Fig 1.
Schema of the experimental protocol.
The N1m responses to tone bursts presented to the left ear at a level of 70 dB with and without contralateral stimuli presented continuously were recorded alternately while decreasing the level of contra-stimuli from 80 to 30 dB. In most cases, the contra-music and contra-noise experiments were performed on different days, considering the mental and physical burden that they placed on the subjects.
Fig 2.
Representative example of the effects of contralateral “music” stimuli (at 50 dB) on the N1m response obtained from the right hemisphere.
A: Superimposed magnetic signals with and without contra-music stimuli, B: Isofield maps and ECDs superimposed on MR images without contra-music stimuli, C: Isofield maps and ECDs superimposed on MR images with contra-music stimuli, D: Averaged waves (root mean square [RMS] waves) of all channels in the right hemisphere measured with contralateral sound were superimposed with those of the control measurement (measurement without contra-sound) just before and after the measurement with contralateral sound.
Fig 3.
Representative example of the effects of contralateral “noise” stimuli (at 50 dB) on the N1m response obtained from the right hemisphere.
A: Superimposed magnetic signals with and without contra-noise stimuli, B: Isofield maps and ECDs superimposed on MR images without contra-noise stimuli, C: Isofield maps and ECDs superimposed on MR images with contra-noise stimuli, D: Averaged waves (root mean square [RMS] waves) of all channels in the right hemisphere measured with contralateral sound were superimposed with those of the control measurement (measurement without contra-sound) just before and after the measurement with contralateral sound.
Fig 4.
Average effect of contra-sound on N1m amplitude (A) and latency (B) obtained from the right hemisphere for each contra-sound level. Values are compared between music and noise stimuli for all 12 subjects. Error bars indicate standard error (SE). Asterisks indicate significant difference (p<0.05) between the effects of contra-music and contra-noise for each contra-sound level (Bonferroni post-hoc analysis of ANOVA) (see text for further details on statistics).
Fig 5.
Average effect of contra-sound on N1m amplitude (A) and latency (B) obtained from the left hemisphere for each contra-sound level. Values are compared between music and noise stimuli for 8 subjects in whom the latency and amplitude of N1m could be assessed reliably under all measurement conditions. Error bars indicate standard error (SE). Asterisks indicate significant difference (p<0.05) between the effects of contra-music and contra-noise in each contra-sound level (Bonferroni post-hoc analysis) of ANOVA (see text for further details on statistics).
Fig 6.
Acoustic reflex thresholds and psychophysical thresholds for contra-music and contra-noise stimuli for participants in the MEG study.
The upper figure (A) shows the acoustic reflex threshold (open triangles) and psychoacoustic threshold (open squares) for music stimuli, and the lower figure (B) shows the acoustic reflex threshold (open triangles) and psychoacoustic threshold (open squares) for noise stimuli.
Fig 7.
Effects of the contralateral music stimuli vs. noise stimuli on the response time to the probe sound presented to the left ear (“change in response time” indicates the response time relative to those measured without contra-sound).
The black dots in the box-plots indicate the mean values.