Poster #62 - From Ears to Eyes: Brainstem Encoding of Speech and Lexical Access

• In Event: Poster Session 17

Abstract

Background
For users of an oral language, successful communication depends in large part upon quickly and accurately encoding the spoken utterances of others. Previous research has used auditory brainstem responses (ABRs) to show positive relationship between robust neural encoding of speech and children’s phonological abilities (Bonacina et al, 2019; Lam et al., 2017). Two ABR dimensions, consistency, (similarity of responses to a repeated stimulus), and differentiation (degree to which responses to different stimuli differ) have been related to language performance but have not to date been examined in the same group of children. Furthermore, phonology in these studies has been measured via standardized tests, which may not provide a realistic picture of online use of phonology in speech processing. As speech unfolds in time, candidate words compete for recognition based on their phonological features; eye-tracking can be employed to record eye movements during a lexical access to examine this process (Allopenna et al., 1998). In this project, the relationship between two dimensions of brainstem encoding of speech and phonological competition during lexical access is examined.
Methods
Thirty-nine typically developing children aged 5 to 12 years (Mage 8.52(1.8) years) participated (20 assigned male at birth). ABRs were recorded to three speech stimuli: a 40-millisecond (ms) /da/, a 170 ms /ba/ and a 170 ms /ga/. Response consistency (similarity of responses to /da/) and response differentiation (degree to which responses to /ba/ and /ga/ differ) were calculated. Phonological competition was assessed using eye-tracking and the visual world paradigm. Sixteen trials were presented that included pictures of the target word (e.g., a button), a phonological cohort competitor (e.g., butter, a word starting with the same sounds), and two phonologically unrelated distractors (e.g., horse and car). To establish competition average looks to the competitor were calculated and compared to average looks to distractors.
Results
Response consistency (Mr-value =.64(.13)) and differentiation (Mradians =0.61(.67)), fell into typical ranges, but were not correlated, (r=-.239 p=.142). Time course plots for the lexical decision task showed that the children, overall, had a typical competition effect (more looks to competitors than unrelated objects) during the part of the trial when the acoustic input matches both the target and cohort competitor. The children were divided into subgroups based on their ABRs: high-consistency-high-differentiation; high-consistency-low-differentiation; low-consistency-high-differentiation; low-consistency-low-differentiation. When these subgroups were compared only the Low Consistency High Differentiation group did not show a competition effect.
Discussion
The strength of the neural difference between /ba/ and /ga/ was not related to the consistency of their responses to /da/, indicating these ABR dimensions may differentially index language. While overall children showed a typical phonological completion effect, more differentiated neural encoding, in the absence of consistent encoding, may reduce competition between phonological cohort members during lexical access. Potentially, the greater ability to differentiate between sounds may allow the children to pick up on small, coarticulation-based differences that typically go overlooked. This indicates within typically developing populations, the process of lexical access may not be uniform and the role of sensory level hearing deserves more investigation.

Authors

• Lee Tecoulesco, Boys Town National Research Hospital
  Presenting Author

• Erika Skoe, University of Connecticut

• Eiling Yee, University of Connecticut

• Letitia R Naigles, University of Connecticut