Dependence of vibrotactile thresholds on the psychophysical measurement method
Objectives: 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. Methods: 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. Results: 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. Conclusions: 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.
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