Working Memory and Severe Learning Difficulties (PLE: Memory)

Charles Hulme, Susie Mackenzie

• Publisher: Taylor & Francis
• Year: 2014
• Print ISBN: 9781848723627
• eBook ISBN: 9781317748427
• Edition: 1
• Topic: Psychology
• Subtopic: Cognitive Psychology & Cognition
• Index: Psychology

"Working memory" is a term used to refer to the systems responsible for the temporary storage of information during the performance of cognitive tasks. The efficiency of working memory skills in children may place limitations on the learning and performance of educationally important skills such as reading, language comprehension and arithmetic.

Originally published in 1992, this monograph considers the development of working memory skills in children with severe learning difficulties. These children have marked difficulties with a wide range of cognitive tasks. The studies reported show that they also experience profound difficulties in verbal working memory tasks. These memory problems are associated with a failure to rehearse information within an articulatory loop. Training the children to rehearse material is shown to help alleviate these problems.

The implications of these studies for understanding normal memory development, and for models of the structure of working memory and its development are discussed. It is argued that the working memory deficits seen in people with severe learning difficulties may contribute to their difficulties on other cognitive tasks.

CHAPTER 1

Severe Learning Difficulties: History, Definitions, and Terminology

People differ in how clever they are. Some people can learn a wide range of complex skills with ease, while others find learning even comparatively simple skills very difficult. When someone has learning difficulties of a general nature they may be described as mentally handicapped. In the past, a variety of terms that we would now consider offensive have been used to describe individuals with learning difficulties, such as natural fools, idiots, morons, slow-witted or feeble-minded. Whatever term is used it is generally agreed that mental handicap affects the individual’s capacity to learn. Mental handicap results in people having incomplete, or arrested development of intellectual capacities. People with severe learning difficulties are most commonly described in terms of a lack of general intelligence or mental capacity, and a resulting impairment of mental development and learning.

IQ tests are central to our current definitions of learning difficulties. These tests, which derive directly from the pioneering work of Binet and Simon (1916) at the turn of the century, sample a range of skills, such as memory processes, knowledge of vocabulary, construction of visuo-spatial puzzles, verbal reasoning, and conceptual knowledge. The tests are standardized, by testing large and representative samples of people of different ages, to obtain norms for performance. Standardization results in the tests having an average score of 100. The tests have also been developed to have normally distributed scores with a standard deviation of 15 points. Well-standardized tests should also be free from any sex bias. In spite of their statistical sophistication IQ tests are often heavily criticized. A common criticism has been the lack of any coherent underlying theory of what they measure. However, from a practical standpoint, they have proved extremely useful because they are simple to administer and correlate well with measures of scholastic achievement and other external criteria of learning ability.

Another measurement, related to IQ, that is often used to express the level of intellectual development is mental age (MA). Mental age is given simply by the level of attainment reached on a test in relation to the normal population. So, for example, if a child performs on an IQ test at a level equivalent to a 7-year-old they would be assigned a mental age of 7 years, even though their actual or chronological age might be substantially higher than this if they have learning difficulties.

The terminology used, and explanations given, as to why some individuals fail to develop normal learning abilities have changed over the centuries, reflecting changes in attitudes and increasing knowledge.

HISTORICAL BACKGROUND

Ann M. Clarke and A.D.B. Clarke (1974) mention historical documents from as early as the thirteenth century which make distinctions between a “born fool” and a “lunatic”. If a man was classed a lunatic the Crown took possession of his land for the duration of his illness. However, a man found to be an idiot forfeited his property to the Crown permanently, but the Crown had the duty to provide for him. The purpose of classification during that period was, therefore, administrative.

Superstition ruled during the Middle Ages and there were commonly held beliefs that the “natural fool” (or his mother in pregnancy) had somehow been interfered with by fairies, witches or the devil. For example, the stories of “changelings”, where the newly born child was said to be spirited away and replaced by another, may well have been used to explain why some people looked and acted differently from others.

