Magnitude and frequency of reinforcement and frequencies of interresponse times.
One concurrent VI schedule on a single key creates two stable pecking speeds, and you can move the split by changing food size or rate.
01Research in Context
What this study did
Shimp (1968) worked with pigeons pecking a single key.
The birds lived under a concurrent VI schedule.
Food size and how often it came both changed while the team logged the time between pecks.
What they found
The birds showed two clear pecking speeds.
Big or frequent food made the short-gap pecks grow.
Small or scarce food let the long-gap pecks take over.
How this fits with other research
Shimp (1971) added a second key and saw the same split speeds on each key.
The extra key proved the one-key pattern still holds when birds can switch.
Weissman et al. (1966) earlier saw messy timing under similar schedules with rats, so P’s clean two-bump result sharpens the picture.
Hart et al. (1968) found VI schedules give sloppy control; P shows that mixing two VI values in one key tightens the timing into two clear groups.
Why it matters
If you run concurrent schedules on one device, expect two response speeds, not one smooth rate.
To shift a client toward quicker responses, thicken the faster-reinforced side or enlarge the payoff.
To slow things down, do the opposite.
Watch for these twin speeds in your data; they tell you which schedule is winning.
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02At a glance
03Original abstract
The relative magnitude and relative frequency of reinforcement for two concurrent interresponse times (1.5 to 2.5 sec and 3.5 to 4.5 sec) were simultaneously varied in an experiment in which pigeons obtained grain by pecking on a single key. Visual discriminative stimuli accompanied the two time intervals in which reinforcements were arranged by a one-minute variable-interval schedule. The resulting interresponse times of each of three pigeons fell into two groups; "short" (1.0 to 2.5 sec) and "long" (3.0 to 4.5 sec). Steady-state relative frequencies of these interresponse times were orderly functions of both reinforcement variables. The combined effects of both independent variables were well summarized by a linear function of one variable, relative access to food. Unlike corresponding two-key concurrent variable-interval schedules, the present schedule did not produce an equality between the relative frequency of an operant and either the relative magnitude or the relative frequency of reinforcement of that operant. A tentative account is provided for this difference between one-key and two-key functions.
Journal of the experimental analysis of behavior, 1968 · doi:10.1901/jeab.1968.11-525