Jan De Houwer (Ghent University, Henri Dunantlaan 2, B-9000 Ghent, Belgium. E-mail:
Handling editor: Yoav Bar-Anan (Ben Gurion University, Beer-Sheva, Israel)
Although propositional models of associative learning are often referred to in the literature on evaluative conditioning (EC), it has not yet been clearly stipulated what propositional models of EC entail. The aim of this paper is to describe in more detail the assumptions of propositional models of EC. This includes a discussion of the core assumption that EC is mediated by propositions about stimulus relations, as well as assumptions about the processes via which those propositions are formed and influence liking. Based on this discussion, I put forward the Integrated Propositional Model that combines a number of these assumptions and discuss some of the predictions that can be derived from this model. The paper ends with a reflection on the limitations and strengths of propositional models of EC.
This article is part of SPB's special issue on “
More than 40 years after
While acknowledging that EC research would benefit from an increased focus on the practical use of EC, within the context of this special issue, the current paper focuses on ideas about the mechanisms that mediate EC. More specifically, I try to clarify some of the assumptions that propositional models make about the nature of those mechanisms. The propositional models that are typically referred to in the EC literature (e.g.,
I will not, however, put forward a formalized model that can easily be falsified. Although there are advantages to having falsifiable formalized models, at least in current psychology, such models tend to oversimplify inherently complex psychological phenomena. This often results in an emphasis on moderators that are important primarily because they have the potential to falsify models while ignoring other moderators simply because the models have little to say about them. Moreover, because formalized models often have a protective belt of parameters that can be adjusted to rescue the model in the face of falsification (
The class of propositional models of EC encompasses all current and future models that postulate that stimulus pairings can influence liking only after a proposition has been formed about the relation between the stimuli.
Propositions are fundamentally different from associations. Whereas propositions are defined in terms of their informational
Some have argued that because associative structures could
As I noted above, propositional models of EC are defined by the assumption that stimulus pairings result in a change in liking only if a proposition is formed about the relation between the stimuli. Different propositional models might, however, differ with regard to the assumptions they make about the way in which propositions are formed, the precise content of the mediating propositions, as well as the way in which propositions influence evaluative behavior. In this section, I discuss specific ideas that have been put forward about these additional components of propositional models.
First, just like other forms of problem solving, the formation of propositions about stimulus relations does not result from a mere passive registration of events in the world but from constructive processes that can deploy all the channels of information that organisms have at their disposal. This includes information that is available in memory, that is received from others via instructions, or that can be inferred from the observation of others or from directed interventions in the world. Hence, EC is not an inevitable consequence of stimulus pairings; it arises only when those pairings are mentally constructed in a specific manner. Moreover, because all of these channels produce propositional knowledge, information gained from different channels can easily be combined and used to infer new propositions.
Second, because problem solving is usually considered to be a non-automatic process, proponents of propositional models have typically also characterized the processes underlying proposition formation as non-automatic. More specifically, those processes are assumed to involve awareness (i.e., of the propositions that are produced)
Proponents of propositional models of EC have also said little about whether and how differences in relational content lead to differences in the magnitude and direction of the changes in liking. This seems to imply that, in principle, any proposition that relates a neutral stimulus to a valenced stimulus could result in a change in liking. In an earlier paper (
Inferential processes are processes via which propositions are derived or validated on the basis of other propositions. They can operate in non-automatic ways, that is, only when awareness, time, effort, and intention are involved and in ways that meet rational normative standards as put forward by philosophers. It might well be that some instances of EC involve non-automatic inferential processes that lead to normatively correct conclusions. However, even non-automatic inferential processes can lead to irrational conclusions and thus irrational behavior (e.g., when starting from incorrect premises or following normatively incorrect inference rules). Moreover, it is important to realize that inferential processes can also operate automatically to some degree. In fact, predictive coding models of human cognition (e.g.,
It is important to realize that propositions might also be operated upon by similarity-based retrieval mechanisms. This possibility is often ignored because of a tendency to confound operating principles and mental representations (see
Note, however, that episodic memory models currently do not take into account the impact of (automatic and non-automatic) inferential processes on EC and are therefore unlikely to capture the full complexity of the mechanisms underlying EC. Also note that allowing for similarity-based retrieval leaves open the question of which propositions can influence liking via
One might argue that permitting similarity-based retrieval of propositions is undesirable for several reasons. First, it renders the class of propositional models virtually immune to falsification. In fact, a propositional model in which changes in liking can result from both (automatic) inferential processes and direct effects of similarity-based retrieval is effectively a dual-process model in that it incorporates two mechanisms via which propositions can lead to EC effects. It thus falls prey to the same criticisms that have been directed at dual-process models in general (e.g., the fact that these models often lack clear assumptions about how the various processes interact;
In response to these concerns, it is important to point out that they relate only to propositional models that allow for direct effects of similarity-based retrieval of propositions. Propositional models that postulate only indirect effects of similarity-based retrieval would not qualify as dual-process retrieval models in the strict sense (i.e., all instances of EC would be mediated by inferential processes) and would be as fundamentally different from associative models than propositional models that do not incorporate similarity-based retrieval. In fact, for reasons of parsimony, there is merit in seeing how far one can get with single-process inferential models of EC according to which propositions about stimulus relations can influence liking only via inferential processes (e.g., a variant of the model put forward by
Nevertheless, there is little point in dismissing offhand the possibility of direct effects of similarity-based retrieval of propositions simply because it makes it more difficult to falsify or differentiate between theoretical models. As noted in the introduction, there are downsides to focusing too much on falsification. Instead, theoretical models can be thought of as tools that help organize existing knowledge about the moderators of phenomena (heuristic value) and discover new moderators (predictive value) with the aim of increasing our capacity to influence those phenomena and the real life behaviors that are instances of those phenomena. There is merit in acknowledging that EC might be mediated by both inferential and similarity-based retrieval processes because it raises interesting new questions about the conditions under which both types of processes result in EC effects. Even propositional models that allow for both these processes would still differ from associative models in so many ways (e.g., the non-automatic formation of propositions, the impact or relational content, instances of EC that are mediated by inferential processes) that there is enough fuel left to continue the debate between both types of models.
