A systems neurophysiology approach to voluntary event coding
Introduction
The mechanisms responsible for the integration of perceptual events into appropriate actions (i.e. sensorimotor processes) have been subject to intense research in cognitive psychology and neuroscience for decades. One influential account trying to conceptualize these processes is the “Theory of Event Coding (TEC)” (Hommel et al., 2001). The TEC is a theoretical framework (Hommel, 2011) that provides conceptual tools to explain information processing aiming at integrating perception (stimuli) and action (responses) (Hommel et al., 2001). Briefly, TEC assumes that perceptual processing of an object establishes an ‘object file’ (Hommel, 2004) containing information about the relationship, i.e. the binding, between different object features (e.g. shape, colour, intensity, and location). Action planning similarly involves assembling (binding) of action features (‘action file’). Binding of codes of perceptual events (object files), current task context and actions (action files), is mediated by multi-layered networks to the effect of creating ‘event files’ (Hommel, 2004). Event file coding thus appears to be particularly important for the understanding of goal-directed behavior and is therefore examined in the current study.
Currently event-file coding has been extensively investigated concerning the relevance of specific neurobiological processes including the importance of the dopaminergic system using pharmacological, molecular genetics and substance abuse approaches (Colzato et al., 2012, Colzato et al., 2004, Colzato et al., 2013, Colzato and Hommel, 2008). Using functional brain imaging and brain stimulation it has been shown that event-file coding is mediated via a widely distributed network including the supplementary motor areas, the dorsolateral prefrontal cortex and the hippocampus (Elsner et al., 2002, Kühn et al., 2011, Melcher et al., 2014, Zmigrod et al., 2014) suggesting that the perceptional and/or attentional mechanisms as well as response selection and memory encoding mechanisms are important. However, while TEC in general, and event-file coding in particular, have inspired a wealth of instructive studies in cognitive psychology (Hommel, 2009, Shin et al., 2010), behavioral neuroscience and functional imaging, the underlying cognitive-neurophysiological mechanisms are unclear. Thus, it is largely unknown what temporally segregated stages of information processing are involved during event-file coding, which can be segregated using electrophysiological methods with high temporal solution including EEG and event-related potentials (ERPs) combined with source localization methods. These methods have previously been used to examine attentional processes during event integration (Akyürek et al., 2007), but have not been used to examine further response-selection related processes during event file coding and have not delineated the functional neuroanatomical networks underlying these processes (e.g. using source localization methods). EEG neurofeedback studies have also been conducted to enhance feature binding (Keizer et al., 2010) but the effects of this have not been evaluated on an electrophysiological level during an event file coding task.
While these latter studies suggest that perceptual processes and networks possibly encompassing posterior and frontal brain areas are important for event coding, the precise nature of the modulation of temporally dissociable cognitive-neurophysiological sub-processes from perception to response selection during event file processing, as reflected using ERPs, are unclear. This is particularly the case for “voluntary event-file coding”: In previous studies examining event-file coding specific stimulus features (e.g. shape) are automatically bound to a certain response, whereas other stimulus features (e.g. color or location) are behaviorally irrelevant. In such conditions response selection is relatively straightforward, because only one feature is response relevant. If, however, the other stimulus dimensions become also relevant to some degree, response selection and event-file coding becomes more complicated and needs to be voluntary controlled. We hypothesize that mechanisms of perceptual gating and early stimulus categorization reflected by the P1 ERP (Klimesch, 2011) are important for voluntary event file coding because these processes build the basis for any action to be executed after a sensory event has been processed and are especially demanded because more than one stimulus feature is response relevant. Probably, for these processes parietal networks are particularly relevant, since these have previously been shown to be engaged in encoding of stimulus properties (Donner et al., 2002, Nobre et al., 2003, Pollmann et al., 2014) relating these aspects to appropriate actions (Geng and Vossel, 2013, Zmigrod et al., 2014). In contrast, attentional selection processes, as reflected by the N1 ERP (Herrmann and Knight, 2001), are not expected to be modulated because there is good evidence that a given stimulus is automatically bound to a response largely independent of attentional selection mechanisms (Hommel, 2005). In contrast, electrophysiological correlates of response selection and the “decision” processes between stimulus evaluation and responding (i.e. what response to select) are most likely to be important for event-file coding. These processes are reflected by amplitude modulations of the N2 and P3 ERP, respectively and reflect parietal-medial frontal cortical network activity (Azizian et al., 2006, Di Russo et al., 2006, Falkenstein et al., 1994, Gajewski et al., 2008, Hohnsbein et al., 1998, Mückschel et al., 2014, Ritter et al., 1983, Ritter et al., 1982, Twomey et al., 2015). Similar networks may therefore be of importance for voluntary event file coding in which response selection processes are more demanding.
To better understand what cognitive-neurophysiological sub-processes within the processing cascade are particularly relevant for voluntary event-file coding we introduce a manipulation of rewards. Reward manipulations are well-known to modulate the dopaminergic system (Schultz, 1998), which has already been shown to be relevant for event coding (see above), but not yet for voluntary event coding. We expected that voluntary event coding becomes more efficient during reward anticipation. However, each of the above-mentioned sub-processes may be potentially affected by rewards during voluntary event coding. This is because rewards do not only modulate medial frontal networks important for response selection and cognitive control processes, but also processes of perceptual and attentional gating in parietal networks (Maunsell, 2004, Platt and Glimcher, 1999).
Section snippets
Participants
A sample of 51 young healthy participants between 18 and 31 years of age (M = 23.7; SD = 3.4) was recruited. 26 participants (M = 22.77; SD = 3.3) served as a rewarded group and were complemented by a control group of 25 participants (M = 24.84; SD = 3.16), who were studied without reward. 5 participants (n = 3 rewarded participants) had to be excluded because of poor data quality. In total, the final sample comprised 46 participants (N = 23 in each group). All participants gave written informed consent and
Accuracy
The mixed-effects ANOVA of the percentage of hits on the S2-stimulus using the within-subject factors “feature overlap” and “response” and the between-subject factor “group” revealed a significant main effect for “response” (F1,44 = 8.92; P = 0.005, η2 = .17) with more correct answers for alternated responses (96.68% ± 0.62) than for repeated responses (94.66% ± 0.85). While there was no main effect, “feature overlap” (F3,132 = 2.01; P > 0.1) and “group” (F1,44 = 0.23; P > 0.6), there was a significant
Discussion
In this study we examined the systems neurophysiological mechanisms underlying voluntary event file coding (Hommel et al., 2001) and in which way the integration of visuo-motor features into an event-file during voluntary event file coding is modulated by reward. To the best of our knowledge, the study is the first to approach the question what neurophysiological processes underlie voluntary event file coding processes as conceptualized in the theory of event coding (TEC) (Hommel et al., 2001).
Conclusions
In summary, the study examined the system neurophysiological basis of voluntary event-coding, a major aspect in the “theory of event coding” (TEC), which has been proposed as an influential framework of how perceptions are transformed into the appropriate actions. The results show that neurophysiological correlates of processes of stimulus categorization, as well as feature unbinding and response selection processes are central to voluntary event-file coding. Attentional selection processes do
Acknowledgements
This work was supported by Grants from the Deutsche Forschungsgemeinschaft (DFG) BE4045/10-2 and BE4045/19-1 to C.B. and MU 1692/4-1 to A.M.
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