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Cognitive Neuropsychology, Methods of Saskia Kohnen and Lyndsey Nickels, Macquarie University, Sydney, NSW, Australia Ó 2015 Elsevier Ltd. All rights reserved. This article is a revision of the previous edition article by T. Shallice, volume 3, pp. 2128–2133, Ó 2001, Elsevier Ltd.
Abstract This article provides an overview of some of the most commonly used methodologies in the discipline of cognitive neuropsychology: dissociations, associations, single case studies, case series, intervention research, computational modeling and the cognitive neuropsychological approach to studying developmental disorders of cognition.
Cognitive neuropsychologists study impaired cognition to inform theories of normal cognition. They do so by observing cognitive behavior in people with impaired cognition, for example, people who have acquired a brain injury. Cognitive neuropsychologists are interested in what data from these individuals reveal about the processes and representations of cognitive systems (McCloskey and Caramazza, 1988).
Dissociations and Associations Cognitive neuropsychological studies have made major contributions to our understanding of the functional architecture of cognition (e.g., reading: Coltheart et al., 2001; Marshall and Newcombe, 1973; spoken language production: Badecker et al., 1995; Dell et al., 1997; spelling: Miceli and Capasso, 2006; Tainturier and Rapp, 2001). Under assumptions of modularity (Fodor, 1983; see Caramazza, 1992; Coltheart, 1999 for different versions of this assumption), the architecture of cognitive systems is composed of information-processing components that each fulfill a different purpose. These relatively autonomous components can also be independently damaged, for example, as the result of a brain injury. When such a functionally independent component is selectively impaired this will result in a ‘dissociation.’ Shallice (1988) distinguishes between classical, strong, and trend dissociations. In the most powerful dissociation, the classical dissociation, performance on one task is in the normal range, while performance on another task is very impaired. Strong and trend dissociations consist of less marked differences in task performance. These three dissociations rely on the use of control subjects (who are unimpaired in performing the tasks in question) to determine what score should be considered normal or impaired. John Crawford and his colleagues have provided the statistical means to allow detection of a deficit in a single patient compared to a (relatively small) control group, deliver a point estimate of the abnormality of the patient’s score and determine the difference between scores on two tasks (Crawford and Garthwaite, 2006; Crawford and Howell, 1998; Crawford et al., 2009). An example of an interesting, theoretically important dissociation is that of JOH, who showed an intriguing pattern of performance (Costello and Warrington, 1987). JOH presented with a reading disorder – left neglect dyslexia – that led to
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reading errors at the beginning of words (e.g., reading make as ‘cake’ or least as ‘beast’). However, this was not due to a general neglect of the left hand side of space. In fact, he showed evidence of a right-sided visuospatial neglect. That is, when processing (e.g., copying) pictures or figures, he omitted information on the right hand side. For example, when asked to copy a row of three shapes he would omit the last (rightmost) shape. This dissociation shows that there is not a single mechanism underlying neglect in both visuospatial tasks and reading, but rather there are two separate mechanisms, which can be separately impaired. Note that this dissociation is particularly clear as the argument is not in terms of the extent of the impairment in one task or another (both tasks were impaired) but the type of impairment (reading impaired on the left and intact on the right, visuospatial tasks impaired on the right and intact on the left). In cases where the dissociation is in terms of one task being impaired and the other intact, it could be that this is due to a difference in the difficulty of the two tasks rather than independent mechanisms. For example, interpretation can be open to the potential argument that one task is simply harder than the other (requires more processing resources). Imagine a dissociation between recognition of faces and recognition of printed words. Could it be that this dissociation in fact reflects damage to a single system that impairs face recognition without impairing visual word recognition, because faces are visually more complex, and so stress this system more. However, if there is a case where printed word recognition is impaired and face processing is intact, this would refute the difficulty argument. This pair of opposite dissociations makes up a ‘double dissociation,’ which has long held to be the strongest evidence for separate processing components. While cognitive neuropsychology has been accused of being overly interested in dissociations (Laine and Martin, 2012), the study of human cognition often requires testing for associations. Hence, many cognitive neuropsychological studies set out with the explicit aim to discover associations. One example of looking for associations can be found in a multiple single case study on letter position dyslexia (Friedmann and Rahamim, 2007). The main symptom of letter position dyslexia is a disproportionately high number of anagram reading errors (e.g., slime read as ‘smile’). Friedmann and Rahamim proposed that this error type is caused by an impairment early on in the reading process (the
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orthographic visual analyzer). Hence, they predicted that anagram errors should occur in all reading tasks (whether reading of nonwords or words, whether they included reading aloud or not). This association was indeed what they found (also see Section Computational Cognitive Neuropsychology for more examples of studying systematic associations).
Single Case Studies The investigation of a single case is considered an important (but not the only) methodology in cognitive neuropsychology. Single cases may present with a behavior that cannot be explained by current theories and hence may be used to test, extend, and/or change current understanding in an area of cognition. One of best known single cases to inform cognitive theory is probably that of HM (Scoville and Milner, 1957). The first report of HM has not only attracted over 4000 citations (by 2013) but also has been argued to represent the beginning of the modern study of memory (Squire, 2009). HM was an epilepsy patient who after brain surgery had lost his capacity to remember daily events. At the same time, his intellectual and perceptual functioning remained intact. Before Brenda Milner and her colleagues began to study HM, memory function was thought to be integrated with intellectual and perceptual processes. HM’s case helped establish the theory that memory is independent from these other processes. The main reason why single case studies are considered both powerful and valid rests on the finding that individuals with cognitive disorders are by their nature variable (Caramazza and Coltheart, 2006). Due to the high number of possible functional lesions, there is only a theoretical chance that two patients will ever display the exact same impairment (Caramazza, 1986; Caramazza and Coltheart, 2006; Coltheart, 1984). In commenting on the huge variability in the actual presentation of hemispatial neglect in patients, Buxbaum (2006) evokes the analogy of snowflakes, each of which, of course, is unique. The snowflake analogy is probably valid for most areas of cognition. For example, Schmalzl and colleagues (Schmalzl et al., 2008) studied seven members of a family who had face-processing difficulties (prosopagnosia). These individuals all had difficulties recognizing the faces of family members, four of them could not even identify their own face reliably in a photograph. However, a more detailed investigation showed different underlying impairments for these family members’ difficulties in recognizing face. In fact, there were no two family members that showed the exact same pattern of difficulties. For example, some but not all of the family members had difficulties detecting facial expressions. Similarly, some but not all family members had problems detecting when spacing between features of the faces (e.g., nose, mouth) was changed. This is an example of a study that shows how face processing difficulties can be caused by different underlying processes, even within the same family. Due to this variability, cognitive neuropsychologists tend not to study syndromes. Labels such as prosopagnosia, surface dyslexia, or even Broca’s aphasia may be used but they are mere ‘short hand’ terms for a gross level of symptomatology (i.e.,
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problems recognizing faces; problems reading irregular words; limited syntactic structure in speech production) that hide the complexity of each patient’s presentation and the high variability between patients. Studying the average performance of groups of patients that belong to the same syndrome complex could mask important differences between individuals as well as produce averages that do not describe a single individual in this group. However, single case studies have been criticized for their lack of generalizability, lack of control, and poor statistical methods (but see e.g., Robey et al., 1999). Lack of control and statistical problems are easily taken care of by using appropriate designs including converging evidence from replications, multiple experiments of the function in question, and employing some of the myriad of appropriate statistics (e.g., McNemar’s, Fisher’s exact, Wilcoxon). Generalizability can be improved by studying symptoms (rather than syndromes) in multiple single cases (Friedmann and Rahamim, 2007; Warrington, 1975). Indeed, many reports of new dissociations within a syndrome describe multiple cases, which are examined for their differences and similarities in performance; both in reference to previous cases and within the sample reported in the new paper. If patients are so highly variable in terms of their functional deficits, how is it ever possible to generalize beyond the level of the individual? This relies on two assumptions. First, the assumption of ‘universality’ poses that neurologically intact people do not differ from each other in regard to their cognitive architectures (Caramazza, 1986). It is worthwhile to note that this assumption underlies all studies of cognitive psychology, otherwise inferences about cognition could not be made from small study samples drawn from the general population. Moreover, some degree of individual difference is not incompatible with the universality assumption (Rapp, 2011). Second, if inferences can be drawn from neurologically impaired patients to normal cognition, it needs to be the case that the injury simply subtracted one or more cognitive functions without also altering or adding new functions (Saffran, 1982). Therefore, studying an individual with a selective impairment provides a unique experimental technique for studying human cognition, in particular, a system that misses exactly one function. However, single case studies are only one of the methodologies available to the cognitive neuropsychologist.
