Vibrotactile intensity discrimination measured by three methods

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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, narrow‐band noise centered at 250 Hz, or wideband noise. Thresholds were measured by two‐interval, forced‐choice tracking under three methods of stimulus presentation. In the gated‐pedestal method, subjects had to judge which of two 700‐ms bursts of vibration separated by 1000 ms was more intense. In the continuous‐pedestal method, subjects had to detect a 700‐ms increment in the amplitude of an ongoing pedestal of vibration. In the two‐burst–continuous‐pedestal method with 1500‐ms pedestals, the subject had to detect which of two successively presented pedestals contained a 500‐ms amplitude increment. Thresholds were consistently lower for detecting increments in the amplitude of a continuous pedestal of vibration than for detecting amplitude differences between briefly presented successive pedestals or amplitude increments in successive pedestals. A ‘‘near miss’’ to Weber’s law was found both for sinusoidal and for noise stimuli. The difference threshold was not affected by stimulus frequency condition.

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