Distributional learning beyond perceptual reorganization: enhanced discrimination in children and adults after bimodal training

Infants and adults use statistical information from the speech input to form phonetic categories. This ability has been shown by numerous experiments presenting the participants with either a bimodal or a unimodal distribution of sounds from an acoustic continuum. However, this ability seems to decrease across the first year of life in parallel with infants’ establishment of the native language phonetic categories. So far, it is unclear whether this decrease continues beyond infancy, as studies comparing children’s and adults’ capacities are rare. The present study intended to fill this gap. In three studies, German-learning 12-month-olds were tested using a bimodal distribution, and 4-year-olds and adults were trained with either a bimodal or unimodal distribution of a sound continuum for the non-native Hindi dental-retroflex contrast. Infants were tested using an Alternating/Non-Alternating looking time paradigm, and children and adults were tested in an online AX paradigm. Results revealed an enhancement of the ability to discriminate the contrast only after bimodal training in 4-year-old children and adults but not in 12-month-old infants. Our findings extend previous research by testing infants at 12 months of age, revealing that the effectiveness of unattended distributional learning is reduced by this age. Results from children and adults showed that both age groups were able to discriminate the contrast after exposure to a bimodal distribution and thus the ability for distributional learning is maintained beyond infancy.