Disorders of perception Flashcards
What information is required for perception?
> Visual sensory information
Deriving a semantic meaning
Naming
What visual sensory information is required for perception?
> Colour
Shape
Movement
What did Sacks and Wasserman (1987) report?
> (JI)
Visual acuity was good
Achromatopsia (judging colour)
Damage to V4
Who linked colour judgement to V4?
Sacks and Wasserman (1987)
What did Zihl, von Cramon and Mai (1983) report?
> (LM)
Colour and object recognition fine
Akinetopsia
Damage to V5 / MT
What is achromoatopsia?
The inability to judge colour
What is akinetopsia?
The inability to judge motion
What are the stages of object recognition?
> Visual sensory information > Grouping - perception > Feature binding > View normalisation > Structural description system > Semantic system > Accessing a name
What is apperception?
The inability to create a coherent percept
What is association?
Attaching a meaning to a percept
Who demonstrated the perceptual effects of apperceptive agnosia?
Warrington and James (1988)
What did Warrington and James do?
Demonstrated apperceptive agnosia effects using:
> Object matching
> Copying
> Understanding of overlapping and obscuring
> Unusual views test
What are the features of apperceptive agnosia?
> Recognition intact
Unable to copy, match or internally manipulate objects
Inability to form internal percepts
What are the features of associative agnosia?
> Visual acuity intact
Can copy, match and internally manipulate objects
Inability to recognise objects or determine purpose
What did Rubens and Benson (1971) find?
Individual with associative agnosia, can’t identify objects or determine their function
Who demonstrates that associative agnosia impairs the ability to understand or infer an object’s function?
Rubens and Benson (1971)
What did Taylor and Warrington (1971) report?
> (FL)
Associative agnosia
Couldn’t match functions to objects
Couldn’t name objects
What did Riddoch and Humphreys (1992) demonstrate?
Associative agnosiac can copy images, but can’t commit them to memory or draw from memory
Who demonstrated that associative agnosiacs cannot maintain precepts?
Riddoch and Humphreys (1992)
Theoretically, where must the visual perception model be damaged to cause apperceptive agnosia?
The grouping stage
Theoretically, where must the visual perception model be damaged to cause associative agnosia?
Stored visual representations and meaning
What are the limitations of the apperceptive / associative agnosia dichotomy?
> Disagreement about whether shape agnosia is apperceptive
Fractionation
Usefulness of unusual views questioned
Validity of intact percepts in associative
What arguments are there that shape processing must be intact in apperceptive agnosia?
> Problems in shape discrimination is a sensory impairment
> Pseudo-agnosia
What arguments are there that fractured shape processing can be apperceptive agnosia?
> Shape perception is part of the perceptual process
> Problems with copying or discriminating shapes is a symptom of apperceptive agnosia
What evidence is there of fractionation in apperceptive agnosia?
The symptoms of those with apperceptive agnosia are variable
What are the criticisms of the unusual views experimental design?
> Most who fail only show impairment in labs
Are problems matching unusual views the same as matching different views?
Suggested location of impairment unlikely
What evidence is there that perception may not be intact in associative agnosiacs?
> Type of visual input affects recognition
> Performance on apperceptive tests is good, but method is abnormal
What is the object decision task?
> Two objects joined to form a non-object
Presented as either a silhouette or a line drawing
Time taken to determine object as fake recorded
What did use of object decision tasks establish?
> Globals forms of stimuli
> Integrative agnosia
What is integrative agnosia?
The inability to see objects hollistically
Which stages in the stages of recognition model are associated with apperceptive agnosia?
> Grouping - perception
Feature binding
View normalisation
Which stages in the stages of recognition model are associated with associative agnosia?
> Structural description system
> Semantic system
What evidence is there that there is fractionation in associative agnosia?
> Warrington and Shallice (1984)
Hillis and Caramazza (1991)
Hart, Berndt and Caramazza (1985)
Damasio et al (1996)
What did Warrington and Shallice (1984) report?
> (JBR)
Associative agnosia
Ok at identifying living things
Bad at identifying non-living things
What did Hillis and Caramazza (1991) report?
> (JJ and PS)
Temporal lobe lesions
Double dissociation between recognition of living and non-living objects
What did Hart, Berndt and Caramazza (1985) report?
Category specific associative dissociations
What did Damasio et al (1996) repot?
> PET study
agnosiacs and healthy controls
Neural evidence for category specific recognition