A treatise by Paracelsus (published 1567) on the Begetting of Idiots is a colourful example of an early attempt to understand the nature of learning difficulties.

“It is astonishing that God, who redeemed man through the great price of His death and blood, lets men be born unwise

… that a thing is inborn is difficult; for what birth gives, who can take it away or remove it?

… as there is no disease, they are incurable [we] have no stones nor herbs whereby they might become intelligent.”

Paracelsus (1567),
translated into English by Cranefield and Federn (1967).

The problem for Paracelsus lies in understanding why God allows some men to be born in a less than perfect state, especially when fools are born to normal parents. His explanation considers fools the fault of inexperienced craftsmen in God’s “workshop”. Parents provide the basic materials and God’s craftsmen form the individual. Fools are produced not by the poor material provided by parents, but by the inexperienced apprentices who make mistakes and carve badly! (Cranefield & Federn, 1967).

The term “idiot” and the distinction of learning difficulties from insanity and lunacy were also well known in the seventeenth and eighteenth centuries. The following quotations show that their understanding of the nature of learning difficulties was not so very different from current views.

Madmen put wrong ideas together, and so make wrong propositions, but argue and reason right from them; but idiots make very few or no propositions, and reason scarce at all. John Locke (1623–1704).

… idiocy is not a disease, but a condition in which the intellectual faculties are never manifested; or have never been developed sufficiently to enable the idiot to acquire such an amount of knowledge as persons of his own age, and placed in similar circumstances as himself, are capable of receiving. Esquirol (1772–1840).

The nineteenth century brought certain changes. A growing medical interest in learning difficulties brought awareness of different degrees of “idiocy” and—by Itard and Seguin—the first systematic attempts at education or training for the subnormal. An “idiot” was now distinguished from an “imbecile”, a “moron” or the “feeble-minded”; the feeble-minded being closest to normal, and idiots the very bottom of the range. These terms appear vague and confusing to us (is an idiot less intelligent than an imbecile, or vice versa?), but they were then the accepted scientific terms for differentiating the “mentally deficient”. Translated into current IQ terms the feeble-minded and morons would be around 75 to 50 IQ points, imbeciles 50 to 20 IQ points, and idiots below 20 IQ points.

Our current definitions of learning difficulties centre on the use of IQ tests. The use of IQ tests as a means of defining mental handicap was formalized by a report of the World Health Organization. This used the term “mental subnormality” (World Health Organization, 1954); an individual was defined as mentally subnormal if their score was more than two standard deviations below the mean on an IQ test (i.e. an IQ of less than 70).

Distinctions about degrees of intellectual impairment have also been related to types of educational provision. Before 1971, many mentally handicapped children were considered ineducable and attended Junior Training Centres rather than schools. In the Education Act of 1971 a distinction was made between Educationally Subnormal (ESN) mild and severe. Generally, children with IQs in the 50 to 75 point range would attend an ESN (M) school, whereas children with a lower IQ would attend an ESN (S) school (the old Junior Training Centres). The equivalent American terminology was to speak of Educable Mental Retardates and Trainable Mental Retardates. There is no longer a distinction made between educable and ineducable children (Segal, 1967). All children with a mental handicap or subnormality, including the profoundly handicapped, now receive education adapted to their individual needs or “learning difficulties”. These schools have been “redefined” in accord with the recommendations of the Warnock Report (1978) and are now referred to as “schools for children with moderate learning difficulties” and “schools for children with severe learning difficulties”.

To summarize modern terminology: “mental subnormality” is a general term for all individuals with IQs of less than 70 points, “severe subnormality” (SSN) referring to those with an IQ of 50 to 20 points; “mental handicap” refers to a specific pathology which is known to affect mental development (and therefore results in a low IQ); “severe learning difficulty” (SLD) describes the effect of having a mental handicap or being severely subnormal, and has replaced the term “severely educationally subnormal” (ESN S); those with less severe impairments are said to have “moderate learning difficulties” (ESN M). To talk of learning difficulties is thought to be less pejorative than subnormality. In this text we will follow current terminology and use the term “learning difficulties” rather than “subnormality, even when describing research that used the older terminology. Finally, for reasons of clarity, the term “learning difficulties” should be distinguished from another term in wide current usage—“specific learning difficulties”. This is a term used to refer to children who are experiencing difficulties with basic school subjects in the absence of any general learning difficulties, i.e. in children of average or near average IQ. Probably the most common problem of this sort is in children who have specific difficulties in learning to read and spell; this is sometimes referred to as developmental dyslexia.

