Lateralisation of Emotion: Which Brain Hemisphere Specializes in Emotional Perception.
Lateralisation of Emotion: Which Brain Hemisphere Specializes in Emotional Perception?
Melissa N Pike: 7733515
Lab 110 (Sabrina Goh)
April 29, 2015
1
Lateralisation of Emotion: Which Brain Hemisphere Specializes in Emotional Perception.
2
Abstract
The aim of this study is to investigate which brain hemisphere is specialized for the perception of
emotion. To test this, the hypothesis of the experiment was that the participants would judge
chimeric faces with the smile presented in the left visual field as happier more often than
chimeric faces with the smile presented in the right visual field. The participants of the study
were students ages 18-24 in psychology. The task that was to be completed was a computerized
trail where participants were presented with a 14 different pair of chimeric faces and they had to
decide which appeared happier. The measured variable of the experiment was the percentage of
chimeric faces that were chosen as happier due to whether the smile was presented in the left or
right visual field. The result of the study was that the left visual field had a greater percentage of
faces chosen as happier.
Lateralisation of Emotion: Which Brain Hemisphere Specializes in Emotional Perception.
3
Lateralisation of Emotion: Which Brain Hemisphere Specializes in Emotional Perception?
The control system for a human is its nervous system. This includes the brain, which
functions day and night and controls everything that one does. Since the brain controls what a
human does it has become a very important part of the body to study. According to Gleitman,
Gross, and Reisberg (2011) lateralisation of the brain is a very important function to understand,
and investigate. Lateralisation means that the brain is symmetrical from right to left, splitting it
in to two hemispheres. Further investigation of the brain though determined that there are special
function for the left side and the right side of the human brain and that though they are seemingly
similar, they are very different.
Some techniques used to determine differences in the brain is by the use of
neuroimaging, or taking photographs of the brain. A CAT and MRI provide pictures of brain
structure while EEG, PET, and fMRI’s all show levels of activity in the different parts of the
brain (Department of Psychology, 2015). With these images, data was collected that helped to
discover which hemisphere is responsible for specific tasks. For example, the left hemisphere is
better suited for math and language whereas the right hemisphere is better suited for spatial
abilities and melodic patters. The right hemisphere is also able to do one very important process,
which is recognize faces (Department of Psychology, 2015).
When looking into the brain’s ability to recognize faces it is also important to note that
the visual system plays a role. If one is not able to see, then they cannot take in visual cues that
help with recognition. Another important part of how the brain takes in visual information is
through crossed pathways. Crossed pathways mean that information in the right visual field goes
into the left hemisphere for processing and information in the left visual field goes into the right
hemisphere for processing. This will only affect someone if they have a split brain, meaning that
Lateralisation of Emotion: Which Brain Hemisphere Specializes in Emotional Perception.
4
their corpus callosum has been cut and the information coming in from a visual cue cannot cross
to the correct side of the brain it needs to be in to be processed. If the corpus callosum is intact,
information, such as faces, should be recognized and brain function ought to be normal. A study
on facial recognition and processing by Heller and Levy had findings about the perception of the
faces depending on if one is a right hander or a left hander (Heller and Levy, 1981).
The study was made up of 12 right-handers and 12 left-handers that were tested with the
use of chimeric faces to determine if the hand they wrote with dealt with the discrimination of
facial emotion, and if they showed more emotion in their physical smile. (Heller and Levy,
1981). The study found that even though “ cognitive lateralization may be a poor predictor of
which side of the face is dominant in expressing emotion, facial asymmetry in emotional
expressivity may be strongly correlated with asymmetry in the perception of emotion”( Heller
and Levy, 1981, p. 271). Their findings support the idea that the right hemisphere of the brain is
used for the perception of emotion. This study also accompanies one by Ley and Bryden (Ley,
R., & Bryden, M. 1979, cited in Laboratory Manual: Psychology 111/112, 2015). Ley and
Bryden used a different test in their study to determine if the right hemisphere dealt with
perception of emotion (1979, cited in Laboratory Manual: Psychology 111/112, 2015). In their
study they used cartoon faces with many different emotional expression. These were flashed at
participants in either the left of right visual field using a tachistoscope, then flashed a face in both
fields and the participant had to determine if the face matched the first one base on emotional
expression. This study’s results found that there were greater mistakes made when the face was
presented in the right visual field than in the left visual field. This means that the right
hemisphere is more capable of matching emotional expression. In psychology lab 110 a study
was conducted on the lateralisation of emotion as well.
