Dissertations, Theses, and Capstone Projects

Date of Degree

5-2015

Document Type

Dissertation

Degree Name

Ph.D.

Program

Speech-Language-Hearing Sciences

Advisor

Valerie L. Shafer

Subject Categories

Psychology

Keywords

Adolescents; Attention; Development; MMN

Abstract

The ability to perceive speech sounds and contrasts continues to be refined throughout the course of development. While emerging models suggest that development is characterized by shifts from an attentionally demanding mode of processing speech sounds to one that occurs relatively automatically, the specific developmental time-course of these changes remains unclear. The present work reports the findings of two experiments that aimed to provide insights into the time-course by which neural processes underlying speech discrimination in children and adolescents becomes automatic. The experiments used event-related potentials (ERP) measures, with a particular focus on mismatch negativity (MMN) - a developmentally-sensitive index of automatic speech discrimination.

The first experiment focused on children ages 6.0-11.9 years old, comparing the MMN responses elicited by English vowel contrasts under differing attentional conditions in an oddball design, to those observed in adults. Specific attentional conditions included: 1) an auditory-attend condition during which listeners silently counted deviants, 2) an auditory-ignore condition in which listeners ignored auditory stimuli while they being required to solve mathematical equations, and 3) an auditory-ignore condition in which listeners ignored auditory stimuli while passively viewing a silent video. Speech perception was hypothesized to be more automatic in children than adults; accordingly, the MMN was predicted to be more sensitive to manipulations of attention in children than in the adults. Consistent with our predictions, attention-related modulation (i.e., auditory-attend vs. -ignore) of the MMN observed in frontal and central leads was greater in children than adults. Of note, despite obvious differences in the attentional demands of the two ignore conditions (passive, math), the modulation of the MMN produced by the two conditions differed minimally.

The second experiment focused on children ages 10.9-16.9 years old, again comparing their responses to adults. We hypothesized that the maturation of speech discrimination processes would still not be complete in this group and thus expected to find of continued attentional dependencies, in comparison to adults Given the relative lack of differences in modulation produced by the two ignore conditions under experiment 1, we refined our paradigm to include two ignore conditions that differ on a specific cognitive construct -- working memory demands. This was accomplished by having participants perform either a 0- or 2-back during the auditory-ignore conditions. Consistent with our prediction, we found greater attention-related modulation of the MMN in the left inferior and anterior pole regions for the child group relative to adults; analyses treating age as a continuous variable were supportive of such distinctions. We also found evidence of continued age-related difference in the late discriminatory negativity (LDN) and P3b.

Together, these two experiments highlight the value of expanding the scope of examination for speech discrimination to consider a broader range of ages than leading models, which tend to emphasize early life. Our findings of continued age-related changes in the MMN, P3b and LDN during adolescence highlight the need to consider the effects of both bottom-up and top-down attentional influences in developmental models of speech perception.

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