PSYC3013

Question 1

What is umwelt?

Answer 1

perception in the service of action

Question 2

What are the two functional roles of perception?

Answer 2

1. control of behaviour/action

2. recognition and awareness of the world

Question 3

What are the sources of image structure that the brain parses into sources?

Answer 3

1. 3D shape
2. Reflectance and Transmittance properties
3. illumination
4. occulsion

Question 4

What is the difference between specular and diffuse reflectance

Answer 4

Specular refelctance is where there is a single outgoing direction for each incoming light. Specular surfaces appear glossy.

Diffuse reflectance i where the incoming light rays scatters evenly in all directions. What reaches your eye is the sum of light reflected. Diffuse surfaces = Lambertian surfaces, which are matte.

Question 5

What is the relationship between luminance and reflectance?

What is the equivalent relationship (just with different words)

Answer 5

Luminance = refelctance x illumination

Brightness = lightness x illumination

Question 6

Describe the Anchoring theory as an account for lightness perception

Answer 6

• percieved lightness is derived through a set of heuristic rules that the visual system uses to map luminance onto percieved lightness.
• luminance ratios are used to derive information about relative lightness.
• when the full 30:1 range of physically realizable reflectances are present, the true reflectance of surfaces can be serviced on the basis fo these ratios alone. However in scenes containing less than this full 30:1 range, some additional information is needed to transform the information about relative lightness into an estimate of absolute surface reflectance.
• Anchoring theory asserts that this ambiguity must be resolved with an anchoring rule, such that a specific relative image luminance is mapped onto a fixed lightness value (such as white). All other lightness values in a scene are putatively derived by computing ratios relative to his anchor value.

Question 7

Describe the phenomenon of colour constancy.

Answer 7

Changes in illumination result in changes in luminance (spectral reflectance), but we sill perceive the object as the same colour. We are discounting the illumination to recover the lightness properties from the luminance.

Question 8

Describe Land’s Retinex Theory, and identify the problem with this theory.

Answer 8

Three kinds of cones in the eye act as a filer for the scene. An area that is lightest in the short cone (blue cone) will be experienced as blue. Same for red and green. But, only solves problem of relative colours, not absolute colours.

Question 9

Describe what is going on in the strawberry picture

Answer 9

The picture has been covered with a blue translucent colour, making the strawberries grey. The actual reflectance/pixels in the photo are grey. However, we perceive the strawberries as red? Our brain knows that that particular grey is a result of blue and red mixed, so it discounts the blue so we see red.

Question 10

What additional information is provided by a 3D scene to recover lightness?

Answer 10

Shadow strength, percieved shape

Question 11

What does it mean bt ‘specular reflectance must be in the right places’?

Answer 11

• position congruent - must cling to regions of high surface curvature
• orientation congruent - must have orientation consistent with surface shading.

Question 12

According to the image statistics theory of gloss, what does the histogram look like for a glossy vs matte surface.

Answer 12

glossy - positive skew

matte - negative skew

Question 13

What are the cues for gloss?

Answer 13

1. Coverage - how much surface appears to be covered by specular reflections
2. sharpness - how smooth or edgy the specular reflections appear. slope of luminance gradient at edge of reflection
3. contrast - how visible the specular reflections are against the diffuse component.

Question 14

Does 3D shape effect perceived gloss, and what does this mean?

Answer 14

3D shape effects perceived gloss, therefore computations of gloss occur at the level of representation where 3D shape is made explicit.

Question 15

Describe the constraints on transparency

Answer 15

Geometric constraints - must be geometric continuity of contours. Central contour has to be aligned.
Photometric constraints - the contrast polarity (sign) of an underlying contour must be preserved.

Question 16

Describe the transmittance of opacity anchoring principle

Answer 16

Metelli and recent results suggest that lightness judgments (black-white) were modulated by stimulus transmittance and transmittance judgments were modulated by stimulated variances in lightness. For example, a white episcotter will be percieved as less transmissive than a dark episoctter (lightness modulating transmittance). It was discovered that the magnitude of contrast change provides information about the opacity of the transparent surfaces. The higher the contrast change, the lower the percieved opacity, even though opacity has nothing to do with lightness. So the visual system is using the wrong image properties to generate our experience of transmittance.

Question 17

How is the decision criterion calculated? Outline what value the decision criterion is for neutral, liberal and conservative decisions.

