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Sammy2x sammy2x at aol.com
Thu May 29 02:28:05 EST 1997

I'm writing a paper on the right hemisphere's role in face processing and
I could use any feedback...please take 5 minutes to read my paper and let
me know what you think...thank you very much...please email me with
comments (Sammy2x)

Right Hemisphere Specialization in Face Processing
      For over a hundred years science has known that the two sides of the
human brain differ profoundly in their processing abilities and
preferences.  In 1865 John Hughlings Jackson wrote, "If it should be
proven by wider experience that the faculty of expression resides in one
hemisphere, there is no absurdity in raising the question as to whether
perception- its corresponding opposite- may be seated in the other"
(Springer, 14).  This was said over 130 years ago.  Over the past 30 years
there has been a dramatic increase in the knowledge base regarding this
subject.  Consequently, many new and exciting areas of research have
emerged.  Such research has produced results suggesting dramatic
processing differences between the left and right hemisphere.  For example
the left hemisphere is generally recognized as dominant for language,
whereas the right hemisphere is more specialized for spatial tasks.  It is
this right hemisphere that I wish to focus my discussion upon.        Even
within the hemispheres one finds a wide variety of localized functions. 
Lesions to different areas of the same hemisphere, and even corresponding
areas of different hemispheres, result in distinct manifestations.  Within
the right hemisphere, lesions in the secondary occipital and
occipitoparietal zones, result in a lack of recognition and integration of
visual information.  The most appealing of the syndromes related to these
lesions is prosopagnosia (facial agnosia), an inability to recognize
familiar faces (unfamiliar faces can still be discriminated from each
other).  My goal is to discuss the role of the right  emisphere role in
face processing, as well its role in the processing of emotional content
in faces.  In the context of this discussion, I will refer to relevant
examples relating prosopagnosia with normal brain function of the right
hemisphere.   As humans we have an amazing capacity to recognize perhaps
thousands of faces,
often after only a single exposure, despite the constant anomalies of
extraneous noise such as hats, beards, glasses, and physical aging of both
the faces we look at and of our own memories.  A study by Bahrick,
Bahrick, and Wittlinger (1975) attests to this capacity. Subjects' ability
to recognize yearbook pictures of their high school classmates was tested.
 Each target face appeared with four distracter faces from the same time
period. Amazingly, 35 years later, recognition rates were over 90% for
class sizes ranging from 90 to 800 (Levine; Ed: Best, 160).  We take it
for granted that we recognize our mother's face at the dinner table, our
professor walking down the corridor, and even our own face in the bathroom
mirror.  Persons with prosopagnosia have no trouble actually recognizing
that a face is in fact a face, only whose face it is.      We owe this
ability to the hemisphere occasionally referred to as the minor, or
nondominant hemisphere (Ardila, ix).   Within this minor, right
hemisphere, and more specifically, within the parieto-temporal-occipital
regions, we find the area generally associated with face processing. 
Every time we look at someone, or a picture of someone, even animals, we
use this portion of our brain.  On the other hand, when we recognize
pictures and scenes, damage to this region does not seem to have any
debilitating effects.  Research tell us that face processing depends on
two processes. First, there is the ability to recognize a face as a whole,
"as something more than just the sum of the component features, but via
the pattern of interrelationships between and otherwise independent of
individual features;" this is what the right hemisphere is good for.
Second, there is an ability to perform feature-by-feature analysis, a more
left hemisphere ability (Bradshaw, 351).  This is why even patients with
prosopagnosia can learn to identify persons based on superficial piecemeal
features such as a mole or particular hairstyle.  
     Let me put to rest any notions that face processing is a left
hemisphere  rocess.  Studies of prosopagnosia, a clinically rare syndrome,
are usually based on single case reports or reports on a small number of
cases.  Neurological observations (e.g. visual field deficits in the upper
left quadrant) and X-ray or CAT scan evidence suggest right hemisphere
damage.  Although this is a unilateral reference, all nine cases of
prosopagnosia that have come to autopsy were reported with bilateral
damage. "Whereas the right hemisphere lesion is consistently
occipitotemporal, the location of the left hemisphere lesion is more
variable.  Perhaps a bilateral lesion is a prerequisite for prosopagnosia
because patients with unilateral right hemisphere lesions may be able to
recognize familiar faces by relying on the face recognition abilities of
the intact left hemisphere that have been demonstrated in commisurotomy
patients."  Regardless, even the autopsy results on prosopagnosic patient
would not predict a left hemisphere advantage for the recognition of known
faces. (Levine; Ed: Best, 164).  One inference made by Levy, Trevarthen,
and Sperry (1972) is that perhaps the deficit in the ability to associate
names and faces may be due to the disconnection of the verbal naming
functions of the left hemisphere from the facial recognition skills of the
right (Springer, 38).  
     Another facet of face processing has to do with emotional content. 
The right hemisphere is also specialized for relaying emotional
information.  Such information is reflected in the production and
perception of facial expressions, speech, or tone of speech.  Heilman
reported that patients with right hemisphere damage have greater
difficulty picking up on the emotional messages conveyed by speech
intonations than do patients with left hemisphere damage.  Regarding faces
we find similar results.  Studies with normal subjects support a major
role for the right hemisphere in the perception of emotion. Usually we
find that emotional expressions are asymmetrical.  In one particular
study, performed by Sackheim in 1968, full-face photographs and their
mirror reversals were split down the midline.  Composites were then put
together from two left sides or two right sides.  Normal subjects were
asked to rate the intensity of the emotional expression present in a
series of presented pictures.  Left-side composites were judged as having
