Differential effect of right and left hemispheric lesions on two memory tasks: free recall and frequency judgement

We investigated the relationship between lateralized cerebral damage and two memory tasks; free recall and frequency judgement. Free recall is considered to be processed effortfully while frequency judgement is considered to be processed automatically (Hasher and Zacks). Nine right brain-damaged patients (RBD), nine left brain-damaged patients (LBD) and nine control subjects participated in this study. It was hypothesized that RBD would show an advantage over LBD on the free-recall task, whereas LBD would show an advantage over RBD on the frequency-judgement task. In accordance with our hypothesis, free-recall was more impaired in LBD than in RBD. In the frequency-judgement task, an effect of laterality of lesion was found in high (4-6) and low (0-1) frequencies, but not in the medium (2-3) frequencies. The anticipated LBD advantage was shown in judgement of the high frequencies, but unexpectedly RBD performed better than LBD in low frequencies. The results are discussed in terms of the relationship between effortful and automatic memory processes and cerebral lateralization.