“…For the doubt expression case, we found that the distance and angle features presented small changes between cases where labels were positive or negative, mainly due to the type of expression which is characterized by a slight contraction of the eyes and mouth; thus, we included two extra features for the left eyebrow (90,91,92,93,94,21,22,23,24,25), mouth (48,49,50,51,52,53,54,55,56,57,58,59), and left eye (0, 1, 2, 3, 4, 5, 6, 7), which are the enclosed area [66] and the principal axes ratio or eccentricity [67], which allowed us to better identify the characteristic patterns of this expression. Additionally, for the doubt expression case, we did not concatenate the features that belong to each frame in a window.…”