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In human neuroscientific research, there has been an increasing interest in how the brain computes the value of an anticipated outcome. However, evidence is still missing about which valuation related brain regions are modulated by the proximity to an expected goal and the previously invested effort to reach a goal. The aim of this dissertation is to investigate the effects of goal proximity and invested effort on valuation related regions in the human brain. We addressed this question in two fMRI studies by integrating a commonly used reward anticipation task in differential versions of a Multitrial Reward Schedule Paradigm. In both experiments, subjects had to perform consecutive reward anticipation tasks under two different reward contingencies: in the delayed condition, participants received a monetary reward only after successful completion of multiple consecutive trials. In the immediate condition, money was earned after every successful trial. In the first study, we could demonstrate that the rostral cingulate zone of the posterior medial frontal cortex signals action value contingent to goal proximity, thereby replicating neurophysiological findings about goal proximity signals in a homologous region in non-human primates. The findings of the second study imply that brain regions associated with general cognitive control processes are modulated by previous effort investment. Furthermore, we found the posterior lateral prefrontal cortex and the orbitofrontal cortex to be involved in coding for the effort-based context of a situation. In sum, these results extend the role of the human rostral cingulate zone in outcome evaluation to the continuous updating of action values over a course of action steps based on the proximity to the expected reward. Furthermore, we tentatively suggest that previous effort investment invokes processes under the control of the executive system, and that posterior lateral prefrontal cortex and the orbitofrontal cortex are involved in an effort-based context representation that can be used for outcome evaluation that is dependent on the characteristics of the current situation.
Which factors determine whether a stimulus is consciously perceived or unconsciously processed? Here, I investigate how previous experience on two different time scales – long term experience over the course of several days, and short term experience based on the previous trial – impact conscious perception. Regarding long term experience, I investigate how perceptual learning does not only change the capacity to process stimuli, but also the capacity to consciously perceive them. To this end, subjects are trained extensively to discriminate between masked stimuli, and concurrently rate their subjective experience. Both the ability to discriminate the stimuli as well as subjective awareness of the stimuli increase as a function of training. However, these two effects are not simple byproducts of each other. On the contrary, they display different time courses, with above chance discrimination performance emerging before subjective experience; importantly, the two learning effects also rely on different circuits in the brain: Moving the stimuli outside the trained receptive field size abolishes the learning effects on discrimination ability, but preserves the learning effects on subjective awareness.
This indicates that the receptive fields serving subjective experience are larger than the ones serving objective performance, and that the channels through which they receive their information are arranged in parallel. Regarding short term experience, I investigate how memory based predictions arising from information acquired on the trial before affect visibility and the neural correlates of consciousness. To this end, I vary stimulus evidence as well as predictability and acquire electroencephalographic data.
A comparison of the neural processes distinguishing consciously perceived from unperceived trials with and without predictions reveals that predictions speed up processing, thus shifting the neural correlates forward in time. Thus, the neural correlates of consciousness display a previously unappreciated flexibility in time and do not arise invariably late as had been predicted by some theorists.
Admittedly, however, previous experience does not always stabilize perception. Instead, previous experience can have the reverse effect: Seeing the opposite of what was there, as in so-called repulsive aftereffects. Here, I investigate what determines the direction of previous experience using multistable stimuli. In a functional magnetic resonance imaging experiment, I find that a widespread network of frontal, parietal, and ventral occipital brain areas is involved in perceptual stabilization, whereas the reverse effect is only evident in extrastriate cortex. This areal separation possibly endows the brain with the flexibility to switch between exploiting already available information and emphasizing the new.
Taken together, my data show that conscious perception and its neuronal correlates display a remarkable degree of flexibility and plasticity, which should be taken into account in future theories of consciousness.
The current work investigated the association of trait anxiety and the neural efficiency of cognitive processing for affectively neutral (not threat-related) information. In a sample of 46 healthy volunteers, three fMRI experiments were conducted to test the prediction derived from attentional control theory (Eysenck et al., 2007) that high as compared to low trait-anxious individuals expend more neural effort on tasks requiring the top-down control of attention to reach a given level of performance. In a colour-word Stroop task requiring the inhibition of irrelevant stimulus information and associated responses as well as in a working-memorymanipulation task requiring the shifting of attention between items in working memory, trait anxiety (as measured with the State-Trait Anxiety Inventory; Spielberger et al., 1970) was positively associated with task-related increases in the activation of two adjacent regions in the right dorsolateral prefrontal cortex (DLPFC). The finding that along with a stronger activation of this brain region commonly implicated in top-down control processes, the high-anxious subjects showed equal (working memory manipulation) or worse (Stroop) performance when compared to low-anxious subjects, does support the assumption that processing is less efficient in the high anxious. However, in contrast to the predictions, trait anxiety did not show a significant association with task-related brain activation in a task-switching paradigm requiring shifting between task sets. It is discussed how different attentional control demands of the task may account for differences in the effects of trait anxiety on overt behavioural performance and underlying neural processes. In addition to DLPFC activation, trait anxiety modulated the functional connectivity of distributed regions involved in processing of the Stroop and the working-memory-manipulation task. It is discussed how the observed differences in regional DLPFC activation and network connectivity relate to each other. A possible interpretation suggests that activation increases in the DLPFC reflect an attempt to compensate for suboptimal connectivity by investing more effort in prefrontally supported control processes. Overall, the current work shows an association of trait anxiety with the neural efficiency of cognitive processing in affectively neutral tasks involving attentional control. Furthermore, it suggests that investigations of neural efficiency should take into account difference in functional integration in addition to regional activation.