Vibrotactile intensity difference thresholds measured by two methods

Abstract

The difference threshold for the detection of changes in vibration amplitude was measured as a function of the intensity and frequency of stimuli delivered through a 2.9‐cm2 contactor to the thenar eminence. Stimuli were either 25‐ or 250‐Hz sinusoids or narrow‐band noise centered at 250 Hz or wideband noise. Thresholds were measured by two‐interval forced‐choice tracking under two methods of stimulus presentation. In the twoburst method, subjects had to judge which of two 700‐ms bursts of vibration separated by 1000 ms was more intense. In the increment‐detection method, subjects had to detect an increment in the amplitude of vibration. Thresholds were consistently lower for detecting increments in the amplitude of continuous vibration than in detecting amplitude differences between successive bursts. Amplitude increment detection, however, was relatively poor when the standard stimulus was brief rather than continuous. The near miss to Weber's law was found for both sinusoidal and noise stimuli under both methods of stimulus presentation. The difference threshold was not affected by stimulus frequency. [Work supported by NIH.]