PSYC2013 Tutorial Material

Question 1

the blind spot is ___ degrees to the nasal side of the fovea

Answer 1

12-15

Question 2

the blind spot is ___ degrees below the fovea

Answer 2

1.5

Question 3

how big is the blind spot

Answer 3

5.5 degrees wide and 7.5 degrees high

Question 4

what is the formula for the visual angle calculation

Answer 4

VA = 2tan-1(s/2D)

Question 5

what are floaters?

Answer 5

residue from tissues or red blood cells floating in vitreous humor. They cast shadows on your retina.

Question 6

What are blue field phenomena or AKA sky sprites

Answer 6

caused by white blood vessels shooting through capillaries. Since they take up the whole gap of blood vessels, the gap before the white blood cell is permeable to light so it appears as though a bright light is darting about.

Question 7

what is the troxler effect?

Answer 7

if something is stationary, in the periphery –> brain will tune out.

Question 8

information in the left visual field lands on the ___ half of the retina in each eye, which converges to the ____ LGN and eventualy reaches the ____ primary visual cortex. From here it splits into the ____ (___) and ___ (___) streams.

Answer 8

right 
right
right 
dorsal (where) 
ventral (what)

Question 9

layers of cells from the vitreous humor to the most posterior surface of the retina is:

Answer 9

gangloin cells, (amacrine), bipolar (horizontal), rods/cones

Question 10

describe an example of convergence in the retina

Answer 10

125 million photoreceptors connect to 1 ganglion cell.

Question 11

take a centre surround cell (on centre, off surround) Describe what would happen if light stimulates:

• the whole cell
• the centre of the cell
• the out of the cell

Answer 11

• nothing, stimulation will remain at base rate
• increase in AP
• decrease in AP (inhibition

Question 12

Describe why centre surround cells like edges.

Answer 12

for on centre off surround, they like it when only the centre is stimulated, and the surround is not stimulated –> results in net increase in AP. This occurs with edges.

for off centre on surround, they like it when only the surround is stimulated, and the centre is not –> results in net increase in AP. This occurs with edges.

Question 13

increase in eccentricity in the retina =

Answer 13

increase in receptive field size

NB: eccentricity means deviation from the fovea

Question 14

Describe the receptive fields in the fovea vs the periphery

Answer 14

ganglion cells have small receptive fields, therefore good spatial resolution, unlike periphery where ganglion cells have large receptive fields

Question 15

Is there convergence in LGN cells.

Are LGN cells centre surround like in the retina?

Answer 15

yes, 1 LGN cell connects to a bunch of ganglion cells

yes

Question 16

describe simple V1 are tuned to detecting edges

Answer 16

V1 cells respond to specific orientations. each V1 cell will only fire if it receives input from a select specific combination of LGN neurons. These LGN neurons must be aligned in a particular location.

Question 17

What are complex V1 cells

Answer 17

also respond to particular orientation, however also particular direction and sometimes spend. They are broadly tuned, and will respond to ‘close enough’ stimuli

Question 18

Describe the receptive field of cells in the IT cortex and identify what stimuli they respond to.

Answer 18

very large

respond to face looming stimuli, in a particular viewpoint

Question 19

What is an alternative account for the selectivity of neurons in the IT (FFA) cortex responding specifically to faces.

Answer 19

area is for whatever we are visually expert at

Question 20

What is optic flow

Answer 20

when moving there is motion contrast between the periphery and the focus of expansion. Appears that the periphery is moving a lot faster.

Question 21

How do we gage object motion?

Answer 21

tau - tau is a concept that suggests that we measure the size of an objects occupation of the retinal image against the rate at which that size expands.

Question 22

Describe a simple Riecheart detector

Answer 22

Brain takes sample at space and time A and then B. Holds the first one in delay so they meet at the same time. Only responds to specific direction and speed

Question 23

Does a simple Reichardt detector respond to two flickers in space at different times.

Answer 23

yes - apparent motion or phi motion.

Question 24

Describe the problem with the simple Reichardt detector

Answer 24

If have something that is moving infinitely fast, such that it occupies both space A and space B at the same time, the simple Reichardt detector says we will perceive it as motion. But we don’t!

Question 25

Describe a fully opponent Riecheart detector

Answer 25

two detectors. Responds preferentially to one direction, however the response detector will be neutralized if it also detect somethig moving in the opposite direction

Question 26

Why is the fully opponent riecheart detector better than the simple one

Answer 26

adequately predicts perception. Won’t be fooled by something moving infinitely fast at time 1 and infinitely fast at time 2. This is because if something is moving infinitely fast then its like a direction going both ways – so if this is the case the direction cancel each other out to get no perceived motion.

Question 27

what is phi motion,

what is reverse phi motion?

Answer 27

phi motion - regular apparent motion –> something appearing in location one then location two.

reverse phi motion –> something appearing in location one then appearing in location two but of reversed contrast

Question 28

How can the fully opponent Reichart model account for phi motion and apparent motion

Answer 28

phi motion - recives input at A1 then at B2. hold A1 input in delay so meets B2 at same point.

reverse phi motion - reieves + input at A1 then - input at B2 (because reversed contrast), so get overall -1 input, so perceive as moving in opposite direction to flicker motion.

Question 29

how do you calculate beta? Describe the value of beta for a neural, liberal and conservative criterion

Answer 29

beta = number of hits/number of false alarms

neural - beta = 1
liberal - beta < 1
conservative - beta >1

Question 30

What is sensitivity?

Answer 30

Measure of the distance between the means of the two distributions, also affected by the variance of each distribution. essentially, how well you discriminate the stimuli of interest.