Assumptions in Cognitive Neuropsychology

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Assumptions in Cognitive Neuropsychology

• Aims and Objectives
• By the end of this lecture you will have learned
• The key aims of cognitive psychology
• The core assumptions relevant to cognitive
  neuropsychology and their implications
• Required Reading
• Rapp Ch1.

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Clinical Neuropsychologyvs Cognitive
Neuropsycholgy?

• Both approaches linked on many levels, but there
  are also significant differences in their
  empahsis.
• CLINICAL - focuses on the effects of brain damage
  on psychological processes
• Determine pathology
• Characterise deficit
• Establish baseline
• COGNITIVE - focuses on undestanding impairments
  in psychological processes in terms of
  disruptions to information processing elements
  involved.
• e.g. cognitive approach requires a MODEL of
  healthy function - this may or may not be tied
  back to neuroanatomy

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Aims of Cognitive Neuropsychology

• 1. Model confirmation / development
• According to Ellis and Young, cognitive
  neuropsychologists
• explain patterns of impaired and intact
  cognitive performance seen in brain injured
  patients in terms of damage to one or more of the
  components of a theory or model of normal
  cognitive functioning
• draw conclusions about normal, intact cognitive
  processes from the patterns of impaired and
  intact capabilities seen in brain-injured
  patients
• These two approaches are obviously linked, but
  differ in emphasis.

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Aims of Cognitive Neuropsychology

• 2. Cognitive localisation -
• The attempt to specify specific areas of the
  brain as being involved in certain processes
• - some researchers NEVER do this (Ultra or
  Radical CNs)
• - others talk about it but know that it is a
  separate issue from the cognitive theories
  themselves
• - cognitive neuroscientists (e.g. Damasio /
  Goldman-Rakic) are particularly concerned with
  this and use data from patients, NCs, animal
  studies, molecular studies etc..
• Theoretical vs Anatomical paradigms Mackay (2001)

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Assumptions in Cognitive Neuropsychology

• These are the topics of considerable debate
• The debates are very complex! (see extended
  reading list for some examples)
• These asumptions have very important
  implications for the methodologies used in
  cognitive neuropsychology (e.g single case vs
  group studies) and the inferences which cognitive
  neuropsychologists can draw from their data
• These assumptions are also important to bear in
  mind when interpreting functional neuroimaging
  data.

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Cognitive Neuropsychology
Assumptions
Modularity - Mental life is orchestrated by
multiple cognitive processors or modules
Neurological specificity (isomorphism) - there is
a correspondence between the organisation of the
mind and the organisation of the brain (both lead
to locality assumption)
Transparency - observable behaviour will indicate
which module is dysfunctional
Subtractivity - Performance reflects total
cognitive system minus the impaired module(s)
Universality - There are no individual
differences in the organisation of cognitive
modules
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Assumption of Modularity
Mental life is orchestrated by multiple cognitive
processors or modules Marr (1982) - Principle of
Modular Design - any large computation should be
split up into a collection of small, nearly
independent, specialized subprocesses

• Advantages of modularity
• Reduces computational costs
• Makes complex systems easier to improve / evolve
• Simplifies error-detection / correction
• Local damage remains local

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Assumption of Modularity

• Concept of modularity extended by Fodor in The
  Modularity of Mind (1983)
• Modules are
• Domain specific
• Innately specified
• Informationally encapsulated
• Fast
• Hardwired (neurally specific)
• Autonomous
• Not assembled
• Operation is mandatory
• Only 1 3 are generally accepted by
  neuropsychologists

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Assumption of Modularity
Domain Specificity Each module can only process
one type of input
E.g. is there a single Person Recognition Module
that operates on visual and acoustic inputs?
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Assumption of Modularity
Domain Specificity Each module can only process
one type of input
Not if modules are truly domain specific.
Face Recognition Module
Voice Recognition Module
OUTPUT
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Assumption of Modularity
Informationally Encapsulated The processes are
carried out in isolation from and ignorance of
processing in other modules
Some psychologists have interpreted this in a
very strict way (e.g. Farah) One implication is
that information processing can only proceed in a
bottom up fashion. E.g. evidence of top-down
influences on processing can be used as evidence
against the assumption of modularity. Fodor was
himself less strict, arguing that it meant not
having access to a persons expectations,
beliefs, presumptions or desires
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Assumption of Modularity

• Modularity in a strictly Fodorian sense causes
  problems for cognitive neuropsychology-
• Reading is clearly not innate
• Not all cognitive modules appear mandatory
  (e.g.Recognition may be mandatory but is name
  recall?)
• What about top-down processing?
• Fodor also argued that only input (and possibly
  output) processes are modular
• Most cognitive psychologists assume that
  central processes (e.g. reasoning, decision
  making) are also modular to some extent.

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Assumption of Modularity
Neo-Fodorian account of modularity (Coltheart,
1999)
The other Fodorian criteria are not necessary
features of modules.
Whether or not a module possesses any of these
features becomes an interesting empirical question
Assumption of modularity is linked with
assumption of locality (Farah, 1994) and logic of
double dissociation
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Assumption of Isomorphism

• There is a correspondence between the
  organisation of the mind and the organisation of
  the brain
• A critical assumption, that is rarely
  acknowledged
• Very important for the interpretation of
  functional neuroimaging data.
• Also important for clinical neuropsychology
• Its importance depends on how cognitive you
  like your cognitive neuropsychology.

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Assumption of Isomorphism

• HOWEVER
• It is possible to have functional modularity but
  not anatomical modularity
• E.g cognitive modules may be distributed across
  wide areas of cortex
• This would imply that any brain damage ought to
  impair a large number of modules
• The fact that so many patients exist with highly
  selective disorders suggest that the assumption
  is broadly tenable.

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Assumption of Transparency

• observable behaviour will indicate which module
  is dysfunctional
• E.g. careful analysis of the pattern of impaired
  / intact performance, and the ways in which
  patients perform neuropsychological tests will
  allow valid conclusions to be drawn.
• Brain damaged performance reflects
• True contribution from disruption to one or
  more hypothesised modules
• Individual Differences (c.f. Lecture on
  Methodologies)
• Effects of compensatory mechanisms
• Effects from disruption to modules other than the
  hypothesised modules (c.f. Lecture on
  Methodologies)

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Assumption of Transparency

• HOWEVER
• Individual differences Deficit may have preceded
  the injury The Martian within us problem
  (Caramazza).
• (Individual differences may become increasingly
  tractable given modern techniques.)
• Compensatory Mechanisms According to CN these
  must reflect the strategic use of existing
  modules rather than the generation of new
  modules.
• E.g brain damage does not result in the de novo
  creation of cognitive modules resulting in a
  system which is uninterpretable in terms of
  models of normal systems.
• Multiple Modules Strictly localised brain damage
  is incredibly rare (see next lecture)
• Easy to ascribe performance to damage in module
  A, when in fact it is module B that is damaged.

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Assumption of Subtractivity

• Performance reflects total cognitive system minus
  the impaired module(s)
• The cognitive system of the brain damaged
  subject is the same as that of a normal subject
  apart from a local modification
• - The existing modules carry on exactly as
  before
• - No new modules are formed
• - The organisation of the existing modules
  remains unchanged.
• Neuroscience research suggests the brain may have
  much more plasticity than previously assumed.

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Assumption of Universality

• This assumption is crucial for any group studies
  in cognitive science
• Allows us to consider the average performance of
  a group of individuals to be representative of
  any individual in the population from which the
  group was drawn.
• HOWEVER
• Individual differences are increasingly obvious
  and difficult to ignore
• Patients rarely have exactly the same brain
  damage.