the musicians versus non-musicians comparison as revealed by the flexible factorial model for the time window of 190 to 240 ms. Threshold: AlphaSim corrected at p<0.001 by taking into account peak voxel significance (threshold p<0.001 uncorrected) and cluster size (threshold size,>73 voxels). Left: Grand average global field power for standard (black line) and deviant (gray line) response. The gray bar indicates the time interval where the analysis was performed.

Figure 5. Statistical parametric maps and grand averaged global field power of the auditory MMN response.

Right: Statistical parametric maps of the auditory MMN response and the musicians versus non-musicians comparison as revealed by the flexible factorial model for the time window of 190 to 240 ms. Threshold: AlphaSim corrected at p<0.001 by taking into account peak voxel significance (threshold p<0.001 uncorrected) and cluster size (threshold size,>197 voxels). Left: Grand average global field power for standard (black line) and deviant (gray line) response. The gray bar indicates the time interval where the analysis was performed.

Figure 6. Behavioral results of the correct answers in percent, plotted separately by group (musicians in dark grey and non-musicians in light grey) and condition (incongruent, congruent, auditory deviant and tactile deviant, x-axis).

Error bars represent the 95% confidence interval.

Figure 7. Glass brain view of activations for the main effects of all conditions (audio-tactile, tactile, and auditory) and both time windows (125–165 ms and 190–240 ms).