- Email: [email protected]
Handbook of dichotic listening: Theory, methods and research
Acta Psychologica North-Holland
87
76 (1991) 87-95
Book reviews Kenneth Hugdahl (ed.), Handbook of Dichotic Listening: Research. Wiley, New York, 1988. 650 pp., 20 chs.
Theory, Method
and
Since the introduction of the dichotic listening task by Kimura in 1961 in the field of hemispheric specialization, many researchers and clinicians have employed this technique for assessing the functions of the cerebral hemispheres in both normal and clinical populations. In these task, competing stimuli are presented simultaneously to the left and right ear and the subjects are asked to report what they have heard. In general, studies reveal a right ear advantage (left hemisphere) for verbal tasks and a left ear advantage (right hemisphere) for nonverbal tasks. The rationale underlying these findings is (a) that the contralateral auditory pathways from the ear to the cortex are more efficient than the ipsilateral pathways, (b) that, under dichotic stimulation, information transmitted via the contralateral pathways suppresses information ascending the ipsilateral pathways, and (c) that stimuli are processed more easily when stimuli are projected directly to the specialized hemisphere than when stimuli are first projected to the nonspecialized hemisphere and then transmitted across the corpus callosal pathways to the specialized hemisphere. The studies employing the dichotic listening procedure have grown to a tremendous size over the past quarter-century so that is is very difficult to integrate the large amount of reported findings. The main purpose of the book is to provide a theoretical and practical ‘handbook’ for those who wish to use the dichotic listening method in research and clinical practice. The book covers a lot of theoretical and methodological issues of dichotic listening in normal subjects and discusses the applications of this method in clinical subjects; however, the reader who thinks that this book is an easy entry for the use of dichotic listening in practical settings for assessment and diagnosis, will be disappointed. This book is an edited book written by different researchers in this field of study. An advantage of this approach is that topics of interest can be treated thoroughly, but a disadvantage is that some topics are scattered over the chapters or that they overlap each other in different chapters. Another disadvantage is that many of the authors devote the major part of their chapter to their own research findings rather than reviewing the topic under OOOl-6918/91/$03.50
0 1991 - Elsevier Science Publishers
B.V. (North-Holland)
88
Book
reviews
discussion. This approach leads to a book being heterogeneous in organization and quality. The Handbook of Dichotic Listening: Theory, Methods and Research is divided in 8 sections: Dichotic listening and cerebral asymmetry (A), Anatomical and neurological considerations (B), Methodological, acoustic, and phonetic considerations (C), Nonverbal and affective processes (D), Electrophysiological and autonomic correlates (E), Children and reading disorders (F), Psychopathology (G), and Group and individual differences (H). Section A can be viewed as an introduction of the basic issues of the dichotic listening procedure and its relationship to hemispheric specialization. This section deals mainly with the research findings of normal subjects. Bryden opens this book with a clear introduction and overview of dichotic listening as a method to assess hemispheric lateralization. In this chapter a variety of verbal and nonverbal dichotic techniques are briefly described, and the theoretical bases that underlie the dichotic ear effects are discussed. This chapter also includes the effects of handedness and sex on dichotic listening performance. Bradshaw (chapter 2) challenges Kimura’s view that ear asymmetries only emerge under conditions of dichotic simulation. In reviewing a number of studies, Bradshaw convincingly shows that ear asymmetries can be demontrated with monaural stimulation in numerous task situation. Clark, Geffen and Geffen (chapter 3) report an experiment employing a dichotic monitoring procedure. They find that ear asymmetries obtained with this task are quite stable and unaffected by practice and attention strategies. Wexler (chapter 4) emphasizes that dichotic listening tasks with a high degree of temporal and auditory spectral overlap between the competing stimuli, such as the fused, rhymed dichotic words test, can be considered as a reliable and valid method of presenting stimuli to a single hemisphere. Wexler also provides some examples of experimental applications; however, this part of the chapter deals with a variety of topics and is not very cogent and well organized. Section B gives valuable information about the anatomical correlates of the dichotic listening technique in brain-damaged patients. Strauss (chapter 5) deals with the validity of verbal and nonverbal dichotic listening tasks in a group of epileptic patients who have undergone carotic Amytal speech testing. The author focuses on both the relationship between dichotic laterality effects and cerebral speech representation and the relationship between laterality measures and neuroanatomical differences. Eslinger and Damasio (chapter 6) present evidence for the anatomical correlates of ear extinction effects by investigating patients with neurologically identified locations of lesions. The studies reported here show that contralateral ear extinction is associated with damage to auditory cortices or auditory pathways. Moreover, left ear extinction is also associated with lesions involving the corpus callosum. Of particular
