Visual perception Flashcards
What are the two visual receptor cells in the retina?
cones and rods
where are cones usually located? specialisation?
fovea and specialise in colour and detail perception .
where are rods usually located? specialisation?
located in the periphery and specialise in vision in dim light
How is information transmitted through the lateral geniculate nuclei to the brain?
Retinal ganglion cells receive input from a few cones or hundreds of rods.
Explain the steps of the retina-geniculate- striate system
From retina , optic nerve goes through the optic chasm to the LGN which has 6 layers. Cells have monocular input and the layers alternate inputs from each of the two eyes. The top four are parvocellular layers, two layers from each eye . Parvo LGN cells receive inputs from midget ganglion cells, mostly cones. The bottom two are magno cellular layers, one layer from each eye. Magno LGN cells receive inputs from parasol ganglion cells (mostly rods).
V1 and V2 function?
involved in early stages of processing e,g basic colour, form
V3 and V3A function?
cells in these areas response to form (especially the shapes of objects in motion) but not colour
V4 function?
respond to colour and many are so responsive to line orientation
V5 function?
visual motion
How is V4 important for colour processing?
Colour processing in V4, important but not the ‘’colour centre’’ . There is evidence of this such as more fMRI activation in V4 with full colour movie clips compared to black and white.
What V is involved in motion processing?
Motion processing in V5, is heavily involved in motion processing
What is the binding problem ?
How are features combine and integrated? This is hard to solve but feature integration theory says that selective attention plays a role.
What are the two suggestions to solve the binding problem?
-Suggestion 1: binding-by-synchrony, features from single object fire synchrony
Suggestion 2: patterns of neural activity over time help coordinate binding (Guttman et al. 2007)
How does the dorsal and ventral visual streams operate ?
- two streams of neuron activity flow from V1 and into parietal and temporal lines. ventral helps identify shapes and objects. dorsal processes spatial and movement
Describe the ventral stream
vision for perception
identifies objects
allocentric
usually conscious
Describe the dorsal stream
vision for action
processes spatial information to guide movement
egocentric
usually unconscious
What has visual illusions in studies demonstrated?
Visual illusions in some studies have shown he ventral stream is more susceptible to illusions compared to the dorsal steam. Independence of the dorsal and ventral system is not absolute. Double disassociation between optic ataxia and visual form agnosia is not clear cut
define Trichromatic theory
three types of colour receptors or cones identified by microspectrophotometry
define Dual process theory
combination of trichromatic and opponent process theory
define Colour constancy theory
the tendency for a surface or object to appear to have the same colour despite a change in the wavelengths contained in the illuminant
define Binocular disparity theory
slight difference in the two retinal images
define Size constancy theory
The tendency for objects to appear the same size whether their size in the retinal image is large or small
What does the opponent process theory claim?
This theory claims it is impossible to see blue and yellow together or red and green but the other colour combinations can be seen. There is strong physiological evidence for the existence of opponent cells
What theory combines trichromatic and opponent process together?
dual process theory
list monocular cues to depth perception
- linear perspective
- texture
- interposition
- familiar size
- motion parallax
what is a receptive field?
the region of the retina within which light influences the activity of a particular neuron
what is lateral inhibition ?
reduction of activity in one neuron caused by activity in a neighbouring neuron , increases contrast
what is a retinotopic map?
nerve cells occupying the same relative positions as their respective receptive fields have on the retina
What is functional specialisation theory?
Zeki proposed that different parts of the cortex are specialised for different visual functions. Early knowledge of this came from monkeys.
