14 October 2019 Lecture responses

43

Dorsal pathway

Various parietal areas,

Not retinotopic

44
• Last time:
– Description of some of the problems the brain needs to solve to
accomplish its goals
– In some cases we have maps, other cases on-the-fly computation
of the coordinates of only individual objects (rather than whole map)
• Some/most of that happening in parietal lobe

• Today
– Now, having understood what the brain needs to do, we’re in better
shape to interpret data on effects of injury to parietal lobe

par
i e ta
l

45

par
• Parietal lobe function i e ta
l
– Using sensory signals for
– Calculating position of body parts relative to objects
– Representing space for consciousness
– Patients: dyspraxia, neglect
– Memory input to spatial representation, with parietal injury
• Memory map’s still intact, but half neglected when used
– Map located elsewhere
– Gets unpacked by parietal cortex

– How much visual processing happens without parietal cortex and

awareness
• House on fire
• Words
– Coordinate systems for recognition, cognition

46
 Spatial processing in the brain, as revealed by injury

Stroke (cerebrovascular accident)

• If you live to 85, about 1 in 5 chance of having one1
1 Bonita, R. (1992).
Epidemiology of
stroke. Lancet,
339(8789), 342-44.

Croot pr

The most common cause of a stroke is a

thrombosis – when a blood vessel supplying
vital nutrients to the brain becomes blocked with 47
a blood clot.

Structural MRI

48
Left visual field à Right hemisphere
Right visual field à Left hemisphere

Top view; RH pulled back and

everything except corpus
callosum ignored

51

Stroke to one side of brain: Hemispatial Neglect

Patient does fine on standard vision tests

Drawing task

Bisection task

Neglect – “attention”, awareness of that side is impaired

52
 Anton Räderscheidt
https://www.karger.com/ProdukteDB/Katalogteile/isbn3_8055/_82/_65/artists2_02.pdf

A stroke has taken me away from the scene of life; offstage the play is going on with me. I am no longer the director of this play….
Nothing is staying in its place, nothing is keeping the shape. [About painting]: Perhaps I will be able to get hold of a credible shape now if I can use
this permanent motion…. In the past it felt like hunting [shape], now it feels more like catching a trout in moving water using bare hands… Painting
is like taming beasts of prey” Neurological Disorders in Famous Artists p. 4

Neglect – “attention to that side” impaired

• Parietal lobe function

– Using sensory signals for locations
– Calculating position of body parts relative to objects
– Representing space for consciousness

par
i e ta
l

57
 Bilateral parietal injury balints_short (Too low-contrast to see stimuli)

• Balint’s patient (pp.84-5 of Wickens

3rd edtn, p.203 of Carlson 9th edtn)

– Getting more specific than generic

dyspraxia/apraxia term
• Optic ataxia- deficit of reaching under visual
guidance
• Ocular apraxia- cannot scan visually

– Simultanagnosia
• Spatial map of left gone AND right
gone?
• Only one item selected

balintsLongerRaw.mp4
• Starts with reaching test
• Perception test starts at 0:39
• Also possibly on youtube, e.g. at
http://www.youtube.com/watch?v=4odhSq46vtU

61

– Ch. 7 (anosognosia- less important)

• Parietal lobe function par
i e ta
– Using sensory signals for locations l
– Calculating position of body parts relative to objects
– Representing space for consciousness
– Memory input to spatial representation, with parietal injury

62
 At what level is neglect occurring?
Deficit in spatial processing of sensory information.

What about long-term spatial memory?

- Allocentric

Egocentric
DORSAL – where/how
V3 MT MST Parietal
(motion areas)
V1 V2 Hippocampus +

V4 etc… FFA
LO PPA
VENTRAL
what
Allocentric
63

Bisiach imagery neglect

•Imagery uses signals going from allocentric memory map -> parietal and visual areas
• Allocentric -> Egocentric

Piazza del Duomo Bisiach and Luzzatti (1978)

64
 Bisiach imagery neglect
Bisiach and Luzzatti (1978)

Looking from one end Looking from the

other end

•Memory of both sides of piazza intact

•When projected into egocentric person-centred coordinates, left side neglected

65

Parietal lobe function

Live n
– Using sensory signals for
– Calculating position of body parts relative to objects
– Representing space for consciousness
– Patients: dyspraxia, neglect
– Memory input to spatial representation, with parietal injury
• Memory map’s intact, but half neglected when used
– Map located elsewhere hippocampus
– Gets unpacked by parietal cortex

– How much visual processing happens without parietal cortex and

awareness
• House on fire
• Words
– Coordinate systems for recognition, cognition

67

Selection (b/c limited

 At what level is neglect occurring?
Incoming sensory information is affected
• Imagery experiment
– suggests memory map intact
– Imagery uses same mechanisms as that which causes neglect of
real stimuli

• Unconscious processing of stimuli in neglected half of field

• Are objects recognized? (What pathway)

DORSAL – where/how
V3 MT MST Parietal
(motion areas)
V1 V2 Hippocampus +

V4 etc… FFA
PPA 70
VENTRAL what LO
Unconscious processing in neglect

Marshall and Halligan (1988)

-Which house would you rather live in?
-Smoke processed

Smoke recognized as smoke?

