Implicit Learning Impairments in Individuals with Autism and First Degree Relatives

Background: The neurobiology of autism spectrum disorders (ASD) likely affects learning and perception of information from the environment such that development is pervasively delayed.  Implicit learning (IL) is a complex cognitive process that occurs primarily without conscious effort.  Such a process may be crucial for typical development of communication and socialization skills, and impairments in these skills are core deficits associated with ASD.  Thus, impairments in the implicit system may be associated with the onset of this complex developmental disorder.  If individuals with autism demonstrate IL impairments and their first degree relatives demonstrate similar impairments, then IL performance may serve as an endophenotype to facilitate genetic studies.  Previous investigations of implicit processes in individuals with ASD have demonstrated conflicting results, thus it is unclear whether the underlying implicit processes are disturbed or if specific tasks or stimuli affect learning processes.  Implicit functioning needs to be further investigated in individuals with ASD and their family members. Objectives:   To examine the stimulus-related performance differences of individuals with autism and their first degree relatives on two IL tasks. Methods: In the sequence reaction time task (SRT) stimuli are presented in a sequence.  Subjects learn the sequence largely without conscious effort and their reaction time decreases.  When the sequence is replaced with random presentation of stimuli, RT increases, and when the sequence returns RT decreases again. Two tasks were designed for the present study.  One presented a sequence with facial expressions of emotions, and the other presented the sequence with images of furniture.  Both tasks presented ten stimuli in a complex sequence, ten times per block for five learning blocks.  The sixth block was random presentation. In the seventh block, the sequence was restored but it was presented with different images of the same context (emotions or furniture).  Individuals with autism and aged matched controls were tested on both tasks.  Parents, other first degree relatives, and age matched controls were also tested on both tasks. Results: There were no significant between group performance differences in the learning and random phase of each SRT task.  In the seventh block on the facial expression task the RT for the autism group increased from the RT for block 6.  In the seventh block of the furniture task, the RT for both the autism group and the first degree relative group increased from the RT for block 6. Conclusions: These results suggest autism-related familial IL impairments associated with the transfer of complex information that is implicitly learned.  Both the autism group and the relative group had slower RT to the sequence when presented with novel stimuli.  Their knowledge of the sequence implicitly acquired during the learning phase of the experiment was not applied when the same sequence was presented with novel stimuli.  The autism group demonstrated this impairment in both tasks while the relatives demonstrated this impairment only in the furniture task.  Both groups may share a similar underlying impairment, but the relatives may be able to overcome this impairment with expertise for specific stimuli (i.e. facial expressions).