Dyslexics are impaired on implicit higher-order sequence learning, but not on implicit spatial context learning.

Developmental dyslexia is characterized by poor reading ability and impairments on a range of tasks including phonological processing and processing of sensory information. Some recent studies have found deficits in implicit sequence learning using the serial reaction time task, but others have not. Other skills, such as global visuo-spatial processing may even be enhanced in dyslexics, although deficits have also been noted. The present study compared dyslexic and non-dyslexic college students on two implicit learning tasks, an alternating serial response time task in which sequential dependencies exist across non-adjacent elements and a spatial context learning task in which the global configuration of a display cues the location of a search target. Previous evidence indicates that these implicit learning tasks are based on different underlying brain systems, fronto-striatal-cerebellar circuits for sequence learning and medial temporal lobe for spatial context learning. Results revealed a double dissociation: dyslexics showed impaired sequence learning, but superior spatial context learning. Consistent with this group difference, there was a significant positive correlation between reading ability (single real and non-word reading) and sequence learning, but a significant negative correlation between these measures and spatial context learning. Tests of explicit knowledge confirmed that learning was implicit for both groups on both tasks. These findings indicate that dyslexic college students are impaired on some kinds of implicit learning, but not on others. The specific nature of their learning deficit is consistent with reports of physiological and anatomical differences for individuals with dyslexia in frontal and cerebellar structures.

Intermanual transfer of procedural learning after extended practice of probabilistic sequences.

Previous studies using simple, repeating patterns have suggested that the knowledge gained in early sequence learning is not effector-specific in that it transfers to muscle groups other than those used during training. The current experiments extended these findings to transfer after extensive practice with probabilistic sequences using a task on which people fail to gain declarative knowledge of the regularity. Specifically, an alternating serial reaction time (ASRT) task was used in which predictable and unpredictable trials alternated. Participants responded for the first five sessions using their right hand, then switched to the left hand for the sixth session. Stimuli were spatial in the first experiment and nonspatial in the second. Significant near-perfect transfer of pattern knowledge was seen in both experiments, suggesting that muscle-specific information for either the fingers or the eyes cannot explain the observed learning.