Case Series Another form of study with multiple participants that is popular in cognitive neuropsychology is the case series (Schwartz and Dell, 2010). McCloskey and Caramazza (1988) distinguish between two ways of studying groups of people: Group studies, which report average performance of the group in a way that individual results are invisible vs case series, in which individual data for each participant are reported. Averaging is only appropriate when variability in the data is assumed to be due to noise (McCloskey and Caramazza, 1988). As noted above, one of the problems in reporting agglomerate data in classical group studies is that what describes the whole group may not describe any single individual. Case series do not suffer from this problem. Case
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series designs have the potential to allow the identification of central tendencies in the data, which reflect the actual performance of several individuals, while still including variability typical of larger populations (Shallice and Buiatti, 2011). In patient data, heterogeneity may be informative in that it may reveal systematic relationships among different variables (Schwartz and Dell, 2010). While heterogeneity in the dependent variable is required to carry out such investigations, it is important that the source of the variability is relevant to the question in hand (Nickels et al., 2011). For example, when investigating word retrieval in a group of aphasic speakers, the individuals should vary in terms of their naming accuracy. At the same time, factors that could potentially impact on performance on the dependent variable (e.g., picture naming), but are not subject of the particular investigation, such as attention or object recognition need to be kept similar between the individuals. Which exact variables need to be kept similar and which should vary depends on what theory a study aims to investigate. There are certain theoretical questions that require a case series methodology. Rapp (2011: p. 437) summarizes them as “As X increases (or decreases), Y should increase (or decrease).” Hence, the study would select patients with varying degree of deficits in skill X and test their ability to do Y. Rapp’s examples of X and Y include the severity of a semantic impairment and accuracy for exception word reading (Woollams et al., 2007); or severity of sublexical damage and perseveration errors in spelling (Fischer-Baum and Rapp, 2012). Note that all of these studies are interested in a theoretically relevant association between two functions. Ideally, case series should include a combination of standard background assessment and experimental tests. These should be performed on all participants in a case series and also take into account items and tasks that have been used in previous studies (Nickels et al., 2011). Using similar tasks and items not only makes it easier to compare cases across studies but also helps in testing and designing computational models of cognition.
Computational Cognitive Neuropsychology The architecture of cognitive processes is often described in verbal or diagrammatic models. These consist of verbal descriptions or box and arrow type diagrams. Seidenberg and McClelland (1989) were the first to design a computational model of reading aloud. Since then, more cognitive theories have been implemented computationally, including one of the most well-known reading models, the Dual Route model (e.g., implemented as the Dual Route Cascaded model: Coltheart et al., 2001), but also models of spelling (e.g., Houghton and Zorzi, 2003) and spoken language (Dell et al., 1997; Levelt et al., 1999; Roelofs, 1997). A good model, be it verbal, diagrammatic, or computational, should be able to account for the full body of evidence pertaining to both normal and impaired cognition. Cognitive neuropsychological principles can also be applied to these computational models. They can be ‘lesioned’
in order to display symptoms described in patients (Coltheart, 2006). Lesioning a model can be achieved in different ways, depending on the model. For example, the strengths of connections can be adjusted or noise may be introduced. Whatever change to the ‘normal’ computational model best fits the patient data, can be regarded as an account of the type of impairment to the cognitive system. Damaging a computational model in ways that will match the data of patients can provide converging evidence for a certain theory, and it can also allow a specification in how exactly cognitive processes are impaired when a certain pattern of impairment is shown. Case series (see Section Case Series) can play a great role in testing these models. Nickels (1995) examined the errors produced in picture naming by a case series of people with aphasia. Specifically, she examined the relationship between production of semantic (doctor named as ‘nurse’) and phonological (doctor named as ‘doptor’) errors and the psycholinguistic variables that affected these errors. Imageability was found to affect the production of semantic errors (but not subjective frequency, or length). Whereas for phonological errors subjective frequency and number of phonemes showed significant effects (but not imageability). Nickels used these patterns to adjudicate between the predictions of highly interactive and strictly feedforward models, arguing that the data were inconsistent with the interactive models of speech production.
