L2 - High level vision

Viusal Agnosia - Lissauer (1889 - 1890)

• first to identify visual agnostic patient; impairments in visual perception, not intelligence

• distinguished between 2 stages of recognition; Apperceptive and associative

Agnosia

impairment to recognise object

Viusal Agnosia - Lissauer (1889 - 1890) - apperceptive recognition

• unable to draw and replicate simple objects e.g. square, can’t name of copy the object

• perception is impaired

• impairment in conscious visual representations (e.g., shape blindness)

Viusal Agnosia - Lissauer (1889 - 1890) - associative recognition

• Assume that perception is intact but devoid of any meaning

• E.g. p’s can draw what they are looking at accurately

• normal percept stripped of its meaning (Tuber, 1968)

is there a true distinction between apperceptive and associative agnosia in humans? - Riddooch and Humphreys (1987)

• Patient HJA passes test used to diagnose apperceptive agnosia, but didn’t pass associative agnosia (impaired recognition not perception)

• But nonetheless shows higher order impairments that are perceptual in nature

is there a true distinction between apperceptive and associative agnosia in humans? - Riddooch and Humphreys (1987) - PATIENT HJA - results

• performance (reaction time) at recognising overlapping objects is impaired

• Performance at discriminating real/unreal objects is impaired

• Also performs better when fewer details are present

Riddoch and Humphreys (1987) - integrative agnosia

• these tests and their results suggets something more complex than simple apperceptive/ associative dissociation

• The term integrative agnosia was introduced to desire patients like HJA

• BORB (Birmingham object recognition battery) is a series of tests designed to identify the level of processing at which a recognition impairment exists

Riddoch and Humphreys (1987) - integrative agnosia - definition

describes a high-level perceptual perceptual impairments in integrating the form and features of an object t

• can’t intergrate information to produce a single precept

BORB - Birmingham object recognition battery

Associative agnosia - evidence for this associative kind? - critics may argue that

associative agnosia is explained by subtle sensory impairments (Bay, 1953) - Ettlinger (1956) tested this

Associative agnosia - evidence for this associative kind? - Ettlinger (1956) - tested critics claim in..

a comprehensive test of basic visual functions in 3 groups of patients with cerebral lesions

• GA - no visual detect, no agnosia

• GB - visual field defect, no agnosia

• GC - Visual field defect, agnosia

Associative agnosia - evidence for this associative kind? - Ettlinger (1956) - tests

Brightness discrimination - Flicker fusion
- Acuity for small objects
- Local adaptation
- Tachistoscopic acuity
- Apparent movement

Associative agnosia - evidence for this associative kind? - Ettlinger (1956) - tests - GA

• slightly impaired relative to control with no brain damage

Associative agnosia - evidence for this associative kind? - Ettlinger (1956) - tests - GB (visual field defect)

• marked Impairment in this group compared to control, presence of a visual field detect is associated with impairment om visual perception on the battery of tests

Associative agnosia - evidence for this associative kind? - Ettlinger (1956) - tests - GC (visual field defect and agnosia)

• dont perron any worse than group B

Associative agnosia - evidence for this associative kind? - Ettlinger (1956) - findings

showed that impairments in visual sensory abilities were associated with visual field defects...not agnosia

... but not the presence of higher perceptual disorders (only one of which had “agnosia”).

However, the ests Ettlinger (1956) used don’t fully account for the functional organisation of the visual system (and he didn’t focus on object agnosia)

There are a number of dissociable visual “features” - Lightness
- Colour
- Movement

Texture

Shape

However, the ests Ettlinger (1956) - without proper tests of basic visual function…

it isn’t possible to disntigush associative from apperceptive agnosia

Evidence for associative agnosia - DeHann et al (1995) repeated ettlingerger study focusing on agnosia

• used more appropriate tests:

  Shape discrimination
  - Location discrimination - Colour discrimination
  - Lightness discrimination - Shape from motion
  - Texture discrimination
  - Line orientation

  Modification of Efron shapes test

Evidence for associative agnosia - DeHann et al (1995) repeated ettlingerger study - Results

GA - agnosia patients - less sig impairments

GB - no agnosia (some brain damage, but didn’t result in higher order perceptual deficit) - found most sig impairments

• No evidence that these visual functions are necessary or sufficient to cause agnosia

no evidence that associative agnosia is dependent

on lower level visousensory impairments

• what about apperceptie agnosia

An example of apperceptive agnosia - Is a visual form agnosia (benson and Greenberg, 1989)

• MR S, fails at basic tests at apperceptive agnosia, couldn’t distinguish/draw shapes

• The impairment seemed specific to visual form (or shape) perception

• Identified as having visual form agnosia (to distinguish from other kinds of apperceptive agnosia)

• The term agnosia is even questionable in this context

An example of apperceptive agnosia - Is a visual form agnosia (benson and Greenberg, 1989) - The term agnosia is even questionable in this context

• We wish to reserve the concept of agnosia for those subcomponents of object recognition processes that implicate the ability to detect, by recourse to stored representations, similarities between representational visual stimuli; that is the ability to categorise stimuli that are different (Warrington and James, 1988

• by recourse to stored respresntaion, only use term agnosia to refer to patients that have to match what their visual information is showing to stored representations (memory), tasks such as copying or categorise stimuli dont test this

  => pseudoagnosia?

Form agnosia - regardless of whether this condition is classified as pseudoagnosia or visual form agnosia

• it points to a very specific and selective impairment at the level of forming a coherent form representation

• Marr’s mode; (1982) - impairment primal sketch stage, so no 2d or 3d shape perception

Form agnosia - caused by low level visuosensory impairments? e.g.