Answer 17

beta = number of hits/number of false alarms

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

Question 18

What is sensitivity and how is it calculated?

Answer 18

Sensitivity is a measure of the distance between the means of two distributions, also affected by the variance of each distribution. essentially, how well can you discriminate the stimuli of interest.

It’s calculated by finding the z score of each peak and minising them.

Question 19

What is the Pelli-Robinson chart?

Answer 19

Contrast sensitivity chart –> difference between paint and background gets lower as you go down

Question 20

What is the Snellen Eye Chart, and what are some of its problems?

Answer 20

Measures the smallest size that can recognise letters at 100% contrast.

Limitations:

• number of letters vary per row - so the number of questions vary per row
• letter-spacing confounded with letter size - lot of features in a letter, as you blur some strokes mush together, so it becomes more of a guessing game.
• kids cant read
• if fail don’t know if its a problem of poor spatial resolution or poor contrast sensitivity
• even if blur the letters, can still make out if good reader

Question 21

Compare human vision versus pixels of a dignital camera

Answer 21

Retinal photoreceptors - 6000000 cones, filling in, receptors unevenly spaced (more dense in middle), no blue cones in centre.

Camera photoreceptors - 12000000 pixels, receptors evenly spaced, uniform spacing, better spatial resolution than retina’s periphery, but poorer than fovea

Question 22

For Merkel disks, Meisners corpuscles, Pacinian corpuscles and ruffinis endings state whether they are/have

(i) rapidly adapting or slowly adapting
(ii) small or large receptive fields
(iii) fast or slow temporal frequencies

Answer 22

Merkel disks

(i) slowly adapting
(ii) small
(iii) slow

Meisners corpuscles

(i) rapidly adapting
(ii) small
(iii) medium/fast

Pacinian corpuscles

(i) rapidly adapting
(ii) large
(iii) fast

ruffinis endings

(i) slowly adapting
(ii) large
(iii) Very fast

Question 23

What cues assist our wetness perception?

Answer 23

1. Cooler temperature

2. nature of mechanical give in water

Question 24

Identify motions temporal limit, and what this means.

Answer 24

60 cycles/second -> anything that cycles above this rate will be perceived as a constant motion, as opposed to flickers.

Question 25

Compare static acuity and dynamic acuity

Answer 25

static acuity - minimum separation that yields perception of two point. Receptive field size determines static acuity.

dynamic acuity - Temporal frequency determines dynamic acuity. temporal frequency = receptors determines ability to resolve changes in surfaces over time.

Question 26

What is Balint’s syndrome?

Answer 26

Inability to process things simultaneously and move hand to specific objects using vision.

Question 27

Describe the Humpty Dumpty problem.

Answer 27

If you have specialized areas where things are processed at different rates, how is this out together to form a coherent image?

Question 28

A hemianopia to the right visual field would mean what?

Answer 28

Lesion to the upper and lower calcrine sulus on the left hemisphere.

Question 29

Describe the phenomenon of superadditivity and inverse effectivness.

Answer 29

weak unimodal input cases strong bimodal response. i.e. Sc response to weak stimuli adds to more than their sum

superadditivity doesn’t occur to strong stimuli

Question 30

Identify the multisensory cortical areas in humans.

Answer 30

PMC, PFC, PPC, STS, IPC

Question 31

Identify evidence for early multisensory information

Answer 31

• primary auditory cortex responds to AV speech - A1 activation from lip reading. Activation in A1 stronger when congruent speech added.
• intersensory feedback - extensive long-range feedback within and between sensory modalities. Revelated from tracer studies, laminar differences and timing differences.
• recording from auditory association areas revelated some tactile information goes straight to auditory association areas
• thalmo-cortico pathways - all senses go via thalamus, projects to corticies other than primary sensory cortices.
• BR experiment show that during bistable perception, congruent sound causes perception to switch for unseen stimulus. Since binocular fusion occurs early (where left and right first combine), this suggests MSI is early.

Question 32

Describe the probability summation theory of multisensory integration

Answer 32

Multisensory integration has occurred if the multisensory hit rate exceeds the probability of summation (POS = sum of detection rates of each unisensory stimuli - probability that hey were both detected).

Question 33

Describe the MLE model of MSI

Answer 33

Perception = (likelihood x priors) / normalisation factor.