Theoretical Impact of Treatment Studies In its aim to understand human cognition, cognitive neuropsychological studies can assess patients’ performance on a multitude of tasks pertaining to the area of cognition under investigation. One way to adjudicate between different theories of cognition is to design an experiment in which different theories predict different outcomes. The experimental design can be an intervention. Hence, another powerful tool to test theories is the use of treatment (Nickels et al., 2010). For example, Biedermann and Nickels (2008a,b) investigated the lexical representation of homophones using treatment (see Nickels et al., 2010 for other examples of studies using intervention to investigate cognitive theories). Homophones are words that are pronounced in the same way but have different meanings (e.g., tank: fish-tank, military tank; flour/ flower). One theory proposes that each version of a homophone has its own lexical representation (Caramazza, 1997), while an opposing theory posits homophones share a representation (Levelt et al., 1999). Biedermann and Nickels designed an intervention study to provide new insights into this debate. Intervention can help people with word finding difficulties to become better at retrieving the words practiced during intervention. However, usually, effects are restricted to practiced words and will not benefit words that were not explicitly practiced during the intervention. Following this logic, Biedermann and Nickels made the following differential predictions: if homophones share representations, treating one partner of a homophone (e.g., flower; (fish) tank) should lead to improvements in retrieving the untrained partner of the homophone (i.e., flour; (military) tank). In contrast, if
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each homophone partner has its own lexical representation, only the trained words (e.g., flower; (fish) tank) should improve. The results favored the theory that homophones share lexical representations since not only the trained homophones but also their untrained partners improved after training. Note that a set of control words that sounded similar to the treated words (but were not homophone partners) or were similar in meaning did not improve. Other than providing insights into theoretical issues cognitive neuropsychological approaches to treatment can be used to assess the efficacy of treatment protocols and procedures. Moreover, there are many examples of treatment studies where the aim was to explain how a particular treatment works within a particular cognitive architecture. Often, these explanations in effect provide converging evidence for one particular theory. An example of this is a treatment study conducted with a person who had both deep dyslexia and anomia (Nickels, 1992; see Nickels et al., 2010 for further examples). Deep dyslexia refers to impaired reading that is marked by the presence of semantic reading errors (e.g., reading wine as ‘beer’), visual errors (e.g., late as ‘lake’), morphological errors (e.g., swims as ‘swimming’), a word class effect (i.e., function words worse than content words), and an inability to read nonwords. Nickels’ participant TC also made many semantic errors when asked to name pictures. The intervention consisted of reteaching letter–sound correspondences. While this did not lead to improved nonword reading (because the participant remained unable to blend sounds together to form a word), the frequency of semantic errors decreased after intervention. These results were later used as supporting evidence for the ‘summation theory’ according to which phonological information feeds back into the phonological lexicon (Hillis and Caramazza, 1995). After the intervention, TC started to ‘self-cue’ by using his knowledge of the initial letter of a word he was supposed to say and generating the sound (Nickels, 1992). For example, if he was asked to name the picture of a tiger, TC would activate semantically related words in addition to the correct word (e.g., leopard, panther, tiger, lion). Being able to retrieve the written word form, and sounding out the initial letter T, provided additional activation to the correct response allowing selection, and reduction of semantic errors. The cognitive neuropsychological approach to intervention also advocates that, with use of a strong design and appropriate statistics, single case intervention studies can provide a high level of evidence for the efficacy of treatment. Many cognitive neuropsychologists would argue, once again, that a series of single case studies can provide stronger and more valid evidence than evaluating average effects over a group study (such as advocated in randomized controlled trials) (also see Wright, 2012 for a discussion of this issue).
Acquired and Developmental Cognitive Neuropsychology Traditionally, the cognitive neuropsychological approach has been applied to studies with individuals with acquired disorders, that is, people who are now impaired in a skill that they had fully acquired prior to their brain injury. However, in
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the 1980s, the methodologies of cognitive neuropsychology were extended to the developmental domain, where a cognitive system is still in the process of being acquired. This work was pioneered by John Marshall, Jane Holmes, and Christine Temple. Developmental cognitive neuropsychology investigates developmental disorders using models of the cognitive architecture of the adult system. The strong claim underlying this approach is that in developmental disorders, highly selective disorders should be observable (Castles et al., 2006; Marshall, 1984; Temple, 1997). This is in contrast to a view according to which a disorder early in development distorts the system in more than one way since development is an interactive process (see Bishop, 1997). For example, if a child has difficulties learning to say words, they may also have difficulties to learn the sounds of a language. The degree to which development of different cognitive functions happens independently is an ongoing topic of research. However, there is now a large literature detailing the vast differences in the presentation of children with developmental dyslexia (see Castles et al., 2006; Marshall, 1984): for almost every processing component in the reading architecture (in this case dual route models of reading), there are published case reports of developmental cases who have a specific difficulty acquiring the skill that is governed by this processing component (for overviews of these disorders see Coltheart and Kohnen, 2012; Jones et al., 2011). These selective difficulties can be taken as evidence that development of cognitive skills can, to some degree, be modular. In the case of developmental dyslexia, cognitive neuropsychologists refer to dual route architecture. Evidence for this architecture is based on data from adult readers. Hence, one could call dual route models ‘adult models’ of reading. What is somewhat controversial is whether developmental disorders should be studied within the framework of an adult system; a cognitive system that is presumably static and not learning and developing. Bishop (1997) argues that the course of development is typically highly interactive, with skills and competencies influencing each other. Therefore, children usually present with complex patterns of associated impairments, rather than highly selective deficits. While pure cases of selective difficulties do indeed tend to be rare (Castles et al., 2006), they nevertheless make contributions to our understanding and advance developmental theories of cognition. For example, one of the most prominent current theories of how children acquire a written vocabulary posits that lexical acquisition depends largely on nonlexical skills (Share, 1999). After one or more exposures where a novel word is sounded out using nonlexical skills, a representation of the word will be developed in the orthographic lexicon. However, some children acquire a reading vocabulary that is at a normal level while their nonlexical skills are severely impaired. This is called developmental phonological dyslexia. While Share’s theory is plausible, it is cases of phonological dyslexia that clearly show that this theory alone cannot explain how children acquire a reading vocabulary. This is just one example of how the study of selective deficits in developmental disorders is important in furthering our understanding of the acquisition of cognitive functions.
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Conclusion Cognitive neuropsychology aims to understand and uncover the cognitive architecture and processing that underlies both normal and impaired cognition. It does so by studying children and adults with cognitive disorders, or lesioning computational models of cognition. Note that many of the methodologies described above are not only used by cognitive neuropsychologists. For example, single case studies form an important methodology in medical science. Similarly, the use of treatment studies to inform theory is also used in many other disciplines, including, for example, in developmental psychology. Embracing multiple methodologies is one way to further understanding of human cognition and ultimately the interaction of brain and mind.
See also: Case Study: Methods and Analysis; Cognitive Neuroscience.
