Dependence of vibrotactile thresholds on the psychophysical measurement method

To investigate the dependence of vibrotactile thresholds on the psychophysical method used in the diagnosis of neurological dysfunction caused by exposure to hand-transmitted vibration. To compare thresholds obtained with (a) 'continuously variable' versus intermittent 'staircase' stimulation using 'yes-no' responses, and (b) 'yes-no' and 'forced-choice' responses using intermittent staircase stimulation.

Vibrotactile thresholds were measured on 12 healthy men by three different psychophysical methods. All measurements were performed with the same vibrometer in which the vibratory stimulus was applied by a probe 6 mm in diameter that protruded through a hole of 10 mm diameter in a surround, controlling both the contact force and the push force. Four stimulus frequencies (16, 31.5, 63 and 125 Hz) were used to obtain responses from FAI and FAII mechanoreceptors.

There was a 3 to 6 dB variation in threshold due to the psychophysical method: thresholds were lower with intermittent stimulation and thresholds obtained with the 'forced-choice' procedure were lower than those obtained with the 'yes-no' procedure. Alternative explanations of the findings were offered.

The dependence of psychophysical measurement method on vibrotactile thresholds was partly due to influencing responses via mechanoreceptor systems. It was suggested that the psychophysical measurement method had a sufficiently large effect on vibrotactile thresholds for it to be taken into account when methods for the diagnosis of neurological disorders are standardised.