Lateralisation of Emotion: Which Brain Hemisphere Specializes in Emotional Perception.
5
The experiment run in Psychology Lab 110 was to test lateralisation of emotion. The aim
of the study was to see which hemisphere specialises in the perception of emotion. In this study
the participants went to an individual computer where they were presented with 2 practice trials
and 28 experimental trails. Each trail presented the participant with a pair of chimeric faces that
the participant had to decide which one was happier seeming. There were 7 posers that equaled
out to 14 different pair of chimeric faces, each which were presented twice as a control. The
hypothesis of the experiment was that participants will judge the chimeric faces with the smile
presented in the left visual field as happier more often than chimeric faces with the smile
presented in the right visual field.
Method
Participants
The participants who took part of the study were 24 University of Otago students enrolled
in Psychology 110. Within this group of participants there were 18 females and 6 males between
the ages of 18 and 24 years old. Of these 24 students, 4 were left handed, 1 was ambidextrous,
and 19 were right handed. They were recruited by being part of their laboratory course.
Materials
The materials used for the experiment on lateralisation of emotion included a computer
generated test that presented chimeric faces of photographed people. In this test, there were 2
practice trials, and 28 experimental trials. These chimeric faces used 7 posers, which equaled to
be 14 pairs of chimeric faces.
Procedure
The manipulated variable in the experiment was the visual field of smile presentation,
meaning that the smile was either presented in the left visual field, or the right visual field. The
Lateralisation of Emotion: Which Brain Hemisphere Specializes in Emotional Perception.
6
measured variable of the experiment was the percentage of chimeric faces that were chosen as
happier due to whether the smile was presented in the left or right visual field. The experiment
on lateralisation of emotion used a with-in subject design because all participants experienced
every level of the manipulated variable. To start the experiment all participants went to a
computer where they sat alone. At the computer the participants took a test where they were
expected to choose which face looked happier upon presentation. This test had 2 practice trials,
and 28 experimental trails. The computer then gathered all data and compiled the results.
Results
The measured variable in this experiment was the percentage of chimeric faces that were
chosen as happier depending the visual field that the smile was presented in. The results were
collected then averaged. The class data is presented in Figure 1 below.
100
Percent of Chimeric Faces
90
80
70
60
50
40
30
20
10
0
Left Visual Field
Right Visual Field
Visual Fields
Figure 1. Mean percentage of left visual field emotion versus right visual field emotion.
As graphed above in Figure 1, the participants chose a majority of happier faces when
they were presented in the left visual field than when they were presented in the right visual
Lateralisation of Emotion: Which Brain Hemisphere Specializes in Emotional Perception.
7
field. When the chimeric faces has a smile in the left visual field 74.70 % of participants chose
that the face was happier. When the smile was presented in the right visual field 25.29% of
participants chose that the chimeric face was happier.
Discussion
When participants responded to the chimeric faces, the majority of happy faces were
found when the smile was presented in the left visual field than when they were presented in the
right visual field. These results support the hypothesis that smiles presented in a left visual field
of a chimeric face is judged happier than a smile presented in the right visual field of a chimeric
face.
The results of this study are constant with the result of Heller and Levy (1981) who found
that the right hemisphere is specialsed for the perception of emotional expression. In the present
experiment images were displayed in both visual fields at the same time. In Heller and Levy’s
experiment the images were presented tachistoscopically in one visual field, and then another
visual field. Even with this difference, participants in both studies identified a happier face when
the smile was presented in the left visual field than the right.
