L7 - 8 Vision Flashcards
How many areas in the cortex associated with vision? How are these areas differentiated?
30 - diff by rep of visual space and functional properties of neurons
What is low level visual processing? Intermediate? High?
Low (retina)
- Colour
- Orientation
- Movement
- Edges
- Contrast
Intermediate (PVC)
- Analysis of layout of scenes
- Distinguishing foreground from background
- Parsing of objects into surface and global contours
High (Beyond PVC)
- Object recognition
- Matching with memories
Dorsal pathway - What cortical area is involved?
AREA MT - detecting where an object is, visual processing is through V1, V2, MT
Ventral pathway - What cortical area is involved?
AREA IT - object recognition, visual processing through V1, 2, 4
Describe the features of a SBAC
- Only dendrites
- Only distal part of cell can send outputs out
- Synapses with DS GC
- GABA is only released when stimulus (light) moves from soma to dendrite (encodes DS)
Input: Glu, GABA, gly
Output: GABA, Ach
*DS has to do with GABA release, nothing to do with Ach (function unknown currently)
What does cortical magnification in the brain mean in reference to vision?
The brain uses more physical space for signals from the fovea than the periphery
M cells synapse onto which layer of LGN? P cells?
M - 4B, 4C alpha, 6
P - 4A, 4CBeta, 6
What is special about neurons in layer 4B?
DS as it gets info from the retina (bigger discharge when left to right)
In V1 we have cytochrome oxidase blobs (colour info) - interblobs code for?
In V2 we have thin stripes (____) and thick stripes (____)
Interblobs = orientation sel Thin = colour Thick = motion
AREA MT not only detects motion but also?
Coherence
What do lesions in MST lead to? Why?
Deficits in pursuit eye movements because MST sends info to brainstem for eye movments
What do right occipito-parietal lesions lead to?
Deficits in pursuit eye movements
V2 makes up _% of all neocortex
10%
Object invariance
Doesn’t matter whether horse is facing you sideways or front on - you can still recognise that it is a horse
e.g. A single hippocampal cell responds to multiple presentations of Jennifer Aniston
Apperceptive (no perception) agnosia - what is it? where is the lesion?
- Cannot match or copy an object
- Can name object
- Cannot integrate and bind visual info into sensory representations of entire objects
LOCATION: Posterior IT lobe
Associative agnosia - what is it? where is the lesion?
- Can match or copy objects
- Cannot name object
- Can integrate and bind visual info into sensory representations of entire objects
- Cannot identify object/cannot associate with meaning
LOCATION: Anterior IT lobe
*Anteriorly (higher level object recognition) has already received input from PVC V2 - higher level of object recognition (hence when lesion is here, object recognition is impaired)
What is the function of cytochrome oxidase staining?
Shows metabolic energy and neural activity
Complex cells have End zone inhibition/ End-inhibited receptive fields - what does this mean?
Neurons respond to lines of a particular length and curvature
V4 neurons have small/large receptive fields that fire to ____ ____ but not simple stimuli (orientation, colour)
There are areas that don’t overlap where one encodes colour and another encodes orientation
Large, coloured patterns
The FFA (Fusiform face area) is located on the dorsal/ventral surface of the __ lobe on the medial/lateral side of the fusiform gyrus
For face recognition, 5 regions are linked by?
Ventral, IT, lateral
Horizontal connections
How many % of neurons in Fusiform face area patches respond to faces?
97
What do neurons in “face-patches” encode?
Neurons encode round objects where shape and aspect of face leads to firing of neurons - there is something about the roundness of the face that stimulates them
What happens when you stimulate the FFA?
Makes the subject think you look like someone else
Columnar organization of the anterior part of the IT lobe
PVC is organised in columns of neurons that represent the same stimulus feature (e.g. orientation or direction of motion)
Different aspects of faces are encoded in columns
Describe the connections of the fusiform face area patches
Stimulation of one patch causes activation in another - there are long horizontal connections between patches
Outputs from IT lobe
- Perirhinal and parahippcoampal cortices
- PFC
Face recognition is similar/different in MZ twins and similar/different in DZ twins
Face recognition is similar in MZ twins (0.7) and different in DZ twins (0.3)
T/F: Neurons in the IT temporal lobe cannot be modified by experience
F - Can be modified by exp
Neurons in PFC and IT cortex continuously fire even after the visual image has been removed. What is this continual firing is thought to be important for maintaining?
Short term memories
Area IT sends input into which area?
Area IT sends input into amygdala = feelings when seeing visual images
C and I organisation of LGN layer
6P- C
5P - I
4P - C
3P- I
2M - I
1M - C
