The isolation of motivational, motoric, and schedule effects on operant performance: a modeling approach.
Use burst-pause math to see if a rate drop is a motivation problem or an effort problem.
01Research in Context
What this study did
The team used pigeons on a variable-interval food schedule.
They changed three things: how hungry the birds were, how hard the key was to press, and the schedule requirement.
They recorded every peck and fed the times into a two-part math model that splits responding into short bursts and long pauses.
What they found
Food deprivation made the birds start new bursts faster. That is a pure motivation effect.
Making the key heavier or the ratio higher made each burst shorter and the pauses longer. That is a motor or effort effect.
The model cleanly tells you which knob you just turned.
How this fits with other research
Grace (1995) already showed that more effort drops rate like mild punishment. J et al. now show you can spot if the drop comes from longer pauses (motor) or fewer starts (motivation).
McIntyre et al. (2002) used the same burst method to study extinction. They found rich histories protect the start rate, matching J’s claim that start rate is the motivation dial.
Sisson et al. (1993) saw food restriction raise rate in one test but lower it in another. J’s model explains the flip: restriction boosts start rate, yet if the bird then limits total pecks to save energy, overall rate can fall.
Why it matters
Next time a client’s response rate falls, run a quick burst-pause check. Count how long each burst lasts and how often new bursts start. If bursts stay long but starts drop, look at motivation—maybe the reinforcer lost value. If bursts shorten and pauses stretch, look at effort—maybe the task got too hard. You can decide in minutes instead of guessing.
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02At a glance
03Original abstract
Dissociating motoric and motivational effects of pharmacological manipulations on operant behavior is a substantial challenge. To address this problem, we applied a response-bout analysis to data from rats trained to lever press for sucrose on variable-interval (VI) schedules of reinforcement. Motoric, motivational, and schedule factors (effort requirement, deprivation level, and schedule requirements, respectively) were manipulated. Bout analysis found that interresponse times (IRTs) were described by a mixture of two exponential distributions, one characterizing IRTs within response bouts, another characterizing intervals between bouts. Increasing effort requirement lengthened the shortest IRT (the refractory period between responses). Adding a ratio requirement increased the length and density of response bouts. Both manipulations also decreased the bout-initiation rate. In contrast, food deprivation only increased the bout-initiation rate. Changes in the distribution of IRTs over time showed that responses during extinction were also emitted in bouts, and that the decrease in response rate was primarily due to progressively longer intervals between bouts. Taken together, these results suggest that changes in the refractory period indicate motoric effects, whereas selective alterations in bout initiation rate indicate incentive-motivational effects. These findings support the use of response-bout analyses to identify the influence of pharmacological manipulations on processes underlying operant performance.
Journal of the experimental analysis of behavior, 2011 · doi:10.1901/jeab.2011.96-17