more emotional expressiveness.  This resulted from the fact that the
muscles responsible for the left side of the face are controlled by the
right hemisphere, the emotional hemisphere (Springer, 211).  So as we can
see from these two examples, emotional content is not only perceived
optimally via the right hemisphere, but produced more meaningfully by the
right hemisphere as well. A supplementary experiment confirming this
hypothesis has to do with chimeric faces.  When people attend to a
person's face, they may subconsciously allocate more attention to their
left visual field, or right hemisphere.  Thus, when presented with
chimeric faces, identical mirror image composites, subjects perceive the
left half of the face as more expressive than the right (see attached
figure).  This is because experts believe that the right hemisphere is
more adept at processing emotional and facial information, which causes a
bias towards the left half of visual space (Banich, 267).        Other
neurological tests done on normal subjects have also shown results
pointing to the fact that it is indeed the right hemisphere which is
responsible for the processing of  emotion.  For example, a study using
visual stimuli presented to the left and right visual fields confirmed the
evidence of different hemispheric involvement.  In this case, the stimuli
were five cartoon characters, each with five emotional expressions- from
extremely positive to extremely negative- presented one at a time to
either the left or right visual field.  The subjects' task was to judge
whether the emotional expression was the same as that of a second cartoon
presented in the center of the visual field.  Results showed left-visual
field superiority with the task, thus, right hemisphere superiority
(Springer, 210-212).  All of these examples confirm our hypothesis that
the right hemisphere is significantly preferred in the production and
perception of emotional content, not only in faces but in speech as well.
     Through all of this how do we know that face processing actually is
done by a pecific locale in the brain and is not just associated with
object recognition in general?  Martha J. Farah asked "Is face recognition
'special'?"  By this, are we correct in saying that face processing 
relies on functionally and anatomically distinct mechanisms from those
required for other kinds of pattern recognition?  According to
neuropsychological dissociations reviewed by both Farah (1996) and Yin
(1970), the answer seems to be yes.  Their collective evidence suggests
that the posterior section of the right hemisphere is specifically
involved in the recognition of upright faces, "over and above any
involvement in the recognition of complex visuospatial patterns in
general" (Levine; Ed: Best, 162).  Morton (1991) disclosed evidence
suggesting that infants are born with a preference to gaze at faces rather
than other objects.  At just 30 minutes of age, they will track a moving
face farther than other moving patterns of comparable contrast,
complexity, and so on (Farah, 181)!  Yin and Farah used a "face inversion
effect", which refers to the loss of our normal proficiency at face
perception when faces are inverted, to illustrate that face perception is
indeed a specialized function.  
     In two separate experiments, each researcher tested the ability of
normal  subjects and of a prosopagnosic patient in a sequential matching
task, in which an unfamiliar face is presented, followed by a brief
interstimulus interval, followed by a second face, to which subjects
responded same or different.  Both faces were always in the same
orientation, but the order of normal and inverted faces was random. 
Results conclusively showed that in the normal subjects they performed
worse when the faces were inverted.  These results alone are
insignificant. On the other hand, prosopagnosic patients actually
performed better when the faces were inverted.  From this two major
conclusions follow.  First, the prosopagnosia results from damage to a
specialized face recognition mechanism.  "Inverted faces are the perfect
control stimulus from this point of view, and [the prosopagnosic's]
disproportionate impairment on upright relative to inverted faces is
therefore strong evidence that an impairment of face processing mechanisms
underlies the prosopagnosia" (Farah, 2092).  Secondly, there is an
apparent mandatory  pplication of face-specific processing mechanisms. 
"It seems paradoxical that if [the prosopagnosic patient] can perform
inverted face matching at a particular level of accuracy, he cannot also
use these mechanisms on upright faces with at least the same degree of
success" (Farah, 2092).  From this we can safely assume that there is one
system that is more important for face recognition than for nonface object
recognition, and another system that is more important for nonface object
recognition than for face recognition.      All of the evidence presented
in the preceding paragraphs illustrates the role of the right hemisphere
in face recognition and emotional production and processing.  As
neuroscientists, we realize that each hemisphere excels in certain
cognitive functions and not in others.  However, current research
emphasizes that in the normal brain with extensive commisural connections
between the two interacting hemispheres, it is not likely that we shall
ever be able to dissociate clearly the specialized functions of the two
hemispheres (Kendall-Schwartz, 837).  As we can see with the advanced
visual imaging techniques of the day, even performance of simple tasks
activates multiple areas of cortex.  Despite this, localization is a well
documented and widely accepted phenomenon.  Even across species similar
results regarding face recognition is present. Yamane, Kaji, and Kawano
(1988) recorded data from single cortical neurons in the right hemisphere
of monkeys that did not respond to nonface stimuli, but did respond to
faces (Bradshaw, 206).  On another note, considering that the right
hemisphere is the major role player in the production of emotion, the left
side of the face is where most emotion is present.  Spontaneous looking
experiments done by Yarbus (1967) shows that peoples' fixation during
prolonged observation of pictures, particularly of faces, tends to focus
most attention on the right side of a person's face (Kahneman, 53).  I
find it intriguing that considering our right hemisphere is more adept at
producing and processing emotional and facial qualities, we proceed to
look at the right side of people's faces rather than the more emotional
left side.  So even though we do not match our best processing abilities
with others' production abilities, we are still quite effective at
perceiving the emotional attributes of others. 

