Speaker
Description
Many natural sounds contain modulation across both the temporal and spectral dimensions. The ability of human listeners to detect such spectro-temporal modulations (STM) has often been assessed using stimuli consisting of a STM pattern (moving ripples) imposed on a carrier signal, measuring the listeners’ detection threshold in terms of the modulation depth. The present study systematically investigated how different carrier signals, different stimulus durations, and different presentation modes affect STM detection in a group of young listeners with normal hearing. Using the most common STM configuration with a spectral modulation frequency of 2 cycles/octave and a temporal modulation rate of 4 Hz, stimuli were constructed using either noise or complex-tone carriers. The thresholds for these two broadband carrier types were measured in a reference condition using 1-second stimuli and binaural headphone-based presentation in a 3-alternative forced-choice paradigm. In addition, the effects of reduced bandwidth, shortened stimulus duration, and monaural presentation were measured for the two types of carriers. The results indicate that STM detection was substantially easier with the complex-tone carrier than with the noise carrier in the reference condition. Furthermore, a large variation in performance was found across listeners for the complex-tone carrier but not for the noise carrier. Interactions between the type of carrier and the effects of reduced bandwidth, shortened stimulus duration, and monaural presentation were observed. The potential mechanisms behind these findings and connections to other studies will be discussed.