Freud famously suggested that infantile amnesia is an active suppression of early traumatic memories. However, a review of the modern cognitive literature suggests that at least in some ways, infantile amnesia may actually be a myth.
Perhaps the most intuitive explanation of infantile amnesia is simply that the infant’s brain is not sufficiently developed to support episodic memory. However, substantial evidence argues against this view. For example, the same factors that affect episodic memory in adults also affect infant memory, including age, retention interval, context change, interference, study time, levels of processing, and serial position effects. These factors influence performance on a variety of infant memory tasks, including visual recognition memory, mobile conjugate reinforcement, and the Rovee-Collier train task (although see yesterday’s post for some caveats to this approach.)
Adult-like memories may be formed even in the womb. As reviewed by Hayne, 3-day-old infants were capable of distinguishing a particular passage (from Dr. Seuss’s “Cat in the Hat”) that had been read to them twice daily for the last 6 weeks of gestation from similar passages (matched for word count, length, and prosody). What’s more, these infants preferred the familiar passage even if spoken by someone other than their mother, strongly suggesting that they had encoded (and retained) a relatively high-level representation of the passage’s auditory content.
This and other evidence led Rovee-Collier to argue that both the explicit and implicit memory systems are functional very early in infancy. Therefore, it seems unlikely that infantile amnesia can be explained solely by the immaturity of cognitive memory systems.
But even if these memory systems are functional in a rudimentary sense, it’s still possible that infantile amnesia results from their immaturity. For example, these systems may be highly limited in retention interval. But here again, new evidence suggests that this too is insufficient for explaining infantile amnesia: simple nonverbal reminders of previous experiences seem sufficient for supporting long-term memory in infants. As noted by Hayne, 6-month-old infants can demonstrate memory for a given experience even more than a year later, if simply placed in the same location as the original experience. Similar results have been found with infants as young as 8 weeks of age.
Therefore, infantile amnesia also cannot be explained by an inability to remember over long delays. Infants are likely to encounter numerous reminders of this variety throughout infancy, just a few of which are demonstrably sufficient for supporting long-term memory.
Thus, infantile amnesia cannot be explained solely by neurological immaturity (since both systems appear to be intact) nor by inability to remember over long delays. Instead, this inaccessibility might result from the profound differences between the kinds of retrieval cues used by adults (i.e., verbal cues) and those that would likely be required to retrieve a memory from preverbal infant experience. The alternative “reinstantiation” theory suggests that while infant memories may exist, they cannot be successfully recalled due to the massive synaptic pruning that takes place throughout neocortex in early childhood. In either of these cases, the apparent lack of early-life memory is due to its inaccessibility, rather than an actual failure of retention.
A far more tantalizing conclusion is hinted at by Rovee-Collier, who suggests that “contextual information disappears from memories that have been reactivated once or twice.” Therefore, adult memory may actually contain some early life experiences, but they simply cannot be identified as such due to a lack of source memory.
In summary, there is some reason to believe that the phenomenon of infantile amnesia has been widely mischaracterized. Infants show surprisingly robust long-term memories, and both the explicit and implicit memory systems appear functional very early in life. Based on this evidence, it seems unlikely that retention failure underlies the apparent loss of all early-life experiences. Rather than being completely forgotten, our earliest experiences may actually be mislabeled.