Objective: The objective of this study was to evaluate laterality and upper/lower face dominance of expressiveness during prescribed speech using a unique validated image subtraction system capable of sensitive and reliable measurement of facial surface deformation.
Rationale: Observations and experiments of central control of facial expressions during speech and social utterances in humans and animals suggest that the right mouth moves more than the left during nonemotional speech. However, proficient lip readers seem to attend to the whole face to interpret meaning from expressed facial cues, also implicating a horizontal (upper face-lower face) axis.
Study design: Prospective experimental design. Experimental maneuver: recited speech.
Outcome measure: image-subtraction strength-duration curve amplitude.
Methods: Thirty normal human adults were evaluated during memorized nonemotional recitation of 2 short sentences. Facial movements were assessed using a video-image subtractions system capable of simultaneously measuring upper and lower specific areas of each hemiface.
Results: The results demonstrate both axes influence facial expressiveness in human communication; however, the horizontal axis (upper versus lower face) would appear dominant, especially during what would appear to be spontaneous breakthrough unplanned expressiveness.
Conclusion: These data are congruent with the concept that the left cerebral hemisphere has control over nonemotionally stimulated speech; however, the multisynaptic brainstem extrapyramidal pathways may override hemiface laterality and preferentially take control of the upper face. Additionally, these data demonstrate the importance of the often-ignored brow in facial expressiveness.
Level of evidence: Experimental study. EBM levels not applicable.