Object and face perception

Question 1

what do we mean by object perception?

Answer 1

we don’t just see features - we automatically put them together into meaningful parts of the scene

Question 2

what is feature detection?

Answer 2

• the brain is selective for different features i.e. colour, orientation and spatial frequency

Question 3

low-level analysis:

Answer 3

encoding features: brightness, colour, contrast, spatial detail, orientation, texture

Question 4

high-level analysis:

Answer 4

understanding the meaning - (the famous smile - da Vinci)

Question 5

grouping

Answer 5

the brain has automatic rules for deciding how to organise features

Question 6

what goes together to form an object?

6 features

Answer 6

• good continuation
• closure
• proximity
• similarity
• common fate
• pragnanz (simplest explanation)

Question 7

what happens at a luminance boundary?

2 points

Answer 7

• in regions of equal luminance, excitation and inhibition cancel each other
• at the boundary, excitation and inhibition are not balanced and thus increase the relative difference of perceived brightness

Question 8

contours for visual objects

spatial scales

Answer 8

we extract objects as different spatial scales
Mona-Lisa example:
- some neurons respond at low frequencies - regions
- high spatial frequencies - details

Question 9

importance of shading:

Answer 9

To recognize an object we have to have an idea of its 3D shape
- shading is important: it adds depth and texture

Question 10

what does ambigious stimuli show?

Answer 10

ambiguous stimuli show that what we expect has a high influence on what we perceive

Question 11

why consider face perception separately?

2 points

Answer 11

important part of our communication with each other
- evolutionary context
difficult problem that we solve very well
- extremely variable, yet highly constrained

Question 12

face detection

Answer 12

• first step
• requires extracting the features that all faces have in common
  
  • this could be achieved by simple “ template matching”

Question 13

face recognition

3 points

Answer 13

• once a face is detected it can be further analysed to categorise it
• we may ascribe various attributes to it (e.g. emotions)
• we may need to identify who it is

Question 14

challenges for face recognition

2 points

Answer 14

discrimination
generalisation
- lighting conditions
- varying context
- rigid and non-rigid transformation

Question 15

what is pareidolia?

Answer 15

tendency to percieve a specific, meaningful image in a random or ambiguous visual pattern

Question 16

what do we have a tendency for?

Answer 16

seeing faces everywhere e.g. pareidolia to make meaning where there is none

Question 17

upside down and negative faces

2 points

Answer 17

• all local image information is preserved, including shape, the distance between features etc.
• the key is that inversion has a greater effect for faces than other objects

Question 18

what did Gautheir et al., 1999 discover?

Answer 18

activation of the middle fusiform face area increases with expertise in recognising novel objects - but still less activation than for faces

Question 19

do our visual systems process faces in a special way?

hollow potato illusion

Answer 19

the perceptual ‘expectation’ for faces to be convex seems to override our knowledge
- The hollow potato illusion demonstrates that the visual system perceives objects as convex, not just faces. However, the illusion is more pronounced for faces

Question 20

what is prosopagnosia?

Answer 20

the specific inability to recognise familiar faces
- usually their object recognition is unimpaired

Question 21

what causes prosopagnosia?

Answer 21

right anterior inferior occipital lesions in the region of the occipital-temporal junction

Question 22

which cells are selective for faces?

Answer 22

cells in the superior temporal sulcus (STS)

Question 23

object centred vs viewer centred

how do some neurons respond?

Answer 23

some neurons respond in a view indepedent way

Question 24

object centred vs viewer centred

what do neurons in STS repond to?

Answer 24

neurons in STS respond to facial motion, posture and eye gaze

Question 25

object centred vs viewer centred

neurons in inferior temporal cortex:

Answer 25

neurons in temporal cortex are more likely to respond on the basis of identity

Question 26

object centred vs viewer centred

what do all the neuron do in relation to cognition?

3 steps

Answer 26

they all form steps in cognition i.e.
* mental rotation
* emotion and speech recognition
* social attention and memeory recall

Question 27

functional imaging (fMRI)

Answer 27

Kanwhisher et al. 1997 - fMRI reveals fusiform face area
- FFA responds to more faces than other common objects

Question 28

what features can faces be decomposed to?

3 points

Answer 28

• eyes, nose, chin etc.
• are faces recognised by feature decomposition and description?
• where does the nose stop and the chin begin?

Question 29

Photofit theory? (Penry & Ryan, 1971)

Answer 29

photographed features to allow subject to build a face

Question 30

what is holistic processing

Answer 30

a perceptual strategy for piecing together fragmented information

Question 31

holistic processing evidence

Answer 31

some evidence suggests that we do not store faces as parts, by ‘holistically’

Question 32

what is composite face effect?

Answer 32

The composite face effect refers to the tendency for people to perceive the top and bottom halves of two different faces as a single, new face instead of two distinct faces

Question 33

composite face effect

Answer 33

Composite faces interfered with recognition of a half
face – the effect disappeared upside down. Holistic processing obliges us to combine information automatically

Question 34

what is the Thatcher illusion?

Answer 34

a visual illusion that occurs when the eyes and brain process a picture of an inverted face.

Question 35

what does the Thatcher illusion tell us?

Answer 35

The holistic processing in the upright faces makes the unusual arrangement instantly noticeable.