Vision and action Flashcards
Patient DF suffers from agnosia but also exhibits other visual impairments e.g. cannot discriminate between…despite an intact V1. On other hand she does…
A horizontal & vertical pencil. Adjust the orientation of her hand when reaching for a horizontal vs. vertical pencil
Can DF draw pictures from memory? Can DF copy pictures?
Yes. No
In Milner’s (1991) postal task patient DF can…but not…
Post a card through a slot. Align a card with a slot
Patient DF shows size scaling in action but not in representation - what does this mean?
She adjusts her hand grip size appropriately when reaching for different sized shapes but does not when indicating the size of these shapes to others
In size scaling experiments X is plotted against Y - what are X and Y? Usually X increases with Y but in the case of DF…
X: width of stimulus (cm), Y: maximum aperture. Y does not change with X
In perceptual matching it is interesting that size scaling is still indicated by a motor response but…
can be dissociated from the same motor response when used to reach
What type of grasping does vs. does not recruit the perception-for-action pathway? DF therefore shows a deficit in…
Does: immediate, online grasping. Does not: delayed, offline grasping via memory. Delayed, offline grasping
Ungerleider & Mishkin (1982) first termed the dorsal & ventral pathways the where & what routes - on what basis did they draw this conclusion?
A lesion to the macaque parietal lobe impairs space perception vs. a lesion to the macaque temporal lobe impairs pattern recognition. Monkeys had to discriminate between un-/rewarded objects/locations
Both where and what pathways begin in the ___ lobe
occipital
fMRI evidence suggests that the dorsal pathway responds when ___ an object, whereas the ventral pathway responds when ___ to an object
Grasping. Pointing
What characterises optic ataxia?
Impaired perception for online action. Intact perception for representation
What is the Effron size matching task?
The size scaling task previously described
Optic ataxia (Ataxi!) is characterised by impaired ___ grasping but intact ___ grasping despite the latter being more difficult for controls
Immediate, delayed
So there is a double dissociation between…&…
visual agnosia & optic ataxia
Give 2 conditions in which perception for action is modulated by ventral info & e.g. patients
1) When complex, relative position info is important e.g. DF is impaired at picking up a ten pin bowling ball. 2) When the action is directed towards a familiar object e.g. an optic ataxic patient who more accurately grasped her lipstick than a same-shaped/sized, unfamiliar stimulus
The familiarity effect in optic ataxia suggests that the ventral stream is required to use ___ ___ to inform actions
pre-existing knowledge
The motor response to visual affordances seems to be mediated by the ventral pathway. What evidence is there for this?
Pps display greater left fusiform gyus activity when objects are positioned correctly for action (interaction) than when not
The effect of positioning on LFG activity is greater for ___ pairs of objects & not confined to when objects are ___
Familiar. Attended
What is utilisation behaviour?
When a patient automatically obeys a visual affordance despite the contextual inappropriateness of doing so e.g. places the presented glasses on even when he’s already wearing glasses
Riddoch (1998) suggests that utilisation behaviour is mediated by visual object properties, finding that
patients made more errors (60% vs. 40%) in a task in which they were required to grasp a mug with their left hand if it was placed on the left & vv, when the side of the mug’s handle afforded the use of the opposite hand
