Using a Reaction-Time Device to Introduce Students to the Oscilloscope

In many undergraduate physiology laboratories students are asked to master operation of an oscilloscope and to interpret its sweep functions. These functions, namely vertical gain (voltage level), time base (sweep speed, seconds/cm-'), and trigger level are essential in measurements of electrical events such as those occurring in muscle or nerve action potentials. Typically, however, many students sweat through these formal laboratories uncertain of what they are measuring or unable to manipulate the oscilloscope controls for proper presentation. This experience can be especially discouraging, because students are fascinated by the prospect of being able to measure discrete events in millisecond resolution. A previous successful "hands-on" experience with the oscilloscope would be helpful. One way to familiarize students with the oscilloscope is to have them experience a black box reactiontime test. The apparatus used is a simple and inexpensively constructed device that allows one student to trigger the sweep of the 'scope beam by discharging a capacitor with a momentary down switch (figs. 1, 2, and 3). A second student presses another button only in response to seeing the 'scope presentation of the positive going trigger pulse initiated at random by the first student. In the procedure, both triggerer and responder stand side-byside and view the oscilloscope trace, so that the reaction time test becomes a contest similiar to "pong" FIG I