Importance of faces:

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17 Νοε 2013 (πριν από 3 χρόνια και 4 μήνες)

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Importance of faces:

Central role in human interactions

Contribute to speech perception (McGurk effect)

Communicate a wealth of social information:

Age, gender, personal identity (physical structure)

Mood and emotional state (facial expression)

Interest / attentional focus (direction of gaze)

Faces as visual stimuli:

Faces as a category

highly homogenous (similar)

Share basic component parts in a fixed configuration

(2 eyes over a nose over a mouth inside an ellipse)

Individual faces

highly different

Vary in many dimensions, including head shape, individual features,
relative feature placement, color, texture, etc.

Dynamic and changeable due to movable parts that change shape
and relative position

Example: a smile vs. an angry frown

the same face?

A single face can produce radically different images on our retina when it changes
expression and/or orientation (Farah, 2000).

Demands of face recognition:

Generally same as for object recognition

Recognition in context (object in a clutter of other objects in the scene)

Object invariance (across different viewpoints, sizes / distances, &
illuminations; in motion, etc.)

Specificity (matching visual object to specific semantic description)


faces require higher specificity!

(exemplar vs. category level)

In most situations, we need to recognize a
specific individual face

as Joe Smith) rather than the general category (“face”)

Find the human face in the display as fast as you can. Ready?

Now find the animal face. Ready?

out effect for faces! (Herschler & Hochstein, 2005)

demonstrates our expertise in face processing

Perceptual expertise:

Humans are experts at face processing (Diamond & Carey, 1986)

Effects of accumulated lifelong experience & daily practice

Face representations always at least partially activated?

Biological predisposition?

Newborn infants will detect and track a human face more readily than
another visual object (Johnson & Morton, 1991)


Impairment in face recognition (“face blindness”)


recognize familiar faces or own face in the mirror


recognize faces as a category vs. other objects


recognize familiar people by voice and other non
facial clues

Vision otherwise OK

Due to brain injury (typically to the right temporal lobe)

Socially crippling

What is it like to be face blind?

People who are ‘tone deaf’ are not deaf to tones.
They can hear tones, they just can't tell them apart.
People who are ‘color blind’ can see things that are in
color. They just can't tell colors apart. Similarly,
I can
see faces. I just can't tell them apart

“If you are face blind, in social settings, or even
when watching TV, people will have come and gone long
before you can identify them. So you never do. By the
eight seconds

have passed, people in your
presence who don’t know of your face blindness will be
offended at your failure to recognize them. And long
before you even get your eight seconds, you know you will
be criticized for ‘staring’…”


Bill Choisser,
Face Blind!

The Capgras delusion:

A form of delusional misidentification due to brain injury

Patients claim that their relatives have been replaced by identical
impostors, clones, robots, Martians, etc. (Capgras & Reboul
Lachaux, 1923)

Recognize relatives visually but have
a deeper, overwhelming sense

that they
are unfamiliar, strange, not who they claim to be, etc.

Carries a serious risk of violence

Loss of appropriate
emotional response

to visual stimuli?

Emotional recognition is faster than perceptual recognition!

Theories of face recognition:

1) Specialized face module

Functionally and anatomically separate

Processes faces

2) Faces processed by the general visual system (no
specialized face module)

Specialized face
module hypothesis:

Fusiform Face Area (FFA)

Right inferior temporal cortex

Along the ventral / occipitotemporal “what” pathway

Case studies of prosopagnosia

damage typically to FFA

cell recordings in monkeys:
face cells
? (Baylis et al., 1985)

fMRI studies of humans: FFA selectively activated by faces
(Kanwisher et al., 1997)


Evidence that prosopagnosia

limited to faces

FFA varies in size and location between individuals

FFA also activated for non
face objects (e.g. in dog experts)

Alternative hypothesis:

FFA = Flexible Fusiform Area
? (Tarr & Gauthier, 2000)

FFA as a system specialized for fine discriminations / subordinate

all complex homogenous objects
(not just faces)

Activation of FFA increases with expertise