The investigators will recruit 60 adults with typical language (TD) and 40 LI participants through a variety of community and university related contacts. 40 TD adults and 20 LI participants will be enrolled in Experiment 1. 20 TD adults and 20 LI participants will be enrolled in Experiment 2.
Both experiments will take place over 3 Sessions.
During Session 1, the investigators will administer various measures in order to validate study eligibility, classify participants into groups, and other measures in order to further characterize our samples. To that end, participants will be administered a pure tone audiometric screening, and complete an interview questionnaire asking for background information such as handedness, language background, language and reading development, and development of motor skills. Trained research personnel will then administer an approximately 2-hour testing battery that includes measures of nonverbal cognition, language ability, reading ability, attention, executive function, and phonological processing. Participants will also complete questionnaires to assess their habitual sleep quality, sleepiness, and individual chronotpyes.
All testing will be completed by a student clinician, and will be supervised by a certified speech-language pathologist. 100% of administrations will be re-scored by a trained student for accuracy. To account for attrition and non-qualifiers, we anticipate enrolling/screening up to 200 individuals in Session 1 in order to arrive at the enrollment targets for Experiments 1 and 2.
In both experiments, Sessions 2 and 3 takes place on two consecutive days. Session 2 will take place in the late evening, and Session 3 will take place in the morning. We have intentionally chosen not to employ a wake-state (AM-PM) control. This is done in order to limit the potential variability in the amount of English exposure between sessions. Between-session sleep duration will be monitored with an Actigraph wGT3X-BT accelerometer (Actigraph, corp) worn on the non-dominant wrist. Actigraphs will be set to collect data in 60-second epochs via a validated algorithm (Cain \& Geremia,2011). This method of recording sleep/wake activity has been independently validated to agree with lab polysomnography at 85% accuracy (Slater et al.,2015).
Experiment 1: behavioral measures During Session 2, participants will complete the three learning tasks, declarative learning, procedural learning, nonnative speech learning (in that order), and immediate post-learning assessments. During Session 3, participants will be re-assessed in nonnative speech learning, declarative learning, and procedural learning (in that order).
* Declarative memory will be assessed using an object recognition task following incidental encoding.
* A version of the Serial Reaction Time task will be used to measure procedural learning.
* Perceptual learning of speech will be measured through performance on identification and discrimination tasks on the dental and retroflex contrast.
Experiment 2: neuroimaging measures During Session 2, participants will complete the nonnative contrast training in the late evening. Then they will enter a magnetic resonance imagine (MRI) scanner, where their blood oxygen-level dependent signals will be recorded while they complete the post-training identification and discrimination assessments. The participants will complete the same in-scanner assessments of the perception of the nonnative contrast during Session 3.
