DOCUMENTS

Mertens, G., & De Houwer, J. (2016). Potentiation of the startle reflex is in line with contingency reversal instructions rather than the conditioning history. Biological Psychology, 113, 91-99.

In the context of fear conditioning, different psychophysiological measures have been related to different learning processes. Specifically, skin conductance responses (SCRs) have been related to cognitive expectancy learning, while fear potentiated startle (FPS) has been proposed to reflect affective learning that operates according to simple associative learning principles. On the basis of this two level account of fear conditioning we predicted that FPS should be less affected by verbal instructions and more affected by direct experience than SCRs. We tested this hypothesis by informing participants that contingencies would be reversed after a differential conditioning phase. Our results indicate that contingency reversal instructions led to an immediate and complete reversal of FPS regardless of the previous conditioning history. This change was accompanied by similar changes on US expectancy ratings and SCRs. These results conform with an expectancy model of fear conditioning but argue against a two level account of fear conditioning.

Mertens, G., & De Houwer, J. (2016). The impact of a context switch and context instructions on the return of verbally conditioned fear. Journal of Behavior Therapy and Experimental Psychiatry, 51, 10-18.

Background and Objectives: Repeated exposure to a conditioned stimulus can lead to a reduction of conditioned fear responses towards this stimulus (i.e., extinction). However, this reduction is often fragile and sensitive to contextual changes. In the current study, we investigated whether extinction of fear responses established through verbal threat instructions is also sensitive to contextual changes. We additionally examined whether verbal instructions can strengthen the effects of a context change.
Methods: Fifty-two participants were informed that one colored rectangle would be predictive of an electrocutaneous stimulus, while another colored rectangle was instructed to be safe. Half of these participants were additionally informed that this contingency would only hold when the background of the computer screen had a particular color but not when it had another color. After these instructions, the participants went through an unannounced extinction phase that was followed by a context switch.
Results: Results indicate that extinguished verbally conditioned fear responses can return after a context switch, although only as indexed by self-reported expectancy ratings. This effect was stronger when participants were told that CS-US contingency would depend on the background color, in which case a return of fear was also observed on physiological measures of fear.
Limitations: Extinction was not very pronounced in this study, possibly limiting the extent to which return of fear could be observed on physiological measures.
Conclusions: Contextual cues can impact the return of fear established via verbal instructions. Verbal instructions can further strengthen the contextual control of fear.

Mertens, G., Raes, A. K., & De Houwer, J. (In press). Can prepared fear conditioning result from verbal instructions? Learning and Motivation.

Evolutionary fear-relevant stimuli such as snakes or spiders are thought to be prepared to elicit fear reactions. This implies that the acquisition of conditioned fear responses is facilitated when these stimuli serve as conditioned stimuli (CSs). Moreover, extinction of conditioned fear responses is delayed when CSs are prepared stimuli. The research presented in this article addresses the question whether such selective learning effects can be obtained even when participants do not experience pairings of CSs and US but receive only instructions about those pairings. Two experiments were conducted in which participants were verbally informed about the relationship between fear-relevant and fear-irrelevant CSs and the presence of an electrical stimulus (US). However, CSs were never actually paired with the US. US expectancy ratings and skin conductance responses were recorded during multiple CS only trials. In the first experiment, we observed acquisition, extinction and reinstatement of fear on the basis of instructions, but these effects were not modulated by the fear-relevance of the CSs. In the second experiment, we manipulated whether participants actually experienced the CS-US contingencies or were merely instructed. We obtained facilitated acquisition for the merely instructed fear-relevant CS+. We discuss these results in relation to the evolutionary fear learning model of Öhman and Mineka (2001) and the expectancy bias model of Davey (1992).

Schmidt, J. R., & De Houwer, J. (in press). Contingency learning tracks with stimulus-response proportion: No evidence of misprediction costs. Experimental Psychology.