THE INCIDENCE OF LEARNING DIFFICULTIES

People with learning difficulties are found in all areas of the world and in all social groups. It is difficult to calculate prevalence as this depends on individuals being diagnosed or identified administratively (Tizard, 1964). With school-age groups it is comparatively easy to make accurate estimates, as children with learning difficulties are often referred to outside agencies, such as psychologists, social services or child guidance centres. In older age groups many individuals with mild or moderate learning difficulties cope with life independently and will no longer be included in statistics. Most estimates cite 2% of the population, which in Britain is approximately one million individuals. In terms of educational provision, in 1967 there were 47,000 places available in schools for the “educationally subnormal” accounting for nearly 1% of the entire school population (A. D. B. Clarke & Ann. M. Clarke, 1975).

THE CAUSES OF LEARNING DIFFICULTIES

In general terms, the causes of learning difficulties can be divided into three broad categories: congenital, environmental, and pathological. In fact, for a large number of individuals there is no single identifiable cause; in practice, a number of factors will interact to affect mental development.

Genetic and Environmental Variation

Because of genetic differences amongst people and variations in the environments in which they develop, mental abilities show a wide dispersion when measured in large groups. The complex interaction between the many environmental and genetic factors that affect the development of intellectual differences amongst people results in mental ability, as assessed by IQ tests, having a normal distribution. This means that there will always be a small proportion of the population of superior ability with very much above average IQ. Conversely, there will always be a small proportion of people of inferior ability with IQs very much below the population average. It is assumed that most cases of mild learning difficulties result from an interaction of normal genetic and environmental variation; that is, from an inherited predisposition to develop a low IQ, in interaction with a range of adverse environmental factors, such as poor nutrition, health care, and educational opportunity.

Congenital Abnormalities

In addition to normal variations in genetic make-up that affect intellectual development, there are a variety of congenital pathological conditions that result in impairments of intellectual development. Some of these conditions are, fortunately, very rare, and it is not possible to give a full review of them here (Berg, 1974 and Milunsky, 1979 give comprehensive reviews of the clinical causes of retardation). The more common congenital disorders that result in mental handicap include metabolic disorders (such as phenylketonuria—PKU—gargoylism, and cretinism) and chromosome disorders, such as Down’s syndrome (trisomy 21) and other rarer trisomies (Edward’s syndrome, trisomy 18, and Patau’s syndrome, trisomy 13).

Brain Damage

Damage to the brain early in life is a common cause of learning difficulties. Such damage may occur for a variety of reasons and at a variety of stages of development.

Prenatal maternal infections, such as rubella and syphilis, can adversely affect the brain of the developing foetus. Similarly, malnutrition or drugs taken during pregnancy can disturb foetal brain development, as may irradiation, or the mother’s own antibodies, as in the case of rhesus incompatibility. Any of a wide range of factors that adversely affect the foetus prior to birth may result in impairments of brain function which later in life lead to learning difficulties.

Injury at birth may also result in brain damage and so to learning difficulties. Most commonly this may result from anoxia or hypoxia: too little or too much oxygen reaching the brain (Towbin, 1970). There may also be a raised incidence of reported obstetric complications, such as prolonged labour and forceps deliveries, amongst individuals who are later found to develop learning difficulties. It has been argued, however, that cause and effect may be difficult to untangle in such cases. At least in some cases, it has been argued, congenital abnormalities already present in the foetus may lead to obstetric problems and subsequent learning difficulties (Drillien, 1963). After birth there are rare cases where normal development is arrested or delayed as a result of an accident involving head injury, or because of infections that affect the central nervous system (such as meningitis, or whooping cough).

