Analyses of facial expressions for the evaluation of seasickness

The authors have been studying the human response to a low-frequency oscillation using a ship motion simulator and several passenger ships so as to develop an evaluation method of ride quality on board vehicles. They take note of facial expression as an objective physiological index of motion sickness. The purpose of the present paper is to establish a quantification method of facial expression and to clarify the relationship between one´s facial expression and his/her mental situation. First, the concept of the Fourier descriptor (FD) was introduced to quantify and characterise facial expression. The subjects were asked to exhibit the six fundamental emotions defined in the field of psychology, and FDs were obtained from the shape of their eye and mouth. Analysis of 15 subjects´ face images shows that the shapes of human eye and mouth can adequately be expressed with FDs and that the reconstructed shapes of these facial factors from average FDs agree well with characteristics that were widely known in psychology. Then, the discriminant analysis was applied to classify facial expressions into the six fundamental emotions, and it was found that the optimised model with a comparatively small number of FDs could be discriminating with a high discrimination rate.