Based on the considerations that were discussed above, it is possible to assemble one version of a propositional model of EC that I will refer to as the Integrated Propositional Model (IPM). It incorporates many of the ideas that were put forward in the first part of this paper and in earlier papers (e.g.,
The Integrated Propositional Model. Pairings, instructions given by others, the observation of others, and the outcome of interventions in the world by the organism (jointly) lead to the formation of propositions about stimulus relations in working memory. New propositions can also be inferred from other currently entertained propositions (large grey arrow) as well as propositions that are retrieved from memory via automatic or non-automatic retrieval processes. Propositions are automatically stored in memory as episodic memory traces, although non-automatic processes such as rehearsal and elaboration can also influence memory storage. Evaluative propositions (propositions about evaluative stimulus properties) that are entertained in working memory can influence liking via both automatic and non-automatic processes.
Although it is impossible to discuss all details of the model within the confines of this article (see
It is important to note, however, that the IPM and other propositional models are not necessarily contradicted by a lack of impact of relational information (e.g., a less than maximal impact of the instruction that stimuli are antonyms;
Regarding the first prediction, it has now been established that mere instructions about stimulus pairings (e.g., “A will be paired with B”) do indeed result in changes in liking (e.g.,
With regard to the third prediction (interactions between different sources of information), research on the impact of verbal relational information on EC (e.g.,
Based on the latter two assumptions, the IPM predicts that stimulus pairings, instructions about stimulus pairings, and instructions about evaluative stimulus properties can influence implicit evaluations. It also allows the IPM to account for instances of EC in which participants no longer consciously remember propositions about stimulus pairings and, relatedly, memory-independent EC effects as captured by multinomial processing tree models (see
Despite my efforts to clarify some of the assumptions of propositional models of EC in general and the IPM specifically, it will remain difficult if not impossible to refute these models. Consider the core assumption that EC is mediated by the formation of propositions about stimulus relations. It is likely that any empirical finding that questions this core assumption can be accommodated by adding or changing assumptions about the content of the mediating propositions or the processes that create and operate on those representations (
Despite their proven predictive value, the capacity of propositional models to specify exact predictions is still constrained by a lack of detail. Without specific assumptions about how propositions are formed, the variables that determine the relational content of the propositions, the link between relational content and changes in liking, the nature of inferential and similarity-based retrieval processes, and the interactions between these factors, it will remain difficult to generate specific predictions for specific situations. Having said this, the current lack of detail is understandable in light of the complexity and multitude of the processes that, according to propositional models, are involved in EC. A fully detailed propositional model of EC would encompass a detailed model of problem solving, attribution, relational processing, memory retrieval, inferences, and liking. In other words, it would require an almost perfect understanding of human cognition and behavior.
The preparation of this paper was made possible by Methusalem Grant BOF16/MET_V/002 of Ghent University.
The author has declared that no competing interests exist.
I thank Sean Hughes, Pieter Van Dessel, Olivier Corneille, and an anonymous reviewer for their helpful comments on earlier drafts of this paper.
In principle, it is also possible that the pairing of a neutral and a valenced stimulus leads to a proposition about the relation between the neutral stimulus and the evaluative response to the valenced stimulus (e.g., “when I see this stimulus, I always get a bad feeling”; see Gast & Rothermund, 2011). That is, the propositions that mediate EC might also involve information about evaluative responses. For reasons of simplicity, in this paper, I consider only propositions about stimulus relations. First, conceptually, it is sometimes difficult to make a distinction between what is a stimulus and what is a response. Second, theoretically, the assumptions and predictions of propositional models are most often unaffected by whether the mediating propositions involve information about evaluative responses.
Although these types of associative network theories of propositional learning can have the benefit of being more formalized, they have the downside of being committed to a particular representational structure. Propositional models that are not committed to a representational structure have more degrees of freedom and thus have more flexibility and scope. Still, it seems easier to reach agreement about representational content and about the environmental events that influence this content than agreement on the representational structures in which this content is embedded (De Houwer & Moors, 2015). Too much focus on representational structure could thus be counterproductive.
