Sequential effects in dimensional contrast.
Dimensional contrast shoulders are driven by schedule signals alone, not by local response history.
01Research in Context
What this study did
Researchers ran pigeons on two-key multiple schedules. One key stayed rich (VI 2-min). The other key alternated between extinction and a lean VI (8-min).
They watched for dimensional contrast shoulders. These are response-rate bumps that spill into the rich component right after the lean one ends.
What they found
The shoulders showed up every time. They did not care about local contrast, stimulus color, or how fast the bird pecked on the last trial.
Only the schedule signal mattered. When the bird saw the rich key again, the bump appeared.
How this fits with other research
Green et al. (1975) saw local rate surges late in VI components. Malouff et al. (1985) rule those out as the cause of dimensional shoulders. The two effects live at different time scales.
Smith et al. (1975) said contrast comes from summing two peck types. Malouff et al. (1985) show the shoulder survives even when you scrub out local rate summation.
Hinson (1988) later confirmed the 1985 message: positive dimensional contrast is about relative stimulus control, not absolute response count.
Why it matters
When you set up multiple schedules, trust the component signals. Dimensional contrast is a stable product of the schedule itself, not carry-over from the last response or reinforcer. You can plan lean-rich alternations without fearing hidden sequential side effects.
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02At a glance
03Original abstract
Two experiments examined pigeons' response rates during short trials signaled by stimuli closely spaced along a wavelength continuum. In Experiment 1 separate halves of the continuum were correlated with different reinforcement schedules. In Experiment 2, the middle stimulus was accompanied by a lower probability of reinforcement than were the remaining wavelengths. Both procedures resulted in dimensional contrast "shoulders," seen as relatively enhanced or depressed response rates in the presence of stimuli between the extreme of the continuum and the border separating the positive and negative stimuli. Sequential analyses addressed possible contributions of the following interactions: (a) local contrast, seen when rate during a given schedule depends on the schedule in the just-preceding trial; (b) modification of local contrast by the similarity of the signaling stimuli (P. Blough, 1983); and (c) schedule-independent rate contrast, seen when rate in a given trial depends on the rate controlled by the stimulus that accompanied the just-preceding trial (Malone & Rowe, 1981). Dimensional contrast functions were similar when isolated according to the schedule, to the similarity of the signaling stimulus, and to the response rate of the just-preceding trial. The interactions noted above do not appear to make important contributions to this effect.
Journal of the experimental analysis of behavior, 1985 · doi:10.1901/jeab.1985.44-233