GENDER-DEPENDENT, SIDE-DEPENDENT AND SITE-DEPENDENT VARIATIONS IN HUMAN PERIORAL SPATIAL-RESOLUTION

Twenty-eight right-handed, young adults participated in a sensory test ing experiment to evaluate spatial resolution at 10 positionally match ed sites on the right- and left-hand sides of the face. An adaptive ps ychophysical (i.e. tracking) procedure was used to estimate the thresh old spatial separation for perceiving two points of contact at each si te. Estimates of the threshold at one site on both sides of the face w ere also obtained with a method-of-limits procedure similar to that em ployed for clinical evaluation of patients. In addition, each individu al was asked to rate (i) his(her) overall facial sensitivity to touch and (ii) the degree to which he(she) could discern subtle changes in l ip, cheek and chin position during speech, chewing and facial expressi on. Analysis of the estimates of the threshold separation obtained wit h the tracking procedure revealed a significant effect of gender (p < 0.04) and of site (p < 0.001). Females were more spatially sensitive t han males: average threshold separations were 1.55 mm less. Most notab ly, the threshold increased ninefold with distance posterolaterally fr om the oral opening. The vermilion of the upper lip was the most spati ally sensitive site (population geometric mean = 2.4 mm) and the preau ricular skin the least spatially sensitive site (20.9 mm). Significant effects of side and of interactions among gender, side and site were not observed. The estimates obtained with the method-of-limits procedu re were very similar to those obtained with the tracking procedure: th e latter were 0.67 mm less on the average. Individuals' ratings of ove rall facial sensitivity to touch were similar for males and females (p > 0.70). Females, however, reported greater ability to discern subtle changes in lip, cheek and chin position than males (p < 0.03). The ra tings of this sensory function correlated negatively with the estimate s of the threshold separation on the vermilion of the upper lip (p ( 0 .03).