Implicit learning in infants with a familial risk of dyslexia: the effects of age and length of training

Abstract

The current study is a follow-up study on the work of Kerkhoff, De Bree, De Klerk & Wijnen (2011; in press) in which the hypothesis was tested that developmental dyslexia is (partly) caused by a deficit in implicit sequential learning. With the help of a head-turn-experiment it was investigated whether 18-month-old infants at familial risk of dyslexia can track non-adjacent dependencies in an artificial language. A deficit in implicit learning can hinder the processing of such dependencies. For this experiment an artificial language is used to test the tracking of these NAD’s, in the form of a-X-c, b-X-d or a-X-d, b-X-c, with fixed first and third elements and 24 different X elements. Family risk (FR) and typically developing (TD) infants were exposed to one of two novel languages containing these dependencies. The results revealed that only the typically developing infants could discriminate between grammatical and ungrammatical sentences. This was in contrast with the results of the family risk infants, who showed no discrimination between the grammars. To test whether the FR group’s poor performance was due to a developmental delay, the current study exposed a group of 24-month-old FR-infants to the same task (Experiment 1). To investigate whether these children might benefit from an increased exposure to the artificial language, a pilot study also examined whether 18-month-old TD and FR infants are able to discriminate between the grammars after a prolonged familiarization phase (Experiment 2). The results show no evidence that the 24 month-old FR group is sensitive to NAD’s. This could be evidence for a delay in implicit sequence learning of at least six months. Furthermore, the TD infants in the pilot experiment showed a trend towards an unexpected change from a novelty preference to a familiarity preference.