Bringing the past into the present: Control by exteroceptive stimuli and key-peck location in a concurrent-chains procedure

Highlights

• We investigated how temporal separation between stimuli and outcomes affects stimulus control.

• Pigeons responded for differentially signaled, delayed outcomes in a concurrent-chains procedure.

• Behavior was controlled by the signals, and by key-peck location.

• Signal control was stronger when the signals remained present until the outcome.

• Interoceptive cues such as key-peck location may help bridge the gap between stimuli and future outcomes.

Abstract

We recently found that initial-link stimuli signaling trial outcomes (signals) in a concurrent-chains procedure exerted imperfect control during initial and terminal links. Here, we conducted a follow-up experiment to investigate further such imperfect control. Five pigeons worked on a concurrent-chains procedure in which one alternative led to a terminal link ending in a smaller-sooner reinforcer delivery, and the other in a larger-later reinforcer. During initial links of some trials, compound stimuli (signals) signaled the trial outcome. We assessed control by signal dimensions in Conflicting trials, in which the dimensions signaled conflicting outcomes. Unlike our previous experiment, signals remained present during terminal links. During initial links, preference favored the signaled key in Signaled trials, and the key signaled by the dimension exerting stronger control in Conflicting trials, suggesting strong signal control. Initial-link choice also depended on trial outcomes; preference was overall biased towards the smaller-sooner key. Terminal-link responding was primarily controlled by the key peck producing terminal-link entry, although some weak signal control was also evident. Thus, signal control during initial and terminal links was enhanced, and control by key-peck location during terminal links persisted, when signals remained present during terminal links. This suggests that our previous findings were partly related to temporal separation between signals and trial outcomes, and to history effects producing strong control by key-peck location.

Introduction

Behavior depends not only on discriminative stimuli in the present, but also on stimuli that occurred in the recent past (e.g., Cowie et al., 2017, Cowie et al., 2020). Control by past stimuli may be adaptive, as when a previously presented stimulus signals the likely location of future reinforcers (e.g., Cowie et al., 2017; Santos et al., 2019), or may impede discriminative performance, as when control by past, now-irrelevant, stimuli compete with control by more recent, relevant stimuli (e.g., Cowie et al., 2017; Edhouse and White, 1988; Gomes-Ng et al., 2018).

Past stimuli control present behavior to the extent that a specific stimulus occurrence can be remembered by the organism – an ability that depends on the organism’s memory systems (e.g., Lind et al., 2015) and on stimulus characteristics. Some reliable stimuli that are separated in time from an outcome fail to exert complete control over behavior (e.g., Cowie et al., 2017, Cowie et al., 2020), while others exert enduring control (Cowie et al., 2020, Gomes-Ng et al., 2019a, Urcuioli, 1984, Urcuioli, 1985, Weaver et al., 1999). This difference may lie in a stimulus’ ability to create the occasion for other cues that ‘bridge the gap’ between the stimulus and reinforcer delivery. For example, when there is a delay between a stimulus and subsequent discrimination (as in delayed matching-to-sample), differential sample behavior (e.g., body positioning) may exert control, sometimes even overshadowing control by the discriminative stimulus itself (e.g., Gomes-Ng et al., 2019a; Urcuioli, 1984, Urcuioli, 1985; Urcuioli and Honig, 1980; Weaver et al., 1999).

Cowie et al. (2020) recently showed that control by pigeons’ key-peck location overshadowed control by past discriminative stimuli in a concurrent-chains procedure in which one alternative led to a terminal link ending in a smaller reinforcer delivered after an 8-s delay, and the other to a link ending in a larger reinforcer after a 48-s delay. In some trials, color-alternating stimuli (hereafter, termed signals) during initial links differentially signaled the trial outcome, or conflicting outcomes (i.e., smaller-sooner and larger-later). During initial links, the signaled key was never chosen exclusively, indicating imperfect signal control, and subjects were biased towards the smaller-sooner alternative, indicating outcome control (i.e., control by the outcomes of each alternative). In terminal links, response patterns were similar in Signaled and Unsignaled trials. This suggests that responding was controlled by the key peck producing terminal-link entry, as opposed to the signals. Such key-peck control was also evident in Conflicting trials.

Why did control by key-peck location overshadow signal control in Cowie et al. (2020)? One possibility is that signals exerted weak control because they were temporally separated from trial outcomes. Although key-peck location was also separated from trial outcomes, enduring differences in body positioning during terminal links may have bridged the temporal gap, resulting in key-peck control. Presently, it is unclear to what extent the temporal separation of signals from trial outcomes contributed to Cowie et al.’s findings. Would control by signals have been stronger, and control by trial outcomes and key-peck location weaker, if signals were temporally closer to trial outcomes? The present experiment addressed this question. We replicated Cowie et al.’s experiment, except that signals remained present during terminal links, thus removing the temporal separation between signals and trial outcomes. If Cowie et al.’s results were caused by the transience of the signals, then control by such signals should be stronger in this experiment. In contrast, if Cowie et al.’s results were related to some other factor, such as outcome control, then they should be largely replicated here.