Relation between slow cortical response measures and categorical loudness judgments assessed by the Contour Test of Loudness in normal-hearing adults

Abstract

Objectives To establish the relation, if any, between the response properties of the slow cortical response (SCR) (i.e., the amplitudes of waves P1-N1 and N1-P2 and the latencies of waves P1, N1 and P2) recorded to a 2000-Hz tonal stimulus and loudness judgments for this same stimulus. Loudness was assessed using the Contour Test of Loudness (Cox et al., 1997). This study also investigated the relation, if any, between annoyance judgments of the 2000-Hz tonal stimuli and the stimulus intensity. Annoyance was assessed using a 6-point scale adapted from Hiramatsu et al. (1988). Design Loudness and annoyance measures were taken from 11 adults with normal hearing (aged 23-26 years). For each subject, the median stimulus intensity obtained from their loudness judgments for the 2000-Hz tonal stimuli for each loudness category determined the stimulus intensity used to record slow cortical responses for that participant. After the SCR recording was completed at each stimulus intensity, each subject was asked to judge the loudness and annoyance of the tonal stimuli at that intensity using the same scales described above. These judgments are referred to as the post loudness and annoyance judgments. Results As expected, as loudness and annoyance categories increased, the mean intensity increased. This pattern was relatively linear for the loudness judgments, with a 10-12 dB increase in stimulus intensity for each loudness category. In contrast, there was a 10-25 dB increase in stimulus intensity for each increase in annoyance category. Listeners assigned a considerable range of stimulus intensities to each loudness category (25-30 dB) for the Comfortable, but Slightly Soft through Loud, but O.K. categories. The range of stimulus intensities for each annoyance category was even larger (i.e., 40-55 dB) for the Very Pleasant through Tolerable categories. The variability in the data, reflected in the standard deviation values, was relatively consistent across categories for both loudness and annoyance. The results of the linear regression analyses revealed that behavioral loudness and annoyance judgments were highly correlated with stimulus intensity. As expected, SCR peak-to-peak amplitudes of waves P1-N1 and N1-P2 increased and the latencies of waves P1, N1 and P2 decreased as loudness category increased. Results of linear regression analyses revealed a stronger correlation of SCR amplitudes with the judgments of loudness (r=0.338-0.54) versus the SCR latencies ( r=0.074-0.221). Conclusion The current study provides encouraging results, suggesting that the response properties of the SCR may hold promise for estimating the subjective growth of loudness for tonal stimuli.