Abstract
First- and second-order modulation detection thresholds were measured in normal hearing and hearing-impaired listeners. ‘First-order’ modulation detection thresholds correspond to the ability of listeners to detect sinusoidal amplitude modulation (SAM); they are measured as a function of the frequency of that modulation, fm. ‘Second-order’ modulation detection thresholds correspond to the ability to detect sinusoidal modulation applied to the modulation depth of a SAM signal; they are measured as a function of the frequency of the modulation applied to the modulation depth (referred to as/ fm1). In this case, the SAM signal acts as a ‘carrier’ stimulus of frequency fm and sinusoidal modulation of the SAM-signal’s modulation depth (at rate fm1) generates two additional components in the modulation spectrum at fm − fm1 and fm + fm1. In both groups of listeners, first-order modulation detection thresholds were measured for modulation frequencies fm ranging between 4 Hz and 32 Hz, and second-order modulation detection thresholds were measured for second-order modulation frequencies fm1 ranging between 1 Hz and 11 Hz, using a fixed first-order modulation frequency fm of 16 Hz. The results showed that, in hearing-impaired listeners: first-order modulation detection thresholds were within the normal range up to fm = 16 Hz and poorer than normal at fm1 = 32 Hz; second-order modulation detection thresholds were within the normal range at fm1 = 3, 5 and 11 Hz, and poorer than normal at fm1 = 1 Hz and 7 Hz. These results suggest that cochlear damage has little effect on the detection of both sinusoidal and complex temporal envelopes.