lecture 4- face perception Flashcards
which cells in mokey’s show selectivity for faces and which researchers found this?
gross 1972- monkey temporal cortex cells (IT and STS)
how did foldiak 2004 represent cell selectivity?
- rastagrams showing cell response- peristimulus time histograms
- thick small bars at the bottom is onset of image
- then cell resopnds
- visual characteristics of image different (colour, lighting) but face present in all
what are grandmother cells?
- extreme specificity, respond to one object only
- i.e grandmother in any circumstance, conscious understanding of grandmother comes from activity of that cell
- generalisation- respond to many instances
what are the problems with grandmother cells?
- not enough cells in brain for everything in entire environment in entire lives
- death of cell results in inability to recognise grandmother but still can
- evidence of population coding in temporal cortex (response to world made of multiple cells activating together)
- unlikely to ever actually find (can’t test every single cell while doing all kinds of tasks)
what is the thatcher illusion?
- inverted features image upside down doesn’t look as gross as upright
- shows upright processed differently from inverted
- upright = features analysed holistically
- inverted = holistic processing impaired, features analysed independently (each coded relative to gravity)
what are the different types of features?
- internal: eyes, mouth, nose
- external: hair, configuration (features have to be in right place in respect to each other)
- external features more important in unfamiliar faces
internal more important for famous
what study did perrett 1982 carry out?
- black bar over eyes and opposite (all blacked out except for eyes)
- one cell: only minor reduction when only opposite, when eyes covered reduces cell activity (cell responds selectively to internal)
- another cell: small reduction when eyes covered, large reduction when opposite
- other cells only respond to feature combinations (some being whole face more than external/internal features separately or smaller combinations)
what are the general features of recognising face identity?
- ability to recognise faces is learnt
- can recognise faces of own race better (maybe because spend more time with own race?)
- learning may operate over short timescales
- evidence for short-term learning = face adaption
what is face identity adaption?
- looking at right, the center will start to look like left (left and right are two different faces, center is merged)
- adaption to face = suppression of those selective cells
- e.g live in japan, adapt to japanese faces so cell suppression for that race -> better at discriminating between different japanese faces
- adaption reduces responses of cells coding common properties of the population?
- means cells then only signal differences between faces
what study did Rhodes (2010) carry out on face adaption?
- p’s adapted to either average caucasian or asian faces for 5 mins
- they were better at discriminating faces of adapted race
- reduced recognition to familiar race
what does face adaption tell us?
- face coding mechanisms (cells) are subject to adaption like lower-level cells
- face adaption causes suppression of face cells
- suggests separate cells coding different identities
- adaptation calibrates our visual system to the statistics of the social environment
how can we measure human cells coding faces?
- use electrodes in epilepsy patients
- treatment for epilepsy = remove area of cortex where focal seizures occur and find where depolarisation starts
- present images to patients over days whilst mapping out cortex
- track onset and offset of activity
what are some examples of a cell that is sensitive to identity of familiar faces?
jennifer aniston cell (even if at different angles, she had different hair etc.) -> any circumstance
- same with halle berry- cell in medial temporal responds really selectively to concept of individual
which cells are sensitive to face view?
STS cells
Perret (1991)- found cell that fires more when face turns toward front, cell that responds to right side view, cell that responds to face at any view
what is view-centered (egocentric) coding?
many cells in the temporal cortex respond preferentially to views of face (front or back or head, left/right profile, both, intermediate views)
what is object-centered coding (allocentric) coding?
some cells respond to all views of face
what did physiological findings in the temporal cortex show?
cell populations selective for faces-
1. combine features
2. generalise over size, position, orientation, lighting
3. some cells show sensitivity to identity
4. most selective for view
how do some cells respond to the body?
- encodes body posture info if head blacked out- e.g fires when appears to be looking down
- but if head included, cell only fires when head is looking down as well
- cell responds less if body is tilted down but head looks up
how does importance go when combining body, face and gaze direction?
eyes > head > body
- tuning (hierarchy) consistent consistent with attention direction
- involved in social attention- helps us decide how we interact with them
how does emotion expressions differ across populations?
- cross-cultural similarity of expressions and causes (different cultures under certain emotional circumstances will produce certain type of expression)
- deaf and blind children’s expressions are normal -> so production of expressions is innate
- universal interpretation of 6 basic emotions (happy, sad, angry, fear, surprise, disgust)
how is hierarchy of importance in cells responses affected in autism?
- some autistic children have problems following the gaze of others
- may suggest that autism may impact STS coding of bodies and faces
what study did Morris et al. carry out on emotion expression?
- fear expressions activate the amygdala
- also when seeing someone else experiencing fear
- stimulating amygdala = stimulates experience of fear
what did Phillips et al. find?
- disgust expressions activate insular cortex
- also when see someone else looking disgusted and when you feel disgusted
what does brain imaging show about different emotion expression?
- different emotions activate different brain systems
- fear = amygdala, disgust = insular cortex
- brain damage can selectively impair emotion recognition (e.g amygdala damage = no recognition of fear)
how does symmetry affect facial attractiveness?
- one half of face same as the other
- symmetrical faces result from good development i.e good genes
- therefore signals person would make good partner
- potentially signal of quality of individual
how is perception biased when looking at masculine faces?
- there is bias toward right side of brain (and therefore left side of persons face) when making judgements about faces
- if left side of face is more masculine- right hemisphere is seeing masculine side
- face seems more masculine than if right side of persons face was more masculine
what perceptual biases are present when judging faces?
- judgements of face identity, sex, age, attractiveness are biased to left side of face
- because right hemisphere is specialised for face identification and emotion
how does averagness affect face attractiveness?
- non-average faces may indicate genotypes that are homozygous for deleterious alleles
- in order to have unusual face, need unusual genes (i.e two unusual homozygous alleles)
- having deleterious (unusual) alleles may signal unhealthiness
what is the flashed face distortion effect?
- each face becomes a caricature when staring at point
- adaptation suppresses what is common
how do secondary sexual traits affect facial attractiveness?
- male and female faces differ in their shapes
- advertise the quality of an individual in terms of their hereditability (i.e good genes, healthy immune systems) -> cues to observer
how does skin health and colour affect facial attractiveness?
- healthy-looking faces appear more attractive (want partner that won’t die on you/give healthy offspring)
- possible to make artificially more attractive (makeup, tanning, eating veg for beta carotene)
