| dc.description.abstract | Comparisons of schedule associated stimuli are readily available from, for example, studies on concurrent and multiple schedules. Little has, however, been done on the effect of schedule associated stimuli which signal entrance into some favorable or unfavorable schedules of reinforcement. Particular schedules can serve as units which are presented, following various cues, comprising a second order schedule. A cue can conceivably influence subsequent responding on the following discriminative stimulus. Responding may also differ in informative ways to the initial cues, designated starting stimuli in the present study. If the relative favorableness of the starting stimulus differs from the relative favorableness of the following discriminative stimulus, contrast to the discriminative stimulus might be predicted. Differential favorableness of the starting and discriminative stimuli was accomplished in the present study by using a multiple schedule, each component of which was another multiple schedule, these, in turn, consisting of two chains: mult {(chain VI 5 VI 30) (chain VI 5 VI 90)} {(chain VI 5 VI 90) (chain VI 5 VI 270)}. All schedules were signalled by visual stimuli projected on a key in an operant box. The two starting stimuli, Stimulus 1 and 2, signalled the first component of each chain, programmed on VI 5. The more favorable, Stimulus 1 lead to, for instance, Stimulus A (VI 30) or Stimulus B (VI 90). The less favorable, Stimulus 2, lead to, for instance, Stimulus a (VI 90) or Stimulus b (VI 270). Shifts were made among these schedules primarily to assess the plausibility of three major accounts of behavioral contrast; carryover, extreme conditioning, and expectancy-shift theory. Behavioral contrast occurred in all birds as Stimulus a, the relatively more favorable, was responded to more rapidly than Stimulus B, the relatively less favorable. The present data was most problematic for carryover theory as the largest contrast effect occurred when the context of Stimulus 1 was separated from the context of Stimulus 2 by a 24 hour interval. Carryover theory predicts the greatest contrast when all stimuli occur within a single session. Interchanging Stimuli a and B produced either no change or a shift over days in the corresponding response rates. Such a finding is inconsistent with expectancy-shift theory, which predicts an immediate shift in response rates, but is congruent with extreme conditioning theory, which predicts some minimum number of trials must pass to stamp in the contrast producing process. | |
