We collect information from our eyes and transmit it to the brain, which is the extension of the brain to the outside world. This sent information (images) is processed in the brain and produces output. The pupil, which transmits the light and image to the retina, is located in the middle of the iris and the muscles in the iris expand or contract according to the light intensity. As a result, changes in pupil size occur. The pupil changes according to the brightness and light intensity in the environment.
Changing the size of the pupil makes easy to do emotion analysis. By examining the pupil’s contraction and dilation in response to emotional stimuli, we can obtain important information about what is going on in the brain.
The pupil size change occurs with the autonomic nervous system and it is not an event that takes place under one’s control. People can control their physical response to emotional stimuli and look neutral from the outside. However, with the autonomic nervous system activity, pupil size, skin conductivity, and heart rate change involuntarily. Various sensors are used to capture these changes and the combination of 3 factors (pupil size, skin conductivity, heart rate) increases the reliability of the result. The autonomic nervous system is divided into two activities as sympathetic and parasympathetic activities. The change of the pupil size occurs by the balanced operation of these two activities. Inhibition of the parasympathetic system increases heart rate, reduces sphincter muscle contraction, and the pupil grows. Sympathetic activity increases skin conductivity, the activity of the dilator muscle increases, and the pupil grows.
According to some researches, it has been observed that emotional stimuli (photo, video, sound, etc.) change the pupil size more than neutral stimuli. When a participant was stimulated with emotional stimuli, it was observed that their pupils dilated regardless of the type of emotion. At the same time, skin conductivity and heart rate were measured, and a correlation was found between these 3 factors. However, the measurement of pupil size has advantages over the other two measurements. There is no need to use a sensor for the measurement of pupil diameter and as with other measurements no signal disturbance due to movement or noise. Participants have not attached electrodes, sensors, etc. directly. The change of pupil diameter can be followed by the Eye-Tracking system which located at a certain distance from the participant. Also, the results are seen and analyzed very quickly. Because the dilation time of the stimulation-pupil is in the range of 1-6 seconds.
The pupil grows against each emotional stimulus. But it is still under investigation and exceedingly small differences are being tried to be detected that how different emotional types cause changes in the pupil size. In some researches, positive and negative emotions were tried to be analyzed by machine learning and reliable results were obtained. In some studies, positive and negative emotions were tried to be analyzed by machine learning and reliable results were obtained. Also, it was observed that negative stimuli increased the pupil diameter more than positives in the last second.
Due to the advantages of pupil change; It is a useful system to be used in psychological treatments, developing video games, analyze the learning process, automatic facial recognition systems, entertainment (cinema, series, etc.). Especially in the fields such as cinema and TV series, using this technology provides convenience for the team that prepares the movie, while increasing the pleasure of watching for the audience. A movie that is still in the production or post-production stage is watched by the participant community and the emotional responses in them are measured. These emotional responses are measured by changing the pupil diameter. While emotionally strong scenes are kept, scenes that do not express any emotion in the audience and because boring are removed. This saves a lot of time for the production team and creates a better-quality product.
Featured IMG Source: Eye Pupil Vectors by Vecteezy