HUL 211 Perception of real world objects - faces

							Perception of real world objects
      Perception of faces




          Snehlata Jaswal


          HUL 211 OBJECT PERCEPTION AND MEMORY
               Faces are special objects
Face perception is concerned with how we recognize individual
instances of a type of object.

Faces are interesting because:
1. We probably see no other object so often as the human face – yet no
   two faces are exactly alike
2. They undergo non-rigid (expressions, gestures) as well as rigid
   transformations.
3. They are used as a channel of communication.
4. Human face perception may have evolutionary significance



                              HUL 211 OBJECT PERCEPTION AND MEMORY
                     Effect of inversion
A number of studies have shown that upside down faces are much more
difficult to recognize. This is probably because we generally see upright
faces, and this reflects in our tendency to see upright faces, i.e.,
expertise with upright faces may result in problems with inverted faces.

Testing the view that expertise leads to problems with face recognition,
Diamond and Carey (1986) tested the ablity of expert dog show judges
and novices to recognize individual dogs drawn from a particular
pedigree breed and found that experts were indeed more affected by
inversion than novices.




                               HUL 211 OBJECT PERCEPTION AND MEMORY
           Features vs. whole configuartion
Another result of inversion studies is that face recognition seems to rely on encoding
the configuration of features rather then identifying individual features. This is clearly
seen in the comparison of feature identification in upright and inverted faces.
Young, Hellawell and Hay (1987) compared the recognition of parts of facial
composites. Parts of inverted facial composites were recognized more quickly when
the composites were presented the right way up. The Margaret Thatcher illusion also
indicates that features are encoded independently in upside-down faces.




                                                    HUL 211 OBJECT PERCEPTION AND MEMORY
HUL 211 OBJECT PERCEPTION AND MEMORY
                      Effect of negation
Faces are also difficult to recognise when presented as photographic
negatives (Phillips, 1972). This suggests that we do not recognize faces
on the basis of image contours, as suggested by Biederman (1972) for
objects, since the process of negation leaves the position of object
contours and the location of features intact.
The effects of negation are probably due to disrupting the shading
information in faces and also altering pigmented regions of the face. For
example the hair and eyes become white after negation. It is argued
that negating an image results in an impossible pattern of shading, and
that this disrupts the formation of a three-dimensional representation
of the surface geometry of the face. Also, identification errors occur as a
consequence of changes to the apparent pigmentation of the face
caused by negating the image.

                                HUL 211 OBJECT PERCEPTION AND MEMORY
Brain activation in face perception
Face perception is an ability that involves many areas of the
brain; however, some areas have been shown to be
particularly important. Brain imaging studies typically show a
great deal of activity in an area of the temporal lobe known as
the fusiform gyrus, an area also known to cause
prosopagnosia (inability to recognise faces) when damaged
(particularly when damage occurs on both sides). This
evidence has led to a particular interest in this area and it is
sometimes referred to as the fusiform face area for that
reason. Other important areas are shown on the next slide.




             HUL 211 OBJECT PERCEPTION AND MEMORY
                     Face selective activation
Three face selective regions are found – FFA along the ventral part of the brain, OFA in the
lateral occipital area, and fSTS in the posterior region of the superior temporal sulcus. The
first two distinguish individual faces, whereas the last also codes other dimensions such as
emotional expression and gaze




                         HUL 211 OBJECT PERCEPTION AND MEMORY
General vs. domain specific expertise
Cognitive neuroscientists Gauthier and Tarr are two of the major proponents
of the view that face recognition involves expert discrimination of similar
objects. Although we often assume that faces are relatively unique,
statistically they are quite similar, so a great deal of effort is needed to
differentiate them.

According to this view, faces are nothing more than a particularly difficult
class of perceptual object which we have learned to distinguish at the expert
level, much as we would learn to distinguish between other similar objects if
much of our communication and survival depended on it.

Studies by Gauthier have shown that the fusiform gyrus is also active when
study participants are asked to discriminate between different types of birds
and cars, and even when participants become expert at distinguishing
computer generated nonsense shapes. This suggests that the fusiform gyrus
may have a general role in the recognition of similar visual objects.


                         HUL 211 OBJECT PERCEPTION AND MEMORY
General vs. domain specific expertise
Others, in particular Kanwisher and her colleagues, argue that face
recognition involves domain specific processes that are face-specific and that
are not recruited by expert discriminations in other object classes.
Xu, a post doctoral fellow with Nancy Kanwisher, replicated the car and bird
expertise study using an improved fMRI design that was less susceptible to
attentional accounts. The activity found by Gauthier when participants
viewed non-face objects was not as strong as when participants were
viewing faces, however this could still be because we have much more
expertise for faces than for most other objects. Other research groups using
different study designs have also found that the fusiform gyrus is specific to
faces and other nearby regions deal with non-face objects.




                         HUL 211 OBJECT PERCEPTION AND MEMORY
             Gender differences
Everhart, Shucard, Quatrin, Shucard (2001) using
electrophysiological techniques, have demonstrated gender-
related differences during a face recognition memory (FRM) task
and a facial affect identification task (FAIT). The male subjects
used a right, while the female subjects used a left, hemisphere
neural activation system in the processing of faces and facial
affect.

Herlitz and Rehnman (2008) found that women have better
episodic memory for faces, particularly female faces.




                         HUL 211 OBJECT PERCEPTION AND MEMORY
           Memory for (angry?) faces
Previous research has shown that capacity for faces was enhanced for familiar
versus unfamiliar faces (Jackson & Raymond, 2004).

Jackson and his colleagues (2006) measured visual WM capacity for angry, happy,
and neutral faces. Stimuli were 18 different male (Ekman) faces: six individuals
each expressed the three emotions. On each trial, between 1 and 4 faces
displaying the same emotion were presented for 2000 ms in a two-by-two matrix.
When less than four faces were presented, all other grid locations were occupied
by a scrambled face. A 1000 ms blank retention interval followed, succeeded by a
single face probe. Participants stated whether the probe was present or absent in
the previous display (identity task).

Emotion was blocked and counterbalanced within subjects and a verbal
suppression task was administered. Task performance was significantly enhanced
for angry compared to happy and neutral faces, and capacity estimates (k)
mirrored the angry face advantage. Happy and neutral face performance did not
differ. Thus, negative emotional expression appears to enhance visual WM for
faces.


                                  HUL 211 OBJECT PERCEPTION AND MEMORY
         Thank you




HUL 211 OBJECT PERCEPTION AND MEMORY