preschool child

Childhood amnesia shifts with time

August, 2011

A new study finds that the earliest memories children can recall shifts with time, providing support for the theory that children’s memories don’t consolidate in the way adults’ memories do.

Childhood amnesia — our inability to remember almost everything that happened to us when very young — is always interesting. It’s not as simple as an inability to form long-term memories. Most adults can’t remember events earlier than 3-4 years (there is both individual and cultural variability), even though 2-year-olds are perfectly capable of remembering past events (side-note: memory durability increases from about a day to a year from age six months to two years). Additionally, research has shown that young children (6-8) can recall events that happened 4-6 years previously.

Given that the ability to form durable memories is in place, what governs which memories are retained? The earliest memories adults retain tend to be of events that have aroused emotions. Nothing surprising about that. More interesting is research suggesting that children can only describe memories of events using words they knew when the experience occurred — the study of young children (27, 33 or 39 months) found that, when asked about the experimental situation (involving a "magic shrinking machine") six months later, the children easily remembered how to operate the device, but were only able to describe the machine in words they knew when they first learned how to operate it.

Put another way this isn’t so surprising: our memories depend on how we encode them at the time. So two things may well be in play in early childhood amnesia: limited encoding abilities (influenced but not restricted to language) may mean the memories made are poor in quality (whatever that might mean); the development of encoding abilities means that later attempts to retrieve the memory may be far from matching the original memory. Or as one researcher put it, the format is different.

A new study about childhood amnesia looks at a different question: does the boundary move? 140 children (aged 4-13) were asked to describe their three earliest memories, and then asked again two years later (not all could provide as many as three early memories; the likelihood improved with age).

While more than a third of the 10- to 13-year-olds described the same memory as their very earliest on both occasions, children between 4 and 7 at the first interview showed very little overlap between the memories (only 2 of the 27 4-5 year-olds, and 3 of the 23 6-7 year-olds). There was a clear difference between the overlap seen in this youngest group (4-7) and the oldest (10-13), with the in-between group (8-9) being placed squarely between the two (20.7% compared to 10% and 36%).

Moreover, children under 8 at the first interview mostly had no overlap between any of the memories they provided at the two interviews, while those who were at least 8 years old did. For the oldest groups (10-13), more than half of all the memories they provided were the same.

The children were also given recall cues for memories they hadn’t spontaneously recalled. That is, they were told synopses of memories belonging to both their own earlier memories, and other children’s earlier memories. Almost all of the false memories were correctly rejected (the exceptions mostly occurred with the youngest group, those initially aged 4-5). However, the youngest children didn’t recognize over a third of their own memories, while almost all the oldest children’s memories were recognized (90% by 8-11 year-olds; all but one by 12-13 year-olds). Their age at the time of the event didn’t seem to affect the oldest or the very youngest groups, but 6-9 year-olds were more likely to recall after cuing events that happened at least a year later than those events that weren’t recalled after cuing.

In general, the earliest memories were several months later at the follow-up than they had been previously. The average age at the time of the earliest memory was 32 months, and 39.6 months on the follow-up interview. This shift in time occurred across all ages. Moreover, for the very earliest memory, the time-shift was even greater: a whole year.

In connection with the earlier study I mentioned, regarding the importance of language and encoding, it is worth noting that by and large, when the same memories were recalled, the same amount of information was recalled.

There was no difference between the genders.

The findings don’t rule out theories of the role of language. It seems clear to me that more than one thing is going on in childhood amnesia. These findings bear on another aspect: the forgetting curve.

It has been suggested that forgetting in children reflects a different function than forgetting in adults. Forgetting in adults matches a power function, reflecting the fact that forgetting slows over time (as is often quoted, most forgetting occurs in the first 24 hours; the longer you remember something, the more likely you are to remember it forever). However, there is some evidence that forgetting in children is best modeled in an exponential function, reflecting the continued vulnerability of memories. It seems they are not being consolidated in the way adults’ memories are. This may be because children don’t yet have the cognitive structures in place that allow them to embed new memories in a dense network.

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How parents can improve their preschoolers’ understanding of number

July, 2011

A new study shows that preschoolers whose parents engage in the right number-talk develop an understanding of number earlier. Such understanding affects later math achievement.

At every level, later math learning depends on earlier understanding. Previous research has found that the knowledge children have of number before they start school predicts their achievement throughout elementary school.

One critical aspect of mathematical development is cardinal-number knowledge (e.g. knowing that the word ‘three’ refers to sets of three things). But being able to count doesn’t mean the child understands this principle. Children who enter kindergarten with a good understanding of the cardinal principle have been found to do better in mathematics.

