De Houwer, J., & Hughes, S. (2016). Evaluative conditioning as a symbolic phenomenon: On the relation between evaluative conditioning, evaluative conditioning via instructions, and persuasion. Social Cognition, 34, 480-494.
Evaluative conditioning (EC) is sometimes portrayed as a primitive way of changing attitudes
that is fundamentally different from persuasion via arguments. We provide a new perspective
on the nature of EC and its relation to persuasion by exploring the idea that stimulus pairings
can function as a symbol that conveys the nature of the relation between stimuli. We put
forward the concept of symbolic EC to refer to changes in liking that occur because stimulus
pairings function as symbols. The idea of symbolic EC is consistent with at least some current
theories of persuasion. It clarifies what EC research can add to the understanding of the origins
of our preferences and has implications for how (symbolic and non-symbolic) EC can be
established, the boundaries of EC research, and cognitive and functional models of EC.
Maes, E., Boddez, Y., Alfei, J. M., Krypotos, A. M., D’Hooge, R., De Houwer, J., & Beckers, T. (2016). The elusive nature of the blocking effect: 15 failures to replicate. Journal of Experimental Psychology: General, 145, e49-e71.
With the discovery of the blocking effect, learning theory took a huge leap forward, because
blocking provided a crucial clue that surprise is what drives learning. This in turn stimulated the
development of novel association-formation theories of learning. Eventually, the ability to explain
blocking became nothing short of a touchstone for the validity of any theory of learning, including
propositional and other non-associative theories. The abundance of publications reporting a
blocking effect and the importance attributed to it suggest that it is a robust phenomenon. Yet, in
the current paper we report fifteen failures to observe a blocking effect despite the use of
procedures that are highly similar or identical to those used in published studies. Those failures raise
doubts regarding the canonical nature of the blocking effect and call for a reevaluation of the central
status of blocking in theories of learning. They may also illustrate how publication bias influences
our perspective towards the robustness and reliablilty of seemingly established effects in the
Braem, S., Liefooghe, B., De Houwer, J., Brass, M., & Abrahamse, E. (2017). There are limits to the effects of task instructions: Making the automatic effects of task instructions context-specific takes practice. Journal of Experimental Psychology: Learning, Memory, & Cognition, 43, 394-403.
Unlike other animals, humans have the unique ability to share and use verbal instructions to prepare
for upcoming tasks. Recent research showed that instructions are sufficient for the automatic, reflexlike activation of responses. However, systematic studies into the limits of these automatic effects of
task instructions remain relatively scarce. In this study, we set out to investigate whether this
instruction-based automatic activation of responses can be context-dependent. Specifically,
participants performed a task of which the stimulus-response rules and context (location on the screen)
could either coincide or not with those of an instructed to-be-performed task (whose instructions
changed every run). In two experiments, we showed that the instructed task rules had an automatic
impact on performance – performance was slowed down when the merely instructed task rules did not
coincide, but, importantly, this effect was not context-dependent. Interestingly, a third and fourth
experiment suggests that context dependency can actually be observed, but only when practicing the
task in its appropriate context for over sixty trials or after a sufficient amount of practice on a fixed
context (the context was the same for all instructed tasks). Together, these findings seem to suggest
that instructions can establish stimulus-response representations that have a reflexive impact on
behavior, but are insensitive to the context in which the task is known to be valid. Instead, contextspecific task representations seem to require practice.
