Dorsal Stream 1. Analysis of Movement o integrating changes in... 2. Analysis of Location o coordinating info about... 3. Higher-level spatial reasoning o judging position of objects... o mentally manipulating spatial...
visual information over time
retinal location to assess distances relative to viewer
relative to one another
relationships amongst stimuli e.g. mental rotation
Dorsal Stream: Analysis of Movement
- can rapidly extract key info about..
- automatic and rapid
fMRI study:
- regions responding to dot movement minus regions responding to static pattern
- area V3A and hMT+ (activation is bilateral)
- hMT+ key region for…
- area hMT+ is…
fMRI study:
- moving vs stationary dot patterns
- RH processes…
- patterns presented to LVF, the…
- patterns presented to RVF, the…
- impairment =
> Patient: Gisela Leibold
– loss of…
– bilateral damage (location of area hMT+)
movement from complex patterns
processing movement info automatically and rapidly
contralaterally organised
LVF, LH processes RVF
RH hMT+ region activated
LH hMT+ region activated
akinetopsia
motion perception
The Dorsal Stream: Analysis of Location:
Extrastriate cortex/posterior parietal lobe important for….
Important for reacting to…
Damage –
Private M:
– intact…
– location processing…
– object perception…
Egocentric Localisation Task:
- task: which is further blue or green bin?
- control task: which bin is lying on its side?
- dorsal stream activated…
- subtraction analysis (regions activated that differ in tasks)
- activated…
Allocentric Localisation Task:
– judging position of one object relative to another
– (task) which bin closest to red ball?
– (control task) which bin is on its side?
– overlaps with previous, but…
– object-centred analysis (independent of person’s position)
analysing location relative to viewer (= egocentric localisation) immediate environment (e.g., deciding which of two objects is nearer to you, locating objects in 2D, reaching objects)
can’t navigate or interact properly with environment (“visual disorientation”)
V1
is impaired
is preserved
(more extensive in RH) – occipital-parietal border
dorsal area, superior to PVC
posterior parietal lobe activity
The Dorsal Stream: Spatial Reasoning Mental Rotation Task: - fMRI metanalysis suggests... - Activation in.... - parametric design
MRT:
– mark position of square on white sheet
– tested tumour patients
– patients with poorest scores had…
Q. Why are the fMRI results and the brain damage results different?
regions more active with greater rotation
LH and RH (bilateral activation)
(change that occurs as parameter alters)
right parietal damage (posterior part of RH - critical for this task)
A. the areas that are critical for performing the task are right parietal areas, if don’t have those areas, unable to do task. fMRI does not show areas critical for tasks, only shows the areas active during a task.
The Dorsal Stream: Spatial Reasoning
Rey Figure:
Some spatial tasks involve more complex forms of analysis
Involves creating a map of the relative positioning of features, maintaining and reproducing it.
Patients with right parietal damage lack the ability to…
preserve the spatial organisation of the picture, fail to integrate elements of picture, left neglect.
Spatial Attention: Two Types
1. Stimulus-driven attention:
- Top-down attentional control:
ability to orient to a salient or important stimulus when it unexpectedly appears = EXOGENOUS attention
ability to control where you focus attention, according to what’s currently important (even when there is no current stimulus to draw you) = ENDOGENOUS attention
e.g., waiting at station > focus on direction of train
Unilateral Neglect: Problem with Bottom-Up Attention
- person’s attention cannot easily be drawn to…
- stimuli need to be…
stimuli on the bad side
extra salient to draw their attention
Unilateral Neglect:
Three major types of tasks used to diagnose neglect:
- Cancellation Tasks
- Line Bisection Tasks
- Picture Copying Tasks
Voxel-based lesion symptom mapping:
- Damage to RH (border between dorsal and ventral streams) significantly predictive of…
- Spatial attention is…
acute neglect
contralaterally organised
Neglect is an exogenous attentional not a perceptual problem
1. Neglect affects…
- Neglect evident even no…
- Neglect influenced by…
- double simultaneous stimulation technique:
- participants less likely to report O when…
- the stimulus on the good side appears to… - Meaning affects…
- Neglected info may be processed…
- Q. houses same or different
- A. same
- Q. preference to live in?
- A. bottom one (house without fire)
internal representations (e.g., Milan Square Study)
leftward eye movements required
stimuli on good side
X is present
“compete” for attention > EXTINCTION
what and how much is neglected (e.g., dog study)
without awareness
Top-Down Attentional Control
Posner task:
- arrow indicated the most probable location of upcoming stimulus: normal people are…
- able to shift attentional resources towards location
fMRI study:
- regions activated when arrow cue is presented before stimulus
- posterior intraparietal sulcus, ventral intraparietal sulcus, hMT+
- activation is bilateral
- activation in dorsal posterior parietal cortex regions
- the damaged area is different (more dorsal) than neglect brain damage
- endogenous attention controlled by different parts of brain than exogenous
The posterior parietal lobe (on both sides) is important for…
…is impaired in…
- can identify objects but can’t…
- only able to comprehend…
- bilateral parietal lesions
R.M: – which shape is taller?
– able to do this when shapes presented…
– but not when shapes are presented…
– requires strategic shifting of focus of attention
In simultanagnosia, patients appear…
It appears that once attention is drawn by a stimulus, it can’t then be easily shifted and reattached to another
faster to respond than if no clue given = ENDOGENOUS
endogenous control of attention
simultanagnosia
shift attention between them
parts of information
one after the other
simultaneously, even if display duration is long
“fixed” to a stimulus/location, cannot freely explore
