Hemispheric asymmetries in the perception of rapid (timbral) and slow (nontimbral) amplitude fluctuations of complex tones

Hemispheric asymmetries for processing rapid (timbral) and slow (nontimbral) amplitude fluctuations of complex tones were investigated in 32 right-handed nonmusicians. Two monaural matching-to-sample tests with contralateral white noise and attention directed to 1 ear were used, 1 with tones presenting slow fluctuations of amplitude and 1 with tones presenting rapid fluctuations of amplitude perceived as different timbres. Stimuli were generated by altering the amplitude envelope of a steady state complex tone. Dependent variables were reaction time and accuracy. The results suggest an important role for the right hemisphere in the perception of temporal variations of intensity of sounds both when these variations are rapid and perceived as timbral qualities and when they are slow and perceived as changes of loudness.