Cognitive Neuropsychology Methods

1. Cognitive Neuropsychology Methods • Aims and Objectives By the end of this lecture you will have learned: • The key methodological approaches used in cognitive neuropsychology • The importance of double dissociations in cognitive neuropsychology • The main arguments on both sides of the single-case vs group study debate • Required Reading • Parkin, Ch1 or E&Y, Ch1. • Vallar G (1991) Current methodological issues in human neuropsychology. In F Boller & J Grafman (Eds) Handbook of neuropsychology, Vol 5. P343-378. This chapter contains a good discussion on assumptions too. • Caramazza A (1984) The logic of neuropsychological research and the problem of patient classification in aphasia. Brain and Language, 21, 9-20.

2. Cognitive Neuropsychology: Methods • Associations • Dissociations • Double Dissociations • Single case vs group studies • Functional neuroimaging. • Neural network modelling • Animal studies

3. Associations An association implies a link or connection between two phenomena. • Between two cognitive deficits (e.g. comprehending written and spoken words) • Between a cognitive deficit and a lesion site (e.g. left hemineglect and right parietal lobe lesions) • Problems - can’t determine causality, nearly always exceptions found. • Association may occur for biological rather than cognitive reasons.

4. Dissociations Patient A: Performance on task X impaired, but performance on task Y intact • Performance on tasks X and Y dissociates • E.g. task X = word recognition, task Y = face recognition • Implication is that face recognition and word recognition are handled by different sets of cognitive processes, and only the word recognition system is damaged in paient A.

5. Normal range Performance X X X Y Y Y CLASSICAL STRONG TREND Dissociations • Shallice (1988) described 3 types of dissociations • Classical dissociations presumed to be the most ‘powerful’

6. Dissociations • Interpretation of dissociations is not always straightforward. • It could be argued that tasks X and Y involve one process (e.g. recognition of "something") but that word recognition is a very hard task and face recognition is a much simpler task. • Maybe brain damage affects difficult tasks first? • Task difficulty effect / resource artefact

7. Double Dissociations • But Patient B: Performance on task X intact, but performance on task Y impaired • E.g. Facial recognition impaired but word recognition intact • The performance of patients A & B provide a DOUBLE DISSOCIATION • Strong evidence that there are cognitive processes involved in Task X that are not involved in Task Y and vice versa • Patients don't have to be perfectly intact on either task - they just need to be consistently better at one task than the other

8. How important are DDs? • DDs traditionally assumed to be “gold standard” in CN research BUT - not all CN’s agree - • Caramazza argues that associations, dissociations and DDs are all equally valid forms of inference (if the cognitive model is well developed) • A DD between two tasks does not necessarily imply a DD between cognitive processes (Shallice, 1988) • Most CNs agree that converging evidence is desirable • The utility of DDs is predicated on modularity being true - Van Orden et al, 2001: Endless fractionation

9. Single case vs Group studiesThe concept of ‘syndromes’ Traditional neuropsychology often based on ‘syndromes’ - a collection of symptoms which often co-occur in individuals. Early syndromes were anatomically based (e.g. Broca’s Aphasia) Gerstmann’s Syndrome: Acalculia, left-right disorientation, pure agraphia, finger agnosia Can the study of GS provide information about the functional architecture of cognitive processes? • Association of deficits on these tasks implies they share an underlying process • Requires a model with a component common to all symptoms

10. Single case vs Group studiesThe concept of ‘syndromes’ • Such a cognitive process is not obvious • It is more likely that these symptoms depend on a number of functionally distinct processes which are anatomically related. (Danger of over-interpreting associations) This is one reason why some cognitive neuropsychologists favour single-case studies over group (syndrome) studies “Research based on classical syndrome types should not be carried out if the goal of the research is to address issues concerning the structure of cognitive processes” Caramazza (1984) • In other words, “classical” syndromes based on anatomical considerations have no role in cognitive neuropsychology

11. Single case Vs Group studies Caramazza’s arguments: • ONLY the single-case approach can provide information relevant to our understanding of cognitive architecture WHY? • Group studies rest on assumption that cognitive processes are homogenous (patients grouped to minimise sampling error - noise) • BUT Brain damage may disrupt cognitive processes in a variety of different ways • Therefore performance differences within a group of brain damaged subjects CANNOT be dismissed as noise. • Therefore averaging over a group of patients is inappropriate

12. Single case Vs Group studies Caramazza’s arguments: • Negative consequences of averaging: • Group differences may not reflect performance of any patient. No individual patient is impaired on both tasks

13. Single case Vs Group studies One response is to study Functional Syndromes - based on IP models of normal function E.g. specify criteria on basis of cognitive model which will identify a group of patients who are homogenous with respect to the proposed cognitive impairment E.g. deep dyslexia, surface dyslexia, phonological dyslexia BUT - • Patients may be homegenous with respect to task(s) used to select them, but not with respect to experimental task. • Selection criteria often poorly specified / theoretically weak

14. Single case Vs Group studies Objections to Caramazza’s position: • The same logic may be applied to the study of normal behaviour, resulting in the rejection of group studies throughout psychology. (Shallice) • Single cases may simply be the most “extreme” examples of a larger, ignored group. (Robertson et al , 1993). • Single cases make establishing brain-behaviour relationships difficult. (Robertson et al , 1993).

15. Single case vs Group studies Other arguments against a single case only position: • single case studies cannot address theories to do with relationships between two variables (e.g. brain size and intelligence) since correlational designs need many subjects • Single case studies do not permit purereplication • patients can sometimes be atypical from the outset (Caramazza's "martian within us" problem), e.g. split-brain patients whose brains have developed non-conventionally.

16. Single case vs Group studies • The “real” debate is very detailed and complicated • E.g. Caramazza & Badecker (1991) Clinical syndromes are not gods gift to cognitive neuropsychology - a reply to a rebuttal to an answer to a response to the case against syndrome-based research. Brain & Cognition, 16: 211-227 • The debate addresses many of the assumptions outlined in Lecture 1. • It has involved philosphers as well as cognitive neuropsychologists… …cognitive neuropsychology practice not only must steer clear of the Scylla of sole reliance on a standard reductionist approach that relies soley on group studies, but also would do better to avoid the Charybdis of ultra-cognitive neuropsychology” Shallice, 1988.

17. Functional Neuroimaging • Many different techniques, eg: • SPECT • PET • fMRI • TMS / rTMS • EEG • MEG • Currently fMRI, TMS and MEG are the most popular techniques • Techniques are increasingly combined

18. Functional Neuroimaging

19. Functional Neuroimaging Utility of functional neuroimaging for cognitive neuropsychology: • Field is largely split • PROs: • Can potentially localise function in healthy controls • Has revealed activity in brain areas previously thought to be uninvolved (e.g. cerebellum) • CONs: • Interpretation of imaging data not straightforward • No “standard” vocabularly for describing results • Replication of results often poor • Does nothing for theory development (Parkin,2001).

20. Computational Modelling • Generally uses connectionist (PDP) architectures to model aspects of cognition. • Models are built, and then “lesioned” in various ways (e.g. units knocked out, weights changed) • Model a success if resulting output resembles patterns observed in brain damaged humans. • Advantages: • Non-invasive • Forces researchers to specify cognitive theory adequately. • Disadvantages: • Biological plausability unclear

21. Animal studies • Many (non-language) cognitive functions are also studied in animals • E.g. Memory, Attention, Executive functions. • Advantages: • Discrete, replicable lesions (permanent or temporary) • Age, environmental effects controlled • Single cell recording • Neuropharmacology of cognition • Disadvantages: • Not very nice for animals • Unclear how far data can be generalised to humans