We investigate the processes involved in human contingency learning using the colour-word contingency learning paradigm. In this task, participants respond to the print colour of neutral words. Each word is most often presented in one colour. Results show that participants respond faster and more accurately to words presented in their expected colour. In Experiment 1, we observed better performance for high relative to medium frequency word-colour pairs, and for medium relative to low frequency pairs. Within the medium frequency condition, it did not matter whether the word was predictive of a currently-unpresented colour, or the colour of a currently-unpresented word. We conclude that a given word facilitates each potential response proportional to how often they co-occurred. In contrast, there was no evidence for costs associated with violations of high-frequency expectancies. Experiment 2 further introduced a novel word baseline condition but also did not provide evidence for competition between retrieved responses.

Van Dessel, P., De Houwer, J., Gast, A., Smith, C. T., & De Schryver, M. (2016). Instructing implicit processes: When instructions to approach or avoid influence implicit but not explicit evaluation. Journal of Experimental Social Psychology, 63, 1-9.

Previous research has shown that linking approach or avoidance actions to novel stimuli through
mere instructions causes changes in the implicit evaluation of these stimuli even when the actions
are never performed. In two high-powered experiments (total N = 1147), we examined whether
effects of approach-avoidance instructions on implicit evaluations are mediated by changes in
explicit evaluations. Participants first received information about the evaluative properties of two
fictitious social groups (e.g., Niffites are good; Luupites are bad) and then received instructions to
approach one group and avoid the other group. We observed an effect of approach-avoidance
instructions on implicit but not explicit evaluations of the groups, even when these instructions
were incompatible with the previously obtained evaluative information. These results indicate
that approach-avoidance instructions allow for unintentional changes in implicit evaluations. We
discuss implications for current theories of implicit evaluation.

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.

Muhle-Karbe, P.S., Duncan, J., De Baene, W., Mitchell, D.J., & Brass, M. (2016). Neural Coding for Instruction-Based Task Sets in Human Frontoparietal and Visual Cortex. Cerebral Cortex.


Task preparation has traditionally been thought to rely upon persistent representations of instructions that permit their execution after delays. Accumulating evidence suggests, however, that accurate retention of task knowledge can be insufficient for successful performance. Here, we hypothesized that instructed facts would be organized into a task set; a temporary coding scheme that proactively tunes sensorimotor pathways according to instructions to enable highly efficient “reflex-like” performance. We devised a paradigm requiring either implementation or memorization of novel stimulus–response mapping instructions, and used multivoxel pattern analysis of neuroimaging data to compare neural coding of instructions during the pretarget phase. Although participants could retain instructions under both demands, we observed striking differences in their representation. To-be-memorized instructions could only be decoded from mid-occipital and posterior parietal cortices, consistent with previous work on visual short-term memory storage. In contrast, to-be-implemented instructions could also be decoded from frontoparietal “multiple-demand” regions, and dedicated visual areas, implicated in processing instructed stimuli. Neural specificity in the latter moreover correlated with performance speed only when instructions were prepared, likely reflecting the preconfiguration of instructed decision circuits. Together, these data illuminate how the brain proactively optimizes performance, and help dissociate neural mechanisms supporting task control and short-term memory storage.

Teuchies, M., Demanet, J., Sidarus, N., Haggard, P., Stevens, M. A., & Brass, M. (2016). Influences of Unconscious Priming on Voluntary actions: role of the Rostral Cingulate Zone. Neuroimage, 135, 243–252.


The ability to make voluntary, free choices is fundamental to what it means to be human. A key brain region that is involved in free choices is the rostral cingulate zone (RCZ), which is part of the medial frontal cortex. Previous research has shown that activity in this brain region can be modulated by bottom-up information while making free choices. The current study extends those findings, and shows, for the first time, that activation in the RCZ can also be modulated by subliminal information. We used a subliminal response priming paradigm to bias free and cued choices. We observed more activation in the RCZ when participants made a choice that went against the prime’s suggestion, compared to when they chose according to the prime. This shows that the RCZ plays an important role in overcoming externally-triggered conflict between different response options, even when the stimuli triggering this conflict are not consciously perceived. Our results suggest that an important mechanism of endogenous action in the RCZ may therefore involve exerting an internally-generated action choice against conflicting influences, such as external sensory evidence. We further found that subliminal information also modulated activity in the anterior insula and the supramarginal gyrus.

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.

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.

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.

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.

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.

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
on patterning.