NOTE ON RESPONSE DIFFERENTIATION DURING A SIMPLE DISCRIMINATION¹

Abstract

Apart from other requirements set by the experimenter, bar-pressing situations have at least one characteristic in common: the animal must learn how hard to press the bar if it is to procure reinforcement. (Notterman, 1959, has described the emission of forces over the course of operant level, CRF, and extinction.) This requirement is to be distinguished from additional demands placed upon the organism in the typical experiment involving discrimination of exteroceptive stimuli. In the latter instance, and in addition to the intensive requirements, the animal must learn when to press and when not to press. The eventual disparity in SD_&A rate of responding has been used as an indicator of the extent of the discrimination thus established (Frick, 1949;Dinsmoor, 1951;Smith & Hoy, 1954).Since the organism is not reinforced in SD unless it presses hard enough, and since it goes unreinforced in St no matter how hard it presses, experiments concerned with the establishment of a discrimination to exteroceptive stimuli inevitably and concomittantly involve the possibility of interaction between the "when-to-press" and "how-hard-to-press" aspects of bar-pressing behavior. This report is a preliminary attempt to describe the relation between response differentiation and stimulus discrimination during the development of stimulus discrimination. METHODBy means of a pair of strain gauges used as a force pick-off, the force-related voltages characteristic of successive bar-pressing responses during the establishment of a discrimination were passed through the amplifiers of an analog computer, and the peak force of each response noted. (Apparatus details are available in Notterman, 1959.) A total of 15 discrimination sessions was given, preceded by two unreinforced basal or operant-level sessions. In order to preclude any temporal conditioning, each of the daily sessions consisted of periods of SD and St having the following irregular sequence: 80 seconds of SD; 80 of St; 40, SD; 20, St; 20, SD; 160, SI; 10, SD; 40, St; 160, SD; and 10, VA. This sequence was programmed on a continuous tape such that daily sessions could begin at any point in the schedule and run either forward or backward. A daily experimental session consisted of two entire sequences, making for a total time of 20 minutes and 40 seconds. A CRF schedule was maintained during SD, with a required force of 3.0 grams'minimum for both reinforcement and recording, and with The P. J. Noyes Company 0.45-milligram pellets as reinforcements. RESULTS AND DISCUSSIONFigures 1 and 2 represent the data for the first Wistar rat exposed to this procedure; they are typical of data obtained from some 20 additional animals during a related parametric study currently underway as a dissertation by the junior author.The first figure reveals the customary SD_SA separation in number of responses emitted during each session as a function of successive discrimination sessions. The SD responding is

Response duration during an operant discrimination.

“…(The top frame is mean response rate, the middle is mean first response duration, and the bottom represents the mean duration of all responses under the two stimulus conditions.) Herrick, 1963;Notterman & Block, 1960). The gradual, but monotonic, decrease in the reinforced duration replicates Margulies' (1961) results for duration under regular reinforcement.…”

“…For example, S 4 response amplitudes are greater (Burke, 1963) and more variable (Herrick, 1963) than S D amplitudes. Similar patterns are evident in duration measures and force indexes (Notterman & Block, 1960). Interestingly, these effects persist throughout training.…”

CONFIRMATION OF LINEAR SYSTEM THEORY PREDICTION: RATE OF CHANGE OF HERRNSTEIN'S k AS A FUNCTION OF RESPONSE‐FORCE REQUIREMENT

“…DISCUSSION The results summarized in Table 3 and Figure 1 confirm the linear system theory's third prediction concerning k-namely, that the rate of change of k over a given magnitude range varies directly with the force requirement on the operandum. The existing literature on response force (e.g., Notterman, 1959;Notterman & Block, 1960;Notterman & Mintz, 1962) does not address this rate-of-change effect. However, Chung (1965) found that the absolute rate of pigeon's key pecking on single-alternative VI schedules was a decreasing function of the force requirement on the key.…”

The Principal Components of Response Strength

“…But response magnitude is easily affected by the topography of the unconditioned response (Allan, 1992;Ploog & Zeigler, 1996). There are instances in which, even when contingencies are held constant, response force may covary negatively with other measures of strength (Amsel, 1962;Logan, 1956;Notterman & Block, 1960;Svartdal, 1993).…”