Perceptual Learning and Memory Consolidation in Adults With and Without Language Impairment

This study tests a memory-based account of atypical speech perception in adults with language-based learning disability (also known as developmental language impairment [LI]). One perspective regarding the its etiology considers impoverished speech sound representations to be central to the linguistic symptoms observed in LI. This project examines a potential abnormality in the process of building speech sound representations in LI.

Previous work by the PI has found that sleep is important for learning speech sounds. Furthermore, different measures of speech perception (identification and discrimination), reveal distinct patterns of learning that are consistent with that of declarative and procedural memory consolidation. A division of labor by declarative and procedural memory systems in the building of speech representations may imply that problems with phonology may stem from selective weaknesses in declarative or procedural memory in predictive ways.

The first project Aim is to identify the memory substrates of novel phonetic category formation. In Experiment 1, the investigators will obtain behavioral measures of declarative, procedural, and speech sound learning before and after post-training sleep in 40 typical adults and 20 adults with LI. Among typical adults, a double dissociation is predicted in which speech identification will be predicted by individual differences in declarative memory, and speech discrimination will be predicted by individual differences in procedural memory. Moreover, adults with LI are predicted to demonstrate consolidation deficits across memory types.

The second project Aim is to identify the neural substrates of phonetic category formation. In Experiment 2, the investigators will obtain functional magnetic resonance (fMRI) recordings of 20 TD and 20 LI adults performing post-training identification and discrimination tasks on a trained speech contrast before and after sleep. In typical adults, a Time by Speech-task interaction is predicted. Speech identification will recruit episodic (hippocampal) information on Day 1 relative to classic regions for phonological processing on Day 2. Speech discrimination will result in a change in magnitude of activation from Days 1 and 2 in the left inferior frontal gyrus (IFG), reflecting an overnight decrease in effort. LI (n=20) is predicted to demonstrate reduced overnight change in neural activation relative to TD in both tasks.