Occasion Setting

Serial compounds such as that shown in Table 6.9 (Tone Clicks Food) can lead to a type of learning that seems to have unique properties. When a short Click stimulus is followed by Food if preceded by a long, diffuse Tone, but not if presented by itself (Click-only), the Tone facilitates responding to the Click. In this case, the Tone is called an occasion setter because it sets the occasion for responding to the Click (Fraser & Holland, 2019). Three properties of such response facilitation are highlighted here: (1) the occasion setter fails to control behavior on its own; (2) occasion setters continue to facilitate responding to another CS even after extensive nonreinforced presentations—they are insensitive to extinction treatments; and (3) response facilitation transfers to other CSs trained with other occasion setters. Let’s consider these properties.

Pigeons do not peck at or show specific behavioral changes to diffuse stimuli, but diffuse stimuli can become occasion setters. In one experiment (Rescorla, 1985), pigeons pecked at a localized key Light that signaled Food when preceded by a diffuse Tone (Tone^Light^Food), but not when the same Light was presented by itself (Light-only). There was no responding to the Tone alone. Moreover, the occasion-setting ability of the Tone was not disrupted whether the Tone was previously paired with Food or with the absence of Food. In fact, previous Tone^Food pairings did not transform the Tone more easily into an occasion setter. These results suggest that Pavlovian conditioning and occasion setting are dissociable properties of signals.

The second property was also tested with pigeons. After the training described earlier, the Tone was repeatedly presented alone (an extinction procedure). In a subsequent test, the Tone retained its ability to facilitate responding to the Light (Rescorla, 1986). The occasion-setting function appears to be intact after various conditioning treatments of the diffuse stimulus.

The third property, transfer, was examined in an experiment in which rats received concurrent training with the following trials (Holland, 1995). One serial compound involved the presentation of a Clicker followed by a Door Light terminating with Food delivery (C"^DL-^F), whereas a second serial compound involved a Panel Light followed by a Tone terminating with Food delivery (PL^T^F). There were also DL-only and T-only trials designed to establish C and PL as occasion setters. The two lights (DL and PL) were lights placed in different locations. The first stimulus in the serial compound was the occasion setter (C and PL), whereas the second stimulus was the CS (DL and T). Finally, animals also received trials with Noise followed by Food in half of the trials and by itself in the other half

(N"^F, N-only); this CS was not preceded by any specific stimulus, but it was reinforced just as frequently as the other CSs (DL and T).

The results showed that the occasion setters facilitated responding to their respective training CS (C^DL, PL-^T), and also to the CS trained in the other serial compound (C~^T, PL-^DL). However, the occasion setters failed to facilitate responding to the Noise, which had not been trained as part of a serial compound. Thus, occasion setters can facilitate responding to other CSs provided they have also been trained as part of a serial compound.

These properties of occasion setting attracted attention because they seem to contrast with those of typical CSs. Rather than eliciting or provoking responses directly, as done by typical associative signals, occasion setters seem to modulate responding to other stimuli. Modulation implies that the occasion setter controls the validity of the entire CS^US association in a hierarchical manner, rather than exerting control over one element of the association, either the CS or US.

What is the relevance of occasion setting to understanding animal behavior? Active animals are exposed to changing situations containing a degree of ambiguity. For example, a signal for food may be approached in a relatively safe location, but not when there are also signs that the reward would be absent or predators may be nearby. Contextual cues acting as occasion setters may disambiguate these two situations, cueing signal approach in one case but signal avoidance in the other. Moreover, “context” may refer to external stimuli characterizing a location or to internal states arising from motivational, emotional, or even circadian changes that have stimulus properties. An interesting example of an internal context is provided by the aftereffects of drugs (Palmatier & Bevins, 2008). For example, rats treated with Nicotine received training in which a Noise was paired to Sucrose (Nic^N^S), whereas the same rats treated with CDP (chlordiazepoxide, an anxiolytic drug) were exposed to pairings between a Light and Sucrose (CDP-^L-^S). When a placebo was administered instead, then N-only and L-only were the outcomes. For these animals, the internal states induced by Nicotine and CDP facilitated responding to the Noise and Light CSs, but their facilitatory effect transferred across discriminations (e.g., Nicotine also facilitated responding to the Light CS, while CDP did the same to the Noise CS). Importantly, none of the two CSs, Noise and Light, controlled responding when presented alone. It makes intuitive sense that occasion setters facilitate responding for various signals of the same reward.