Memory across the Lifespan

Chapter Overview:

Chapter 9 discusses the research on memory and how it changes over our lifetime, from before birth and into old age.

Doing research on preverbal humans, including fetuses, provides some challenges but several clever techniques have been devised including the habituation, exposure learning, and high-amplitude sucking paradigms. Habituation is a decrease in response to a stimulus following repeated presentation. Researchers will typically present a stimulus like a tone to a fetus and measure movement or heartrate in response to the tone. After repeated presentations of the tone, the fetus will typically stop responding, i.e., habituate to the tone. Habituation shows that the fetus remembers the stimuli and has been measured as young as 22 weeks gestation. Likewise, in exposure learning, the fetus or infant is repeatedly exposed to a stimulus and then their response to that stimulus is compared to that of an unfamiliar stimulus. Research using exposure learning suggests that memory for sensory events develops between 30 and 37-week gestation. In the high-amplitude sucking paradigm, infants can control what they hear or see based on their rate of sucking. In these studies, it is apparent that infants can remember stimuli presented to them even before they were born.

After an infant reaches three months old, researchers use other techniques to measure infant memory including sensory preconditioning, potentiation, paired-comparison tasks, and associative chains. In sensory preconditioning, infants are first exposed to two stimuli, then one of the stimuli are presented with a source of reinforcement (e.g., kicking results in a pleasing tone). The infants are then exposed to the other stimuli; if they respond to that stimuli like they did for the other one, it is assumed that they remember the association. Infants as young as three months have shown that they have developed this association even after only two days of pre-exposure and older infants have displayed the association after a delay of two weeks. Potentiation, or associating a strong stimulus with a weaker one, has been documented in infants. This type of learning occurs in infants by six months of age and can last up to four weeks. The paired-comparison task measures the amount of time infants spend looking at two stimuli—one stimulus they have been previously exposed to, the other a novel one. As infants generally prefer novel stimuli, looking at it longer indicates that they remember the first one. Some research has found that infants as young as three months can remember the exposure even after three months. And finally, research with associative chains has been used to measure memory. In these studies, infants are shown a stimulus (e.g., puppet A), with another one (puppet B); then puppet B is shown with puppet C, and, finally, puppet C is presented with puppet D. If the infants associate puppet A with D (a process called transitivity), they must explicitly recall the relationships between the other puppets. Infants have been shown to retain these associations for a day only unless potentiation was used.

Interestingly, young infants seem to readily make and remember associations between stimuli (as described above) but this exuberant learning slows down after nine months. The mechanism behind this fast-paced learning is referred to as fast-mapping.

Not surprisingly, younger infants forget more quickly than older ones, with six-month olds retaining information for about five weeks. However, when infants retrieve the memory just before they are likely to forget it, retention is prolonged. This effect is more pronounced in younger infants than older ones.

Infant memory differs from adults in that infants are more likely to make associations and these associations are retained for less time. Two models of memory development have been proposed to explain these differences. The neuroanatomical model focuses on the division between implicit memory and explicit memory. It proposes that the implicit memory system is present at birth (early-maturing) and facilitates simple procedures, perceptual, and motor skills but does not allow for complex encoding. The late-maturing system emerges at about eight or nine months and processes explicit memories. On the other hand, the ecological model asserts that infants are born fully able to create both implicit and explicit memories and that differences in memory processes are related to differences in how memory is used. For example, it makes sense that young infants need to gather as much information as possible, so they encode exuberantly whereas older, more mobile youngsters need to encode specific, more complex information. The ecological model is consistent with the behavioural research on memory in infants presented above.

Not surprisingly, memory changes over childhood and these changes result in an improvement in metamemory which, in turn, allow for better strategies and better retention. Research on the working memory in children has demonstrated that there is a steady improvement in the capacity of the phonological loop, central executive, and visuospatial sketchpad from ages four or five to twelve. These changes seem to echo the development of the frontoparietal cortical network. Rehearsal strategies to maintain information in working memory develop with age: by two, children use basic precursors to rehearsal; by five, they use basic rehearsing out loud tactics; and, by 10, they rehearse groups of items. Likewise, there are developmental improvements in memory and retrieval strategies; for example, by 12 years of age, children organize material to be learned into groups for easier retrieval. This ability seems to be related to an increase in working-memory capacity. The speed in which children can perform memory tasks increases. This ability might be tied to an increased speed of speaking. While most people experience infantile amnesia, there is evidence to support the notion that some people can actually remember events from as young as two years old for six years. No developmental changes to implicit memory seem to occur in childhood.

While there is some measurable decline in memory in older adulthood, much of that perception may be more stereotype than reality. Research has shown that there is typically a slight decrease in both verbal and spatial short-term memory span. Working memory research has shown mixed results with some tasks showing large effects, some showing slight, and some none. These discrepancies can be explained by the assumption that older adults have more difficulty with suppressing irrelevant information so the decline as a function of age in some working memory tasks is better explained by proactive interference. Recall from long-term memory seems to decrease with age overall. More specifically, older adults appear to use recall cues less effectively perhaps because of reduced encoding. These deficits are reduced when older adults are more involved in the community and are from a higher socioeconomic status. Older adults tend to recall more positive autobiographical memories and perceive the bad memories as less negative than the reality. On the more positive side, older adults tend to perform better than younger ones on prospective memory tasks. Similar to the development in children, there appears to be no change in implicit memory as people age. Data from the Victoria Longitudinal Study is consistent with other research that demonstrated reduced performance in fact recall, working memory, and speed of comprehension with age and that declines in working memory predicted declines in other cognitive tasks.

As healthy people age, the brain shrinks in size with the front part of the brain shrinking faster than the back. As a result, deficits in frontal lobe tasks, including working memory and attention, are more apparent in older adults. Neural imaging has shown that there is less asymmetry in the frontal lobe activity when older adults are conducting these tasks. Also, the decrease in dopamine in aging brains may also be related to some declines in episodic memory performance.

Learning Objectives:

Having read this chapter, you will be able to do the following:

  1. Describe what habituation, exposure learning, and high-amplitude sucking paradigms have revealed about the memories of fetuses and newborns.
  2. Explain how associative-chain experiments have been used to demonstrate transitivity in infants.
  3. Summarize what research has revealed about the nature and duration of memory in infants.
  4. Define fast mapping and explain how exuberant learning changes as infants age.
  5. Compare and contrast the neuroanatomical model of memory development with the ecological model of memory development.
  6. Explain how memory span, retrieval strategies, and organization of memory change over childhood.
  7. Explain how memory span, working memory, long-term memory, prospective memory, and implicit memory are affected by age.
  8. Discuss how the aging brain affects memory.
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