Yesterday I outlined a few reasons to think that we may not actually forget all of our earliest memories; instead, they may merely be mislabeled due to a failure of source monitoring. According to a 2002 article by Drummey and Newcombe, a similar problem may underlie childhood amnesia – the fragmentary nature of autobiographical memory prior to age 6.
Failures of source monitoring are more frequent in patients with brain damage to the frontal cortex (and may be especially reliant on the right frontal lobe). Just like these frontal patients, preschool-aged children have a prefrontal cortex that is not yet fully functional, and so they show similar deficits in source monitoring. If childhood amnesia results from these deficits, source monitoring should markedly improve around age 6 – the same time that childhood amnesia seems to subside.
To investigate this possibility, Drummey & Newcombe brought over 160 4-year-olds, 6-year-olds and 8-year-olds into the lab. Each child learned 10 novel facts, five of which were described by the experimenter; the other five were described by a finger puppet manipulated by the experimenter. A week later, the same children were brought back and asked questions related to facts they had learned previously. For each fact that was correctly remembered, children were asked to specify how they learned that fact.
Therefore children could show complete source amnesia (e.g., “I learned it on the playground”) or partial source amnesia (e.g., “I learned it from the finger puppet” when in fact the experimenter had said it). In terms of both measures, 4-year-olds did significantly worse than 6-year-olds, who themselves did not differ from 8-year-olds. Based on these results, source monitoring shows exactly the developmental profile predicted for a capacity involving in childhood amnesia.
On the other hand, it’s possible that four year olds merely didn’t understand the task. But a subsequent experiment confirmed that 4-year-olds showed almost no source memory errors if “quizzed” immediately after learning the facts, which indicates their poor performance was not due to merely pragmatic issues. So these results seem genuinely due to a memory failure that increases with elapsed time.
The authors also found preliminary support for the idea that source monitoring depends on the prefrontal cortex. 4-year-olds were also given a modified version of the Wisconsin Card Sort – a task frequently used in the diagnosis of patients with damage to the prefrontal cortex. Roughly the top 50% of 4-year-olds in terms of source monitoring performance were more likely to show complete source amnesia if they did more poorly on the modified Wisconsin Card Sort. This trend remained even after controlling for differences in IQ – suggesting that source monitoring may share some similarities with the “executive functions” that such prefrontal tasks are thought to measure.
Drummey and Newcombe conclude that source monitoring may be at least partially responsible for childhood amnesia. This echoes similar claims about infantile amnesia: Rovee-Collier has suggested that we may actually remember some of our earliest experiences, but attribute the incorrect source to those memories.
Of course, there are some caveats to this finding: other abilities show similar developmental profiles but are not argued here to be involved in childhood amnesia (i.e., theory of mind); the card sorting task seemed too difficult for most 4-year-olds; and the performance metric used for the card sorting task was highly unusual. But this experiment also represents a significant advance over previous work: by adapting the “fictitious fact” paradigm for use with children, Drummey & Newcombe allowed for complete source amnesia (most studies use a “multiple-choice” type paradigm, in which complete source amnesia is not possible), which appears to be the most sensitive measure for this age group.
Future research is needed to identify whether source monitoring difficulty underlies performance on a variety of tasks in this age group. For example, this period of development also shows drastic increases in the ability to flexibly switch between rules, to answer questions about the mental states of others’, and to overcome habit in favor of novel but currently-appropriate responses. Variance in such tasks that is not explained by indices of active maintenance (probably related to left prefrontal function) may be well-explained by indices of source monitoring, following the functional roles of left & right prefrontal cortex described in selection/monitoring models..