71

Perception Without Awareness?

 Unconscious processing shown by stroop

Stroop Experiment (Berti, Frassinetti, & Umilta, 1994)

Left Right

BLUE
Incongruent

BLUE Congruent

Task: Determine color of block

72

Unconscious processing in neglect

Brain imaging of processing of unperceived stimuli

Structural MRI brain scan of patient CW (axial slices), showing focal

damage in inferior posterior parietal cortex (angular gyrus, thick arrows),
extending into the subcortical white matter of the right hemisphere
(dashed arrows).

“By comparing fMRI signals for shapes presented

Neural fate of seen and unseen faces in
alone in the normal RVF and the same shapes visuospatial neglect: A combined event-
related functional …
presented with an extinguished face in the LVF (i.e., P. Vuilleumier, N Sagiv, E Hazeltine, RA
Poldrack, … - Proceedings of the National
different stimuli but same percept), we found that Academy of Sciences, 2001

unseen faces activated right visual cortex (V1) and

inferior temporal areas, just lateral to fusiform regions
with face-specific responses. This activation was weak
compared with seen stimuli” 73
Summary of visual processing in hemispatial neglect:

- Imagery still works, but half neglected

- Meaning of smoke still processed even when neglected?
- Words still read, even when neglected
- But locations not available to consciousness

• Coordinate systems for cognition,

recognition
• Sele
•
•

74

Coordinate frames for recognition

78
Coordinate frames / maps for object recognition

For directing gaze For processing

need to know orientation of each For word
coordinates relative shape (e.g. arrows) recognition
to visual field
Defined by
canonical object
orientation

Hillis, A. E. (2006).
Neurobiology of unilateral
spatial neglect. (USN)
Neuroscientist, 12(2), 153-
63.

= =

79

Coordinate frames / maps for object recognition

For directing gaze For processing

need to know orientation of each For word
coordinates relative shape (e.g. arrows) recognition
to visual field
Defined by
canonical object
orientation

Hillis, A. E. (2006).
Neurobiology of unilateral
spatial neglect. (USN)
Neuroscientist, 12(2), 153-
63.

= =

80
 Coordinate systems for object recognition

- Stimulus-centred
- To recognise arrow as right-pointing or left-pointing
etc. arrow, need to calculate location of arrowhead
relative to its centre, not relative to overall visual field
- Object-centred
- To recognise words, need to know which letter is first,
which second, etc. even for unusual word orientation

• Sele
•
•

81

centered neglect

Perfusion-
Diffusion- weighted
weighted imaging:
imaging:
Areas of low
Swelling, blood flow

Viewer-centered

Stimulus-centered

82
Coordinate frames for cognition, not just action
• Word recognition aligns letter strings?
• Object recognition compensates for object movement, and eye
I. Harr
movements? (Carlson, pp.202-3)

Some features
may be
orientation
dependent
(d vs. p)
Won’t work if
system input
has wrong
orientation
deer
Facial expression recognition system does 83
not

At what level is neglect occurring?

compensate well for orientation

Egocentric
DORSAL – where/how
V3 MT MST Parietal
(motion areas)
V1 V2 Hippocampus +

V4 etc… FFA
LO PPA
VENTRAL
what
Allocentric

84
Summary of visual processing in hemispatial neglect:

- Imagery still works, but half neglected

- Meaning of fire still processed? even when neglected
- Words still read, even when neglected
- But locations seemingly not available

• Coordinate systems for recognition, cognition

• Sele
•
•

85

The Guugu Yimithirr people

have no words denoting
egocentric directions, but
instead exclusively refer to
compass directions, even
when describing small-scale
spaces.

Haviland, J. B. (1998). Guugu Yimithirr

cardinal directions. Ethos, 26(1), 25-47. "Natives of Endeavour River in a canoe, fishing." From Phillip Parker
King's Survey. 1818. Wikimedia
86
 socrative.com
Room: ATHK

So long, and thanks for

all the questions!

Alex.Holcombe@sydney.edu.au
t: @ceptional

#4 Describe one of the main points

23/8/2017 Holcombe first lecture