Profound retroactive interference in anterograde amnesia: What interferes?

Anterograde amnesia is characterized by a profound inability to retain new information. Recent research suggests that at least some of this severe memory impairment may be the product of retroactive interference. What exactly interferes with memory in amnesic patients, however, remains unknown. The aim of the present study was to examine whether or not postlearning material which is highly dissimilar from the material to be remembered would interfere with amnesic patients' memory.

Prose retention was tested in 10 densely amnesic patients and 10 controls following a 10 minute delay period, which was either unfilled (minimal interference) or filled with a tone detection task in which participants were required to listen for piano notes (nonspecific interference).

A significant nonspecific retroactive interference effect was observed in the amnesic patients (p < 0.004): Whereas 7 out of the 10 amnesic patients were able to recall some prose material following the unfilled delay period, only 1 of them was able to recall any material after the tone detection delay.

The data reveal that some amnesic patients have the capacity to retain new material for much longer than usual but that apparently any new postlearning information profoundly interferes with such retention. This nonspecific retroactive interference effect deviates from the item-specific interference effect that is typically assessed in clinical practice and which is frequently observed in patients with executive impairment. We hypothesize that these interference effects are qualitatively different, occurring during distinct memory processes, namely retrieval (item-specific interference) and consolidation (nonspecific interference).