These results are also consistent with the findings in Ley and Bryden’s (1979, cited in
Laboratory Manual: Psychology 111/112, 2015) study that an emotional expression will be
greater recognized when it is presented in the left visual field than that of the right. The main
difference between their study and the current study is that none of the current studies faces were
neutral and the current study did not use a tachistoscope.
The findings are clear that the left visual field, and right hemisphere deals with
lateralisation of emotion but one thing that is not clear in the study is how much right, or left
Lateralisation of Emotion: Which Brain Hemisphere Specializes in Emotional Perception.
8
handedness plays a part in the study. This study did take down who was left handed and who was
right handed, but from there, data was not collected based on those specifics.
A major limitation of this study is that it used free vision. This means that the chimeric
faces presented were not isolated to one visual field at a time like they would have been if a
tachistoscope was used, but that the images were presented in both at the same time. Heller and
Levy’s experiment made use of the tachistoscope (1981). Since the faces were not isolated both
visual fields had access to the information which could skew the results. Either showing that
there were higher left, or higher right visual field recognition.
Other limitations of this study include color and presentation of the chimeric faces. There
was color to the chimeric faces. This could have altered results by highlighting and lowlighting
some parts of some faces than others, giving way to altered results because a lighter face may
appear happier than a darker face. If the images were black and white it could remove this factor.
Also, the participants read up to down and right to left, meaning that they would take in the left
image first, then the right. This could affect the results because then each participant is looking to
the left first involuntarily, not the right. It may make it so that faces presented in the left are
observed more closely than in the right.
Future research could take into account free vision and isolated vision. Does it matter if
the image is projected into just the right visual field or just the left visual field, or can it be
presented into bother at the same time? That is something that could be looked into that neither
Ley and Bryden (1979, cited in Laboratory Manual: Psychology 111/112, 2015) nor Heller and
Levy (1981) did in their studies. Other future research that could be conducted is whether being
left or right eye dominant matters to the results. If the participants who are left eye dominant
bring in different results than those that are right eye dominant.
Lateralisation of Emotion: Which Brain Hemisphere Specializes in Emotional Perception.
9
An implication of the result that the right hemisphere specialises in emotional perception
would be that lateralisation of function matters to how the world is perceived and information is
gathered. Knowing what each side of the brain is used for is very important because if any part
of the brain is damaged it can have serious repercussions on specific lateralisation effects.
Knowing what each part of the brain does and studying that part thoroughly can help a variety of
people if an injury occurs.
An application of this study would be that someone who has severe damage to their right
hemisphere due to a head injury would not be good with determining emotion based on visual
cues. It would be very difficult for them to see a smile and process it as a happy emotion since
the part of the brain concluded by our study to process emotion in the right side. Knowing what
we know about lateralisation of emotion telling said person that visual cues alone will not give
them accurate emotional will help him or her to rely on vocal cues and other forms of
understanding human emotion than just that of a facial emotion.
To conclude, the present study tested lateralisation of emotion just as Ley and Bryden
and Heller and Levy did. Smiles presented in the left visual field will appear happier than smiles
presented in the right visual field. In the study participants chose more faces with the smile in the
left than the right visual field to conclude that the hypothesis is supported. There is still need to
figure out whether showing the chimeric faces in an isolated way, or a free way affects the
results. Future studies can test this as part of their experiments.
Lateralisation of Emotion: Which Brain Hemisphere Specializes in Emotional Perception.
10
References
Department of Psychology (2015, April 25). Lateralisation of emotion. Powerpoint slide
presented in Psychology 111, University of Otago.
Gleitman, H., Gross, J., & Reisberg, D. (2010). Psychology (8th ed.). New York: W. W. Norton
& Company, Inc.
Heller, W., & Levy, J. (1981). Perception and expression of emotion in right- handers and lefthanders, Neuropsychologia, 19, 263-272.
Laboratory Manual: Psychology 111/112 (2015). Dunedin: Department of Psychology,
University of Otago.