Figure 2.
Stimulus selection experiment. Method: Data from two groups of younger subjects were analyzed as part of a stimulus selection experiment. One group listened to narrowband noises with weakly ramped/damped envelope shapes (N = 25; 18 females; age range: 18-25 years, mean = 20.2 years, ± SD = 2.3 years), while the other group listened to noises with strongly ramped/damped envelope shapes (N = 25; 16 females; age range: 18-32 years, mean = 21.8 years, ± SD = 3.2 years) and EEG was recorded as described in Materials and Methods. Analysis: Neural synchronization was analyzed using identical methods as the ITPC analysis of the main experiment. To examine whether neural synchronization strength differed as a function of envelope shape strength, ITPC at the AM frequency (4 Hz) and for the 4 Hz fundamental/harmonic series (4:4:20 Hz) was submitted to separate ANOVAs, each with envelope shape (ramped, damped) and carrier frequency (low, high) as within-subject factors and envelope shape strength (weak, strong) as a between-subjects factor. Results: The results indicate that synchronized neural activity was larger for strong compared with weak envelope shapes (effect of shape strength: F(1,48) = 4.44, p = 0.04, η2p = 0.09), but this effect was only observed when considering responses to the harmonic series (4:4:20 Hz). Figure: (a) ITPC and (b) mean ITPC at the stimulation frequency (4 Hz) and at the 4 Hz fundamental/harmonic series (4:4:20 Hz) are plotted as a function of envelope shape strength (weak, strong) and envelope shape (ramped, damped). Topographies in (a) represent mean ITPC at the 4 Hz stimulation frequency and are shown for each envelope shape (ramped, damped) and age group (younger, older). Error bars indicate SE. *p < 0.05.