Flashcards in Week 8 Deck (17):
What is visual agnosia?
Impairment of object recognition, failure to recognise that an object as a whole, recognition of parts is intact (i.e. colour, shape and movement perception are all intact)
What are the two cortical pathways for vision?
Ventral (occipital to temporal), Dorsal (occipital to parietal).
Describe the function of the ventral pathway.
Important for object perception, process information regarding the objects appearance and identity. Occipital to temporal.
Describe the function of the dorsal pathway
Important for guiding object related action, processes spatial information, occipital to parietal.
Describe the functional impairments that lead to optic ataxia, and symptoms
Lesions to the dorsal pathway (parietal), intact object recognition, but can't use visual info to guide action
Describe the recognition by component theory
3d version of the feature analysis theory. A 3d object is first segmented into an array of sub-objects called geons, which are then recognised as a pattern composed of geons
Neurons in _____ order visual areas (i.e. further away from the retina, respond to ______ patterns
higher, increasingly complex
Explain the grandmother hypothesis, and its fallibilities.
The higher up the visual areas we go, the more complex patterns are recognised by the neurons, therefore, if we go far enough up, there will be a specific neuron to recognise your grandmother. -ve's, neurons firing is not that reliable, loss of neuron would equate to losing the recognition for that object, perception of novel objects not explained, nor perception of altered objects i.e.no flexibility
Describe patients DF's agnosia
Visual acuity and nonvisual object recognition intact. Can't tell which way a slot is orientated. Severe agnosia. Ventral stream damaged, dorsal stream (action guidance, action perception) is fine!
Describe optic ataxia
Dorsal stream damage. Intact object recognition, inability to use visual information to guide action.
Describe Gestalt principles of object recognition.
Tendency to group objects according to conventional shapes, and groups. "generating whole forms"
Describe feature analysis
a visual pattern is perceived as a combination of individual elements. E.g. detecting vertical lines, horizontal lines, recognition occurs when the brain 'listens' to the most influences and subsequently identifies stimuli. "Only the detector for 'r' fires, partially 'p', partially 'd'd
Describe template matching theory
matching stimuli with small differences in characteristics.
Describe feature analysis experiment
When 'HB' is presented wit eye movement, entire features disappear simultaneously, rather than random gradual fade.
In an experiment testing recognition by component theory, what findings could be found?
Midsegment deletion objects illicit more errors than segment deleted, particularly with short exposure to object.
Describe 'ensemble style' firing for neural pattern recognition
Object recognition results from the firing from an ensemble of cells.