Browsing by Subject "Perceptual learning"
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Item Tracing the trajectory of training-induced sensory plasticity across different stages of speech learning expertise(2018-04-27) Reetzke, Rachel Denise; Chandrasekaran, Bharath; Henry, Maya L.; Hamilton, J Liberty; Church-Lang, Jessica A.Language-specific perception of speech sounds is shaped early in life (Kuhl, 2004; Werker & Hensch, 2015); however, with training, adults can learn to perceive non-native speech sounds (Logan, Lively, & Pisoni, 1991; Wong & Perrachione, 2007). While training has been found to alter the sensory encoding of newly learned speech sound patterns (Chandrasekaran, Kraus, & Wong, 2012; Song, Skoe, Wong, & Kraus, 2008), the behavioral-relevance, time-course, and long-term retention of such sensory plasticity is unclear. Some theories argue that sensory plasticity underlying signal enhancement of trained stimuli is a critical and immediate precursor for perceptual learning (Gold, Bennett, & Sekuler, 1999; Jurjut, Georgieva, Busse, & Katzner, 2017). Other theories, like the reverse hierarchy theory, suggest a slower time-course for the emergence of training-induced sensory plasticity (Ahissar, Nahum, Nelken, & Hochstein, 2009), indicating that changes in low-level sensory encoding are an enduring outcome, rather than a driving force, of perceptual learning. In this dissertation, I examine training-induced sensory plasticity utilizing the frequency-following response (FFR), a sound-evoked potential which reflects synchronous neural activity predominantly from subcortical neural ensembles (Bidelman, 2015; Skoe & Kraus, 2010). The FFR is well-suited to examine sensory plasticity related to non-native speech learning, as it mirrors the acoustic characteristics of the incoming speech signal with high fidelity (Skoe & Kraus, 2010). Utilizing the FFR, the results of this dissertation show that language-specific sensory encoding of speech sound patterns is highly stable across multiple days of testing. Mere exposure to non-native speech sound patterns does not elicit plasticity, rather behavioral-relevance of non-native speech categories is critical for sensory plasticity to occur. Findings further demonstrate different time-courses of perceptual and sensory plasticity, with robust sensory plasticity emerging only after stable non-native categorical perception is achieved. Both perceptual changes and sensory encoding gains are retained 8-weeks post-training. Altogether these findings suggest that sensory enhancement of incoming stimulus features is not critical for early stages of speech perceptual learning. Rather, in line with the reverse hierarchy theory, enhanced sensory encoding of non-native speech sound patterns may be an enduring outcome of perceptual mastery, facilitating the maintenance of the learned behavior.