Outlook for Future Research

The present thesis not only provides novel insights into controlled feedback processing and its relation automatic feedback processing, it can also prove to be inspiring for future studies. Two lines of research seem to be of particular interest, namely, research on the top-down modulation of reinforcement learning and the FRN, and research testing predictions derived from the information theory account of the feedback-P300.

As mentioned before, the dual-process account of feedback processing fits nicely to recent learning and decision models (Collins & Frank, 2012; Frank & Claus, 2006) and to research investigating the effect of instructions on learning (Doll et al., 2011; Doll et al., 2009; Walsh & Anderson, 2011). Study 2, and particularly Study 3, implicate that

reinforcement learning can be biased by top-down processes. Not only should these results generalize to established reinforcement learning paradigms (e.g., the time estimation task), but they also suggest that other kinds of additional information than feedback validity and feedback reliability should result in top-down modulation of the FRN effect and the feedback-P300. For instance, the presence of monetary incentives, which are known to affect attentional effort (Hübner & Schlösser, 2010; Sarter, Gehring, & Kozak, 2006), could lead to top-down

21 As anecdotal evidence, several participants in Studies 2 and 3 indeed reported that they often recalled which Chinese character they had chosen, but were unable to remember whether this choice had been correct or incorrect. Under these circumstances, they resorted to repeating their choice.

biases on reinforcement learning. More specifically, informing participants on certain trials that successful learning of the correct choice for the subsequent pair of stimuli will result in a larger-than-average monetary win (or that an error will result in a greater loss) should lead to improved performance, a more pronounced feedback-P300 amplitude, and possibly an increased FRN effect.

Furthermore, feedback processing should be influenced by prior information, but also by information that is provided alongside the feedback stimulus itself. As an example, akin to a person expressing uncertainty while providing feedback (“That’s right… I guess.”), a feedback stimulus that includes information about the likelihood of valid feedback (e.g., a pale red stimulus could not only indicate that the response was incorrect, but also that this information might be false) might result in a reduced FRN effect compared to certain feedback, replicating the interaction found in Study 3.

Even more, the feedback-P300 should also be reduced after uncertain feedback reflecting the fact that it is subjectively²² less informative than feedback expressed with certainty. Thus, such an experiment could not only contribute to the understanding of top-down process in feedback processing, but also help to test predictions derived from the information theory of the P300 (Johnson Jr., 1984, 1988a). As discussed before, the assumption that the feedback-P300 reflects the accumulation of evidence, i.e., information that the previous response was correct, is motivated by this theory and prior research on the Pe (Steinhauser & Yeung, 2010), and was used to explain the effect of feedback valence on the feedback-P300 in Study 2. Considering the lack of a comprehensive theory of the feedback-P300 warrants further experiments aimed at testing this theory. Furthermore, the connection to information theory (Shannon, 1948) could allow for a quantification of transmitted information and thus the feedback-P300 amplitude, which is not possible with current theories. More precisely, feedback information R can be considered as the reduction of uncertainty H, with

R = Hbefore − Hafter, and

H = log (M),

22 Because participants have to give a response in the test phase and cannot recruit additional information about the correct stimulus, they can only rely on feedback provided in the learning phase. Thus, the best strategy would be to completely ignore the uncertainty information, similar to the irrelevant feedback provided in Study 2.

and with M being the number of response options²³. When feedback decreases the number of response options then R can be calculated for any individual feedback. The relation of

feedback-P300 amplitudes should reflect the relation of individual R values. In an experiment with a multiple-choice task where the response options are varied and individual feedback stimuli reduce the number of response options to a different degree (e.g., from four to two plausible options, from three to two, etc.), the relation of feedback-P300 amplitudes should reflect the relation of individual R values of feedback. That is, the recorded feedback-P300 should reflect the informational value of a stimulus with respect to the question whether the response was correct or not. If this assumption is true, then more practical applications are possible. For instance the relative feedback-P300 amplitude could be used to determine how informative certain feedback is in a given economic decision situation or for individuals with psychopathological disorder.

Together, these considerations show that the dual-process account of feedback processing can provide a promising framework for future research. Moreover, they suggest that research on controlled feedback processing can considerably improve the understanding of learning and adaptive behavior in decision situation, to which the original studies reported in this thesis also contributed.

23 Shannon’s general formula of uncertainty is

= − ∑

with being the probability of a choice being associated with a (positive) outcome; however, because in an initial experiment a response option should not be more or less likely to be correct than expected by chance, a simple version of this formula appears to be sufficient for explanatory purposes.