Book reviews
89
interest is the finding that left ear extinction may even be caused by damage to cerebral regions outside the auditory system. The authors suggest that left ear extinction in these cases may be the result of altered attention mechanisms, leading to an ‘enhanced right ear advantage’. Sidtis (chapter 7) also demonstrates the importance of callosal transfer in the dichotic listening model by studying commissurotomy patients. It is argued that structural variability in the corpus callosum or asymmetries in the subcortical auditory system may represent factors that systematically influence ear effects. Section C deals with both the methodological issues of the dichotic listening method and the acoustic and phonetic aspects of the dichotic stimuli. Statistical properties of several dichotic listening paradigms employing speech signals (consonant-vowel nonsense syllables) are discussed by Speaks (chapter 8). This chapter especially focuses on the analysis of data in terms of intialistener variability in ear advantage over blocks of trials. Harshman and Lundy (chapter 9) provide a thorough review of the dichotic listening task as a method for measuring ‘degree of lateralization’. The authors critically discuss the pros and cons of laterality indices. This chapter contains a number of essential issues concerning the interpretation of dichotic listening scores. Tartter (chapter 10) provides an overview of studies investigating the effects of auditory and phonetic feature manipulations on ear asymmetries and fusions in verbal dichotic listening tasks. Section D reviews studies employing nonverbal stimuli and affective processes. Peretz and Morais (chapter 11) describe a number of studies emphasizing the specificity of laterality effects reported for the different components of music perception. The authors make clear that laterality effects for musical perception are very susceptible to both task demands and musical training. They argue that the information-processing approach to music perception may be helpful in the understanding of ear asymmetries. The next chapter (chapter 12), written by Bryden, summarizes the lateralization studies of affect in dichotic listening. Most of the studies reported in this chapter have shown a left ear advantage for the perception of affective stimuli. As Bryden rightly notes, a major problem encountered in these studies is that most of them did not make a distinction between the specific aspects of affect and the effects of doing a nonverbal task. Section E deals with the use of physiological measures in combination with dichotic listening procedures. The relationship between verbal dichotic listening and event-related potentials (ERPs) is addressed by Molfese and Adams (chapter 13). The few studies described here demonstrate that the ERP findings are rather inconsistent. The authors discuss a number of problems which could have influenced the results obtained across investigations. Hugdahl (chapter 14) introduces a series of new paradigms, called the ‘dichotic conditioning paradigms’ for the study of lateralization of associative learning, or
90
Book reviews
classical conditioning. In these studies, associations are formed between a verbal or non-verbal auditory conditioned stimulus and an unconditioned stimulus; skin conductance responses are employed as dependent measures. The author discusses the theoretical bases underlying these paradigms. The clinical applications of this approach, however, must be still proved. Section F is dedicated to developmental issues and reading disturbances. Hiscock and Decter (chapter 15) provide a good overview of studies focused on developmental changes in ear asymmetries in normal children. This chapter clearly shows that there is no evidence for a developmental increase in lateralization. Nevertheless, the dichotic listening data are not very consistent across studies. Hiscock and Decter discuss a lot of methodological difficulties encountered in measuring ear asymmetries in children, such as problems with task difficulty, report order, directional attention, task demands, reliability and validity, and the use of laterity indices. Obrzut and Boliek (chapter 16) review the data on ear asymmetries in learning and reading disabled children. The authors evaluate several theories of lateralization concerning the relationship between hemispheric specialization and learning and reading disabilities. They claim that attentional deficiencies contribute to perceptual asymmetries in these children. More specifically, Obrzut and Boliek propose that these children probably exhibit a weaker underlying structural system whereby the left hemisphere is not capable of suppressing the right hemisphere. Their conclusion, however, must be considered with caution since most of the evidence supporting their view is based on studies employing consonant-vowel syllables, and the group described