Bibliography Badecker, W., Miozzo, M., Zanuttini, R., 1995. The two stage model of lexical retrieval: evidence from a case of anomia with selective preservation of grammatical gender. Cognition 5, 193–216. Biedermann, B., Nickels, L., 2008a. The representation of homophones: more evidence from remediation of anomia. Cortex 44, 276–293. Biedermann, B., Nickels, L., 2008b. Homographic and heterographic homophones in speech production: does orthography matter? Cortex 44, 683–697. Bishop, D.V.M., 1997. Cognitive neuropsychology and developmental disorders: uncomfortable bedfellows. The Quarterly Journal of Experimental Psychology: Section A 50, 899–923. Buxbaum, L.J., 2006. On the right (and left) track: twenty years of progress in studying hemispatial neglect. Cognitive Neuropsychology 2, 156–173. Caramazza, A., 1986. On drawing inferences about the structure of normal cognitive systems from the analysis of patterns of impaired performance: the case for singlepatient studies. Brain and Cognition 5, 41–66. Caramazza, A., 1992. Is cognitive neuropsychology possible? Journal of Cognitive Neuroscience 4, 80–95. Caramazza, A., 1997. How many levels of processing are there in lexical access? Cognitive Neuropsychology 14, 177–208. Caramazza, A., Coltheart, M., 2006. Cognitive Neuropsychology twenty years on. Cognitive Neuropsychology 23, 3–12. Castles, A., Bates, T.A., Coltheart, M., 2006. John Marshall and the developmental dyslexias. Aphasiology 20, 871–892. Coltheart, M., 1984. Acquired dyslexias and normal reading. In: Malatesha, R.N., Whitaker, H.A. (Eds.), Dyslexia: A Global Issue. Martinus Nijhoff, The Hague, The Netherlands. Coltheart, M., 1999. Modularity and cognition. Trends in Cognitive Sciences 3, 115–120. Coltheart, M., 2006. Acquired dyslexias and the computational modelling of reading. Cognitive Neuropsychology 23, 96–109. Coltheart, M., Kohnen, S., 2012. Acquired and developmental disorders of reading and spelling. In: Faust, M. (Ed.), The Handbook of the Neuropsychology of Language. Wiley-Blackwell Publishers, Chichester, pp. 892–920. Coltheart, M., Rastle, K., Perry, C., Langdon, R., Ziegler, J., 2001. DRC: a dual route cascaded model, of visual word recognition and reading aloud. Psychological Review 108, 204–256. Costello, A.D., Warrington, E.K., 1987. The dissociation of visuospatial neglect and neglect dyslexia. Journal of Neurology, Neurosurgery & Psychiatry 50, 1110–1116. Crawford, J.R., Garthwaite, P.H., 2006. Methods of testing for a deficit in single case studies: evaluation of statistical power by Monte Carlo simulation. Cognitive Neuropsychology 23, 877–904. Crawford, J.R., Garthwaite, P.H., Howell, D.C., 2009. On comparing a single case with a control sample: an alternative perspective. Neuropsychologia 47, 2690–2695. Crawford, J.R., Howell, D.C., 1998. Comparing an individual’s test score against norms derived from small samples. The Clinical Neuropsychologist 12, 482–486. Dell, G.S., Schwartz, M.F., Martin, N., Saffran, E.M., Gagnon, D.A., 1997. Lexical access in normal and aphasic speech. Psychological Review 104, 801–838.
Fodor, J.A., 1983. The Modularity of Mind. MIT Press, Cambridge. Fischer-Baum, S., Rapp, B., 2012. Underlying causes of letter perseveration errors in dysgraphia. Neuropsychologia 50, 305–318. Friedmann, N., Rahamim, E., 2007. Developmental letter position dyslexia. Journal of Neuropsychology 1, 201–236. Hillis, A.E., Caramazza, A., 1995. Converging evidence for the interaction of semantic and sublexical phonological information in accessing lexical representations for spoken output. Cognitive Neuropsychology 12, 187–227. Houghton, G., Zorzi, M., 2003. Normal and impaired spelling in a connectionist dualroute architecture. Cognitive Neuropsychology 20, 115–162. Jones, K., Castles, A., Kohnen, S., 2011. Subtypes of developmental dyslexia: recent developments and directions for treatment. Acquiring Knowledge in Speech, Language and Hearing 13, 79–83. Laine, M., Martin, N., 2012. Cognitive neuropsychology has been, is, and will be significant to aphasiology. Aphasiology 26, 1362–1376. Levelt, W.J.M., Roelofs, A., Meyer, A.S., 1999. A theory of lexical access in speech production. Behavioral & Brain Sciences 22, 1–75. Marshall, J.C., 1984. Toward a rational taxonomy of the developmental dyslexias. In: Malatesha, R.N., Whitaker, H.A. (Eds.), Dyslexia: A Global Issue. Martinus Nijhoff, The Hague. Marshall, J.C., Newcombe, F., 1973. Patterns of paralexia: a psycholinguistic approach. Journal of Psycholinguistic Research 2, 175–199. McCloskey, M., Caramazza, A., 1988. Theory and methodology in cognitive neuropsychology: a response to our critics. Cognitive Neuropsychology 5, 583–623. Miceli, G., Capasso, R., 2006. Spelling and dysgraphia. Cognitive Neuropsychology 23, 110–134. Nickels, L., 1992. The autocue? Self–generated phonemic cues in the treatment of a disorder of reading and naming. Cognitive Neuropsychology 9, 155–182. Nickels, L.A., 1995. Getting it right? Using aphasic naming errors to evaluate theoretical models of spoken word production. Language and Cognitive Processes 10, 13–45. Nickels, L., Kohnen, S., Biedermann, B., 2010. An untapped resource, treatment as a tool for revealing the nature of cognitive processes. Cognitive Neuropsychology 27, 539–562. Nickels, L., Howard, D., Best, W., 2011. On the use of different methodologies in cognitive neuropsychology: drink deep and from several sources. Cognitive Neuropsychology 28, 475–485. Rapp, B., 2011. Case series in cognitive neuropsychology: promise, perils, and proper perspective. Cognitive Neuropsychology 28, 435–444. Robey, R.R., Schultz, M.C., Crawford, A.B., Sinner, C.A., 1999. Single-subject clinicaloutcome research: designs, data, effect sizes, and analyses. Aphasiology 13, 445–473. Roelofs, A., 1997. The WEAVER model of word-form encoding in speech production. Cognition 64, 249–284. Saffran, E.M., 1982. Neuropsychological approaches to the study of language. British Journal of Psychology 73, 317–337. Scoville, W., Milner, B., 1957. Loss of recent memory after bilateral hippocampal lesions. Journal of Neurology, Neurosurgery, and Psychiatry 20, 11. Schmalzl, L., Palermo, R., Coltheart, M., 2008. Cognitive heterogeneity in genetically based prosopagnosia: a family study. Journal of Neuropsychology 2, 99–117. Schwartz, M., Dell, G., 2010. Case series investigations in cognitive neuropsychology. Cognitive Neuropsychology 27, 477–494. Seidenberg, M.S., McClelland, J.L., 1989. A distributed, developmental model of word recognition and naming. Psychological Review 96, 523. Shallice, T., 1988. From Neuropsychology to Mental Structure. Cambridge University Press, Cambridge, UK. Shallice, T., Buiatti, R., 2011. Types of case series: the anatomically-based approach. Cognitive Neuropsychology 28, 500–514. Share, D.L., 1999. Phonological recoding and orthographic learning: a direct test of the self-teaching hypothesis. Journal of Experimental Child Psychology 72, 95–129. Squire, L.R., 2009. The legacy of patient HM for neuroscience. Neuron 61, 6–9. Tainturier, M.-J., Rapp, B., 2001. The spelling process. In: Rapp, B. (Ed.), The Handbook of Cognitive Neuropsychology: What Deficits Reveal about the Human Mind. Psychology Press, Philadelphia. Temple, C., 1997. Developmental Cognitive Neuropsychology. Psychology Press, Hove, UK. Warrington, E.K., 1975. The selective impairment of semantic memory. The Quarterly Journal of Experimental Psychology 27, 635–657. Woollams, A.M., Lambon Ralph, M.A., Plaut, D., Patterson, K., 2007. SD-squared: on the, association between semantic dementia and surface dyslexia. Psychological Review 114, 316–339. Wright, M., 2012. Cognitive neuropsychological approach to aphasia treatment: implications for evidence-based clinical practice. Aphasiology 26, 1391–1396.