Interactions Between Congenital and Environmental Factors

It is important to emphasize, in the context of this brief discussion of pathological conditions that result in learning difficulties, that such conditions do not mean that development is fixed. Development in any individual will depend upon a complex interaction between inherited predispositions and environmental conditions. So, even in cases of severe learning difficulties that depend upon some clear pathology, the quality and quantity of environmental stimulation will almost certainly affect development. It is quite wrong to believe that a pathological condition results in some clear fixed limit to development.

One of the main types of study that has been used to demonstrate this has been to compare the development of children with severe learning difficulties living in different environments. A number of studies have compared the intellectual and social development of Down’s syndrome children with severe learning difficulties, cared for at home rather than in institutions. There is evidence for better outcomes for such children when they are cared for at home (for reviews of these studies see Carr, 1985, and Gibson, 1978). There is some controversy over the interpretation of these studies, particularly as it is difficult to ensure comparability between groups before their placement in different settings. Gibson (1978) argued that many positive results in such studies may be artefacts of selective placement, whereby more severely handicapped children were more likely to be institutionalized. If this were true, it would be impossible to be sure whether differences in outcomes were really due to differences in the environmental stimulation that the children had received. However, as Carr (1985) points out, the consistency of the superiority of outcomes for home reared, as compared to institutionalized, Down’s syndrome children is striking, and in some studies there is evidence for equivalent status between the groups compared at initial placement. Furthermore, in some studies institutionalization occurred at a very early age, before selective placement could operate on any sound basis. It seems reasonable to conclude, perhaps unsurprisingly, that environmental stimulation has beneficial effects on the development of Down’s syndrome children, just as it does for normal children.

We may reflect on how fortunate it is that one of the practical aims of this research (to assess the advisability of placing children in institutions) has now become redundant. Current social policy has moved away from the idea of institutionalizing children whether they suffer from Down’s syndrome or other forms of handicap. Theoretically, however, these studies provide important evidence for the plasticity of development in Down’s syndrome and the potential for environmental influences on development. The range and magnitude of such influences, and whether they differ between normal and handicapped children are complex issues that are as yet far from resolved.

More recent studies of the effects of environmental stimulation on the development of Down’s syndrome children have focused on the effects of early intervention programmes to provide added stimulation for the children. For example, Ludlow and Allen (1979) compared the development of two groups of Down’s syndrome babies. The mothers of one group, from a single geographical area, attended a clinic twice a week with their children aged between 2 and 8 years. The children participated in nursery type activities and the mothers were encouraged to continue this stimulation at home. The control group from another area did not receive this extra stimulation. The results showed that the stimulated group were consistently ahead of the control group on standard measures of intellectual development (the Griffiths and Stanford-Binet scales), although both groups showed equivalent (and marked) intellectual decline as they got older. Cunningham (1982) also found that Down’s syndrome infants, whose parents were given advice on ways of stimulating their babies, showed improvements. Babies for whom intervention started early showed least decline with increasing age in this study.

This brief discussion of the interaction between innate and environmental influences on development has implications for the interpretation of studies presented in later chapters. When differences in memory performance are documented between normal children and those with severe learning difficulties, it should not be assumed that such differences are in any way immutable. Being realistic, intellectual differences between normal children and those with severe learning difficulties may ce...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Orginal Copyright Page
• Table of Contents
• Acknowledgements
• 1. Severe Learning Difficulties: History, Definitions, and Terminology
• 2. Working Memory: Structure and Function
• 3. Working Memory Development, Cognitive Development and Learning Difficulties
• 4. Memory Span Development in Severe Learning Difficulties
• 5. The Articulatory Loop in Severe Learning Difficulties
• 6. Improving Memory Span in Severe Learning Difficulties
• 7. Working Memory and Severe Learning Difficulties: A Synthesis
• References
• Author Index
• Subject Index