in this chapter appears to be heterogeneous in nature. Bakker and Kappers (chapter 17) discuss the problems encountered in their studies concerning the relationship between dichotic listening and reading (dis)ability. They found that ear asymmetries show different developmental patterns and that these patterns are associated with reading (dis)ability in a complex way. It is argued that particularly the operationalization of the concepts reading (dis)ability may account for the different ear asymmetry patterns. Section G deals with cerebral laterality in psychiatric patients. Bruder (chapter 18) provides an overview of dichotic listening studies in patients with schizophrenia and affective disorders. On the basis of these studies, the author suggests that, at least under certain conditions, schizophrenic patients show abnormal activation patterns in the left hemisphere and depressed patients show abnormal activation patterns in the right hemisphere. Bruder also demonstrates that abnormal laterality patterns are particularly influenced by the nature of the task, the subtypes of patient groups, and the stages of the disease. Nachson (chapter 19) describes the major dichotic listening models of cerebral deficit in schizophrenia. The author comes to the conclusion that an integrated model associating schizophrenics’ performance with the interactive
Book reviews
91
effects of left hemisphere dysfunction and callosal structural damage seems to fit the data best. Contrary to Bruder, Nachson proposes that the left hemisphere dysfunction in schizophrenics must not be considered in terms of overactivation, but in terms of dysfunctional underactivation. Each of the chapters provides valuable information about cerebral laterality in schizophrenia, but, unfortunately, there is a lack of integration across the two chapters. In section, H, Harshman (chapter 20) critically reviews the methodological and practical issues concerning the meaningfulness of variation in degree of dichotic asymmetry of different groups and individuals. Harshman pays much attention to the ‘construct validity’ of dichotic findings. Evidence for ‘construct validity’ may be obtained by relating group or individual differences in dichotic asymmetry to other theoretically relevant variables, such as sex, handedness, familial sinistrality, and cognitive abilities. Harshman further proposes that there are many different natural patterns of brain organization between individuals. For example, some of the brain variation might involve individual differences in degree of lateralization for a particular function, while other variation might involve individual differences in anterior-posterior localization, or differences in transcallosal, cortical, and subcortical interconnections among different functional systems. Harshman argues that this variation in brain organization may explain much of the inconsistent findings obtained in laterality studies. Taken together, the studies reported in this book make clear that a wide range of variables affect the direction and degree of dichotic ear asymmetry. These include the choice of stimulus material (verbal or nonverbal nature of the stimulus, familiarity, difficulty, etc.), the choice of task characteristic (accuracy, recognition or speed as dependent variable, degree of practice, monaural or dichotic stimulation, nature of response, e.g, free recall or directed attention), and the specification of subject groups (sex, handedness, age, individual differences in cognitive ability and/or mode of processing, individual differences in anatomical asymmetries, lesion characteristics, psychiatric patients, learning and reading disabilities, etc.). Moreover, this book makes also clear that ear asymmetries can be influenced by factors other than hemispheric specialization. On the basis of these findings, it is obvious that it is very difficult to make inferences about the cerebral functions of the individual person. The Handbook of Dichotic Listening: Theory, Method and Research is a book which gives the reader a good impression of research findings and research problems in the field of dichotic listening. However, this book cannot, in may opinion, be considered as a ‘handbook of dichotic listening’. The main difficulty is that the book as a whole lacks the type of structure which would be helpful for a reader to get a systematic overview of dichotic listening research. There is a lack of integration of individual chapters, and some topics
92
Book reoiews
are presented with different views in different chapters, without sufficient editorial guidance. The chapters vary greatly in organization and quality: some chapters provide thorough and critical overviews of the subject under discussion, while others present only fragmented information. Besides that, this book delivers much redundant information, especially when theoretical and methodological issues of the dichotic listening method are discussed. On the other hand, the book addressed a lot of relevant and interesting topics. I would recommend this book more for those interested in research and methodology than for the clinicians in practice. Anke Bouma Dept. of Clinical Psycholoa Free University Provisorium I, Cl25 De Boelelaan I1 I5 1081 H V Amsterdam Netherlands P. Kanerva, Sparse Cambridge, 1988.
