PS4029/30 Perspectives on social attributions Lecture 3.
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Transcript of PS4029/30 Perspectives on social attributions Lecture 3.
PS4029/30
Perspectives on social attributions
Lecture 3
1. Symmetric faces are attractive: recap
2. Simple perceptual bias account
3. Prototype-based perceptual bias account
4. Problems for perceptual bias accounts
Lecture 3: Perceptual bias accounts of symmetry preferences
Methods for symmetry manipulation 1.[good method - Perrett et al. 1999]
Warping face shape (natural proportions)
1. Symmetric faces are attractive: recap (methods)
attractive, symmetric
less attractive, less symmetric
Methods for symmetry manipulation 2.[bad method - Samuels et al. 1994]
LL/RR Chimeric faces (unnatural proportions)
1. Symmetric faces are attractive: recap (methods)
Symmetric faces have been found to be attractive in diverse cultures [Rhodes et al: Asia, Perrett et al: UK]
It has been suggested that this stability in (or high agreement for) symmetric faces occurs because symmetric faces have a biological basis
1. Symmetric faces are attractive: recap (x-cultural comparison)
Although most researchers agree preferences for symmetric faces have a biological basis, there is enormous debate about the nature of this basis
1. Perceptual bias account (trick of the visual system)
2. Evolutionary advantage view (symmetry preferred because it signals health, fertility)
1. Symmetric faces are attractive: recap (biological basis)
preference for bilateral symmetry may occur simply because the human visual system
is particularly sensitive to bilateral symmetry
ocular musculature is bilaterally symmetrical and
the left and right visual field is processed in different hemispheres (allowing L-R matching
and easy symmetry detection) (Mach, 1887; Herbert & Humphrey, 1996)
2. Simple perceptual bias account of symmetry preferences
Evidence for Simple Perceptual Bias
Symmetry preferences seen in:– objects
– decorative art
Original Symmetrical
Gombrich, 1984
Rensch, 1963
Original Symmetrical
These effects suggest there may be nothing ‘special’ about facial symmetry that is attractive - consistent with viewpreferences for symmetric faces are a ‘trick’of the visual system
For each class of stimuli it is possible that the visual system develops an internal
prototype.
Such a prototype is made up of an average of the characteristics of all the different
stimuli of that type that have been seen.
3. Prototype-based perceptual bias accounts
3. Prototype-based perceptual bias accounts
3 faceaverage
asymmetric
10 faceaverage
more prototypical
and moresymmetric
When novel stimuli are seen they are compared to this symmetric prototype
This figure shows that increasing prototypicality increases symmetry - random deviations from symmetric are averaged out
In other words:
symmetric faces may be attractive because they more closely resemble prototypical faces than asymmetric faces do
Evidence: from neural networks and chicken preferences
3. Prototype-based perceptual bias accounts
Neural Networks & Perceptual Bias
• Computer programs trained on stimuli for recognition
• Show that recognition training can create preference (recognition) for symmetry
Johnstone, 1994, NatureEnquist & Arak, 1994, NatureTraining Set
=Novel symmetric stimuli preferred (most reaction)
Prototypes and Perceptual Bias
• Train chickens to discriminate between rewarding and non-rewarding stimuli
• Stimuli were two asymmetric crosses which were mirror images of each other
Jansson et al., 2002, Anim Behav
Both associated with reward
• Train chickens to discriminate between rewarding and non-rewarding stimuli
• On subsequent testing chickens preferred novel symmetric cross to either asymmetric cross
• So symmetry preference can arise as by-product of visual system & experience
Jansson et al., 2002, Anim Behav
PECK!
Prototypes and Perceptual Bias
Novel symmetric
cross
Individual differences in symmetry preferences
If everyone’s visual / recognition systems work in the same way (at least among healthy adults), and symmetry preference is a by-product of the way this system works, then why do some people find symmetric faces more attractive than other people do?
Jones et al. (2001)
4. Problem for perceptual bias account I
Attractivewomen like
symmetric male faces more than
relatively unattractive women do
Little et al (2001)
4. Own attractiveness and symmetry preferences
Opposite-sex bias in symmetry preferences
if symmetry is attractive only because of the way the way the visual system works, symmetry
preferences should be the same regardless of the sex of the faces presented (as both sexes of face thought to be processed in an identical manner by the visual recognition system)
4. Problem for perceptual bias account II
4. Problem for perceptual bias account II
Female judges
(Little et al., 2001)
NB - symmetry attractive in BOTH male and female faces but MORE attractive in opposite-sex than own-sex faces
Next week: Evolutionary advantage view of symmetry preferences
This view posits that facial symmetry signals qualities such as health that are desirable in mates.
Evidence that symmetry preferences are stronger for mate choice relevant stimuli (i.e. faces) than for other objects (e.g. inverted faces) will be discussed.
Evidence that symmetric individuals also possess attractive voices and body odours will also be discussed as implying symmetry signals an underlying attractive quality.
Evidence that symmetry signals health and fertility will also be discussed