In this paper the development of a method for producing facial images depicting emotions was described. An advantage of the resulting facial material is that the physiognomic characteristics of individual facial structures disappear while leaving the facial expression identifiable. Employing facial material produced according to the present method may be of advantage for decoding studies of emotional expression in the face since the facial morphology of the portrayed expressions is standardized. Furthermore, the present facial material based on morphing techniques seems to be more appropriate for use in judgement studies of emotion than schematic drawings of faces produced by computer based animation program. In a study investigating emotion recognition in faces (Burg, 1996) the prototypical facial expressions presented in this paper were employed along with the corresponding expressions of schematic linear drawings of computer produced faces (Musterle, 1984). Judges tended to recognize emotion overall more accurately in the realistic looking morphed faces than in the linear computer drawings. During a debriefing interview after the completion of the task subjects reported that the morphed faces looked more like a real person and thus they could relate easier to the depicted expression. In the linear drawing faces the expressions seemed exagerrated and the lack of texture and shades in face made it seem unreal. These findings seem to suggest that schematically drawn faces may be "read" in a more cognitive manner in terms of what they depict whereas realistic looking morphed faces may also evoke an affective response on the part of the observer. This however needs to be investigated further.
In the present sample certain combinations of facial action units appeared modified in certain prototypes. This seems to be due to individual variability in intensity of muscle activation of the different subjects. This could be remedied by a) employing a much larger sample of subjects, and b) by intensive training of the subjects in activating the face musculature according to FACS.
A future prospect for this method is to comprise a data bank for all individual facial action units and the combinations thereof. Male and female facial structures may be treated separately and aging effects may be taken into consideration as a further variable. Furthermore race and complexion may also be of interest especially when working with color data. Such controlled computer manipulations of facial material may allow the systematic investigation of the relationship and the manyfold interactions between the dynamic aspects of the human face (i.e. facial expression) and the static aspects of facial morphology.