Examining links between sound processing

Examining links between sound processing in auditory midbrain and beat synchronization could inform our knowledge of the biology responsible for transformation of perceived periodicity in auditory stimuli to motor output. Tierney and Kraus (2013a,b) have established a systematic relationship between intertrial stability of subcortical speech encoding and the consistency of beat synchronization in adolescents, proposing auditory system stability as a biological mechanism common to speech processing and beat-keeping. In young children, the ability to synchronize to a beat relates to precision of subcortical speech-envelope tracking, as well as pre-literacy skills thought to predict future reading skills such as phonological awareness and auditory short-term memory (Woodruff Carr et al., 2014). Here, we expand upon previous work (Woodruff Carr et al., 2014) to explore the neurophysiology underlying individual differences in preschoolers who are able to synchronize motor movements to isochronous beats at prosodic stress rates. We predicted more consistent auditory-motor timing, as revealed through beat synchronization, would relate to higher levels of intertrial neural stability for processing speech syllables. Furthermore, our previous work identifying links between beat synchronization and neural envelope tracking precision led us to hypothesize that stability of low-frequency encoding in particular would relate to beat synchronization, because the envelope measure is filtered to capture low-frequency modulations. Our findings suggest that stability of auditory neural encoding may be an important foundation for sensorimotor no precursors in preschoolers. Furthermore, beat synchronization may serve as a useful behavioral tool for assessing developmental auditory neural function in young children.
Methods
Results
Discussion These results suggest that successful beat synchronization in young children relies in part on stable temporal encoding in the auditory system. Less variability when encoding sound may allow for more regularly-timed motor reactions. We propose trial-by-trial neural stability supports the developmental process of coordinating auditory-motor beat synchronization in young children. The present findings are in line with previous studies linking the ability to tap consistently to a beat and stability of subcortical sound processing (Tierney and Kraus, 2013a,b), and provide a unique developmental perspective for a neural timing metric that underlies literacy skills (Hornickel and Kraus, 2013; Tierney and Kraus, 2013a,b). This mechanism appears to be in place at an early age, during the development of many important language skills, and prior to explicit reading instruction. During beat synchronization, perception and production systems must interact synchronously for optimal performance: the brain extracts and estimates stimulus periodicity as well as assesses discrepancies between the stimulus and one\'s own motor output (Rauschecker, 2011). The subcortical nervous system works to detect sub-second differences in intervals (basal ganglia) and integrate this performance feedback across modalities (through connections from the dorsal cochlear nucleus to the cerebellum) to make subtle timing adjustments (Merchant et al., 2008), resulting in error-correction of asynchronies that does not always necessitate conscious effort (Ito, 2008; Repp, 2000; Schwartze and Kotz, 2013). Although the influence of motor variability during beat synchronization cannot be ruled out, we believe this is not a main factor influencing our results. Other work with children this age reports no correlation between motor variability in spontaneous tapping and synchronization tasks (Drake et al., 2000), suggesting that variability in synchronization performance in young children is primarily driven by factors other than motor variability. We suggest our neural stability measure captures auditory-motor integration, and future work is needed to parse the influence of these separate, but connected, systems.