RETROACTIVE STIMULUS INTERFERENCE WITH CONDITIONED EMOTIONAL RESPONSE RETENTION IN INFANT AND ADULT-RATS - IMPLICATIONS FOR INFANTILE AMNESIA

In 7 experiments, 19-day-old and adult rats were given off-baseline tone-footshock pairings so that tone presentation during licking 48 hrs later produced equal suppression in both age levels. Controls showed the suppression to be due to associative factors. Despite equal suppression across ages at 48-hr testing, pups displayed significantly poorer retention (infantile amnesia) when compared with adults 8, 16, 32, or 64 days after conditioning. Performance deficits on 48-hr tests could be induced in pups but not adults if nonreinforced off-baseline presentations of the conditional tone were interposed in the retention interval. This off-baseline extinction procedure also reduced suppression by pups when the nonreinforced tone presentations differed in acoustic frequency from the CS. With the same frequencies, excitatory generalization tests disclosed significant and similar generalization gradients in both pups and adults, suggesting that the greater memorial interference observed in pups stemmed more from their heightened susceptibility to off-baseline extinction than from differences between age levels in generalization. Collectively, findings suggest that extinction-like processes could contribute to ontogenetic retention deficits usually classified as infantile amnesia. (49 ref) (PsycINFO Database Record (c) 2006 APA, all rights reserved). © 1979 American Psychological Association.