Two-point tactile discrimination ability is influenced by temporal features of stimulation.

Two-point discrimination threshold is commonly used for assessing tactile spatial resolution. Since the effect of temporal features of cutaneous test stimulation on spatial discrimination ability is not yet well known, we determined whether the ability to discriminate between two stimulus locations varies with the interstimulus interval (ISI) of sequentially presented tactile stimuli or the length of the stimulus train. Electrotactile stimuli were applied to one or two locations on the skin of the thenar eminence of the hand in healthy human subjects. Tactile discrimination ability was determined using methods based on the signal detection theory allowing the assessment of sensory performance, independent of the subject's response criterion. With stimulus pairs, the ability to discriminate spatial features of stimulation (one location vs. two stimulus locations 4 cm apart) was improved when the ISI was equal to or longer than that required for tactile temporal discrimination. With stimulus trains, the ability to discriminate spatial features of stimulation was significantly improved with an increase in the stimulus train (from 3 to 11 pulses corresponding to train lengths from 40 to 200 ms). These results indicate that temporal features of tactile stimulation significantly influence sensory performance in a tactile spatial discrimination task. Precise control of temporal stimulus parameters should help to reduce variations in results on the two-point discrimination threshold.