Implicit learning deficits among adults with developmental dyslexia

The aim of the present study was to investigate implicit learning processes among
adults with developmental dyslexia (DD) using a visual linguistic artificial grammar learning
(AGL) task. Specifically, it was designed to explore whether the intact learning reported in
previous studies would also occur under conditions including minimal training and instructions
that do not reveal the grammatical nature of the strings. Twenty-nine (14 DD and 15
typical development (TD)) adults were presented with letter sequences in the training phase
and were asked to classify the test strings for their grammaticality. The results of the d′
measures in the implicit task indicated that learning had occurred for both groups, as the
proportion of hits exceeded the proportion of false alarms. However, a significant difference
was found between the groups in their learning measures, as TD readers performed significantly
better than individuals with DD, supporting the assumption of a deficit in implicit
sequential learning processes among individuals with DD. In order to examine whether the
deficit found in the first experiment was indeed due to a deficit in implicit processes, a second
experiment was designed in which explicit instructions were given during an AGL task.
Results of the explicit task strengthen the assumption that the deficit is indeed specific to
implicit sequential processes, as no difference between the groups was found when participants
were aware of the existence of the grammar underlying the strings. Theoretical and clinical
implications are discussed.