Lecture 2 - The brain Flashcards
1
Q
Ganglion cells?
A
- each ganglion cell receives input from 126 photo receptors - input is not simply added but either excites or inhibits a ganglion cell
- this depends on where in a ganglion cell’s receptive field the stimulus is located
2
Q
What is the receptive field of a neuron?
A
the part of the visual field in which a stimulus can modify the neurons firing rate
3
Q
What is the excitatory area (+) of a ganglion cell?
A
- ‘on’ area
- increases the firing rate of a neuron when stimulated
4
Q
What is the inhibitory area (-) of a ganglion cell?
A
- ‘off’ area
- decreases the firing rate of a neuron when stimulated
5
Q
What are the 3 main types of ganglion cells?
A
- magnocellular (M) cells
- mostly input from rods
- not colour specific - parvocellular (P) cells
- input from single M or L cones
- colour specific (green or red on/off) - koniocellular (K) cells
- excitatory input from s cones
- inhibitory input from M and L cones (blue on)
6
Q
Visual cortex?
A
- primary visual cortex = V1
- extra striate visual areas = V2, V3, V4, V5
- as visual information travels through the cortex there is ongoing neural convergence
- the neurons receptive fields increase
- visual information gets more complex with ongoing integration
7
Q
V1?
A
- striate cortex (stripy appearance)
- some V1 neurons are orientation selective =
-> they respond when a stimulus in their receptive field matches their preferred orientation
-> they have elongated receptive fields to capture edges in a particular orientation - the less the stimulus matches the preferred orientation the lower the neurons firing
- other neurons are motion direction selective = they respond when a stimulus in their receptive field matches their preferred motion direction
- other V1 neurons are selective for colour and brightness
8
Q
V2?
A
- V2 receptive fields are about twice as large as V1 receptive fields
- V2 neurons respond to basic stimulus features such as orientation, motion direction and brightness
- they also respond to more complex features such as length, angles, arcs etc.
9
Q
Evidence for 2 separate streams?
A
- the parietal (dorsal) stream processes object locations (where)
- the temporal (ventral) stream processes object identities (what)
- moneys with parietal (where) lesions could distinguish a cube from a triangle (object discrimination) while monkeys with temporal (what) lesions could not
- monkeys with temporal (what) lesions could learn the positions of an object (location discrimination) while monkeys with parietal (where) lesions could not
10
Q
V3?
A
- is in the parietal/ dorsal (where) stream
- receptive fields are 5x larger in V3 than V1
- integrated information over a large area of the retina
- perfect for motion perception (where is an object)
11
Q
V4?
A
- is in the temporal/ ventral (what) stream
- receptive fields are 5x larger in v4 than in v1
- V4 neurons respond to object-defining features (what is an object) such as colour, orientation, complex shapes, texture