Childhood amnesia

Childhood amnesia is the common inability of adults to remember the earliest years of their childhood.

Characterization and background
Infantile, or childhood amnesia is characterized by the relative absence of memory before 3 or 4 years of age. It is important to note that the term does not refer to complete absence of memories, but the relative scarcity of memories during infancy — a scarcity that cannot be accounted for by a forgetting curve. Additionally, the boundary is malleable and can be influenced by both individual experiences (Usher & Neisser, 1993) and cultural factors (Wang, 2001).

Research has demonstrated that children are adept learners and are quick to acquire and retain information. Children do remember events; however, these memories accessible as children are lost to infantile amnesia in adulthood (Bauer, 2004; Fivush, et al., 1987).

Evidence
Much research has been and continues to be conducted about childhood amnesia, adding to the wealth of evidence that is available about this phenomenon. It is worth noting, however, that memories of subjects are often unreliable but are nevertheless an important part of research in this area. Thus, researchers often use for their studies memories like the birth of a sibling that can be easily verifiable (Usher, et al., 1993).

Early observations
Childhood amnesia, despite being the universal human experience that it is, was only first formally studied in 1893 by the psychologist Caroline Miles (Miles, 1893; Bauer, 2004). In 1904 G. Stanley Hall noted the phenomenon in his book Adolescence (Hall, 1904). But it was Sigmund Freud who offered one of the first, most famous, and most controversial descriptions/explanations of childhood amnesia when he tied the phenomenon in with his other psychological theories (Freud, 1916; Bauer, 2004).

Modern observations
Much research in this area today aims to identify new characteristics and possible explanations for the phenomenon. For example, one recent study compared childhood and adult memories and found surprisingly few substantive differences, despite expected differences in the emotional vs factual and episodic vs non-episodic content of the memories (West, et al., 1999). Another example is Eacott & Crawley’s study which found support for childhood amnesia in the very few memories their subjects recalled from before the age of 2 ½. They found that participants’ memories of this time were also characterized by consistent false memories. But when asked about an event they could not possibly have a memory of, the subjects showed they had no problem with telling apart knowledge of an event and a memory of the event, suggesting something peculiar about the false memories observed in childhood amnesia (Eacott, et al., 1998).

Proposed explanations
Since Miles first officially documented childhood amnesia as a psychological phenomenon, many theories of its causes and character have been developed. Some of the most notable are described here to aid in understanding what childhood amnesia may be. It is worth noting that many of these theories are highly controversial and the true nature of childhood amnesia is still being debated.

Freud’s trauma explanation
Sigmund Freud’s theories of psychosexual development are highly intertwined with childhood experiences, and Freud’s explanation of childhood amnesia is one of the most controversial. In what is now published as The Standard Edition of the Complete Psychological Works of Sigmund Freud, Freud theorized that childhood amnesia is the result of the mind’s attempt to repress memories of traumatic events that, according to Freud, necessarily occur in the psychosexual development of every child. This would lead to the repression of the majority of the first years of life (Gleitman, et al., 2004). Some evidence has been found that could support the repression theory. In one study, high school and college students were asked to recall the nature of their earliest memory. In the first phase, high school students were found to have much later earliest retrievable memories, many of which featured traumatic events. In a retest several months later, 42% of the high school students reported a different earliest memory, and many of these new memories were markedly less traumatic than the ones they had recalled the first time (Kihlstrom, et al., 1982). At the same time, Freudian theory, including his explanation for childhood amnesia, has been severely criticized. One criticism is actually about the evidence, often anecdotal rather than purely scientific, and said to frequently permit multiple interpretations (Gleitman, et al., 2004). Criticism specifically of the Kihlstrom experiment includes the observation that no part of the study actually involved children, but rather adolescents and young adults (Bauer, 2004).

Physical development explanation
Another often-cited explanation of childhood amnesia is that the infant’s mind is not mentally mature enough to create long-lasting autobiographical memories. In particular, it is not until the age 3 or 4 that toddlers have a mature hippocampus and prefrontal cortex. These regions of the brain are known to be associated with the formation of autobiographical memories of the type notably missing from adult recollection of early childhood (Gleitman, 2004; Newcombe, et al., 2000).

Language explanation
The incomplete development of language in young children may be a cause of childhood amnesia in that infants do not have the language capacity to encode autobiographical memories in a manner that their language-based adult selves can interpret correctly. Indeed, the typical schedule of language development seems to support this theory. Babies of one year old tend to be limited to one word utterances, and childhood amnesia predicts that adults have very few, if any, memories of this time. By the age of three, however, children are capable of two or three word phrases, and by age five their speech already resembles adult speech. This language development seems to very much correspond to childhood amnesia because it is around the age of three to four that is the time of most adults’ earliest recallable memory (Gleitman, et al., 2004).

Emotion explanation
One explanation notes the connections between the emotion or amygdala-governed memory pathway and the autobiographical or hippocampus-governed pathway. While these two memory systems do have much independence, it is also known that emotions and the amygdala play a role in the encoding of memories typically associated with the hippocampus (Phelps, 2004). Knowing this, it has been suggested that the differences between the emotions experienced by infants and adults may be a cause of childhood amnesia (West, et al., 1999). One problem with this explanation, however, is that one of the most widely proclaimed examples of emotion influencing memory, the “flashbulb memory" mechanism, may not exist at all. If so, it would be unlikely for emotion and memory to be so intertwined as to cause an inability to recall the first several years of memories (McCloskey, et al., 1988)...

Context explanation
The difference in perspective that children and adults experience of the world may be a cause of childhood amnesia. For children, their physical perception of objects and their understanding of people and events are very different from the world of the adult. Moreover, an infant’s basic understanding of the universe, like object permanence or occlusion effects, is not innate at birth. This leads to a disparity in retrieval cues used by the adult and those used by the infant, who will encode memories without many of these principles that are ingrained in the mind of the adult trying to recollect. This different context could lead to the inability of the adult to remember his earliest years at all (Gleitman, et al., 2004). For example, one study showed that an infant’s development of a theory of mind is linked to his ability to form episodic memories. The conclusion was that the context explanation may be justified, especially since infants develop the ability to perceive the world as adults do around the age of 3 to 5, when many people also have their earliest retrievable memory (Perner, et al., 1995).

Patterns of childhood amnesia
Much recent research has found patterns in the extent of childhood amnesia. The most prominent patterns are gender and race.

Males versus females
Research has found that in general the earliest recollections of females are earlier and more vivid than those of males (Gleitman, et al., 2004). One study found that when 8-year old subjects were asked to recall events they had been interviewed about between 40 and 70 months old, the females provided significantly more vivid memories than the males (Fivush, et al., 1999). A similar study with adults found that women generally can recall earlier and more vivid memories than men (MacDonald, et al., 2000). It has been suggested that this pattern is due to differences in how males and females interact as children, especially the types of conversations they have (Gleitman, et al., 2004).

Race and ethnicity
Race has also been shown to play a role in the effect of childhood amnesia. One study found that Europeans had later first retrievable memories than New Zealand Maoris, and Asians had still later ones. This suggests that the importance of the past in Maori culture may have something to do with their particularly early first retrievable memory (MacDonald, et al., 2000). It is not known definitively, however, why the racial pattern of childhood amnesia is observed.