Temporal distributions of schedule-induced licks, magazine entries, and lever presses on fixed- and variable-time schedules.

Abstract

In this article, schedule-induced drinking (SID) refers to increased drinking by hungry rats exposed to intermittent delivery of food pellets. Two major accounts of SID differ in their explanation of why such drinking tends be concentrated soon after pellet delivery. Temporal discrimination theories propose that drinking is a form of displacement activity that occurs when a pellet is least likely. Adventitious reinforcement theories propose that drinking is displaced to early in an interpellet interval (IPI) by magazine-directed behavior that occurs toward the end of an IPI. The main aim of this study was to examine the latter response-competition account by recording distributions of both licking and magazine entries as SID developed when pellets were delivered to different groups either on a fixed-time (FT 30 s) or on a variable-time schedule (VT 30 s), as in Experiment 1. Although VT 30-s schedules produced essentially flat distributions of magazine entries, licking still tended to be concentrated early in an IPI. Furthermore, there was no indication (Experiments 1 and 2) that magazine entry distributions developed ahead of licking distributions. Experiment 3 examined distributions of lever presses instead of licks: Initially high rates of lever pressing declined both with response-independent schedules (FT and VT) and when a minimal response-dependency was introduced (recycling conjunctive schedule), yet this response also tended to be most frequent soon after pellet delivery. Overall, the data were generally consistent with temporal conditioning theories.

Reinforcement of schedule-induced drinking in rats by lick-contingent shortening of food delivery

“…The first peak is not very interesting from the point of view of the learning mechanisms involved, but the second peak is (see Boakes, Patterson, Kendig, & Harris, 2015, for similar results with constant FT 30-s schedules), as it can be presumed to compete with drinking (e.g., Aristizabal, Callejas-Aguilera, Ogallar, Pellón, & Rosas, 2015;but see below). Competition between licking a waterspout and magazine entering is a normal finding in temporal schedules (e.g., Reid & Dale, 1983), as well as for other operant responses (Dragoi & Staddon, 1999), and in the present results, it can be seen how distributions of licking (see Fig.…”

“…However, the 50 % contingency group was the one that showed the highest level of magazine entries, more than the 0 % contingency rats; thus, the order in which animals engaged in licking cannot be attributed solely to competition from magazine entries (despite the master rats showing the highest licking and the lowest entries; see also Boakes et al, 2015). In general, during Phase 1, licks increased as sessions progressed but magazine entries did not decrease (see the lack of an effect of sessions for magazine entries in the Results section; see also Kirkpatrick & Church, 2003).…”

Does learning history shape the associability of outcomes? Further tests of the outcome predictability effect

“…Consistent with magazine training experiments [e.g. 38,39], we compared this response rate during the presentation of a cue with the response rate immediately before its presentation. The final dependent variable used in the statistical analyses was the proportion of time participants spent looking at the correct goal area during the cue presentation before outcome onset (cue interval) minus the gaze time at the same goal area during an equally long interval before cue onset (pre-cue interval).…”

Responses compete and collaborate, shaping each others’ distributions: Commentary on Boakes, Patterson, Kendig, and Harris (2015).

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Boakes, Patterson, Kendig, and Harris (2015) showed that schedule-induced drinking (SID), typically concentrated in the first half of the interpellet interval, is not moved there exclusively by competition from magazine entries, and that not all arbitrary responses can be maintained by adventitious reinforcement. They attribute such inferences to Killeen and Pellón (2013) and Patterson and Boakes (2012), and on that basis reject their explanation for the excessive nature of many adjunctive responses as a result of reinforcement.

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