Our method provides a new approach to measuring tactile spatial acuity. Our semiautomated system is easy to operate and can be used to control movement, speed, distance and contact duration. To prepare tactile angle stimuli, use a milling machine to cut an acrylic sheet into an 8 milliliter long, 1.5 millimeter wide, 1 millimeter high polyline with two equal lines symmetrically distributed along an imaginary bisector.
And a 40 milliliter long, 40 millimeter wide, 3 millimeter high square base. Glue the polyline to the center of the square base. Degrade a 2-D raised tactile angle stimulus.
Make pieces with angle sizes ranging from 50 to 70 degrees in 2-degree increments. And make up to 20 pairs of discriminated angles including 20 identical reference angles and 10 pairs of identical comparison angles with measured accuracies of plus or minus 0.2 degrees. Before beginning an experiment in the data editing software, set the motion type of the device to Increment Model.
The motion distance to 80 millimeters, the motion speed to 20 millimeters per second. The motion function to single and the axis as ID equals 0. To set the electronic slide movement, distance and speed parameters, respectively.
When the software parameters have been set, have the subject sit at a table with the apparatus and place a blindfold on the subject. Instruct the subject to lightly place the right index finger at the opening of the hand plate. Next, clamp a pair of angles, including the reference angle and the comparison angle, onto the slide.
Instruct the subject to report which of the angles is larger as perceived by touch, and click the button. The pair of angles will slide passively across the index fingers at a speed of 20 millimeters per second for 80 millimeters. If the subject cannot identify which angle is larger, they can indicate that the angles are the same.
Register the answer of the subject as the response data. Then, replace the angles and repeat the presentation in the same manner 10 times, recording the subjects response after each analysis. To avoid uncomfortable sensations on the index finger, have the subject take a three-minute break after each series of 20 trials.
To apply the logistic curve to describe the angle discrimination threshold, the three alternative force-choice result must be expressed as a frequency distribution. In this coordinate, a logistic curve could be fitted by the least-square method. And the angle discrimination threshold was defined as half of the difference between the angle at accuracy rates of 25 and 75%So this technique may provide a new approach for the tactile interplay of sensory and high-order processing.
