Weber's Law

ARTICLE The Journal of Undergraduate Neuroscience Education (JUNE), Spring 2011, 9(2):A71-A74 An Undergraduate Laboratory Exercise to Study Weber’s Law Jameson K. Holden, Eric M. Francisco, Zheng Zhang, Cristina Baric & Mark Tommerdahl Biomedical Engineering Department, University of North Carolina, Chapel Hill, NC 27599. 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; vibrotactile amplitude discrimination; just noticeable difference The perceived intensity of a sensory stimulus relative to other stimuli is often difficult to quantify; a subject cannot easily tell whether one stimulus felt twice, half, or three quarters as strong as another. Nevertheless, it is easy to determine which of two stimuli is stronger, provided that the difference between the stimulus intensities is sufficiently large. The minimum physical difference that the subject can perceive -- the just noticeable difference (JND) or difference limen (DL) -- can be measured (Geschieder, 1991). Ernst