Distributed
Memory.
A Bradford Book, The MIT Press,
This brief but concentrated book deals with two main problems: (1) how to organize a memory for efficient retrieval, and (2) how to realize such a memory from neuron-like components. Coming from the perceptron tradition, it presents a mathematical analysis of a very high-dimensional space of binary vectors. It is not a connectionist or PDP approach at all; since it is basically a linear model, the development depends solely on mathematical analysis and no simulations are needed. The three main contributions are to show the neuron can function as an address decoder, the mathematical feasibility of a sparse distributed memory using neurons in this way, and the similarity of this mathematical abstraction to the structure of the cerebellar cortex. Patterns serve as addresses to memory, and the storage of information is designed for optimal retrieval. Conventional address decoders respond to only one input, but with a threshold notion the response region increases as the threshold increases. The two main memory problems the book deals with are categorization (or classification) and sequencing. There is frequent reference to redintegration (the ability of a part to reinstate the whole), but this feature (‘content addressability’) is used more as a means to an end than as an end in itself. For categorization, the linear threshold units are basically an extension of the original perceptron idea, and sequencing deals with the classic serial-order problem; namely, how memory for discrete episodes gets entered into an
87
76 (1991) 87-95
Book reviews Kenneth Hugdahl (ed.), Handbook of Dichotic Listening: Research. Wiley, New York, 1988. 650 pp., 20 chs.
Theory, Method
and
Since the introduction of the dichotic listening task by Kimura in 1961 in the field of hemispheric specialization, many researchers and clinicians have employed this technique for assessing the functions of the cerebral hemispheres in both normal and clinical populations. In these task, competing stimuli are presented simultaneously to the left and right ear and the subjects are asked to report what they have heard. In general, studies reveal a right ear advantage (left hemisphere) for verbal tasks and a left ear advantage (right hemisphere) for nonverbal tasks. The rationale underlying these findings is (a) that the contralateral auditory pathways from the ear to the cortex are more efficient than the ipsilateral pathways, (b) that, under dichotic stimulation, information transmitted via the contralateral pathways suppresses information ascending the ipsilateral pathways, and (c) that stimuli are processed more easily when stimuli are projected directly to the specialized hemisphere than when stimuli are first projected to the nonspecialized hemisphere and then transmitted across the corpus callosal pathways to the specialized hemisphere. The studies employing the dichotic listening procedure have grown to a tremendous size over the past quarter-century so that is is very difficult to integrate the large amount of reported findings. The main purpose of the book is to provide a theoretical and practical ‘handbook’ for those who wish to use the dichotic listening method in research and clinical practice. The book covers a lot of theoretical and methodological issues of dichotic listening in normal subjects and discusses the applications of this method in clinical subjects; however, the reader who thinks that this book is an easy entry for the use of dichotic listening in practical settings for assessment and diagnosis, will be disappointed. This book is an edited book written by different researchers in this field of study. An advantage of this approach is that topics of interest can be treated thoroughly, but a disadvantage is that some topics are scattered over the chapters or that they overlap each other in different chapters. Another disadvantage is that many of the authors devote the major part of their chapter to their own research findings rather than reviewing the topic under OOOl-6918/91/$03.50
0 1991 - Elsevier Science Publishers
B.V. (North-Holland)
88
Book
reviews
