Procedural learning in Broca's aphasia: Dissociation between the implicit acquisition of spatio-motor and phoneme sequences

Procedural learning of spatio-motor and phoneme sequences was investigated in patients with Broca's and Wernicke's aphasia and age-matched controls. I n Experiment 1, participants performed a standard serial reaction task (SRT ) in which they manually responded to a repeating sequence of stimulus loca tions. Both Broca's and Wernicke's aphasics showed intact sequence learning , as indicated by a reliable response time (RT) cost when the repeating seq uence was switched to a random sequence. In Experiment 2, Broca's aphasics and controls performed a new serial search task (SST), which allowed us to investigate the learning of a spatio-motor sequence and a phoneme sequence independently from each other. On each trial, four letters were presented v isually, followed by a single auditorily presented letter. Participants had to press one of four response keys to indicate the location of the auditor y letter in the visual display. The arrangement of the visual letters was c hanged from trial to trial such that either the key-presses or the auditory letters followed a repeating pattern, while the other sequence was random. While controls learned both the key-press and the phoneme sequences, Broca 's aphasics were selectively impaired in learning the phoneme sequence. Thi s dissociation between learning of spatio-motor and phoneme sequences suppo rts the assumption that partially separable brain systems are involved in p rocedural learning of different types of sequential structures.