Figure 8.

Context-dependent M100 response magnitudes, controlling for sensation level difference between age groups. A, Histograms of sensation levels for the 14 selected participants of each age group. Dots and error bars reflect the mean sensation level and SEM, respectively, for each group. For this subset of participants, no difference in sensation level (hearing threshold) was observed between age groups (n.s., not significant; p = 0.382). The sensation levels reflect dB values from the threshold estimation procedure written in MATLAB. B, Responses to different sound levels in the 15 and 45 dB SL contexts. Bar graphs show the response range in the 15 and 45 dB SL contexts calculated as the difference between the maximum and the minimum response amplitude across sound levels. The main effect of age group as well as the main effect of context was significant (p < 0.05; no interaction). C, Sensitivity to sound level in the 45 dB SL context for levels lower than the high-probability region. Left, Data from the 45 dB SL context displayed in B. The dashed vertical line at 45 dB SL marks the center of the high-probability region. The colored solid lines reflect the averaged predicted values from participant-specific linear fits. Right, Slope of a linear function relating sound level to response amplitudes below the high-probability region revealed a significantly positive slope for older but not for younger adults (right). *p < 0.05. Error bars indicate SEM.