Expiriment in Pupilometry

Introduction:

Pupilometry is the study of how a pupil reacts to different emotions and stimuli. The research on the topic of pupilometry is scattered and fairly shallow. Related research has been conducted on facial expressions and their reaction and relation to emotion. There are some relationships to the facial expression research and pupilometry, but these relationships do not tell the whole story. Some interest has been brought up through research in the field of pupilometry and its predictive powers on emotion.

Pupilometry has to do with the dilation and contraction of the pupil relative to the stimulus or emotion being studied. In the early stages of pupil dilation research, there was intrigue as to the response of the pupil to emotional situations. That focus shifted toward information processing, and soon emotional studies were completely ignored.

One emotional study that was done questioned whether pupil size change, as a response to seeing nudity, was a general indicator of arousal. Fifty women and fifty-seven men of the heterosexual college student variety, with a mean age of 21.4 years were studied. Results of that experiment indicated that pupils did dilate significantly more for nude test group than they did for the clothed group, regardless of the sex of the subject or the sex of the pictured person. It was the study's conclusion that the pupils dilated because of the increased emotional presence of arousal (Aboyoun and Dabbs 1998).

Often, the eyes are poetically quipped as "the window to your soul", "mirror of you heart", or "the gauges showing fleeting feelings and changes" (Whiteside 1974). It has been studied that facial expressions can be inhibited by cognitively trying to hide them. In a study by Ursula Hess and Robert E. Kleck, spontaneous vs. deliberate facial emotions were studied. It was concluded that people could deliberately control facial expression. Pupil reaction on the other hand is not controllable by cognitive means. The dilation and contraction of the pupils is an involuntary response based on reaction to stimulus and or emotion. Even if a person tried to hide their reaction to some stimulus physically, the size of the pupil could still be measured to observe a person's reaction to a situation (Hess, U. and Kleck 1997).

Eckhard Hess states in his book that normal reactions to the emotion "happy" should indicate significantly larger pupil size than the emotion "mad". He goes on to suggest that large doe-eyed pupils are seen as happy, and small beady-eyed pupils are seen as mad (Hess, E. 1974). We will expand this theory even further, looking at the additional emotions of indifferent, sad, and surprised. It is our hypothesis that no difference exists between the means of each emotion. Ho: m Happy=m Mad = m Sad = m Indifferent = m Surprised. Ha: otherwise.

Methods:

Initially our group explored potential concepts of how ideas and memories were evoked related to music. We were unable to develop a hypothesis from this area of study that interested us, and that had significant background information. Upon further research, we came upon the study of pupilometry, and how the size of the pupil may be an indicator of emotion. We came across a book written by Eckhard Hess. He has tested this theory of correlating the pupil size and emotions. The two emotions that he tested were Happiness and Anger. We have developed a hypothesis similar to Hess's. We have also expanded the testing to include the emotions of surprise, indifference, and sadness.

A survey was created that recorded personal information from each subject. This survey consisted of three double-sided pages. The first page collected personal data, the second through sixth focused on different emotions. For each emotion we have displayed five faces, all of which are identical in appearance (per emotion) changing only the pupil size. The size ranges from 20 pixels to 40 pixels in an increasing increment of 5 pixels, (20...25...30...35...40,). This increment is an interval scale. The subject views the 5 faces and then makes a decision based on which face matches the emotion labeled.

Upon completion of the survey, data was tabulated the data and statistical testing was initiated. Analysis of Variance (ANOVA) was initially the statistic of preference, but due to non-normal data and inconsistent variation, two assumptions of the ANOVA test, we were unable to use that test. Instead, pair wise comparisons of each emotion were conducted using paired t-tests. This data was used to fuel our discussion. A sample survey is attached at the end of this paper.

Results:

Several statistical tests were applied to our data to try and determine whether pupil size is a good predictor of how people perceive emotion. Initially, using Minitab, we output some basic descriptive statistics for all the different emotions. These outputs included a histogram, box plot, and confidence intervals for both the mean and median of each emotion, among others.

Additionally, a box-plot of scores for each emotion was created to get a visual indication of what was going on.

The evaluation of the descriptive statistics showed non-normality in both the mad and surprised emotion scores. Normality is intrinsic assumption of both regression and ANOVA. The box-plot also showed non-constant variance, which is another rejection criterion when using regression or ANOVA. Without normality and constant variance, these tests cannot be trusted as to their outputs. Instead, we used paired t-tests between all of the different combinations of emotions. This allowed us to analyze each emotion and how it scored relative to each other emotion. The following are the results of the t-tests:

Paired T for Happy - Sad

N Mean StDev SE Mean

Happy 135 3.259 1.321 0.114

Sad 135 3.022 1.395 0.120

Difference 135