Week 2: Visual perception and object recognition
19 September 2022 20:47
VIDEO 1: KEY CONCEPTS OF OBJECT RECOGNITION LIVE-SEMINAR 22.09.22
READING chapter2 55-64
How we process visual stimulus Marr’s three levels of analysing a cognitive function
•3 different types of analysis of an information-processing system
• Computational – TASK ANALYSIS
• Algorithmic – WHICH PROCESSES & OPERATIONS ARE NEEDED
• Implementational – THE PHYSICAL STRUCTURE THAT DOES THE WORK.
STAGES IN VISUAL PERCEPTION
How different part of the cortex become progressively complexed
The journey of visual information
Evidence for stages in visual processing: visual agnosia patient
HJA Humphreys & Riddoch (1987)
61 year old man
Post-op stroke
THE "WHAT" and "WHERE/HOW" PATHWAYS
Impaired reading, face and object recognition
Dorsal stream:
Ventral stream:
• "How" pathway Loss of colour vision
• "what" pathway
• Vision-for-action
• Vision-for-perception Visual field defect but normal visual acuity
• Egocentric (body-centred) coding
Normal discrimination of length, orientation and position
EVIDENCE FROM PATIENTS: Stereoscopic vision intact
Optic ataxia (dorsal damage)
==> Could take in information but can't identify objects, places and faces!
Visual form agnosia (patient DF)
BUT double dissociation not robust He CAN draw objects from memory!! But couldn’t see their meaning
•HJA can describe objects from memory: Has intact knowledge of object appearances and
Inferior temporal cortex functions
•HJA can copy drawings of objects he can’t recognise
The seperation of different streams is not as distinguished as thought before.
Interwined, operating together
WHERE IS HJA'S PROBLEM?
EVALUATION PERCEPTION-ACTION MODEL
• Very influential theoretical approach
• TWO systems less independent and more interactive than assumed
• Separate dorsal streams: Herpes Simplex Patients
○ Dorso-dorsal system – grasp object fast Warrington and Shallice (1984)
○ Ventro-dorsal system – memorised object knowledge to use objects Normal visual perception
appropriately
Problems with recognising or describing living things
Read: cap 2 pp 55-64 Can name objects from verbal/functional description (“what animal is used to obtain ham?”)…
VIDEO 2: THEORIES VISUAL PERCEPTION
...but not from a visual description (“an insect with broad, coloured ornate wings”)
Problems with concrete words but not abstract ones
MODEL OF OBJECT RECOGNITION
Navon (1977) stimuli
Where is the probem in HERPES SIMPLEX?
Semantic agnosia
Warrington (1975)
Patient AB (dementia)
Verbal IQ = 122, normal acuity, matching objects across views
Couldn’t name common objects (0/12), pictures of objects (11/20) or photos of faces (2/15)
Notes Page 1
19 September 2022 20:47
VIDEO 1: KEY CONCEPTS OF OBJECT RECOGNITION LIVE-SEMINAR 22.09.22
READING chapter2 55-64
How we process visual stimulus Marr’s three levels of analysing a cognitive function
•3 different types of analysis of an information-processing system
• Computational – TASK ANALYSIS
• Algorithmic – WHICH PROCESSES & OPERATIONS ARE NEEDED
• Implementational – THE PHYSICAL STRUCTURE THAT DOES THE WORK.
STAGES IN VISUAL PERCEPTION
How different part of the cortex become progressively complexed
The journey of visual information
Evidence for stages in visual processing: visual agnosia patient
HJA Humphreys & Riddoch (1987)
61 year old man
Post-op stroke
THE "WHAT" and "WHERE/HOW" PATHWAYS
Impaired reading, face and object recognition
Dorsal stream:
Ventral stream:
• "How" pathway Loss of colour vision
• "what" pathway
• Vision-for-action
• Vision-for-perception Visual field defect but normal visual acuity
• Egocentric (body-centred) coding
Normal discrimination of length, orientation and position
EVIDENCE FROM PATIENTS: Stereoscopic vision intact
Optic ataxia (dorsal damage)
==> Could take in information but can't identify objects, places and faces!
Visual form agnosia (patient DF)
BUT double dissociation not robust He CAN draw objects from memory!! But couldn’t see their meaning
•HJA can describe objects from memory: Has intact knowledge of object appearances and
Inferior temporal cortex functions
•HJA can copy drawings of objects he can’t recognise
The seperation of different streams is not as distinguished as thought before.
Interwined, operating together
WHERE IS HJA'S PROBLEM?
EVALUATION PERCEPTION-ACTION MODEL
• Very influential theoretical approach
• TWO systems less independent and more interactive than assumed
• Separate dorsal streams: Herpes Simplex Patients
○ Dorso-dorsal system – grasp object fast Warrington and Shallice (1984)
○ Ventro-dorsal system – memorised object knowledge to use objects Normal visual perception
appropriately
Problems with recognising or describing living things
Read: cap 2 pp 55-64 Can name objects from verbal/functional description (“what animal is used to obtain ham?”)…
VIDEO 2: THEORIES VISUAL PERCEPTION
...but not from a visual description (“an insect with broad, coloured ornate wings”)
Problems with concrete words but not abstract ones
MODEL OF OBJECT RECOGNITION
Navon (1977) stimuli
Where is the probem in HERPES SIMPLEX?
Semantic agnosia
Warrington (1975)
Patient AB (dementia)
Verbal IQ = 122, normal acuity, matching objects across views
Couldn’t name common objects (0/12), pictures of objects (11/20) or photos of faces (2/15)
Notes Page 1