discussion. This approach leads to a book being heterogeneous in organization and quality. The Handbook of Dichotic Listening: Theory, Methods and Research is divided in 8 sections: Dichotic listening and cerebral asymmetry (A), Anatomical and neurological considerations (B), Methodological, acoustic, and phonetic considerations (C), Nonverbal and affective processes (D), Electrophysiological and autonomic correlates (E), Children and reading disorders (F), Psychopathology (G), and Group and individual differences (H). Section A can be viewed as an introduction of the basic issues of the dichotic listening procedure and its relationship to hemispheric specialization. This section deals mainly with the research findings of normal subjects. Bryden opens this book with a clear introduction and overview of dichotic listening as a method to assess hemispheric lateralization. In this chapter a variety of verbal and nonverbal dichotic techniques are briefly described, and the theoretical bases that underlie the dichotic ear effects are discussed. This chapter also includes the effects of handedness and sex on dichotic listening performance. Bradshaw (chapter 2) challenges Kimura’s view that ear asymmetries only emerge under conditions of dichotic simulation. In reviewing a number of studies, Bradshaw convincingly shows that ear asymmetries can be demontrated with monaural stimulation in numerous task situation. Clark, Geffen and Geffen (chapter 3) report an experiment employing a dichotic monitoring procedure. They find that ear asymmetries obtained with this task are quite stable and unaffected by practice and attention strategies. Wexler (chapter 4) emphasizes that dichotic listening tasks with a high degree of temporal and auditory spectral overlap between the competing stimuli, such as the fused, rhymed dichotic words test, can be considered as a reliable and valid method of presenting stimuli to a single hemisphere. Wexler also provides some examples of experimental applications; however, this part of the chapter deals with a variety of topics and is not very cogent and well organized. Section B gives valuable information about the anatomical correlates of the dichotic listening technique in brain-damaged patients. Strauss (chapter 5) deals with the validity of verbal and nonverbal dichotic listening tasks in a group of epileptic patients who have undergone carotic Amytal speech testing. The author focuses on both the relationship between dichotic laterality effects and cerebral speech representation and the relationship between laterality measures and neuroanatomical differences. Eslinger and Damasio (chapter 6) present evidence for the anatomical correlates of ear extinction effects by investigating patients with neurologically identified locations of lesions. The studies reported here show that contralateral ear extinction is associated with damage to auditory cortices or auditory pathways. Moreover, left ear extinction is also associated with lesions involving the corpus callosum. Of particular
Book reviews
89
interest is the finding that left ear extinction may even be caused by damage to cerebral regions outside the auditory system. The authors suggest that left ear extinction in these cases may be the result of altered attention mechanisms, leading to an ‘enhanced right ear advantage’. Sidtis (chapter 7) also demonstrates the importance of callosal transfer in the dichotic listening model by studying commissurotomy patients. It is argued that structural variability in the corpus callosum or asymmetries in the subcortical auditory system may represent factors that systematically influence ear effects. Section C deals with both the methodological issues of the dichotic listening method and the acoustic and phonetic aspects of the dichotic stimuli. Statistical properties of several dichotic listening paradigms employing speech signals (consonant-vowel nonsense syllables) are discussed by Speaks (chapter 8). This chapter especially focuses on the analysis of data in terms of intialistener variability in ear advantage over blocks of trials. Harshman and Lundy (chapter 9) provide a thorough review of the dichotic listening task as a method for measuring ‘degree of lateralization’. The authors critically discuss the pros and cons of laterality indices. This chapter contains a number of essential issues concerning the interpretation of dichotic listening scores. Tartter (chapter 10) provides an overview of studies investigating the effects of auditory and phonetic feature manipulations on ear asymmetries and fusions in verbal dichotic listening tasks. Section D reviews studies employing nonverbal stimuli and affective processes. Peretz and Morais (chapter 11) describe a number of studies emphasizing the specificity of laterality effects reported for the different components of music perception. The authors make clear that laterality effects for musical perception are very susceptible to both task demands and musical training. They argue that the information-processing approach to music perception may be helpful in the understanding of ear asymmetries. The next chapter (chapter 12), written by Bryden, summarizes the lateralization studies of affect in dichotic listening. Most of the studies reported in this chapter have shown a left ear advantage for the perception of affective