Discovery of simple binary sequences in brain damaged patients

A test of 'Temporal Rules Induction' was administered to 59 normal controls, 113 right and 162 left brain damaged patients. The patients were shown two tokens of different color (red/R/ and blue/B/ respectively) following three established sequences: simple alternation (R-B, R-B,...); double alternation (RR-BB, RR-BB,...) and asymmetric alternation (RBB, RBB,...). Patients were informed that presentation of the tokens followed a rule, so that if they concentrated on the temporal order in which the stimuli were presented, they could get the correct sequence. Since it has been reported that subjects with left hemisphere damage are impaired in tasks requiring careful analysis of temporally ordered information, the expectation was that left brain damaged patients would fare worse than patients with lesions in the right hemisphere. The hypothesis was not confirmed by the authors' results. No difference was found between LH and RH patients, and between LH patients with aphasia and RH patients. No relationship was also found between severity of aphasia and scores on the Temporal Rules Induction test, but within the aphasic group the worst scores were obtained by patients with semantic-lexical impairment (despite the absence of any obvious link between sequencing processes and operations of lexical choice). The results are at variance with the hypothesis that temporal sequencing ability 'per se' may be a basic endowment of the left hemisphere, more fundamental than (actually accounting for) the left hemisphere dominance for language.