•  Luminance

• -  Colour

• -  Motion

• -  Visual fields

• -  Depth

generally performance is intact, but small impairments are common

Form agnosia - Campion and Latto (1985) - possible sensory defects to explain agnosia

• measured content sensitivity in an agnosic patient (patient RC) - visual form agnosia

• Abnormal thresholds relative to controls

• indicate a possible sensory deficit (dependent on spatial frequency and orientation)

Form agnosia - Campion and Latto (1985) - possible sensory defects to explain agnosia - suggested that

Suggested an account based on peppery field defects – a“masking” account, loss of very small parts of visual field

• Assessed using fine grained perimetry

• Subject rates brightness of single dot presented in 1° portions of visual field

• agnosia - island of visual fields loss with patients of visual form agnosia

Form agnosia - Campion and Latto (1985) - possible sensory defects to explain agnosia - peppery field experiment

• Agnosia explained not by form-specific impairment, but peppered field defects (scotoma)

Form agnosia - Campion and Latto (1985) - possible sensory defects to explain agnosia - peppery field experiment - but is this account enough to explain visual form agnosia?

• Other types of agnosia, and examining the functional organisation of the visual system as a whole, might offer some answer

• Can a person with visual form agnosia still use visual form for some other goal?

Ventral and dorsal streams - Ungerleider and Mishkin (1982) lesioned monkeys either in the temporal lobe or the parietal lobe

Object recognition - parietal (where pathway) - dorsal

Spatial judgement - Temporal stream (what - ventral

Ventral and dorsal streams - where pathways - ungerlieder and Mishkin

describes the “dorsal stream”. It is concerned with recognising the spatial location of objects and their movement.

Ventral and dorsal streams - what pathways - ungerlieder and Mishkin

describes the “ventral stream”. It is concerned with recognising objects and their properties (e.g. colour and shape) and complex objects such as faces.

Ventral and dorsal streams - is it really accurate to say these streams process different visual features? - A patient tested by David Milner and Mel Goodale (1991, 1992) suggested a different dissociation

• Patient DF - profound visual from agnosia

• (ventral stream damage)

• Accompanied by other deficits (brightness, motion, depth) but largely intact low level vision

• Those with apperceptive agnosia cannot copy

• Those with associative agnosia can copy

• Found that although patient df doens’t have conscious visual access to shape information,

• if he had to hold an envelope, and post it through an imaginary slot - she can’t do it

• if had to hold a card and post it through a physical slot - very little difficulty doing the task

• Suggest that what is impaired is having access to information about the slot - promoted slightly diff fraweworo for the visual streams

vVentral and dorsal streams - is it really accurate to say these streams process different visual features? - A patient tested by David Milner and Mel Goodale (1991, 1992) suggested a different dissociation - different streams

Dorsal stream

- Visuomotor interaction - Egocentric
- No access to memory
- Unconscious

Ventral stream

• -  Object recognition

• -  Access to memory - Conscious

• Allocentric

Updates Ventral and Dorsal stream - Malach et al (1995)

• fMRI study measuring responses to objects and non-objects (textures) e.g. stripes/ dots or teddy

• Response in lateral occipital complex does not distinguish familiarity, similar response in brain areas in brain areas those with visual form recognition and those normal

• segregation of function between shape vs non shape

- A patient tested by David Milner and Mel Goodale (1991, 1992) suggested a different dissociation - different streams - Support - Culham et al (2003)

• anterior intraperital sulcus,

• used device, to reach and grasp objects in front of them, make an appropriate grasp based on the type of object/shape/ size of object

• Found - response not in the lateral occipital complex (ob recognition), instead the anterior intrapartiteal sulcus ( intact in patient DF)

• anterior intraperital sulcus - responsible for shape guided actions

Updated ventral and dorsal streams - dissociation vision-for-perception and vision-for-action in neurotypical observers? - aglioti, de soiuza, and goodie

• if we alter a persons conscious perception to an object size (but not its physical size) , does that persons visually guided interaction with the object change

• centre crinkles are graspable 3D objects, measures maximum grip aperture during visually guided grasp of central circle

• central cycle size can be adjusted so that they appear to match (but are physically different)

Updated ventral and dorsal streams - dissociation vision-for-perception and vision-for-action in neurotypical observers? - aglioti, de soiuza, and goodie - findings

• maximum grip aperture scales with physical size, not perceived size

• Although these processing streams are largely independent, there is some interaction between them

• Patient DF has difficulty with complex shapes; dorsal stream cant do everything alone - needs to be some communication

Face processing - ventral stream

• damage to

Face processing - Kanwisher, McDermitt and Chun (1997)

• compared brain activity in response to reviewing faces or other objects e.g. houses, using fmri

• Face specific activity in ventral stream (fusiform face area) is not explained by: low level features and attention, but consistent patterns of fusiform face area which are involved in processing faces

Face processing - is the fusiform face area specialised for faces or for recognising exemplars from any category (Gathier et al (2000)

• just an expertise effect, we are just experts of reading and recognising faces

• e.g. show people who are expects in models of cars or bird watchers and ask them to make the same distungsuhments in an fmri - same patern in the fusifoirm face area - not just for faces

• But expertise effect are not resctricted to FFA, and can be confounded with attention (Harel, 2010)

People seem to process faces holistically - Thompson

• this only occurs for upright faces

• these effects don’t occur for other-non face object

• are faces a specific category of object with dedicated neural processing circuits?

prosopagnosia

deficit in recognising faces, but no probkem with recognising other objects

Summary