Likelihood is calculated by the product of the probabilities of the two cues. This is a weighted average based on reliability. The more variable a cue, the less reliable, therefore the less the weight.

Priors are expectations.

Question 34

Describe the experiments illustrating bistable perception in BR tasks, and describe the conclusions.

Answer 34

Perception alternates between rotating sitmulus in one eye, and looming image in another eye. Ask participants to focus on looming stimulus. Then, deliver auditory looming stimulus. Attending to looming sound enhances ability to hold looming stimulus.

Conclusions: Auditory congruence enhances control over visual ambiguity, but active attention is necessary. Also, facilitation of attention control is not automatic.

Question 35

Describe how BR reveals early multisensory interaction. Identify evidence for this.

Answer 35

Binocular fusion occurs early, where left and right eye combines. Since images suppressed from vision in BR show multisensory integration. Therefore, multisensory link must be early.

Congruent sound causes perception to switch for unseen stimulus.

Question 36

What causes multisensory asynchrony?

Answer 36

• Audition depends on distance
• vision depends on contrast
• trasnduction tiem differences.

Question 37

What is Rapid intertrial temporal recalibration

Answer 37

very rapid recalibration of point of subjective simultaneity towards leading stimulus in each preceding trial.

Question 38

Describe the conclusions from experiments involving rapid intertrial temporal recalibration

Answer 38

• audiovisual temporal recalibration is very rapid
• prolonged adaption is not necessary
• recalibration is asymmetrical - vision can lead audition open-endedly, however there is a limit to how much audition can lead vision
• rapid recalibration does not depend on whether the previous trial was perceived as synchronous
• rapid recalibration still occurs when interleading active response trails with passive no response trials (doesn’t require active response).

Question 39

Identify the differences between intertrial recalibration and sustained adaptation.

Answer 39

intertrial recalibration - fast requires only one single asynchronous trial, doesn’t decay

sustained adaptation - sluggish, requires repeated exposure to asynchrony, decays

Question 40

Do you get intertrial recalibration and sustained adaption

(i) between other modalities
(ii) within modalities
(ii) between different stimuli

Answer 40

(i) between other modalities - no for intertrial, yes for sustained
(ii) within modalities - no for intertrial, yes for sustained
(ii) between different stimuli - yes for intertrial

Question 41

What do you use to localize sound sources in the auditory system?

Answer 41

binaural and monaural cues

Question 42

bineural cues encode ____, moneural cues encode _____.

Answer 42

azimuth, elevation

Question 43

What is the inducer and concurrent in synesthesia?

Answer 43

inducer - the sensory input which induces the event

concurrent - the synesthetically induced sensory percept

Question 44

Identify the evidence that synesthesia is real

Answer 44

• high test-retest reliability
• efficient pop-out search rather than serial search (normal people) in tasks involving finding 2’s among 5’s.
• colour priming from numbers
• Cg show more activation in V4 when hear spoken words.
• greater conenctivity in fusiform gyrus

Question 45

Describe the two neural accounts of synesthesia

Answer 45

Cross-talk hypothesis/neural priming - synesthesia results from an abnormally high connectivity between the brain areas corresponding to the synesthetic fusion. Results from a genetic mutation which disrupts neural pruning early in life.

Disinhibition hypothesis - lack of inhibition in synesthetic brain.

Question 46

Describe differences between high and low synesthete’s

Answer 46

High - cross-wiring in angular gyrus, more common, thinking about the concept elicits the percept,
lower - cross-wiring in fusiform gyrus, rare, see colours on printed letters,.,

Question 47

What is the pip and pop effect? what can you conclude from this effect?

Answer 47

‘pip’ sound synchronous with a ‘pop’ visual stimuli increased efficiency of visual search - serial to parallel.

conclusion: audiovisual temporal coincidence can guide visual attention. (also works with tactile synchrony)

Question 48

Does gradual change drive multisensory binding through temporal synchrony? why or why not?

Answer 48

no! multisensory binding through temporal synchrony requires abrupt events. gradual change is loosely defined in time.

Question 49

What is Signal Detection Theory and why is it used?

Answer 49

SDT is a form of analysis applied to scenarios where the responses that a person could make to indicate their detection or discrimination tend to be binary.

Allows us to discover at what point a person decides to make that decision and some overall estimate of their ability to make accurate decisions based on what happened.