Week 3 Flashcards Preview

3019PSY Midsem > Week 3 > Flashcards

Flashcards in Week 3 Deck (16):
1

Apperceptive agnosia

problems with
distinguishing figure from ground, or inability to
form a proper visual description of an object from
visual descriptions of its parts

Corresponds to final stage of “perceptual”
processing.

Associated with damage to perceptual
mechanisms

2

Associative Agnosia:

problem (difficulty) occurs
at a later stage of processing

Problem associating a visual configuration with
information about its meaning

normal visual representations but cannot use
this information to recognise things

3

Apperceptive agnosia and Associative agnosia

Lissauer (1890; 1907) distinction between
apperceptive agnosia and associative agnosia

Geschwind (1965) suggests this is due to a
disconnection between an intact perceptual
representation and its stored association

Simplistic explanation for this

ie. Disconnection between visual and speech
areas of the brain

For example, patient with serious injury to the
posterior part of the left cerebral hemisphere,
which deprives the left hemisphere speech area
of visual input

There is also a disconnection of the corpus
callosum so visual information cannot be
processed from the right hemisphere to the left
speech area

So in patients the intact left hemisphere speech
area and right hemisphere visual area are both
disconnected

4

Viewer-Centred Impairment

Patient Mr S (Benson & Greenberg, 1969)

Soldier who suffered carbon monoxide
poisoning

Intact initial visual representations (colour,
movement etc)

Name colours

Describe some perceptual qualities of objects

eg. Safety pin = “silver and shiny like a watch or
nail-clippers”

impaired on tasks requiring perception of visual
form

random eye movements in picture scanning

at recognition of objects, pictures,
numbers, faces and could not do picture
matching

could identify and name object presented in
other sensory modalities

impairment one of an inability to analyse
perceptual form = problem with viewer-centred
object representation

5

Problem Object-Centred Representation

Apperceptive Agnosia Test:

Gollin Picture task and Incomplete Letters task

Can patients recognise objects in degraded
format?

Warrington (1985)

Patient with unilateral cerebral lesion in the right
hemisphere and normal visual acuity

Using both the Gollin Picture task and the
Incomplete Letters task

patients with right sided lesions did worse than

control subjects or patients with lesions in the
left hand side

but left hand patients has greater/severe
language problems

Concluded that impaired perceptual
categorisation eg, problems with object
constancy

Tested this hypothesis using the Unusual Views
Objects Test

Test Object Naming

normals few errors

patients ( right side lesions) - poor at unusual
views but ok from the usual viewpoint

Therefore problem not loss of visual knowledge

Test Same/Different Matching Task

Photos of pairs of objects

same object different views or different objects

Right side posterior damage patients were
worse than normals or patient controls


Apperceptive agnosia – patients with right
hemisphere lesions because cognitive
processes associated with posterior part of right
hemisphere linked to the role of perceptual
categorisation (problem object-centred
representation)

6

Associative agnosia (case study)

Failure of visual object recognition not attributed
to perceptual abilities

patients have normal performance on perceptual
tasks

Patient FRA (McCarthy & Warrington, 1986)

Infarct to left posterior cerebral artery

Lesion occipital region of the left hemisphere
extend to posterior temporal cortex

Could copy shapes and point to objects to
spoken word, could segment a complex drawing
into parts and could colour common objects

But could only name or describe the function of
half the line drawings of common objects

Poor at size judgements of animals from the
same category but could do size judgements to
spoken names

Therefore problem was visual - impaired ability
to recognise name from visual information

Test Matching by Function test

Three pictures and patient points to the two
functionally similar

Requires patients to categorise stimuli based on
semantic properties

Patients with posterior lesions in either
hemisphere impaired on this task

Warrington- this is for two different reasons

Patients with RS - fail to recognise the object

Patients with LS - recognise in isolation but
cannot make a functional connection between
objects

7

Loss of Semantic Access

Probe task using objects, words and or speech

Marin (1987) lady with pre-senile dementia

Turns pictures to their correct orientation (stored
visual knowledge)

Couldn’t do picture matching eg candle-light-
bulb, trumpet-violin

Unable to do categorisation tasks on the basis of
functional or associative knowledge

General loss of semantic access, since the
problem occurred regardless of the modality of
input

8

Impairment at Semantic Representation
Level

Category Specific agnosia: patients with
category specific object recognition deficits

JBR: severe associative agnosia

worse for living than non-living things

Herpes simplex encephalitis

dense amnesia, memory loss, word finding
difficulties

Normal on tests of apperceptive agnosia but
severe associative agnosia

90% correct on pictures of common objects eg
keys

6% correct on pictures of living things

Category specific disorder - selective loss of
knowledge in semantic system

Semantic knowledge is structured categorically
on the basis of objects that share common
features

Patients with categorical deficits support this
from of semantic organisation

Due to dissociation expect to find patients who
are better at recognising animate compared to
inanimate object

Patient data does exist

Target (visual or auditory) presented and the SS
task is to choose the object in the array that is
from the same category as the target

Both modalities patient slower and less accurate
for inanimate than animate

Evidence double dissociation between agnosia
for living and non-living things

caution as the area of semantic access is not
really as clear cut as this

9

Category Specific agnosia

patients with
category specific object recognition deficits

10

Initial Raw Visual Representation

Basic visual features
-colour, motion, shape(edges), depth, orientation

Tests for functioning:
-size matching (two shapes same or different size?)
-length matching (two lines, same size?)
-gap matching (gap in circle in same place?)
-colour vision test (see the number in a field of dots of different colour?)
-orientation matching (are the lines the same orientation?)

11

Viewer Centered Description (functions/tests)

spatial locations
visible surfaces
uses deth and location
object represented from viewer's perspective

Tests
over-lapping figures
incomplete letters
gollin picture task
copy drawings 1

12

Arrow between viewer centered description and object centred

tests
unusual views matching
unusual views naming

13

Object Centred Description - functions and tests

Real shape of objects and surfaces
independent of viewpoint of viewer

test
copy drawings 2

14

Object Recognition units

Stored Object Representations

tests
draw from memory
object decision test
colour decision test 1
heads test
tails test

15

Semantic system function/tests

knowledge about object uses and properties

tests
colour decision test 2
function matching test
associative matching
living/non-living decision
definition tasks
semantic matching tasks
(pic-pic, pic-word, pic-catlabel)

semantic word tests
synomym matching
verbal definition
matching spoken and p[rinted words

16

Speech output lexicon

store of verbal output

test
picture naming
picture pouinting
written picture naming
mime function./use