Positive reinforcement by light: Comments on Lockard's article.

Abstract

Lockard's (1963) review of studies exploring the conditions controlling light-onset and light-offset reinforcement and theories of light-reinforced bar pressing is discussed. The evidence is reexamined in terms of temporal and response variables and it is shown, contrary to Lockard's conclusions, that the data can then be seen as relatively systematic. Lockard's discussion of theories is criticized on the grounds that in the case of the facilitation hypothesis, the stimulus-change hypothesis, and the discrepancy hypothesis, the position discussed is much more powerful than Lockard suggests. Evidence contrary to Lockard's "preference theory" is cited in the course of the discussion.

Initial-consequent-change surface in light-contingent bar pressing.

“…For the first 3 days, the curves for amount of change are in full accord with the predictions; however, after Day 3 the increment portion dropped out while the decrement side maintained itself. Since decline over days is the most frequent observation in this type of situation (Kiernan, 1964;McCall, 1965a) why did the decrement cells yield a different trend?…”

“…The essential tenet of the stimuluschange hypothesis with respect to lightcontingent bar pressing (LCBP) has been that as the amount of change in either direction from some referent increases, response rate also increases at least up to a point (Hebb, 1949;McCall, 1965b;Mc-Clelland, Atkinson, Clark, & Lowell, 1953). Although Lockard (1963) declared the stimulus-change position untenable, Kiernan (1964) cited more recent evidence which lent support to the hypothesis if preadaptation sessions and increment-decrement procedures have been used.…”

Facilitation or impairment of learning by d-amphetamine as a function of stimuli

“…To a lesser extent, deprivation increased responding for light onset (Kiernan, 1964) since total responding of saline-treated rats was significantly increased by both levers being rewarded with light only when deprivation was increased. Thus, accuracy was improved in all stimulus conditions with increased deprivation.…”

Competing exploration and pre-adaptation in the course of light-contingent bar pressing over time.

“…At the time of his review, however, Lockard (1963) rejected the explanatory role of pre-adaptation and suggested that other variables must be found to explain the differences between studies. A year later, Kiernan (1964) argued forcefully in favour of the competition hypothesis, supporting his position by reporting that 15 of 17 studies reported that LCBP rates declined over time if pre-adaptation sessions were given and five of eight experiments showed no decline or an increase over time if no pre-adaptation experience was given. Although the tallying of experiments tends to line up in favour of the "competition'' hypothesis, no single experiment has manipulated pre-adaptation experience and observed its differential effect on the course of LCBP behaviour over time.…”

“…If, however, no apparatus adaptation was allowed prior to LCBP, then all of the extraneous stimuli in the cage would compete with the light change, and the organism might well delay exploring the light change in favour of the cage stimuli, resulting in steady or increasing LCBP rates over time. Such an explanation was proffered orginally by Hurwitz (1956) and Appel and Hurwitz (1959), and later by McCall (1965aMcCall ( , 1965b and Kiernan (1964).…”