Abstract This article provides an overview of some of the most commonly used methodologies in the discipline of cognitive neuropsychology: dissociations, associations, single case studies, case series, intervention research, computational modeling and the cognitive neuropsychological approach to studying developmental disorders of cognition.
Cognitive neuropsychologists study impaired cognition to inform theories of normal cognition. They do so by observing cognitive behavior in people with impaired cognition, for example, people who have acquired a brain injury. Cognitive neuropsychologists are interested in what data from these individuals reveal about the processes and representations of cognitive systems (McCloskey and Caramazza, 1988).
Dissociations and Associations Cognitive neuropsychological studies have made major contributions to our understanding of the functional architecture of cognition (e.g., reading: Coltheart et al., 2001; Marshall and Newcombe, 1973; spoken language production: Badecker et al., 1995; Dell et al., 1997; spelling: Miceli and Capasso, 2006; Tainturier and Rapp, 2001). Under assumptions of modularity (Fodor, 1983; see Caramazza, 1992; Coltheart, 1999 for different versions of this assumption), the architecture of cognitive systems is composed of information-processing components that each fulfill a different purpose. These relatively autonomous components can also be independently damaged, for example, as the result of a brain injury. When such a functionally independent component is selectively impaired this will result in a ‘dissociation.’ Shallice (1988) distinguishes between classical, strong, and trend dissociations. In the most powerful dissociation, the classical dissociation, performance on one task is in the normal range, while performance on another task is very impaired. Strong and trend dissociations consist of less marked differences in task performance. These three dissociations rely on the use of control subjects (who are unimpaired in performing the tasks in question) to determine what score should be considered normal or impaired. John Crawford and his colleagues have provided the statistical means to allow detection of a deficit in a single patient compared to a (relatively small) control group, deliver a point estimate of the abnormality of the patient’s score and determine the difference between scores on two tasks (Crawford and Garthwaite, 2006; Crawford and Howell, 1998; Crawford et al., 2009). An example of an interesting, theoretically important dissociation is that of JOH, who showed an intriguing pattern of performance (Costello and Warrington, 1987). JOH presented with a reading disorder – left neglect dyslexia – that led to
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reading errors at the beginning of words (e.g., reading make as ‘cake’ or least as ‘beast’). However, this was not due to a general neglect of the left hand side of space. In fact, he showed evidence of a right-sided visuospatial neglect. That is, when processing (e.g., copying) pictures or figures, he omitted information on the right hand side. For example, when asked to copy a row of three shapes he would omit the last (rightmost) shape. This dissociation shows that there is not a single mechanism underlying neglect in both visuospatial tasks and reading, but rather there are two separate mechanisms, which can be separately impaired. Note that this dissociation is particularly clear as the argument is not in terms of the extent of the impairment in one task or another (both tasks were impaired) but the type of impairment (reading impaired on the left and intact on the right, visuospatial tasks impaired on the right and intact on the left). In cases where the dissociation is in terms of one task being impaired and the other intact, it could be that this is due to a difference in the difficulty of the two tasks rather than independent mechanisms. For example, interpretation can be open to the potential argument that one task is simply harder than the other (requires more processing resources). Imagine a dissociation between recognition of faces and recognition of printed words. Could it be that this dissociation in fact reflects damage to a single system that impairs face recognition without impairing visual word recognition, because faces are visually more complex, and so stress this system more. However, if there is a case where printed word recognition is impaired and face processing is intact, this would refute the difficulty argument. This pair of opposite dissociations makes up a ‘double dissociation,’ which has long held to be the strongest evidence for separate processing components. While cognitive neuropsychology has been accused of being overly interested in dissociations (Laine and Martin, 2012), the study of human cognition often requires testing for associations. Hence, many cognitive neuropsychological studies set out with the explicit aim to discover associations. One example of looking for associations can be found in a multiple single case study on letter position dyslexia (Friedmann and Rahamim, 2007). The main symptom of letter position dyslexia is a disproportionately high number of anagram reading errors (e.g., slime read as ‘smile’). Friedmann and Rahamim proposed that this error type is caused by an impairment early on in the reading process (the
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orthographic visual analyzer). Hence, they predicted that anagram errors should occur in all reading tasks (whether reading of nonwords or words, whether they included reading aloud or not). This association was indeed what they found (also see Section Computational Cognitive Neuropsychology for more examples of studying systematic associations).
Single Case Studies The investigation of a single case is considered an important (but not the only) methodology in cognitive neuropsychology. Single cases may present with a behavior that cannot be explained by current theories and hence may be used to test, extend, and/or change current understanding in an area of cognition. One of best known single cases to inform cognitive theory is probably that of HM (Scoville and Milner, 1957). The first report of HM has not only attracted over 4000 citations (by 2013) but also has been argued to represent the beginning of the modern study of memory (Squire, 2009). HM was an epilepsy patient who after brain surgery had lost his capacity to remember daily events. At the same time, his intellectual and perceptual functioning remained intact. Before Brenda Milner and her colleagues began to study HM, memory function was thought to be integrated with intellectual and perceptual processes. HM’s case helped establish the theory that memory is independent from these other processes. The main reason why single case studies are considered both powerful and valid rests on the finding that individuals with cognitive disorders are by their nature variable (Caramazza and Coltheart, 2006). Due to the high number of possible functional lesions, there is only a theoretical chance that two patients will ever display the exact same impairment (Caramazza, 1986; Caramazza and Coltheart, 2006; Coltheart, 1984). In commenting on the huge variability in the actual presentation of hemispatial neglect in patients, Buxbaum (2006) evokes the analogy of snowflakes, each of which, of course, is unique. The snowflake analogy is probably valid for most areas of cognition. For example, Schmalzl and colleagues (Schmalzl et al., 2008) studied seven members of a family who had face-processing difficulties (prosopagnosia). These individuals all had difficulties recognizing the faces of family members, four of them could not even identify their own face reliably in a photograph. However, a more detailed investigation showed different underlying impairments for these family members’ difficulties in recognizing face. In fact, there were no two family members that showed the exact same pattern of difficulties. For example, some but not all of the family members had difficulties detecting facial expressions. Similarly, some but not all family members had problems detecting when spacing between features of the faces (e.g., nose, mouth) was changed. This is an example of a study that shows how face processing difficulties can be caused by different underlying processes, even within the same family. Due to this variability, cognitive neuropsychologists tend not to study syndromes. Labels such as prosopagnosia, surface dyslexia, or even Broca’s aphasia may be used but they are mere ‘short hand’ terms for a gross level of symptomatology (i.e.,
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problems recognizing faces; problems reading irregular words; limited syntactic structure in speech production) that hide the complexity of each patient’s presentation and the high variability between patients. Studying the average performance of groups of patients that belong to the same syndrome complex could mask important differences between individuals as well as produce averages that do not describe a single individual in this group. However, single case studies have been criticized for their lack of generalizability, lack of control, and poor statistical methods (but see e.g., Robey et al., 1999). Lack of control and statistical problems are easily taken care of by using appropriate designs including converging evidence from replications, multiple experiments of the function in question, and employing some of the myriad of appropriate statistics (e.g., McNemar’s, Fisher’s exact, Wilcoxon). Generalizability can be improved by studying symptoms (rather than syndromes) in multiple single cases (Friedmann and Rahamim, 2007; Warrington, 1975). Indeed, many reports of new dissociations within a syndrome describe multiple cases, which are examined for their differences and similarities in performance; both in reference to previous cases and within the sample reported in the new paper. If patients are so highly variable in terms of their functional deficits, how is it ever possible to generalize beyond the level of the individual? This relies on two assumptions. First, the assumption of ‘universality’ poses that neurologically intact people do not differ from each other in regard to their cognitive architectures (Caramazza, 1986). It is worthwhile to note that this assumption underlies all studies of cognitive psychology, otherwise inferences about cognition could not be made from small study samples drawn from the general population. Moreover, some degree of individual difference is not incompatible with the universality assumption (Rapp, 2011). Second, if inferences can be drawn from neurologically impaired patients to normal cognition, it needs to be the case that the injury simply subtracted one or more cognitive functions without also altering or adding new functions (Saffran, 1982). Therefore, studying an individual with a selective impairment provides a unique experimental technique for studying human cognition, in particular, a system that misses exactly one function. However, single case studies are only one of the methodologies available to the cognitive neuropsychologist.
