Effort- and time-cost effects on demand curves for food by pigeons under short session closed economies

Demand curves for food were compared under the effort- and time-cost conditions using response-initiated fixed-ratio (FR) and fixed-interval (FI) schedules. For the effort-cost conditions, two pigeons were exposed to FR 3, 30, 90, and 150 for six sessions each. The time equivalent of each ratio was a FI schedule, each Fl value equal to an average time from the first peck on the ratio to reinforcement (3-s access to mixed grain). The experiment was repeated in 1.5-, 3.0-, and 4.5-11 closed economies in a different order for each pigeon. Food consumption as a function of time-based unit price (time equivalent per reinforcement duration) for each session length showed moderate convergence on a single demand function for the two cost conditions. When the demand function was separately fitted to each cost condition, however, the ranges of inelastic demand were generally larger in time-cost than effort-cost conditions. These curve-fitting analyses suggest that although time is a critical cost factor decreasing consumption at moderate prices, food intake under the effort-cost condition decreases more rapidly than under the time-cost condition as unit price increases. The analyses provide useful descriptions for the functional difference of costs. (C) 2001 Elsevier Science B.V. All rights reserved.