Rapid acquisition of choice and timing and the provenance of the terminal-link effect

Abstract

Eight pigeons responded in a concurrent-chains procedure in which terminal-link schedules changed pseudorandomly across sessions. Pairs of terminal-link delays either summed to 15 s or to 45 s. Across sessions, the location of the shorter terminal link changed according to a pseudorandom binary sequence. On some terminal links, food was withheld to obtain start and stop times, measures of temporal control. Log initial-link response ratios stabilized within the first half of each session. Log response ratio was a monotonically-increasing but nonlinear function of programmed log terminal-link immediacy ratio. There was an effect of absolute terminal-link duration on log response ratio: For most subjects, preference for the relatively shorter terminal-link delay was stronger when absolute delays were long than when absolute delays were short. Polynomial regressions and model comparison showed that differences in degree of nonlinearity, not in sensitivity to log immediacy ratio, produced this effect. Temporal control of stop times was timescale invariant with scalar variability, but temporal control of start times was not consistent across subjects or terminal-link durations.

Keywords: concurrent chains; conditioned reinforcing value; key peck; pigeons; rapid acquisition procedure; temporal control; terminal-link effect.

Fig 1

Log initial-link response ratios plotted as a function of programmed log terminal-link immediacy ratios for individual subjects, Short and Long conditions. Panels labeled Short-Rep and Long-Rep were replications of Short and Long conditions that occurred after the Pigeon responded in the Mixed condition for approximately 50 sessions. Each data point represents performance from blocks 4–6 of a single session. Diamonds and squares represent data from Short and Long conditions, respectively. Parameters and variance accounted for (VAC) by linear regression (solid lines) are also shown.

Fig 2

Log initial-link response ratios plotted as a function of programmed log terminal-link immediacy ratios for individual subjects. Each data point represents performance from blocks 4–6 of a single session in the Mixed condition. Diamonds and squares represent data from short and long sessions, respectively. Parameters and variance accounted for (VAC) by separate linear regressions on data from short sessions (solid lines) and long sessions (dashed lines) are also shown.

Fig 3

Sensitivity coefficients for successive conditions for Pigeons 221–224. Coefficients were estimated by regressing log initial-link response ratios from blocks 4–6 on Lag 0 log immediacy ratios.

Fig 4

Terminal-link effect magnitude for all subjects. Coefficients were estimated by regressing log initial-link response ratios from blocks 4–6 on Lag 0 log immediacy ratios. Separate regressions were calculated for short and long sessions, but data were combined across conditions.

Fig 5

Obtained data and predictions from Linear, Piecewise–Linear and Piecewise Separate-Slopes fits for a representative subject (Pigeon 224), plotted as a function of programmed log terminal-link immediacy ratio. Each diamond data point (top panels) represents the log initial-link immediacy ratio calculated over blocks 4–6 of a single short session. Each square data point (bottom panels) represents the log initial-link response ratio calculated over blocks 4–6 of a single long session. The left, middle and right panels show fitted predictions (grey xs) based on Linear, Piecewise–Linear, and Piecewise Separate-Slopes models, respectively.

Fig 6

Terminal-link effect magnitude plotted as a function of comparative degree of nonlinearity for long and short sessions. Each data point represents data from a single pigeon. Parameters and variance accounted for (VAC) by the linear regression (solid line) are also shown.

Fig 7

Start times (diamonds) and stop times (squares) as a function of terminal-link delay to reinforcement, for Pigeons 221–224. Each data point represents the mean start or stop time for a single session and terminal link alternative (left or right). Solid and open data points were obtained from Short and Long conditions, respectively.