Standard dual process models in the action domain postulate that stimulus-driven
processes are responsible for suboptimal behavior because they take them to be rigid and
automatic and therefore the default. We propose an alternative dual process model in which
goal-directed processes are the default instead. We then transfer the dual process logic from
the action domain to the emotion domain. This reveals that emotional action tendencies are
often attributed to stimulus-driven processes. Our alternative model submits that emotional
action tendencies can also be caused by goal-directed processes. We evaluate the type of
empirical evidence required for validating our model and we consider implications of our
model for behavior change, encouraging strategies focused on the expectancies and values of
The ability to follow new instructions is crucial for acquiring behaviors and the cultural
transmission of performance-related knowledge. In this article, we discuss the observation
that successful instruction following seems to require both the capacity to understand verbal
information, but also the ability to transform this information into a procedural format. Here
we review the behavioural and neuroimaging literature on following new instructions and
discuss how it contributes to our understanding of the functional mechanisms underlying
instruction following. Based on this review, we distinguish three phases of instruction
following. In the instruction phase, the declarative information of the task instruction is
transformed into a task model consisting of a structured representation of the relevant
condition-action rules. In the implementation phase, elements of this task model are
transformed into a highly accessible state guiding behaviour. In the application phase, the
relevant condition-action rules are applied. We discuss the boundary conditions and capacity
limits of these phases, determine their neural correlates, and relate them to recent models
of working memory.
Hütter, M., & De Houwer, J. (2017). Examining the contributions of memory-dependent and memory-independent components to evaluative conditioning via instructions. Journal of Experimental Social Psychology, 71, 49-58.
We investigated whether instructions have the potential to generate memory-independent
attitude acquisition as indexed by a stochastic model of evaluative conditioning that distinguishes
between memory-dependent and memory-independent learning. For that purpose, we instructed
participants about pairings of conditioned and unconditioned stimuli without having participants
experience them. We obtained a significant contribution of memory-independent learning that
depended on whether instructions emphasized the importance of memorization at learning or the
importance of feelings at either learning or retrieval. Our findings call for caution when
interpreting the memory-independent contribution as an indicator of association formation on the
one hand and unaware learning on the other hand. Our research demonstrates the need to clearly
distinguish between processes operating at encoding and processes operating at retrieval in
empirical and theoretical research on evaluative conditioning.
Mertens, G., Van Dessel, P., & De Houwer, J. (2018). The contextual malleability of approach-avoidance training effects: Approaching or avoiding fear conditioned stimuli modulates effects of approach-avoidance training. Cognition & Emotion, 32, 341-349.
Previous research showed that the repeated approaching of one stimulus and avoiding of another
stimulus typically leads to more positive evaluations of the former stimuli. In the current study,
we examined whether approach and avoidance training (AAT) effects on evaluations of neutral
stimuli can be modulated by introducing a regularity between the approach-avoidance actions
and a positive or negative (feared) stimulus. In an AAT task, participants repeatedly approached
one neutral non-word and avoided another neutral non-word. Half of the participants also
approached a negative fear-conditioned stimulus (CS+) and avoided a conditioned safe stimulus
(CS-). The other half of the participants avoided the CS+ and approached the CS-. Whereas
participants in the avoid CS+ condition exhibited a typical AAT effect, participants in the
approach CS+ condition exhibited a reversed AAT effect (i.e., they evaluated the approached
neutral non-word as more negative than the avoided non-word). These findings provide evidence
for the malleability of the AAT effect when strongly valenced stimuli are approached or avoided.
We discuss the practical and theoretical implications of our findings.
Whereas it is widely recognized that both verbal threat information and stimulus pairings
can install strong and persistent fear, few studies have addressed the interaction between these
two pathways of fear. According to the expectancy bias of Davey (1992, 1997), verbal
information can install expectancy biases for aversive events that can result in facilitated fear
learning through stimulus pairings and can delay extinction of fear. However, these predictions
of the expectancy bias account have not been explored fully. Following up on two earlier studies
(Field & Storksen-Coulson, 2007; Ugland, Dyson, & Field, 2013), we investigated the impact of
prior threat information on fear acquisition, extinction and reinstatement. To this aim,
participants received instructions about four unfamiliar animals, two of which that were
described as dangerous whereas the other two were described as harmless. One animal of each
pair was subsequently paired with an electric stimulus. Our results indicated that threat
information resulted in stronger fear responses prior to fear conditioning and in delayed
extinction of fear. However, these effects of instructions were not very pronounced and not
found on all measures of fear. We discuss several methodological and procedural considerations
that may modulate the effects of (verbally installed) expectancy biases.
