Why are amnesic judgements of recency and frequency made in a qualitatively different way from those of normal people?

The Huppert and Piercy (1978) test of recency and frequency judgements was given to a group of 12 non-Korsakoff amnesics of mixed aetiology and to four non-amnesic patients with selective frontal lobe lesions. The results confirmed that non-Korsakoff amnesics show a significant tendency to base their recency and frequency judgements on memory strength and that amnesics with medial temporal lobe damage show this tendency at least with recency judgements. The patients with frontal lobe lesions performed like normal subjects. Patients who were dysexecutive or impaired in cognitive resources were less likely to base recency judgements on trace strength. Such a recency bias was not however, correlated with measures of amnesic severity. The tendency to base frequency judgements on memory strength was not related to either degree of amnesia or reduction of cognitive resources.