Does amnesia after transection of the fornix in monkeys reflect abnormal sensitivity to proactive interference?

Monkeys in whom the fornix had been transected and controls were tested in two versions of delayed non-matching to sample (DNMS). On DNMS-LSS both of the stimuli for each trial were selected from a large set of junk objects that were already familiar to the subjects. On DNMS-CSN the new stimulus at the retention test of each trial was one which the animals had never encountered before. Memory for the sample was assessed with retention intervals of 10, 70 and 130 s. In DNMS-LSS the lesioned animals were impaired, being more susceptible than controls to increases in the retention interval. However, no impairment in DNMS-CSN was observed. The abnormally fast forgetting by lesioned animals in DNMS-LSS seems therefore to reflect abnormal sensitivity to proactive interference. The results are compared with similar findings from amnesic humans and their implications for theoretical accounts of the effects of hippocampal disruption are discussed.