Case Series Another form of study with multiple participants that is popular in cognitive neuropsychology is the case series (Schwartz and Dell, 2010). McCloskey and Caramazza (1988) distinguish between two ways of studying groups of people: Group studies, which report average performance of the group in a way that individual results are invisible vs case series, in which individual data for each participant are reported. Averaging is only appropriate when variability in the data is assumed to be due to noise (McCloskey and Caramazza, 1988). As noted above, one of the problems in reporting agglomerate data in classical group studies is that what describes the whole group may not describe any single individual. Case series do not suffer from this problem. Case
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series designs have the potential to allow the identification of central tendencies in the data, which reflect the actual performance of several individuals, while still including variability typical of larger populations (Shallice and Buiatti, 2011). In patient data, heterogeneity may be informative in that it may reveal systematic relationships among different variables (Schwartz and Dell, 2010). While heterogeneity in the dependent variable is required to carry out such investigations, it is important that the source of the variability is relevant to the question in hand (Nickels et al., 2011). For example, when investigating word retrieval in a group of aphasic speakers, the individuals should vary in terms of their naming accuracy. At the same time, factors that could potentially impact on performance on the dependent variable (e.g., picture naming), but are not subject of the particular investigation, such as attention or object recognition need to be kept similar between the individuals. Which exact variables need to be kept similar and which should vary depends on what theory a study aims to investigate. There are certain theoretical questions that require a case series methodology. Rapp (2011: p. 437) summarizes them as “As X increases (or decreases), Y should increase (or decrease).” Hence, the study would select patients with varying degree of deficits in skill X and test their ability to do Y. Rapp’s examples of X and Y include the severity of a semantic impairment and accuracy for exception word reading (Woollams et al., 2007); or severity of sublexical damage and perseveration errors in spelling (Fischer-Baum and Rapp, 2012). Note that all of these studies are interested in a theoretically relevant association between two functions. Ideally, case series should include a combination of standard background assessment and experimental tests. These should be performed on all participants in a case series and also take into account items and tasks that have been used in previous studies (Nickels et al., 2011). Using similar tasks and items not only makes it easier to compare cases across studies but also helps in testing and designing computational models of cognition.
Computational Cognitive Neuropsychology The architecture of cognitive processes is often described in verbal or diagrammatic models. These consist of verbal descriptions or box and arrow type diagrams. Seidenberg and McClelland (1989) were the first to design a computational model of reading aloud. Since then, more cognitive theories have been implemented computationally, including one of the most well-known reading models, the Dual Route model (e.g., implemented as the Dual Route Cascaded model: Coltheart et al., 2001), but also models of spelling (e.g., Houghton and Zorzi, 2003) and spoken language (Dell et al., 1997; Levelt et al., 1999; Roelofs, 1997). A good model, be it verbal, diagrammatic, or computational, should be able to account for the full body of evidence pertaining to both normal and impaired cognition. Cognitive neuropsychological principles can also be applied to these computational models. They can be ‘lesioned’
in order to display symptoms described in patients (Coltheart, 2006). Lesioning a model can be achieved in different ways, depending on the model. For example, the strengths of connections can be adjusted or noise may be introduced. Whatever change to the ‘normal’ computational model best fits the patient data, can be regarded as an account of the type of impairment to the cognitive system. Damaging a computational model in ways that will match the data of patients can provide converging evidence for a certain theory, and it can also allow a specification in how exactly cognitive processes are impaired when a certain pattern of impairment is shown. Case series (see Section Case Series) can play a great role in testing these models. Nickels (1995) examined the errors produced in picture naming by a case series of people with aphasia. Specifically, she examined the relationship between production of semantic (doctor named as ‘nurse’) and phonological (doctor named as ‘doptor’) errors and the psycholinguistic variables that affected these errors. Imageability was found to affect the production of semantic errors (but not subjective frequency, or length). Whereas for phonological errors subjective frequency and number of phonemes showed significant effects (but not imageability). Nickels used these patterns to adjudicate between the predictions of highly interactive and strictly feedforward models, arguing that the data were inconsistent with the interactive models of speech production.
