Does the terminal-link effect depend on duration or reinforcement rate?

In Phase 1, 4 pigeons were trained on a three-component multiple concurrent-chains procedure in which components differed only in terms of relative terminal-link entry rate. The terminal links were variable-interval schedules and were varied across four conditions to produce immediacy ratios of 4:1, 1:4, 2:1, and 1:2. Relative terminal-link entry rate and relative immediacy had additive and independent effects on initial-link response allocation, and the data were well-described by a generalized-matching model. Regression analyses showed that allowing sensitivity to immediacy to vary across components produced only trivial increases in variance accounted for. Phase 2 used a three-component concurrent-schedules procedure in which the schedules were the same as the initial links of Phase 1. Across two conditions, the relative reinforcer magnitude was varied. Sensitivity to relative reinforcer rate was independent of relative magnitude, confirming results of prior studies. Sensitivity to relative reinforcer rate in Phase 2 did not vary systematically across subjects compared to sensitivity to relative entry rate in Phase 1, and regression analyses confirmed again that only small increases in variance accounted for were obtained when sensitivities were estimated independently compared with a single estimate for both phases. Overall, the data suggest that conditioned and primary reinforcers have functionally equivalent effects on choice and support the independence of relative terminal-link entry rate and immediacy as determiners of response allocation. These results are consistent with current models for concurrent chains, including Grace's (1994) contextual choice model and Mazur's (2001) hyperbolic value-added model.

Section: Discussionmentioning

confidence: 94%

Independence of Terminal‐link Entry Rate and Immediacy in Concurrent Chains

Berg

Grace

2004

“…The terminal‐link effect is well‐known in concurrent chains: With the relative terminal‐link delay held constant, choice for the richer alternative increases with overall delay. This result has been found with both FI FI (Gentry & Marr, ; MacEwen, ) and VI VI terminal links (Grace, ; Grace & Bragason, ; MacEwen, ), but no comparisons between schedule types have been reported. The homogeneous terminal‐link conditions (FI FI, MI MI, VI VI) in the current study provide a well‐controlled comparison, as the relative delay was held constant (2:1) while the average duration increased from 7.5 s to 30 s. Results showed that preference increased similarly with duration for all schedule types (see Fig.…”

Section: Discussionmentioning

confidence: 84%

Effects of schedule type and terminal‐link duration on choice in concurrent chains

Grace

McLean

2019

Four pigeons responded in a three‐component concurrent chains procedure in which the terminal‐link schedules were either both fixed‐interval (FI FI), both variable‐interval (VI VI), both mixed‐interval (MI MI) or variable‐interval fixed‐interval (VI FI). Across components within sessions, overall terminal‐link duration was varied while schedule types were varied across conditions. For the conditions with homogeneous schedules, the strongest preference was obtained with FI FI, intermediate with MI MI, and weakest with VI VI. Preference increased with overall terminal‐link duration for all schedules, but the increase was more rapid for VI FI. The hyperbolic value‐added model (HVA) and cumulative decision model (CDM) were fitted to the choice data and accounted for 83.9% and 76.1% of the variance, respectively. However, deviations from both models' predictions were systematic. A modification of the CDM, which assumed that reinforcers delivered after variable delays were more effective, improved the fit of the model and substantially reduced the systematic deviations in residuals. Comparable modifications of HVA produced only limited improvement. Results show that preference in concurrent chains with homogeneous terminal links depends on the degree of variability in reinforcer delays, and that the CDM can provide an excellent account of results across different terminal‐link schedules.

“…We also tested whether preference for the shorter terminal link would increase as overall terminal-link duration increased, with the immediacy ratio held constant. This result is known as the terminal-link effect, and has been one of the most widely-studied phenomena in concurrent chains, having been obtained when terminal links differ in terms of reinforcer magnitude (Navarick & Fantino, 1976) and probability (Spetch & Dunn, 1989), as well as immediacy (Grace & Bragason, 2004;Grace, 2004;MacEwen, 1972;Williams & Fantino, 1978). In the present experiment, the delays were geometrically spaced so the ratios between 1:1 and 4:1 were the reverse of those between 1:4 and 1:1.…”

Section: Discussionmentioning

confidence: 99%

“…According to the LINOP model, the strength of preference for the left alternative when the right delay is greater than 8 s (i.e., points to the right of the filled symbols) is the same as the strength of preference for the right alternative when the right delay is less than 8 s (i.e., points to the left of the filled symbols). However, the ExtDM predicts that the strength of preference should be overall greater when the right delay is longer than 8 s. This exemplifies the terminallink effect (MacEwen, 1972;Grace, 2004;Grace & Bragason, 2004)-that preference should be more extreme with overall longer delays, with the delay ratio held constant.…”

mentioning

confidence: 93%

Response Allocation in Concurrent Chains When Terminal‐link Delays Follow an Ascending and Descending Series

Christensen¹,

Grace²

2009

Eight pigeons were trained in a concurrent-chains procedure in which the terminal-link immediacy ratio followed an ascending or descending series. Across sessions, one terminal-link delay changed from 2 s to 32 s to 2 s or from 32 s to 2 s to 32 s, while the other was always 8 s. For all pigeons, response allocation tracked changes in delay and was biased towards the 8-s alternative on the descending series, indicating a hysteresis effect, and was more sensitive to changes in the terminal-link delay ratio for relatively long (> 8 s) than short (< 8 s) delays. Both the hysteresis and effect of delay duration were predicted by an extended version of Grace and McLean's (2006) decision model. The extended decision model provided an overall better account of the results than a simple linear-operator model (Grace, 2002), and holds promise for an integrated account of choice in concurrent chains for both acquisition and steady-state conditions.