Choice and terminal-link response topography

Six pigeons responded under concurrent-chains schedules. For 3 birds, pecking was required in both initial links; for 3 others, treadle pressing was required. For all subjects, pecking was required in one terminal link and treadling in the other. The initial links consisted of independent variable-interval 60-s schedules. All birds were exposed to five pairs of terminal-link variable-interval schedules over 10 conditions: 6 s versus 54 s, 18 s versus 42 s, 30 s versus 30 s, 42 s versus 18 s, and 54 s versus 6 s. Comparisons of responding under nominally identical terminal-link variable-interval schedules showed that, without exception, higher choice proportions were obtained for the alternative correlated with terminal-link pecking. Moreover, terminal-link delay to reinforcement was shorter for terminal-link pecking than for terminal-link treadling chains. This factor, along with response force requirements, was implicated in explaining the present as well as previous findings of preference for pecking over treadling. It was found also that the delay-reduction hypothesis provided only a moderately accurate description of performance under concurrent chains in which different terminal-link response topographies are required. These findings suggest that quantitative models neglecting the effects of differing terminal-link topographies may be incomplete.