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Rats worked under a fixed-ratio 45 schedule of reinforcement
during 4-hr long sessions either in sixteen 1S-min work periods (2
rats in Experiments 1 and 3) or in a single work period (3 rats in
Experiments 2 and 4) while receiving varying amounts of external
food. In Experiments 1 and 2, a fixed amount of external food was
provided in different conditions., whereas in Experiments 3 and 4,
both earned and total food intake were fixed to a dally maximum.
Consumption and responding decreased with availability compared
to nonavailability of external food and systematically declined with
increasing amounts of external food in progressively open
economies. The independence-quotient statistic was differentially
sensitive to the "delay" to the external food. Discriminability enhanced
the substitution effect of performance-independent food, resu"ing in
improved efficacy of the statistic and the conditions defined along
economic continuum.