Ardila, Ostrosky-Solis (1994). The Right Hemisphere: Neurology and
Neuropsychology. New York, New York: Gordan and Breach Science,

Arnold (1970). Feelings and Emotions. New York, New York: Academic Press

M. T. Banich (1997). Neuropsychology: The Neural Bases of Mental Function.
Boston MA: Houghton Mifflin Company.

Bradshaw and Rogers (1993) The Evolution of Lateral Asymmetries, Language,
Tool Use, and Intellect. San Diego, CA: Academic Press Inc.

Farah (1995) The Inverted Face Inversion Effect in Prosopagnosia: Evidence
Mandatory, Face-specific Perceptual Mechanisms. Vision Research. Vol. 35.
No. 14. pp. 2089-2093. London: Elsevier Science Ltd.

Farah (1996) Is Face Recognition 'Special'? Evidence From Neuropsychology.
Behavioural Brain Research. Vol. 76. pp. 181-189. London: Elsevier Science

Helige (1993) Hemispheric Asymmetry. London:  Harvard University Press

Kahneman (1973) Attention and Effort. Englewood Cliffs, New Jersey:
Prentice-Hall, Inc.

Levine (1985) Developmental Changes in Right-Hemisphere Involvement in
Recognition. In Best (Ed), Hemispheric Function and Collaboration in the
London: Academic Press Inc. 

Springer and Deutsch (1989) Left Brain, Right Brain. New York, New York:
Freeman and Company
Kendall-Schwartz: This is the large comprehensive book on neuroscience.
I'm not
sure of the exact information, but I used it in my paper.

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