DISCRIMINATION OF BRIGHTNESS DIFFERENCES BY RATS WITH FOOD OR BRAIN‐STIMULATION REINFORCEMENT¹

Abstract

Rats were trained to respond to the brighter of two keys. Four animals were trained with food pellets and four with electrical brain stimulation. Each discrimination sequence was initiated when the animal broke a light beam at the rear of the chamber, turning on the key lights and starting a 30-sec reinforcement period. An initial response on the brighter key was immediately reinforced, and further responses on the brighter key were then intermittently reinforced. Any time the dimmer key was pressed, a 30-sec timeout was introduced. During timeout, no response had any programmed consequence. When the reinforcement period or the timeout ended, a new discrimination sequence could be initiated. Daily 1-hr training sessions were conducted, and after seven or eight sessions, all animals were at or near errorless performance levels. The luminance of the brighter key was then systematically reduced, in seven steps, with two 30-min test sessions at each step. Orderly psychometric functions were generated for individual animals. Initial acquisition, once position preferences were broken, was equally rapid for food and for brain-stimulation animals, and the two reinforcement procedures yielded comparable levels of brightness discriminability.Intracranial self-stimulation (ICS) has been increasingly applied to

DISCRIMINATION OF AUDITORY INTENSITIES BY RATS1

“…The psychometric functions were similar across animals that differed markedly in degree of response bias. These functions differed in detail from those obtained previously in a visual luminance experiment (Terman and Kling, 1968), although in both experiments choice behavior in the region of decreasing stimulus control fit a normal probability model (cf. Engen, in press method of "free-field" presentation, where there is no arranged spatial correlation between the auditory stimulus source and the two response keys.…”

“…Further, it seems likely that the region beyond the point of subjective equality would be less pronounced in experiments where the animal can respond to the stimulus, as in most visual discrimination procedures. Our luminance discriminability functions (Terman and Kling, 1968), for example, did not show such a region.…”

“…As noted in a previous experiment (Terman and Kling, 1968), it is common for an animal to persist in running toward its preferred key on every trial and then to switch sides before making a response on the nonpreferred key. For a strongly biased animal, switching sides would result in generally longer latencies for responses to the nonpreferred key, regardless of stimulus intensity.…”

“…The trend has often been summarized by normalizing per cent correct values and obtaining a straight-line fit to the region of decreasing stimulus control (Terman and Kling, 1968;Engen, in press). Since the straight-line fit is determined by all the points on the psychometric function, the slope (or standard deviation) provides a summary threshold statistic.…”

“…The data are from Exp. 3 of the author's Ph.D. dissertation (Terman, 1968 (Terman and Kling, 1968) was adapted for the presentation of auditory intensities, and sine tone stimuli were chosen to allow a direct comparison of a discriminability estimate with the two-value discrimination acquisition data of Pierrel, Sherman, Blue, and Hegge (1970). Brain-stimulation reinforcement was used to suit a psychophysical design that demanded hundreds of massed trials and stable response patterns.…”