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.
Cognitive Neuropsychology: Methods
• Associations
• Dissociations
• Double Dissociations
• Single case vs group studies
• Functional neuroimaging.
• Neural network modelling
• Animal studies
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.
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.
Dissociations
• Shallice (1988) described 3 types of dissociations
Performance
Normal
range
X Y X Y X Y
CLASSICAL STRONG TREND
• Classical dissociations presumed to be the most
„powerful‟
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
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
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
Single case vs Group studies
The 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
Single case vs Group studies
The 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
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
Single case Vs Group studies
Caramazza‟s arguments:
• Negative consequences of averaging:
• Group differences may not reflect performance of any
patient.
Control s X
Ta s k Y
Ta s k Patients X
Ta s k Y
Ta s k
1 80 75 1 30 80
2 70 80 2 80 25
3 75 80 3 75 20
4 85 90 4 20 75
5 90 70 5 25 85
6 80 85 6 85 30
erage
Av 80 80 erage
Av 52.5 52.5
No individual patient is impaired on both tasks
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
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).
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 pure replication
• 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.
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.
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
Functional Neuroimaging
Technique Advantages Disadvantages
Good temporal resolution Poor spatial resolution
EEG / EEG is cheap Only map surface of cortex
MEG Non-invasive MEG is expensive
Reasonable spatial Very expensive
SPECT / resolution (0.5 cm) Invasive
PET Psychopharmocology Poor temporal resolution
applications
Relatively cheap Very poor spatial resolution
TMS /
Non-invasive (ish) t
CanÕbe used near other
rTMS
scanners
Relatively cheap BOLD effect is small and
Non-invasive unstable
fMRI Good spatial and Movement and interference
temporal resolution artefacts.
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).
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
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