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The Role of Contextual Information in Auditory Perception: Investigating N400 Effects Under Speech Degradation
Poster Session E, Sunday, September 14, 11:00 am - 12:30 pm, Field House
This poster is part of the Sandbox Series.
William Zumchak1, Carmen Tang1, Matthew Ganquan Shi1, Audrey Laun1, Arudhati Chakraborty2, Ellen Lau1; 1University of Maryland Department of Linguistics, 2University of Maryland Department of Philosophy
This study investigates how contextual information influences auditory perception when acoustic signals are degraded. In daily communication, listeners often encounter noisy environments that challenge speech comprehension. Using magnetoencephalography (MEG), we examine how the brain leverages top-down contextual information to compensate for degraded bottom-up acoustic input, focusing on the N400 component as an index of semantic integration difficulty. In Experiment 1, we establish a baseline for auditory perception in noisy environments using a repetition suppression paradigm. For one experiment trial, participants hear a prime word, and subsequently a target word, followed by an intelligibility rating question on the target. Two variables are manipulated on the target: priming (repeated vs. novel) and degradation (clear vs. degraded). The experiment includes 400 trials with 100 repeated targets and 300 novel distractors, balanced between degraded and undegraded conditions. The stimuli consist of 700 words extracted from the MRC Psycholinguistic Database (Coltheart, 1987), each with two syllables and moderate familiarity ratings. All primes are presented clearly, while targets vary in the degradation condition (clear vs 8-band vocoding). Participants rate target word intelligibility on a 1-4 scale (4 being most intelligible) during their MEG recordings. We hypothesize that auditory degradation will increase the number of words that potentially match the acoustic signal. This will render the number of options in the matching and non-matching conditions similar, resulting in similar N400 amplitudes between matching and non-matching words under degradation. In Experiment 2, we continue to examine the interaction between contextual information and auditory processing by introducing additional semantic content via wordlist primes. In a 2x2 design, we manipulate semantic relatedness (related vs. unrelated word lists) and speech quality (clear vs. degraded) in a priming paradigm. The experiment includes 200 trials in four conditions distributed within-subject. For each trial, participants hear a word list followed by a target word and a subsequent intelligibility question on the target. The wordlists have two context types: semantically related (e.g., "horse-dog-sheep" preceding "cat") or unrelated (e.g., "house-doctor-sun" preceding "cat"). Targets appear in either clear or degraded forms. We predict that (a) semantically related contexts will reduce N400 amplitudes, and (b) this facilitation effect is stronger in degraded speech processing, indicating greater reliance on contextual support when acoustic information is compromised. Building on previous findings by Aydelott et al. (2006) and Strauß et al. (2013), who demonstrated that semantic contexts with acoustic degradation affect the amplitude and latency of N400 responses of a target word, this project instead manipulates acoustic input while maintaining the clarity for contexts. This allows us to investigate the role contexts play in the processing of reduced bottom-up information. While Aydelott et al. and Strauß et al. recorded N400 using electroencephalogram (EEG), the MEG data will allow us to compare activation regions between experiments. Our research aims to contribute towards understanding the neural mechanisms of speech perception under adverse conditions and how the brain dynamically balances bottom-up acoustic information with top-down contextual knowledge during language comprehension.
Topic Areas: Speech Perception, Meaning: Lexical Semantics