stimuli. As Bryden rightly notes, a major problem encountered in these studies is that most of them did not make a distinction between the specific aspects of affect and the effects of doing a nonverbal task. Section E deals with the use of physiological measures in combination with dichotic listening procedures. The relationship between verbal dichotic listening and event-related potentials (ERPs) is addressed by Molfese and Adams (chapter 13). The few studies described here demonstrate that the ERP findings are rather inconsistent. The authors discuss a number of problems which could have influenced the results obtained across investigations. Hugdahl (chapter 14) introduces a series of new paradigms, called the ‘dichotic conditioning paradigms’ for the study of lateralization of associative learning, or
90
Book reviews
classical conditioning. In these studies, associations are formed between a verbal or non-verbal auditory conditioned stimulus and an unconditioned stimulus; skin conductance responses are employed as dependent measures. The author discusses the theoretical bases underlying these paradigms. The clinical applications of this approach, however, must be still proved. Section F is dedicated to developmental issues and reading disturbances. Hiscock and Decter (chapter 15) provide a good overview of studies focused on developmental changes in ear asymmetries in normal children. This chapter clearly shows that there is no evidence for a developmental increase in lateralization. Nevertheless, the dichotic listening data are not very consistent across studies. Hiscock and Decter discuss a lot of methodological difficulties encountered in measuring ear asymmetries in children, such as problems with task difficulty, report order, directional attention, task demands, reliability and validity, and the use of laterity indices. Obrzut and Boliek (chapter 16) review the data on ear asymmetries in learning and reading disabled children. The authors evaluate several theories of lateralization concerning the relationship between hemispheric specialization and learning and reading disabilities. They claim that attentional deficiencies contribute to perceptual asymmetries in these children. More specifically, Obrzut and Boliek propose that these children probably exhibit a weaker underlying structural system whereby the left hemisphere is not capable of suppressing the right hemisphere. Their conclusion, however, must be considered with caution since most of the evidence supporting their view is based on studies employing consonant-vowel syllables, and the group described in this chapter appears to be heterogeneous in nature. Bakker and Kappers (chapter 17) discuss the problems encountered in their studies concerning the relationship between dichotic listening and reading (dis)ability. They found that ear asymmetries show different developmental patterns and that these patterns are associated with reading (dis)ability in a complex way. It is argued that particularly the operationalization of the concepts reading (dis)ability may account for the different ear asymmetry patterns. Section G deals with cerebral laterality in psychiatric patients. Bruder (chapter 18) provides an overview of dichotic listening studies in patients with schizophrenia and affective disorders. On the basis of these studies, the author suggests that, at least under certain conditions, schizophrenic patients show abnormal activation patterns in the left hemisphere and depressed patients show abnormal activation patterns in the right hemisphere. Bruder also demonstrates that abnormal laterality patterns are particularly influenced by the nature of the task, the subtypes of patient groups, and the stages of the disease. Nachson (chapter 19) describes the major dichotic listening models of cerebral deficit in schizophrenia. The author comes to the conclusion that an integrated model associating schizophrenics’ performance with the interactive
Book reviews
91
effects of left hemisphere dysfunction and callosal structural damage seems to fit the data best. Contrary to Bruder, Nachson proposes that the left hemisphere dysfunction in schizophrenics must not be considered in terms of overactivation, but in terms of dysfunctional underactivation. Each of the chapters provides valuable information about cerebral laterality in schizophrenia, but, unfortunately, there is a lack of integration across the two chapters. In section, H, Harshman (chapter 20) critically reviews the methodological and practical issues concerning the meaningfulness of variation in degree of dichotic asymmetry of different groups and individuals. Harshman pays much attention to the ‘construct validity’ of dichotic findings. Evidence for ‘construct