UC San Diego

The cocktail party effect describes the human ability to detect a specific sound of interest in a noisy environment. Scientists have evaluated different influential parameters affecting auditory stream segregation. Previous studies have focused on individual cues while the interaction between them appears to be poorly studied. This thesis investigates the interactions between the temporal and spatial

cues, and the spectral and spatial cues in a cocktail party scenario. Two streams were presented at the same time from ±7.5◦ or ±45◦ or ±90◦ . One stream (the target) was to be attended, and the other stream (the masker) was to be ignored. The stimuli were frequency-modulated narrowband noise. The modulation-rates were randomly chosen between 0.7 and 3.3 Hz (prosodic fluctuations in natural speech) so that the interaction of modulation-rate difference and stream segregation could be examined. Transient gaps were embedded in both streams and the task was to report only the gaps in the target. If the subject could detect gaps in the target (not masker), the stream segregation was accurate. Performance was evaluated as a function of source separation using signal detection theory. The overall performance was significantly poorer at ±7.5◦ than at ±45◦ and ±90◦ . The task was evaluated as a function of the difference between the carrier frequency of target and masker that was chosen randomly. The results showed that the effect of the frequency difference on performance was significant at all the angles and it was significantly stronger at ±7.5◦ than at ±45◦ . he task was analyzed as a function of the modulation-rate difference between the streams and showed it did not play the role of a segregation cue at any angle. The reaction time at ±7.5◦ was significantly slower than that at ±45◦ and ±90◦ . In summary, consistent with previous work on stream segregation, spatial cues influenced performance. When they were not strong enough cues, making a decision took a longer time. Frequency was a stronger cue for stream segregation when spatial cues were less clear. Regardless of the location in space, no interaction between the rate and space was found.