Theoretical Impact of Treatment Studies In its aim to understand human cognition, cognitive neuropsychological studies can assess patients’ performance on a multitude of tasks pertaining to the area of cognition under investigation. One way to adjudicate between different theories of cognition is to design an experiment in which different theories predict different outcomes. The experimental design can be an intervention. Hence, another powerful tool to test theories is the use of treatment (Nickels et al., 2010). For example, Biedermann and Nickels (2008a,b) investigated the lexical representation of homophones using treatment (see Nickels et al., 2010 for other examples of studies using intervention to investigate cognitive theories). Homophones are words that are pronounced in the same way but have different meanings (e.g., tank: fish-tank, military tank; flour/ flower). One theory proposes that each version of a homophone has its own lexical representation (Caramazza, 1997), while an opposing theory posits homophones share a representation (Levelt et al., 1999). Biedermann and Nickels designed an intervention study to provide new insights into this debate. Intervention can help people with word finding difficulties to become better at retrieving the words practiced during intervention. However, usually, effects are restricted to practiced words and will not benefit words that were not explicitly practiced during the intervention. Following this logic, Biedermann and Nickels made the following differential predictions: if homophones share representations, treating one partner of a homophone (e.g., flower; (fish) tank) should lead to improvements in retrieving the untrained partner of the homophone (i.e., flour; (military) tank). In contrast, if
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each homophone partner has its own lexical representation, only the trained words (e.g., flower; (fish) tank) should improve. The results favored the theory that homophones share lexical representations since not only the trained homophones but also their untrained partners improved after training. Note that a set of control words that sounded similar to the treated words (but were not homophone partners) or were similar in meaning did not improve. Other than providing insights into theoretical issues cognitive neuropsychological approaches to treatment can be used to assess the efficacy of treatment protocols and procedures. Moreover, there are many examples of treatment studies where the aim was to explain how a particular treatment works within a particular cognitive architecture. Often, these explanations in effect provide converging evidence for one particular theory. An example of this is a treatment study conducted with a person who had both deep dyslexia and anomia (Nickels, 1992; see Nickels et al., 2010 for further examples). Deep dyslexia refers to impaired reading that is marked by the presence of semantic reading errors (e.g., reading wine as ‘beer’), visual errors (e.g., late as ‘lake’), morphological errors (e.g., swims as ‘swimming’), a word class effect (i.e., function words worse than content words), and an inability to read nonwords. Nickels’ participant TC also made many semantic errors when asked to name pictures. The intervention consisted of reteaching letter–sound correspondences. While this did not lead to improved nonword reading (because the participant remained unable to blend sounds together to form a word), the frequency of semantic errors decreased after intervention. These results were later used as supporting evidence for the ‘summation theory’ according to which phonological information feeds back into the phonological lexicon (Hillis and Caramazza, 1995). After the intervention, TC started to ‘self-cue’ by using his knowledge of the initial letter of a word he was supposed to say and generating the sound (Nickels, 1992). For example, if he was asked to name the picture of a tiger, TC would activate semantically related words in addition to the correct word (e.g., leopard, panther, tiger, lion). Being able to retrieve the written word form, and sounding out the initial letter T, provided additional activation to the correct response allowing selection, and reduction of semantic errors. The cognitive neuropsychological approach to intervention also advocates that, with use of a strong design and appropriate statistics, single case intervention studies can provide a high level of evidence for the efficacy of treatment. Many cognitive neuropsychologists would argue, once again, that a series of single case studies can provide stronger and more valid evidence than evaluating average effects over a group study (such as advocated in randomized controlled trials) (also see Wright, 2012 for a discussion of this issue).
Acquired and Developmental Cognitive Neuropsychology Traditionally, the cognitive neuropsychological approach has been applied to studies with individuals with acquired disorders, that is, people who are now impaired in a skill that they had fully acquired prior to their brain injury. However, in
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the 1980s, the methodologies of cognitive neuropsychology were extended to the developmental domain, where a cognitive system is still in the process of being acquired. This work was pioneered by John Marshall, Jane Holmes, and Christine Temple. Developmental cognitive neuropsychology investigates developmental disorders using models of the cognitive architecture of the adult system. The strong claim underlying this approach is that in developmental disorders, highly selective disorders should be observable (Castles et al., 2006; Marshall, 1984; Temple, 1997). This is in contrast to a view according to which a disorder early in development distorts the system in more than one way since development is an interactive process (see Bishop, 1997). For example, if a child has difficulties learning to say words, they may also have difficulties to learn the sounds of a language. The degree to which development of different cognitive functions happens independently is an ongoing topic of research. However, there is now a large literature detailing the vast differences in the presentation of children with developmental dyslexia (see Castles et al., 2006; Marshall, 1984): for almost every processing component in the reading architecture (in this case dual route models of reading), there are published case reports of developmental cases who have a specific difficulty acquiring the skill that is governed by this processing component (for overviews of these disorders see Coltheart and Kohnen, 2012; Jones et al., 2011). These selective difficulties can be taken as evidence that development of cognitive skills can, to some degree, be modular. In the case of developmental dyslexia, cognitive neuropsychologists refer to dual route architecture. Evidence for this architecture is based on data from adult readers. Hence, one could call dual route models ‘adult models’ of reading. What is somewhat controversial is whether developmental disorders should be studied within the framework of an adult system; a cognitive system that is presumably static and not learning and developing. Bishop (1997) argues that the course of development is typically highly interactive, with skills and competencies influencing each other. Therefore, children usually present with complex patterns of associated impairments, rather than highly selective deficits. While pure cases of selective difficulties do indeed tend to be rare (Castles et al., 2006), they nevertheless make contributions to our understanding and advance developmental theories of cognition. For example, one of the most prominent current theories of how children acquire a written vocabulary posits that lexical acquisition depends largely on nonlexical skills (Share, 1999). After one or more exposures where a novel word is sounded out using nonlexical skills, a representation of the word will be developed in the orthographic lexicon. However, some children acquire a reading vocabulary that is at a normal level while their nonlexical skills are severely impaired. This is called developmental phonological dyslexia. While Share’s theory is plausible, it is cases of phonological dyslexia that clearly show that this theory alone cannot explain how children acquire a reading vocabulary. This is just one example of how the study of selective deficits in developmental disorders is important in furthering our understanding of the acquisition of cognitive functions.
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Conclusion Cognitive neuropsychology aims to understand and uncover the cognitive architecture and processing that underlies both normal and impaired cognition. It does so by studying children and adults with cognitive disorders, or lesioning computational models of cognition. Note that many of the methodologies described above are not only used by cognitive neuropsychologists. For example, single case studies form an important methodology in medical science. Similarly, the use of treatment studies to inform theory is also used in many other disciplines, including, for example, in developmental psychology. Embracing multiple methodologies is one way to further understanding of human cognition and ultimately the interaction of brain and mind.
See also: Case Study: Methods and Analysis; Cognitive Neuroscience.
