Asymmetry in Facial Emotional Expression. AbstractResearch in the past has demonstrated that the right hemisphere of the brain is dominant in the perception and expression of emotion. As a result of crossing of the nervous system, the expectation was that the left side of the face would express emotion more intensely than the right. This was tested by using left and right composite faces, showing them to participants, asking them to rate which of the two faces was more intense.
The finding was that participants judges the left composites to be more emotionally intense than the right composites, thus supporting the hypothesis that there is asymmetry in the facial expression of emotion. This finding leads to the conclusion that the right hemisphere is dominant in the perception, expression and general procession of emotional information. Crossing over of the nervous system occurs at the decussation of the pyramids , this is a site just above the medulla-spinal cord junction at which the nerve fibres from either side of the brain cross over to the contralateral side of the body (Marieb, 1998). This means that the sensory information from the right side of the body goes to the contralateral side of the brain, in this case the left hemisphere, and vice versa. Due to this cross over, each hemisphere has motor control over the contralateral side of the body.
The brain’s hemispheres are specialised in their functions, amongst others, the left hemisphere is dominant in language, mathematical reasoning and logical thinking. The right hemisphere is dominant in facial recognition, expression and spatial thinking. These findings that the different hemispheres are specialised in their function have come from experiments performed on those with damage to specific parts of the brain thus being able to isolate the particular damaged area and experiment upon this. Because the hemispheres are specialised in their functions, the psyhcologists in the past have developed theories on asymmetry in emotional perception and expression.
It has been found from previous studies that the right hemisphere is dominant in facial recognition and expression. It has been proposed that the right side of the face is more openly expressive, while the left side of the face is private’ (Sackheim, Gur, 1978). Darwin first proposed the importance of expression as a form of communication that had survival value for the human species (Atkinson, Atkinson, Smith, Bem, Nolen-Hoeksema, 1996). Later studies found that there were six distinct emotions that can be reliably recognised universally in the human face. These emotions are surprise, fear, sadness, happiness, anger and disgust. Furthermore, studies have found that the right side of the face is judged as more similar to the whole face than the left.
This was done by constructing left and right composites of faces. A composite is constructed by taking a photo and then splitting the face vertically down the centre line then mirroring the two halves to obtain two whole faces, one the left composite and one the right. The finding that the right side of the face is more similar to the whole face, thus concluding that there was a bias in the perceiver. This was produced by right hemisphere dominance in facial recognition rather than by actual asymmetry in expression (Sackheim & Gur 1978). Nevertheless, the fact that the subjects can find differences in left and right composites, suggests that there is a difference in the expression of emotion by either side of the face.
To test if there is asymmetry in the facial expression of emotion, in this experiment left and right composites of faces are presented to subjects who have to rate the intensity of emotion of the two faces. Thus the aim of the experiment was to investigate – is facial expression of emotion asymmetrical? As well as are emotions expressed more intensely on the left side of the face as we might expect if the right hemisphere is dominant in the processing and perception of emotional stimuli. Thus,the independent variables are the left and right composite faces and the dependent variable is the proportion of peoplee who chose the left composite face as expressing emotion more intensely. Therefore our hypothesis is that the left side of the face expresses emotion more intensely than the right side of the face.
MethodParticipantsFor this experiment there were 396 Psychology 100 students at the UWA psychology laboratory. This included varied age groups and the sex of the participants had no influence on this experiment. Students were obliged to take part in the experiment due to course requirements. Thus there was no payment of any kind.
Apparatus The materials used in this experiment included a response sheet, which specified top’ or bottom’. MATERIALS CHECK!!Procedure For each trial, two faces were presented simultaneously, one above the other, the faces remained on the screen for 10 seconds. The subjects indicated either the top or the bottom face expressed emotion more intensely. The response of the subjects was limited to top or bottom thus responses such as neither’ were not accepted. There were 16 trials which were separated by 20 second intervals, during this time the screen was blank.
ResultsThe number of trials on which a single subject selected the LL composite as expressing emotion more intensely were tabulated as a score out of 16. This score was then converted to a proportion (varying from zero to one). Then an average was taken of all the different proportions, thus getting a mean of the amount of times the participants judged the LL composite to have more emotional intensity. For this experiment the mean was 0. 546, with a standard deviation of 0. 12 (both rounded to two decimal places).
The 95% confidence interval has an upper bound of 0. 53 and a lower bound of 0. 55. This result for the confidence interval shows that 95% of the time, the percentage of faces being chosen being the LL composite will be between the values of 0. 53 and 0. 55.
Thus the proportion of times the LL composite was chosen is greater than the chance level of 0. 5. Discussion These results show that the LL composites were judged to be more emotionally expressive than the RR composites. This suggests that the left side of the face expresses emotion more intensely than the right side of the face, thus supporting the hypothesis being tested.
This hypothesis is in agreement with Sackheim and Gur’s finding in 1978 that the left side of the face shows more emotion more intensely than the right side.
