Electronic Thesis and Dissertation Repository


Master of Science




Dr. Ingrid Johnsrude


A previous study has found that perceiving degraded speech requires attention, with compromised behavioral and neurological measures of speech processing for degraded speech, but not clear speech, when participants are distracted (Wild et al., 2012b). We extended these findings by examining behavioral and neural correlates of speech perception under different levels of cognitive load using multiple object tracking. We also investigated the role of attention in perceiving degraded speech that was as intelligible as clear speech, in order to separate perceptual outcomes (i.e., intelligibility) from the requisite processing demands. We found that the speech perception system is heterogeneous in its attentional requirements. The bilateral anterior insulae response reflected the cognitive load of the attended task, but not the unattended task, whereas activity in the anterior superior temporal gyrus reflected the cognitive load of both tasks. Under distraction, we found dissociable responses for clear and intelligibility-matched degraded speech.