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 Wernick's aphasia and age-matched controls. In Experiment 1, participants performed a standard serial reaction task (SRT) in which they manually responded to a repeating sequence of stimulus locations. Both Broca's and Wernick's aphasics showed intact sequence learning, as indicated by a reliable response time (RT) cost when the repeating sequence was swithched 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 visually, followed by a single auditorily presented letter. Participants had to press one of four response keys to indicate the location of the auditory letter in the visual display. The arrangement of the visual letters was changed 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. This dissociation between learning of spatio-motor and phoneme sequences supports the assumption that partially separable brain systems are involved in proceedural learning of differenct types of sequential structures.