Session duration and the VI response function: Within-session prospective and retrospective effects.
Long VI sessions can turn a steady response curve into a hump, so session length is a silent variable you must control.
01Research in Context
What this study did
Pigeons pecked a key for food on a variable-interval schedule.
The team ran two session lengths: short and long.
They tracked every peck to see how the curve changed.
What they found
Short sessions gave a smooth, rising curve.
Long sessions gave a hump-shaped curve: pecks rose, then fell.
Session length alone flipped the shape of the VI function.
How this fits with other research
Dove et al. (1974) saw contrast jumps when components changed. The 1993 study shows the whole curve can flip just by staying longer.
Bradshaw et al. (1978) found shorter components boost rate. The new data say the total session clock matters too, not just the chunk size.
Sisson et al. (1993) worked with monkeys that slowed down to save food per session. Pigeons did not slow for savings; the curve bent anyway.
Together, the papers say: time rules VI performance in more than one way.
Why it matters
If you run VI sessions with kids or clients, watch the clock. A short fluency probe may show steady responding, but a long lesson can produce mid-session fatigue that looks like skill loss. Split long teaching blocks or add brief breaks to keep the curve from dipping.
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02At a glance
03Original abstract
Two experiments examined the effects of session duration on responding during simple variable-interval schedules. In Experiment 1, rats were exposed to a series of simple variable-interval schedules differing in both session duration (10 min or 30 min) and scheduled reinforcement rate (7.5 s, 15 s, 30 s, and 480 s). The functions relating response rate to reinforcement rate were predominantly monotonic for the short (10-min) sessions but were predominantly bitonic for the long (30-min) sessions, when data from the entire session were considered. Examination of responding within sessions suggested that differences in the whole-session data were produced by a combination of prospective processes (i.e., processes based on events scheduled to occur later in the session) and retrospective processes (i.e., processes based on events that had already occurred in the session). In Experiment 2, rats were exposed to a modified discrimination procedure in which pellet flavor (standard or banana) predicted session duration (10 min or 30 min). All rats came to respond faster during the short (10-min) sessions than during the first 10 min of the long sessions. As in Experiment 1, the results seemed to reflect the simultaneous operation of both prospective and retrospective processes. The results shed light on the recent controversy over the form of the variable-interval response function by identifying one variable (session duration) and two types of processes (prospective and retrospective) that influence responding on these schedules.
Journal of the experimental analysis of behavior, 1993 · doi:10.1901/jeab.1993.60-543