Bibliography Badecker, W., Miozzo, M., Zanuttini, R., 1995. The two stage model of lexical retrieval: evidence from a case of anomia with selective preservation of grammatical gender. Cognition 5, 193–216. Biedermann, B., Nickels, L., 2008a. The representation of homophones: more evidence from remediation of anomia. Cortex 44, 276–293. Biedermann, B., Nickels, L., 2008b. Homographic and heterographic homophones in speech production: does orthography matter? Cortex 44, 683–697. Bishop, D.V.M., 1997. Cognitive neuropsychology and developmental disorders: uncomfortable bedfellows. The Quarterly Journal of Experimental Psychology: Section A 50, 899–923. Buxbaum, L.J., 2006. On the right (and left) track: twenty years of progress in studying hemispatial neglect. Cognitive Neuropsychology 2, 156–173. Caramazza, A., 1986. On drawing inferences about the structure of normal cognitive systems from the analysis of patterns of impaired performance: the case for singlepatient studies. Brain and Cognition 5, 41–66. Caramazza, A., 1992. Is cognitive neuropsychology possible? Journal of Cognitive Neuroscience 4, 80–95. Caramazza, A., 1997. How many levels of processing are there in lexical access? Cognitive Neuropsychology 14, 177–208. Caramazza, A., Coltheart, M., 2006. Cognitive Neuropsychology twenty years on. Cognitive Neuropsychology 23, 3–12. Castles, A., Bates, T.A., Coltheart, M., 2006. John Marshall and the developmental dyslexias. Aphasiology 20, 871–892. Coltheart, M., 1984. Acquired dyslexias and normal reading. In: Malatesha, R.N., Whitaker, H.A. (Eds.), Dyslexia: A Global Issue. Martinus Nijhoff, The Hague, The Netherlands. Coltheart, M., 1999. Modularity and cognition. Trends in Cognitive Sciences 3, 115–120. Coltheart, M., 2006. Acquired dyslexias and the computational modelling of reading. Cognitive Neuropsychology 23, 96–109. Coltheart, M., Kohnen, S., 2012. Acquired and developmental disorders of reading and spelling. In: Faust, M. (Ed.), The Handbook of the Neuropsychology of Language. Wiley-Blackwell Publishers, Chichester, pp. 892–920. Coltheart, M., Rastle, K., Perry, C., Langdon, R., Ziegler, J., 2001. DRC: a dual route cascaded model, of visual word recognition and reading aloud. Psychological Review 108, 204–256. Costello, A.D., Warrington, E.K., 1987. The dissociation of visuospatial neglect and neglect dyslexia. Journal of Neurology, Neurosurgery & Psychiatry 50, 1110–1116. Crawford, J.R., Garthwaite, P.H., 2006. Methods of testing for a deficit in single case studies: evaluation of statistical power by Monte Carlo simulation. Cognitive Neuropsychology 23, 877–904. Crawford, J.R., Garthwaite, P.H., Howell, D.C., 2009. On comparing a single case with a control sample: an alternative perspective. Neuropsychologia 47, 2690–2695. Crawford, J.R., Howell, D.C., 1998. Comparing an individual’s test score against norms derived from small samples. The Clinical Neuropsychologist 12, 482–486. Dell, G.S., Schwartz, M.F., Martin, N., Saffran, E.M., Gagnon, D.A., 1997. Lexical access in normal and aphasic speech. Psychological Review 104, 801–838.
Fodor, J.A., 1983. The Modularity of Mind. MIT Press, Cambridge. Fischer-Baum, S., Rapp, B., 2012. Underlying causes of letter perseveration errors in dysgraphia. Neuropsychologia 50, 305–318. Friedmann, N., Rahamim, E., 2007. Developmental letter position dyslexia. Journal of Neuropsychology 1, 201–236. Hillis, A.E., Caramazza, A., 1995. Converging evidence for the interaction of semantic and sublexical phonological information in accessing lexical representations for spoken output. Cognitive Neuropsychology 12, 187–227. Houghton, G., Zorzi, M., 2003. Normal and impaired spelling in a connectionist dualroute architecture. Cognitive Neuropsychology 20, 115–162. Jones, K., Castles, A., Kohnen, S., 2011. Subtypes of developmental dyslexia: recent developments and directions for treatment. Acquiring Knowledge in Speech, Language and Hearing 13, 79–83. Laine, M., Martin, N., 2012. Cognitive neuropsychology has been, is, and will be significant to aphasiology. Aphasiology 26, 1362–1376. Levelt, W.J.M., Roelofs, A., Meyer, A.S., 1999. A theory of lexical access in speech production. Behavioral & Brain Sciences 22, 1–75. Marshall, J.C., 1984. Toward a rational taxonomy of the developmental dyslexias. In: Malatesha, R.N., Whitaker, H.A. (Eds.), Dyslexia: A Global Issue. Martinus Nijhoff, The Hague. Marshall, J.C., Newcombe, F., 1973. Patterns of paralexia: a psycholinguistic approach. Journal of Psycholinguistic Research 2, 175–199. McCloskey, M., Caramazza, A., 1988. Theory and methodology in cognitive neuropsychology: a response to our critics. Cognitive Neuropsychology 5, 583–623. Miceli, G., Capasso, R., 2006. Spelling and dysgraphia. Cognitive Neuropsychology 23, 110–134. Nickels, L., 1992. The autocue? Self–generated phonemic cues in the treatment of a disorder of reading and naming. Cognitive Neuropsychology 9, 155–182. Nickels, L.A., 1995. Getting it right? Using aphasic naming errors to evaluate theoretical models of spoken word production. Language and Cognitive Processes 10, 13–45. Nickels, L., Kohnen, S., Biedermann, B., 2010. An untapped resource, treatment as a tool for revealing the nature of cognitive processes. Cognitive Neuropsychology 27, 539–562. Nickels, L., Howard, D., Best, W., 2011. On the use of different methodologies in cognitive neuropsychology: drink deep and from several sources. Cognitive Neuropsychology 28, 475–485. Rapp, B., 2011. Case series in cognitive neuropsychology: promise, perils, and proper perspective. Cognitive Neuropsychology 28, 435–444. Robey, R.R., Schultz, M.C., Crawford, A.B., Sinner, C.A., 1999. Single-subject clinicaloutcome research: designs, data, effect sizes, and analyses. Aphasiology 13, 445–473. Roelofs, A., 1997. The WEAVER model of word-form encoding in speech production. Cognition 64, 249–284. Saffran, E.M., 1982. Neuropsychological approaches to the study of language. British Journal of Psychology 73, 317–337. Scoville, W., Milner, B., 1957. Loss of recent memory after bilateral hippocampal lesions. Journal of Neurology, Neurosurgery, and Psychiatry 20, 11. Schmalzl, L., Palermo, R., Coltheart, M., 2008. Cognitive heterogeneity in genetically based prosopagnosia: a family study. Journal of Neuropsychology 2, 99–117. Schwartz, M., Dell, G., 2010. Case series investigations in cognitive neuropsychology. Cognitive Neuropsychology 27, 477–494. Seidenberg, M.S., McClelland, J.L., 1989. A distributed, developmental model of word recognition and naming. Psychological Review 96, 523. Shallice, T., 1988. From Neuropsychology to Mental Structure. Cambridge University Press, Cambridge, UK. Shallice, T., Buiatti, R., 2011. Types of case series: the anatomically-based approach. Cognitive Neuropsychology 28, 500–514. Share, D.L., 1999. Phonological recoding and orthographic learning: a direct test of the self-teaching hypothesis. Journal of Experimental Child Psychology 72, 95–129. Squire, L.R., 2009. The legacy of patient HM for neuroscience. Neuron 61, 6–9. Tainturier, M.-J., Rapp, B., 2001. The spelling process. In: Rapp, B. (Ed.), The Handbook of Cognitive Neuropsychology: What Deficits Reveal about the Human Mind. Psychology Press, Philadelphia. Temple, C., 1997. Developmental Cognitive Neuropsychology. Psychology Press, Hove, UK. Warrington, E.K., 1975. The selective impairment of semantic memory. The Quarterly Journal of Experimental Psychology 27, 635–657. Woollams, A.M., Lambon Ralph, M.A., Plaut, D., Patterson, K., 2007. SD-squared: on the, association between semantic dementia and surface dyslexia. Psychological Review 114, 316–339. Wright, M., 2012. Cognitive neuropsychological approach to aphasia treatment: implications for evidence-based clinical practice. Aphasiology 26, 1391–1396.