Fig. 47.1
Average hissiness ratings as a function of half-life for ramped (black lines) and damped (grey lines) noises averaged over subjects; the parameter is modulation period. The error bars show standard errors of the mean
The gradiometer waves exhibited strong P50m and P200m components as well as a substantial sustained field. Stable spatio-temporal models were readily fitted to these AEFs in both hemispheres for all 14 subjects. The N100m could not be derived reliably from the waves so it was omitted from further analysis. Figure 47.2 shows six grand-average source waveforms for conditions with a wide range of hissiness ratings (left column) and the corresponding average summary SAIs (right column). Figure 47.3 shows the bandpass filtered grand-average waveforms to demonstrate the correspondence of hissiness values with P200 onset and offset responses.
Fig. 47.2
Correspondence of AEF magnitude and summary SAI hiss correlates. Left panel: Grand-average source waveforms (pooled over both hemispheres) of the sustained field model for a subset of conditions ordered from high to low hissiness. The P200m magnitude increases with higher hissiness values. The right panel depicts the summary SAI for the corresponding stimulus conditions. As indicated by the arrows, SAI activity increases for higher hissiness values
Fig. 47.3
Grand-average P200m source waveforms (1–30 Hz) ordered from low at the bottom to high at the top (pooled over hemispheres). Large hissiness values are associated with larger P200m amplitudes. Note that there are also P200m offset responses whose magnitude corresponds with that of the P200m onsets (r = .82, P < 0.0001)
Figure 47.4 shows scatter plots of hissiness against three AEF measures. There are significant correlations between hissiness and P200m magnitude (r = .85, P < 0.0001) (Fig. 47.4b) and between hissiness and SF magnitude (r = .56, P < 0.01). The correlation between hissiness and the P50m is not significant (r = .33, ns). Figure 47.5 shows scatter plots and regression lines for the SAI hiss correlate against hissiness rating and P200m magnitude, the strongest of the correlations in Fig. 47.4. Both of the plots show strong correlations.
Fig. 47.4
Scatter plots to illustrate the relationship between hissiness value and the P50m (a), the P200m (b), and the sustained field (c)
