Frequency and site-dependent variations in vibration detection thresholds on the face

An adaptive psychophysical procedure was used to estimate the vibration det ection threshold at seven spatially matched sites on the two sides of the f ace and at one scalp site. Repeated measurements over six testing sessions were made for stimuli vibrating at 1, 10 and 100 Hz for each of 21 neurolog ically healthy, young adult females. Approximately 14 stimulus trials were required to obtain each estimate of the threshold amplitude. Thresholds var ied as a function of frequency (p < 0.0001), side (p < 0.001) and site (p < 0.0001). Compared to stimulation at 100 Hz at which the estimates were low est, thresholds were 3.1 times greater at 10 Hz and 5.4 times greater at 1 Hz. Thresholds were lowest on the vermilion and highest on the cheek and ch in. The preauricular skin and scalp exhibited an intermediate level of sens itivity. Whereas thresholds were comparable on the two sides of the face fo r stimulation at 1 Hz, they averaged 1.33 times greater on the right side f or stimulation at 10 and 100 Hz. Moreover, thresholds obtained during the l ast two sessions were 16% higher than those obtained during the first two s essions (p < 0.02), suggesting that subjects on average became more conserv ative in reporting the presence of the stimulus. The sensitivity in discrim inating differences in tactile function favors use of the rapidly administe red testing procedure in a clinical setting.