Maes, E., Vanderoost, E., D’Hooge, R., De Houwer, J., & Beckers, T. (2017). Individual difference factors in the learning and transfer of patterning discriminations. Frontiers in Psychology. 8:1262. doi: 10.3389/fpsyg.2017.01262
In an associative patterning task, some people seem to focus more on learning an
overarching rule, whereas others seem to focus on acquiring specific relations between the
stimuli and outcomes involved. Building on earlier work, we further investigated which
cognitive factors are involved in feature- versus rule-based learning and generalization. To this
end, we measured participants’ tendency to generalize according to the rule of opposites after
training on negative and positive patterning problems (i.e., A+/B+/AB- and C-/D-/CD+), their
tendency to attend to global aspects or local details of stimuli, their systemizing disposition and
their score on the Raven intelligence test. Our results suggest that while intelligence might have
some influence on patterning learning and generalization, visual processing style and
systemizing disposition do not. We discuss our findings in the light of previous observations
Maes, E., Krypotos, A. M., Boddez, Y., Alfei, J. M, D’Hooge, R., De Houwer, R., & Beckers, T. (in press). Failures to replicate blocking are surprising and informative – Reply to Soto (in press). Journal of Experimental Psychology: General.
The blocking effect has inspired numerous associative learning theories and is widely cited in
the literature. We recently reported a series of 15 experiments that failed to obtain a blocking effect
in rodents. Based on those consistent failures, we claimed that there is a lack of insight into the
boundary conditions for blocking. In his commentary, Soto (in press) argues that contemporary
associative learning theory does provide a specific boundary condition for the occurrence of blocking,
namely the use of same- versus different-modality stimuli. Given that in ten of our 15 experiments
same-modality stimuli were used, he claims that our failure to observe a blocking effect is
unsurprising. We cannot but disagree with that claim, because of theoretical, empirical, and
statistical problems with his analysis. We also address two other possible reasons for a lack of
blocking that are referred to in Soto’s (in press) analysis, related to generalization and salience, and
dissect the potential importance of both. While Soto’s (in press) analyses raises a number of
interesting points, we see more merit in an empirically guided analysis and call for empirical testing
of boundary conditions on blocking.
Unpronounceable strings of 4 consonants (conditioned stimuli: CSs) were consistently
followed by familiar words belonging to one of two opposed semantic categories
(unconditioned stimuli: USs). Conditioning, in the form of greater accuracy in rapidly
classifying USs into their categories, was found when visually imperceptible (to most
subjects) CSs occupied ≥ 58 ms of a 75-ms CS–US interval. When clearly visible CSs
were presented in a 375 ms CS–US interval, conditioning was strongly correlated with
measures of contingency awareness, and did not occur in the absence of that awareness.
These experiments delineated two forms of conditioning: Unconscious conditioning
occurred with a brief CS–US interval, with an effectively masked CS, and with no
reportable knowledge of the contingent CS–US relation. Conscious conditioning
occurred with a substantially longer CS–US interval, a perceptible CS, and with subjects’
reportable knowledge of the contingent CS–US relation.
De Houwer, J., Hughes, S., & Brass, M. (2017). Toward a unified framework for research on instructions and other messages: An introduction to the special section on the power of instructions. Neuroscience and Biobehavioral Reviews, 81, 1-3.
Instructions are known to have a profound impact on human behavior. Nevertheless, research
on the effects of instructions is relatively scarce and scattered across different areas of
research in psychology and neuroscience. The current issue of this journal contains six papers
that review research on instructions in different research areas. In this introduction to the
special section, we provide the outline of a framework that focuses on five components that
can be varied in research on this topic (sender, message, receiver, context, and outcome). The
framework brings order to the boundless potential variability in research on the effects of
messages (i.e., it has heuristic value) and highlights that past research explored only a tiny
fraction of what is possible (i.e., it has predictive value). Moreover, it reveals that research in
different areas tends to examine different instantiations of the five components. The latter
observation implies that much can be gained from closer interactions between researchers
from different areas.
