Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Doctor of Philosophy

Program

Psychology

Supervisor

Johnsrude, Ingrid

Abstract

Everyday listening often occurs in the presence of background noise. Listeners with normal hearing can often successfully segregate competing sounds from the signal of interest. To do this, listeners exploit a variety of cues to facilitate the separation of simultaneous sounds into separate sources, and group sequential sounds into intelligible speech streams. One of the cues that has been shown to be an effective facilitator of speech intelligibility is familiarity with a talker’s voice. A recent study by Johnsrude et al. (2013) measured speech intelligibility of a naturally familiar voice (i.e., that of a long-term spouse) and showed a large improvement in intelligibility when a spouse’s voice serves as the target or the masker. This improvement is commensurate with another cue that is well-understood to be a strong facilitator of intelligibility: spatially separating two speech streams. Therefore, the goal of this thesis is to extend the work of Johnsrude et al. (2013) by providing a clearer understanding of voice familiarity as a cue for improving intelligibility. Specifically, the aims of this thesis are 1) to measure the magnitude of intelligibility benefit of different types of naturally familiar voices: friends and spouses, (2) to quantify the familiar-voice benefit in terms of degrees of spatial separation, and (3) to compare the neural bases of voice familiarity and spatial release from masking to determine if these cues improve intelligibility by recruiting similar areas of the brain. The primary findings of this thesis were that 1) the familiar-voice benefit of friends and spouses are comparable to each other and that relationship duration does not affect the magnitude of the familiar-voice benefit, (2) that participants gain a similar benefit from a familiar target as when an unfamiliar voice is separated from two symmetrical maskers by approximately 15° azimuth, and (3) that familiar voices and spatial release from masking both activate known temporal voice areas, but attending to an unfamiliar target voice when masked by a familiar voice also recruits attention areas. Taken together, this thesis illustrates the effectiveness of a naturally familiar target voice in improving intelligibility.

Summary for Lay Audience

Communication typically occurs in noisy environments, where there are competing background sounds such as music, other conversations, and traffic noises. For individuals with normal hearing, it is relatively easy to ignore these background sounds and focus on one person or conversation. However, the processes that make this possible are complex and not completely understood. In this thesis, I aim to gain a deeper understanding of how people understand speech when a competing voice is speaking. Specifically, I want to understand why it is easier to comprehend speech of familiar people compared to speech of strangers. I compared how much intelligibility improved from listening to the voice of a spouse or a friend and found that intelligibility improved by a comparable amount. This means that once a person gains familiarity with a voice, the benefits to intelligibility remain constant over time and does not change depending on the type of relationship. Next, I equated the improvement to intelligibility from a familiar voice in terms of spatial separation and found that the familiar-voice benefit is equal to that of a large spatial separation. This means that familiar voices are highly effective at improving intelligibility. Lastly, I compared the neural mechanisms between speech intelligibility facilitated by voice familiarity and spatial separation and found that brain areas responsible for processing both cues at least partially overlap. Overall, the findings of this thesis highlight the effectiveness of voice familiarity in improving intelligibility and provide preliminary evidence of brain areas responsible for processing intelligibility cues.

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