An Undergraduate Laboratory Exercise to Study Weber's Law

Abstract

Weber's Law describes the relationship between actual and perceived differences in stimulus intensity. To observe the relationship described in this law, we developed an exercise for undergraduate students, as experiential learning is an integral part of scientific education. We describe the experimental methods used for determining the subject's discriminative capacity at multiple vibrotactile amplitudes. A novel four-point stimulator (designed and fabricated at the University of North Carolina) was used for the study. Features of the device, such as automated skin detection, make it feasible to perform this laboratory exercise in a reasonable lab period. At the conclusion of the lab exercise, students will thoroughly understand the principle of Weber's Law as well as fundamental quantitative sensory testing concepts. This introduction to sensory testing will provide a suitable foundation for the undergraduate neuroscience student to investigate other aspects of sensory information processing in subsequent lab exercises.

Keywords: Weber’s Law; just noticeable difference; vibrotactile amplitude discrimination.

Figure 1

Cortical Metrics (CM-4) Stimulator. INSET: Subject’s hand properly positioned on the stimulator.

Figure 2

Example program output after completion of a single test run (Standard = 400 μm).

Figure 3

Graph of Difference Limen vs. Standard Amplitude for each sample set (n=1,5, and 11). Error bars at each point represent the standard error.