Auditory sequence learning with degraded input: children with cochlear implants ('nature effect') compared to children from low and high socio-economic backgrounds ('nurture effect').

Implicit sequence learning (SL) is crucial for language acquisition and has been studied in children with organic language deficits (e.g., specific language impairment). However, language delays are also seen in children with non-organic deficits, such as those with hearing loss or from low socioeconomic status (SES). While some children with cochlear implants (CI) develop strong language skills, variability in performance suggests that degraded auditory input (nature) may affect SL. Low SES children typically experience language delays due to environmental deprivation (nurture). The purpose of this study was to investigate nature versus nurture effects on auditory SL. A total of 100 participants were divided into normal hearing (NH) children, young adults, CI children from high-moderate SES, and NH children from low SES who were tested with two Serial Reaction Time (SRT) tasks with speech and environmental sounds, and with cognitive tests. Results showed SL for speech and nonspeech stimuli for all participants, suggesting that SL is resilient to degradation of auditory and language input and that SL is not specific to speech. Absolute reaction time (RT) (reflecting a combination of complex processes including SL) was found to be a sensitive measure for differentiating between groups and between types of stimuli. Specifically, normal hearing groups showed longer RT for speech compared to environmental stimuli, a prolongation that was not evident for the CI group, suggesting similar perceptual strategies applying for both sound types; and RT of Low SES children was the longest for speech stimuli compared to other groups of children, evidence of the negative impact of language deprivation on speech processing. Age was the largest contributing factor to the results (~ 50%) followed by cognitive abilities (~ 10%). Implications for intervention include speech-processing targeted programs, provided early in the critical periods of development for low SES children.