Figure 4. Response variability.

A shows between-subject direction variability. The arrows represent the mean directions of displacement measured for 10 subjects under 2 stimulus conditions, right mastoid stimulation (black) and left mastoid stimulation (grey). Both groups of angles were significantly clustered (r = 0.83 and 0.57; P < 0.001 and P = 0.03). B shows within-subject direction variability. The bar graph represents the values obtained in 16 subjects for concentration (r) of response direction obtained in 5 successive experiments that used left mastoid vibration. Significant clustering (P < 0.05) is denoted by the horizontal dashed line. Four of the 16 subjects showed non-significant clustering while 12 show significant clustering. The mean directions of the position response recorded in the 5 separate experiments are shown on the right for 2 subjects. C shows trial-by-trial variability as the normalized component of sway size measured in the direction of each subject's mean position response direction. Shown are individual data from a single subject (upper plot) and group mean (±s.e.m.) data (lower plot) from all 10 subjects.