Effects of frequency on the temporal summation in the pacinian psychophysical channel

Abstract

According to the temporal summation theory, increasing stimulus duration causes a decrease in detection psychophysical threshold. Unlike previous psychophysical studies based on the fast adaptive tracking procedure, in this thesis, psychometric functions of the Pacinian channel were measured with the method of constant stimuli to investigate the e ects of frequency on temporal summation in more detail. Six female and four male subjects (age: 25-30) participated in the experiment. Sinusoidal bursts of mechanical displacement were applied on the middle ngertip of each subject by using a cylindrical contactor (r = 2 mm) at six frequencies (100, 150, 250, 350, 500, and 750 Hz), and ve durations (10, 30, 100, 300, and 1000 ms). For each frequency-duration pair, six di erent amplitudes were used with 40 repetitions to obtain detection probabilities in a two-interval forced-choice task. The data points were tted by sigmoidal curves to nd psychometric functions. Average goodness of ts (R2) was 0.88. Midpoints and the slopes of psychometric curves were statistically analyzed. Following aligned rank transform, repeated measures ANOVA was used to study the the e ects of duration, frequency and their interaction. As expected, the thresholds had the characteristic U-shape (F(5,45) = 42.50, p < 0.001); the slopes had an inverted U-shape (F(5,45) = 29.64, p < 0.001). Both thresholds (F(4,36) = 60.34, p < 0.001) and slopes (F(4,36) = 26.58, p < 0.001)) were a ected by duration due to temporal summation. However, there was no interaction between frequency and duration for the thresholds (F(1,9) = 4.84, p = 0.055 ), which means that temporal summation in the Pacinian channel does not signi cantly vary with frequency.|Keywords : Touch, somatosensory, psychophysics, psychometric function, temporal summation, Pacinian channel, vibrotactile stimulation.