There is no reason to assume that the formation of propositions about stimulus relations requires awareness of the processes by which propositions are formed but one could argue that it requires awareness of the input (i.e., the stimuli that are paired) and the output of those processes (i.e., a proposition about how the stimuli are related).
Some might argue that automatic instances of problem solving (and EC) are mediated by associative processes. Although it is difficult to exclude this possibility on an a priori basis, others have convincingly argued that automatic problem solving relies on automatic inferences that are performed on propositional representations (e.g., Sanborn & Chater, 2016).
An anonymous reviewer noted that predictive coding models are closely related to associative models in which the formation of associations depends on prediction error (e.g., Rescorla & Wagner, 1972). However, this does not exclude the idea that predictive coding (and EC) can involve automatic inferences. Moreover, it has been argued that so-called “associative” prediction error models are nothing more than mathematical formalizations of inferential propositional processes that are not inherently associative in nature (i.e., they are situated at Marr’s computational level rather than an algorithmic level of explanation; see Cheng, 1997, p. 370) or even incompatible with the spirit of associative models (Jozefowiez, in press).
It would be interesting to compare the automaticity features of the problem solving processes via which propositions about novel stimulus relations are formed and the inferential processes via which those propositions influence evaluative responses and other behavior. It is likely that these processes have much in common. In fact, problem solving might necessarily involve inferences. Nevertheless, to avoid chaotic behavior, it could be advantageous for living organisms to put more restrictions on the detection of novel spatio-temporal relations (of which there are an infinite number in the environment) than on the combination of already available knowledge (which concerns only a subset of all information in the environment) especially when taking into account that inferential reasoning during retrieval can easily be shaped via reinforcement. This is why I tend to emphasize the non-automaticity of the formation of propositions about stimulus relations and the automaticity of inferential retrieval processes via which already available propositions influence liking and other behavior, being well aware of the fact that all processes possess a mix of features of (non-)automaticity that can vary over contexts (see Moors, 2016, for more details). Most importantly, I assume that, whereas the formation of a proposition requires awareness of its content, the retrieval of a proposition could well be achieved and influence liking in the absence of awareness of its content.
The Associative and Propositional Evaluation (APE) model of Gawronski and Bodenhausen (2006) is built on the distinction between two operating principles: similarity based-retrieval and validation. Although Gawronski and Bodenhausen correctly state that validation requires propositional representations, they incorrectly assume that similarity-based retrieval requires associative representations. This incorrect assumption is probably based on the idea that (1) similarity-based retrieval can be realized only via spreading of activation and (2) spreading of activation requires associative representations. If one allows for the possibility that similarity-based retrieval can also involve propositional representations, however, there is little reason left to insist on the presence of associative representations next to propositional representations within the APE model.
This is a revision of the model that I presented at the EC expert meeting in Ghent (Belgium) on 20 December 2010.
As noted above, other propositional models might allow for direct effects of propositions about stimulus relations (i.e., without requiring inferential processes via which evaluative propositions are formed). The IPM does not allow this route for reasons of parsimony. If it had permitted this route, additional assumptions would have been needed about when which route operates (see De Houwer, 2014b, for similar arguments in favor of single-learning-process propositional models as compared to dual-learning-process models). Unlike other models (e.g., Van Dessel et al., in press), the IPM does permit an impact of evaluative propositions on evaluative responses that are not based on inferences. This choice is based on the idea that one would need to stretch the concept of an inference in order to conceive of ways in which concrete evaluative responses can be inferred from evaluative propositions. For instance, it is difficult to see how increased activity of the corrugator muscle can be inferred from the proposition that something is bad in our definition of an inference as the process of reaching a conclusion on the basis of premises. One could, however, define an inference more broadly, as the probabilistic activation (or prediction) of information on the basis of other information (Van Dessel et al., in press), such that muscle activity might be seen as an (active) inference on the basis of prior information about one’s typical response to negative stimuli (see also Friston, 2010). I believe, however, that the question of how mental representations influence behavior is a complex one that is currently not addressed in a satisfactory manner by either propositional or associative models (see Bouton, 2016, pp. 187-190). Although the choices made in the IPM can thus be justified, I put more value in highlighting theoretical questions as potentially interesting than in opting on an a priori basis for one answer to those questions. Whereas the latter might promote falsification, the former is more likely to facilitate progress in understanding psychological phenomena.
The conclusion that EC depends on all these processes might be disconcerting for those who hoped to find a simple, non-cognitive learning mechanism underlying EC. They might even wonder whether there is any reason for focusing on EC if the processes underlying it are essentially the same as those involved in other well-known phenomena such as persuasion. For me, the true merit of EC research lies in the unique source of liking that it focuses on: spatio-temporal pairings of events. Although the mechanisms via which pairings and persuasive messages influence liking might be fundamentally the same, the difference in the events that set these mechanisms in motion could have important theoretical and practical implications (see De Houwer & Hughes, 2016, for a more detailed discussion). To further our understanding of how our likes and dislikes come about, these complexities should be embraced rather than discounted.