high level vision

Question 1

in terms of colour what is the human visual system.

Answer 1

triochromatic.

Question 2

how many different types of cones are there

Answer 2

3 types of cone small medium large. each look at either S, M, L wavelengths

Question 3

how many types of ganglion cell are there

Answer 3

2. 1 = midget cell looks at red-green coloyr differences uses M+L cones. 2. small bi-stratisfied ganglion cells use S,M,L cones (lime green - violet)

Question 4

what is dichromacy

Answer 4

when either M or L photopigment gene is missing. therefore retina can only has 2 types of cone. occurs during cell division. basically colour blindness.

Question 5

what is anomalous trichomacy

Answer 5

when one gene is hybrid that contains M+L photoreceptors. this means that R-G colour differences are still visible but appear duller/muted.

Question 6

how does visual system deal with different illuminations

Answer 6

via maintaining colour constancy. think pics of a fruit bowl with different filters over it e.g. cool, warm, blue. all the fruits will still be the same colour just slighlty different shades.

Question 7

how does visual system maintain colour constancy.

Answer 7

light that falls on retina is a product of reflectance and illumination spectrum. visual system has to find colour of the illuminant so it looks at highlights, colour memory and 3D structure of shadows.

Question 8

how can you explain the blue dress trend

Answer 8

the dress’ colour seems to change. this happens beacuse of unsual illuminant/reflectance spectrum.

Question 9

what does Wallach say about lightness constancy

Answer 9

our perception of lightness of a patch depends on its background e.g. if two patches have 2 different background colours as long as background:patch ratio are the same we will interpret both patches as being the same colour. 1948

Question 10

what is the Gelb effect

Answer 10

to do with lighness constancy percieved brightness can flip from white to black once true illuminance of illuminations is shown.

Question 11

what is lightness constancy

Answer 11

our ability to perceive the relative reflectance of objects despite changes in illumination

Question 12

what is size constancy

Answer 12

when objects don’t typically seem smaller when further away. our vis system perceptually scales objects according to its perceived distance to maintain a constant perceived size.

Question 13

what is the corridoor effect

Answer 13

when two images of the same size appar different because our visual system perceptually scales up the size of the object to compensate for the greater depth.

Question 14

How can size constancy fail

Answer 14

when we encounter an unfamiliar situation & can’t accurately judge the depth. think corridoor effect.

Question 15

what is Emmert’s law

Answer 15

percieved size is proportional to product of retinal image size and perceived difference. think coridoor effect

Question 16

what did Helmholtz say about unconscious inference.

Answer 16

1867, visual perception is a result of unconscious judgements. rather than corresponding to retinal image what we perceive is a result of what we infer to be the stimulus. think of ‘illusion’ where lines appear to be different sizes but they actually aren’t

Question 17

what does ‘inference’ imply

Answer 17

implies we see what we expect to see. we use info we learn from experience to reconstruct an image. e.g. majority of the time we expect light source to come from above.

Question 18

what is Bayesian inference

Answer 18

its the idea of seeing the expected can be brought to mathematical framework of bayes theorum