validity’ may be obtained by relating group or individual differences in dichotic asymmetry to other theoretically relevant variables, such as sex, handedness, familial sinistrality, and cognitive abilities. Harshman further proposes that there are many different natural patterns of brain organization between individuals. For example, some of the brain variation might involve individual differences in degree of lateralization for a particular function, while other variation might involve individual differences in anterior-posterior localization, or differences in transcallosal, cortical, and subcortical interconnections among different functional systems. Harshman argues that this variation in brain organization may explain much of the inconsistent findings obtained in laterality studies. Taken together, the studies reported in this book make clear that a wide range of variables affect the direction and degree of dichotic ear asymmetry. These include the choice of stimulus material (verbal or nonverbal nature of the stimulus, familiarity, difficulty, etc.), the choice of task characteristic (accuracy, recognition or speed as dependent variable, degree of practice, monaural or dichotic stimulation, nature of response, e.g, free recall or directed attention), and the specification of subject groups (sex, handedness, age, individual differences in cognitive ability and/or mode of processing, individual differences in anatomical asymmetries, lesion characteristics, psychiatric patients, learning and reading disabilities, etc.). Moreover, this book makes also clear that ear asymmetries can be influenced by factors other than hemispheric specialization. On the basis of these findings, it is obvious that it is very difficult to make inferences about the cerebral functions of the individual person. The Handbook of Dichotic Listening: Theory, Method and Research is a book which gives the reader a good impression of research findings and research problems in the field of dichotic listening. However, this book cannot, in may opinion, be considered as a ‘handbook of dichotic listening’. The main difficulty is that the book as a whole lacks the type of structure which would be helpful for a reader to get a systematic overview of dichotic listening research. There is a lack of integration of individual chapters, and some topics
92
Book reoiews
are presented with different views in different chapters, without sufficient editorial guidance. The chapters vary greatly in organization and quality: some chapters provide thorough and critical overviews of the subject under discussion, while others present only fragmented information. Besides that, this book delivers much redundant information, especially when theoretical and methodological issues of the dichotic listening method are discussed. On the other hand, the book addressed a lot of relevant and interesting topics. I would recommend this book more for those interested in research and methodology than for the clinicians in practice. Anke Bouma Dept. of Clinical Psycholoa Free University Provisorium I, Cl25 De Boelelaan I1 I5 1081 H V Amsterdam Netherlands P. Kanerva, Sparse Cambridge, 1988.
Distributed
Memory.
A Bradford Book, The MIT Press,
This brief but concentrated book deals with two main problems: (1) how to organize a memory for efficient retrieval, and (2) how to realize such a memory from neuron-like components. Coming from the perceptron tradition, it presents a mathematical analysis of a very high-dimensional space of binary vectors. It is not a connectionist or PDP approach at all; since it is basically a linear model, the development depends solely on mathematical analysis and no simulations are needed. The three main contributions are to show the neuron can function as an address decoder, the mathematical feasibility of a sparse distributed memory using neurons in this way, and the similarity of this mathematical abstraction to the structure of the cerebellar cortex. Patterns serve as addresses to memory, and the storage of information is designed for optimal retrieval. Conventional address decoders respond to only one input, but with a threshold notion the response region increases as the threshold increases. The two main memory problems the book deals with are categorization (or classification) and sequencing. There is frequent reference to redintegration (the ability of a part to reinstate the whole), but this feature (‘content addressability’) is used more as a means to an end than as an end in itself. For categorization, the linear threshold units are basically an extension of the original perceptron idea, and sequencing deals with the classic serial-order problem; namely, how memory for discrete episodes gets entered into an