Problem 2: The visual brain

Question 1

what is the optic chasm

Answer 1

x shaped bundle of nerves, the crossover between the eyes and the hemispheres, which causes each hemisphere to be connected to the eye on the contralateral side of the brain

Question 2

visual field and contralaterality

Answer 2

visual field is determined by based on where the person is fixating, everything right from the focal points is the right side of the visual field and vice versa, both eyes can see both visual fields

Question 3

visual pathway

Answer 3

retina –> optic nerve –> optic chimes –> Lateral geniculate nucleus (LGN) (90%) and Superior Colliculus (10%) –> visual cortex

Question 4

Lateral Geniculate Nucleus

Answer 4

LGN is located in the thalamus and regulates 90% of the info from the retina. purpose is to regulate neural information as it flows from the retina to the cortex, it also inhibits info from the retina

Question 5

Superior colliculus

Answer 5

other 10% of fibers from the retina, this structure is involved in controlling eye movement

Question 6

Visual receiving are / Striate cortex / Area V1

Answer 6

signals from LGN travel here, part of the brain where the signals are actually being processed

Question 7

how is V1 structured?

Answer 7

layers seperate information from right and left eye (LRLRLR), with a centre surround configuration (center is excitatory, surround is inhibitory)

Question 8

the layers of V1:

Answer 8

-Magnocellular layers (M-cells): large cell bodies, caries info about dynamic visual processes (motion, flicker)
-Parvocellular layers (P-cells): small cell bodies, carries info about color, texture, form and depth
-keniocellular layers (K-cells): very small cell bones

Question 9

what are simple cells

Answer 9

in V1, they have side by side receptive fields and are responsible for orientation

Question 10

what are complex cells

Answer 10

in V1, respond to movement (best to a particular direction), like simple cells but + movement

Question 11

What are end-stopped cells

Answer 11

in V1, fires to moving lines of a specific length or to Cornes and edges

Question 12

feature detectors

Answer 12

name for simple, complex and end-stopped cells because they fire in response to specific features

Question 13

what is selective adaptation and how does it work

Answer 13

neurons that react to specific features in times become adapt and fire less when the stimulus is presented again –> less sensitive neurons –> less sensitive perception

Question 14

what is a contrast threshold

Answer 14

the minimum intensity difference between two adjacent bars that can just be detected

Question 15

how was selective adaptation measured

Answer 15

first a person’s contrast threshold was determined by letting them look at different orientations of lines, then they showed them a high-contrast line set and let them adapt to it, then they showed them the first contrast lines things and measured firing again –> higher threshold (less sensitive)

Question 16

the difference between a orientation tuning curve and a psychophysically determined selective adaptation curve

Answer 16

an orientation tuning curve focuses on how a neuron responds to a certain orientation, the psychophysically determined selective adaptation curve shows the adaptation of nerve cells after exposure and is wider because the adapting neurons activates surrounding neurons

Question 17

what is selective rearing and what is the role of neural plasticity (or experience dependent plasticity)

Answer 17

if an animal is reared in an environment that contains only certain types of stimuli, then neurons that respond to these stimuli will become more prevalent. Neural plasticity is the idea that response properties of neurons can be shaped by perceptual experience. rearing an animal in an environment that only contains vertical lines results in the visual Cortex mainly having simple cells that respond to verticals

Question 18

how do selective rearing and selective adaptation contradict each other and how does it make sense

Answer 18

it seems to contradict each other because selective adaptation would suggest neurons becoming less sensitive after exposure, while selective rearing would suggest neurons becoming more sensitive. it works together because selective adaptation is short term and selective rearing is long term

Question 19

V1 is organised into columns, how does that work?

Answer 19

Location columns: column that contains nerves that respond to the same location on the retina, they are positioned perpendicular to the surface of the striate cortex
Orientation columns: alle the location columns are specialised in different orientations, together they make up the orientation columns
Ocular dominance column: preference for one eye
Hypercolumn: a location column with all of its orientation columns in it

Question 20

Tiling

Answer 20

you location columns cover your entire visual field in an overlapping Tiling manner

Question 21

Single dissociation

Answer 21

2 groups are tested on 2 tasks and a between-group difference is apparent in only one task (can’t see whether functions are independent)

Question 22

Double dissociation

Answer 22

demonstration that one task is affected by one type of manipulation, whereas a second task is affected by a different type of manipulation (works both ways –> functions are independent)