Hand and hand preferences in use of a visual analogue scale

Visual analogue scales are commonly used to measure the intensity of sensations, and their validity and reliability have been reported. However, biases similar to those found in visual line bisection have not been investigated. 23 right-handed and 19 left-handed participants, with a mean age of 30.1 yr., marked three points on a visual analogue scale representing imagined pain, using both the left and right hands, corresponding to 1/4, 1/2, and 3/4 of the way across the scale. In keeping with visual line bisection literature, both right- and left-handed participants marked the scale with the left hand significantly leftward of the point marked with the right hand, thereby underreporting the intensity. Right-handed participants marked 1/4 significantly leftward and 3/4 significantly rightward of veridical points, thereby underreporting and overreporting, respectively, the intensity. However, left-handed participants did not display this bias and consistently erred leftward for 1/4, 1/2, and 3/4 positions, underreporting intensity. These findings were explained in terms of hemispheric specialisation and activation for a manual response to a visuospatial task, with the conclusion that scoring the visual analogue scale to millimetre accuracy is subject to a potential confound of these factors.