Quantitative reanalysis of lesion effects on rate of forgetting in macaques.

In Ringo's reanalysis (Behav. Brain Res., 42 (1991) 123-124), differences between d' discriminability measures of memory performance by macaque monkeys in normal and lesioned groups did not change systematically with retention-interval duration. There was therefore no evidence of an effect of brain lesion on rate of forgetting. Our quantitative analysis in which power and negative exponential functions were fitted to the d' measures yielded a different conclusion. The rate parameter of the best-fitting functions provided a measure of rate of forgetting. Parameter values for rate of forgetting were significantly greater for lesioned groups than for normal groups, whereas the parameter describing performance in the absence of a delay did not differ between normal and lesion conditions.