Following research indicating an association between children’s knowledge of number and the amount of number talk their parents engage in, a new study recorded parental interactions for 44 young children aged 14-30 months. Five 90-minute sessions, four months apart, were recorded in the children’s home, and each instance in which parents talked about numbers with their children was noted and coded. The children were then (at nearly four years) tested on their understanding of the cardinal principle.

The study found that parents’ number talk involving counting or labeling sets of visible objects related to children’s later cardinal-number knowledge, whereas other types of parent number talk were not. Talk of larger sets, containing more than 3 objects, was particularly important. This is probably because children can recognize number sets of three or less in a holistic way.

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Common insecticide associated with delayed mental development of young children

March, 2011

The insecticide which has largely replaced those phased out because of their effects on children’s development has now been found to also be associated with delayed mental development.

A study involving 725 black and Dominican pregnant women living in New York and, later, their 3-year-old children, has found that children who were more highly exposed to PBO in personal air samples taken during the third trimester of pregnancy scored 3.9 points lower on the Bayley Mental Developmental Index than those with lower exposures. This is a similar effect size to that of lead exposure.

PBO is a marker for the insecticide permethrin, which is one of the most common pyrethroid insecticides used in U.S. homes since the EPA phased out the widespread residential use of organophosphorus insecticides in 2000-2001 because of risks to child neurodevelopment.

PBO was detected in the majority of personal air samples (75%).

As this is the first study of these compounds, the results should be considered preliminary.

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Poverty suppresses children's genetic potential

January, 2011

A large study of very young twins confirms evidence that environment affects cognitive ability far more for those from poor homes, compared to those from better-off homes.

A study involving 750 sets of twins assessed at about 10 months and 2 years, found that at 10 months, there was no difference in how the children from different socioeconomic backgrounds performed on tests of early cognitive ability. However, by 2 years, children from high socioeconomic background scored significantly higher than those from low socioeconomic backgrounds. Among the 2-year-olds from poorer families, there was little difference between fraternal and identical twins, suggesting that genes were not the reason for the similarity in cognitive ability. However, among 2-year-olds from wealthier families, identical twins showed greater similarities in their cognitive performance than fraternal twins — genes accounted for about half of the variation in cognitive changes.

The findings are consistent with other recent research suggesting that individual differences in cognitive ability among children raised in socioeconomically advantaged homes are primarily due to genes, whereas environmental factors are more influential for children from disadvantaged homes.

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Girls less likely to be diagnosed autistic even when symptoms severe

December, 2010

A new study finds that gender and maternal assertiveness are factors in determining whether children with autistic symptoms are diagnosed with ASD.

No one is denying that boys are far more likely to be autistic than girls, but a new study has found that this perception of autism as a male disorder also means that girls are less likely to be diagnosed with autistic spectrum disorder (ASD) even when their symptoms are equally severe.

Another factor affecting diagnosis was maternal age — those diagnosed with ASD were likely to have older mothers. It’s suggested that this may be because older mothers are better at identifying their children's difficulties and have more confidence in bringing concerns to the clinic. This is supported by the finding that first-born children were less likely to be diagnosed with ASD, as were children of mothers with depression.

Ethnic origin, maternal class and mother's marital status did not significantly predict a child either having an ASD diagnosis or displaying severe autistic traits.

The findings were based on an analysis of data from a longitudinal UK cohort study, the Avon Longitudinal Study of Parents and Children (ALSPAC).

Reference: 

Russell, G., Steer, C. & Golding, J. 2010. Social and demographic factors that influence the diagnosis of autistic spectrum disorders. Social Psychiatry and Psychiatric Epidemiology. DOI 10.1007/s00127-010-0294-z.
Full text is available at http://springerlink.com/content/a67371l826m1xl76/fulltext.pdf

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An early marker of autism

October, 2010

A strong preference for looking at moving shapes rather than active people was evident among toddlers with autism spectrum disorder.

A study involving 110 toddlers (aged 14-42 months), of whom 37 were diagnosed with an autism spectrum disorder and 22 with a developmental delay, has compared their behavior when watching a 1-minute movie depicting moving geometric patterns (a standard screen saver) on 1 side of a video monitor and children in high action, such as dancing or doing yoga, on the other.

It was found that only one of the 51 typically-developing toddlers preferred the shapes, but 40% of the ASD toddlers did, as well as 9% of the developmentally delayed toddlers. Moreover, all those who spent over 69% of the time focusing on the moving shapes were those with ASD.

Additionally, those with ASD who preferred the geometric images also showed a particular pattern of saccades (eye movements) when viewing the images — a reduced number of saccades, demonstrated in a fixed stare. It’s suggested that a preference for moving geometric patterns combined with lengthy absorption in such images, might be an early identifier of autism. Such behavior should be taken as a signal to look for other warning signs, such as reduced enjoyment during back-and-forth games like peek-a-boo; an unusual tone of voice; failure to point at or bring objects to show; and failure to respond to their name.