Braem, S., De Houwer, J., Demanet, J, Yuen, K. S. L., Kalisch, R., & Brass, M. (2017). Pattern analyses reveal separate experience-based fear memories in the human right amygdala. Journal of Neuroscience, 37, 8116–8130.
Learning fear via the experience of contingencies between a conditioned stimulus (CS) and an
aversive unconditioned stimulus (US) is often assumed to be fundamentally different from
learning fear via instructions. An open question is whether fear-related brain areas respond
differently to experienced CS-US contingencies than to merely instructed CS-US contingencies.
Here, we contrasted two experimental conditions where subjects were instructed to expect the
same CS-US contingencies while only one condition was characterized by prior experience with
the CS-US contingency. Using multi-voxel pattern analysis of fMRI data, we found CS-related
neural activation patterns in the right amygdala (but not in other fear-related regions) that
dissociated between whether a CS-US contingency had been instructed and experienced versus
merely instructed. A second experiment further corroborated this finding by showing a
category-independent neural response to instructed and experienced, but not merely instructed,
CS presentations in the human right amygdala. Together, these findings are in line with
previous studies showing that verbal fear instructions have a strong impact on both brain and
behaviour. However, even in the face of fear instructions, the human right amygdala still shows
a separable neural pattern response to experience-based fear contingencies.
Van Dessel, P., De Houwer, J., Gast, A., & Smith, C.T. (2015). Instruction-based approach-avoidance effects: Changing stimulus evaluation via the mere instruction to approach or avoid stimuli. Experimental Psychology, 62, 161-169.
Prior research suggests that repeatedly approaching or avoiding a certain stimulus changes the
liking of this stimulus. We investigated whether these effects of approach and avoidance training occur also when participants do not perform these actions but are merely instructed about the stimulus–action contingencies. Stimulus evaluations were registered using both implicit (Implicit Association Test and evaluative priming) and explicit measures (valence ratings). Instruction- based approach-avoidance effects were observed for relatively neutral fictitious social groups (i.e., Niffites and Luupites), but not for clearly valenced well-known social groups (i.e., Blacks and Whites). We conclude that instructions to approach or avoid stimuli can provide sufficient bases for establishing both implicit and explicit evaluations of novel stimuli and discuss several possible reasons for why similar instruction-based approach-avoidance effects were not found for valenced well-known stimuli.
Maes, E., De Filippo, G., Inkster, A., Lea, S.E.G., De Houwer, J., D'Hooge, R., Beckers, T., Wills, A.J. (2015). Animal Cognition
Humans can spontaneously create rules that allow them to efficiently generalize what they have learned to novel situations. An enduring question is whether rule-based generalization is uniquely human or whether other animals can also abstract rules and apply them to novel situations. In recent years, there have been a number of high-profile claims that animals such as rats can learn rules. Most of those claims are quite weak because it is possible to demonstrate that simple associative systems (which do not learn rules) can account for the behavior in those tasks. Using a procedure that allows us to clearly distinguish feature-based from rule-based generalization (the Shanks-Darby procedure), we demonstrate that adult humans show rule-based generalization in this task, while generalization in rats and pigeons was based on featural overlap between stimuli. In brief, when learning that a stimulus made of two components (“AB”) predicts a different outcome than its elements (“A” and “B”), people spontaneously abstract an opposites rule and apply it to new stimuli (e.g. knowing that “C” and “D” predict one outcome, they will predict that “CD” predicts the opposite outcome). Rats and pigeons show the reverse behavior – they generalize what they have learned, but on the basis of similarity (e.g. “CD” is similar to “C” and “D”, so the same outcome is predicted for the compound stimulus as for the components). Genuinely rule-based behavior is observed in humans, but not in rats and pigeons, in the current procedure.