The effects of session length on demand functions generated using FR schedules

In comparing open and closed economies, researchers often arrange shorter sessions under the former condition than under the latter. Several studies indicate that session length per se can affect performance and there are some data that indicate that this variable can influence demand functions. To provide further data, the present study exposed domestic hens to series of increasing fixed-ratio schedules with the length of the open-economy sessions varied over 10, 40, 60, and 120 min. Session time affected the total-session response rates and pause lengths. The shortest session gave the greatest response rates and shortest pauses and the longest gave the lowest response rates and longest pauses. The total-session demand functions also changed with session length: The shortest session gave steeper initial slopes (i.e., the functions were more elastic at small ratios) and smaller rates of change of elasticity than the longest session. Response rates, pauses, and demand functions were, however, similar for equivalent periods of responding taken from within sessions of different overall lengths (e.g., total-session data for 10-min sessions and the data for the first 10 min of 120-min sessions). These findings suggest that differences in session length can confound the results of studies comparing open and closed economies when those economies are arranged in sessions that differ substantially in length, hence data for equivalent-length periods of responding, rather than total-session data, should be of primary interest under these conditions.