Device permitting rapid and accurate change of stimulus values and coincident introduction of appropriate circuits.

Abstract

When employing a continuous variable (such as wavelength, frequency, or amplimde of light or sound) in an operant discrimination or psychophysical experiment, E is not only confronted with the problem of setting the dial of the monochromater or audio oscillator with repeatable accuracy berween successive trials but with the matter of changing switch positions for counters and reinforcement contingencies appropriate to particular dial settlnys The modicum of time E frequently permits himself for these tasks leaves little opportunity for checking before the next trial is upon him. The device described here was designed to decrease the work and possible error involved while, at the same time, increasing the accuracy of dial settings. The accuracy is increased, in effect, by increasing the radius of the dial by means of pivoting an arm from the dial and calibrating the enlarged perimeter it circumscribes on a perpendicular panel. Repeatability is gained by seating a spring-loaded pin (situated near the end of the a rm) in close-fitting holes located opposite the calibrations to be used in the experiment. The necessity of manually switching-in contingent circuits is eliminated by leading a wire from ground, down the arm, to the spring-loaded pin, which, when seated in a hole, makes continuity with a metal plate attached across the bottom of the hole on back of the panel. This back plate is wired to the coil of an ungrounded relay. Thus, the act of seating the pin energizes that relay and closes the normally-open contaco, thereby completing a circuit from the manjpulandum to the appropriate counter for that dial setting. If, in addition, a reinforcement contingency is required for responding to a particular stimulus, the wire leading from the backplate of that setting can also ground a second relay, closing a reinforcement circuit across its normallyopen contacts in a manner similar to the above. The latter arrangement eliminates the possibility of erroneously reinforcing responses to discriminative or test stimuli. If different portions of the stimulus continuum are to be employed from time to time, the device can be reset and the same holes and response contingencies utilized by making following adjustment of the arm: set the arm in the hole corresponding to the value or used in the portion last explored; loosen the set screw of the sleeve around the dial; set the dial to the value or to be employed in the other portion of the continuum, and tighten the set screw. When the device is to be used successively in this manner, the calibrations can be indicated in general terms: the center hole can be labeled nominal or CS and each of the holes on either side of this can be identified in terms of the unit-deviations to which their distance from corresponds. The arm was constructed of Plexiglas. This material was particularly suitable for the panel as well, since, in addition to being a non-conductor, it has low surface friction and good resistance to wear at the edges of the holes. The back side of the panel was painted flar black so as to provide a more definitive surface for reading the calibration labels attached below the holes. The paint was applied to the back side instead of the front side so as not to increase the friction of the spring-loaded pin with the surface of the panel as i t approached the hole and, more importantly, to prevent paint building-up on the end of the sliding pin and preventing continuity with the backplate when seated. Accepted January 29, 1968.