Reference: 

[1891] Pierce, K., Conant D., Hazin R., Stoner R., & Desmond J.
(2010).  Preference for Geometric Patterns Early in Life As a Risk Factor for Autism.
Arch Gen Psychiatry. archgenpsychiatry.2010.113 - archgenpsychiatry.2010.113.

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Child's 'mental number line' affects memory for numbers

October, 2010

Young children’s memory for numbers reflects their understanding that numbers, however big, are all evenly spaced.

When children learn to count, they do so by rote. Understanding what the numbers really mean comes later. This is reflected in the way children draw a number line. In the beginning, they typically put more space between the smaller numbers, with the larger numbers all scrunched up at the end (a logarithmic number line). Eventually they progress to a number line where the numbers are evenly spaced (linear number line).

Now a series of experiments with preschoolers and second graders has revealed that the more linear the child's magnitude representations (as seen on the number line as well as in other tasks), the better the child was at remembering numbers (for example, from a story with some numbers included).

This was true for preschoolers for numbers from 1-20 and for elementary school children for numbers from 1-1000, and for four different number tasks measuring numerical-magnitude representations (categorization and number-line, measurement, and numerosity estimation). Other types of numerical knowledge—numeral identification and counting—were unrelated to remembering numbers.

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Building language skills more critical for boys than girls

October, 2010

A study of language and self-regulation skills in toddlers suggests that having a good vocabulary helps boys in particular control their behavior and emotions.

A study involving 120 toddlers, tested at 14, 24, and 36 months, has assessed language skills (spoken vocabulary and talkativeness) and the development of self-regulation. Self-regulation is an important skill that predicts later academic and social success. Previous research has found that language skills (and vocabulary in particular) help children regulate their emotions and behavior. Boys have also been shown to lag behind girls in both language and self-regulation.

The present study hoped to explain inconsistencies in previous research findings by accounting for general cognitive development and possible gender differences. It found that vocabulary was more important than talkativeness, and 24-month vocabulary predicted the development of self-regulation even when general cognitive development was accounted for. However, girls seemed ‘naturally’ better able to control themselves and focus, but the ability in boys was much more associated with language skills. Boys with a strong vocabulary showed a dramatic increase in self-regulation, becoming comparable to girls with a strong vocabulary.

These gender differences suggest that language skills may be more important for boys, and that more emphasis should be placed on encouraging young boys to use words to solve problems, rather than accepting that ‘boys will be boys’.

Reference: 

[1871] Vallotton, C., & Ayoub C.
(Submitted).  Use your words: The role of language in the development of toddlers' self-regulation.
Early Childhood Research Quarterly. In Press, Uncorrected Proof,

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Prenatal exposure to pesticides linked to attention problems

September, 2010

In a study of young Mexican-American children, higher prenatal exposure to pesticides was significantly associated with ADHD symptoms at age 5.

A study following over 300 Mexican-American children living in an agricultural community has found that their prenatal exposure to organophosphate pesticides (measured by metabolites in the mother’s urine during pregnancy) was significantly associated with attention problems at age 5. This association was stronger among boys, and stronger with age (at 3 ½ the association, although present, did not reach statistical significance — perhaps because attention disorders are much harder to recognize in toddlers). Based on maternal report, performance on attention tests, and a psychometrician’s report, 8.5% of 5-year-olds were classified as having ADHD symptoms. Each tenfold increase in prenatal pesticide metabolites was linked to having five times the odds of scoring high on the computerized tests at age 5. The child’s own level of phosphate metabolites was not linked with attention problems.

Organophosphate pesticides disrupt acetylcholine, which is important for attention and short-term memory. While the exposure of these children to pesticides is presumably higher and more chronic than that of the general U.S. population, food is a significant source of pesticide exposure among the general population.

Reference: 

Marks AR, Harley K, Bradman A, Kogut K, Barr DB, Johnson C, et al. 2010. Organophosphate Pesticide Exposure and Attention in Young Mexican-American Children. Environ Health Perspect :-. doi:10.1289/ehp.1002056
Full text available at http://ehp03.niehs.nih.gov/article/fetchArticle.action?articleURI=info%3...

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New technology can help assess autistic & language disorders

August, 2010

New technology offers hope of early diagnosis of both autism spectrum and language disorders, as well as promising help to parents in assessing the effectiveness of therapy.

A new automated vocal analysis technology can discriminate pre-verbal vocalizations of very young children with autism with 86% accuracy. The LENA™ (Language Environment Analysis) system also differentiated typically developing children and children with autism from children with language delay. The processor fits into the pocket of specially designed children's clothing and records everything the child vocalizes. LENA could not only enable better early diagnosis of autism spectrum disorders, but also allow parents to continue and supplement language enrichment therapy at home and assess their own effectiveness for themselves.

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