Unbewusste Wahrnehmung : Einflüsse selektiver visueller Aufmerksamkeit auf die Verarbeitung maskierter primes

Die Suche nach einem Existenzbeweis für das Vorliegen unbewusster Prozesse in der menschlichen Wahrnehmung ist ein seit langem umstrittenes Thema. Im Rahmen von vier Experimenten werden die Effekte effektiv maskierter visueller primes auf motorische Reaktionen untersucht. Dabei steht insbesondere die Frage im Vordergrund, ob sie durch selektive visuelle Aufmerksamkeitsprozesse beeinflussbar sind. Es finden sich (Versuch I) bei Verwendung verschieden effektiver Masken trotz deutlich unterscheidbarer Maskierungsfunktionen nahezu identische priming-Funktionen. Es zeigt sich ferner, dass priming-Effekte durch die Funktionen selektiver visueller Aufmerksamkeit sowohl im räumlichen (Versuch II) als auch merkmalsbasierten Sinn (Versuch III) beeinflussbar sind. Im Rahmen von Exp. IV wird das Zusammenwirken verschiedener prime-Merkmale untersucht. Es wird angenommen, dass die hier gefundenen priming-Effekte nicht ausschließlich auf der Ebene der Verarbeitung spezifischer Merkmale erzeugt werden, sondern dass die prinzipielle Möglichkeit eines Einflusses weiterer Verarbeitungsareale bestehen muss. Die hier dargestellten priming-Effekte scheinen in Zusammenfassung aller bisherigen Befunde einen sehr generellen Verarbeitungsmechanismus unseres Gehirns aufzuzeigen. Eine Aufzeigung der Grenzen und die genauere anatomische Lokalisation der Effekte kann allerdings erst durch den Einsatz neuerer bildgebender Verfahren gewährleistet werden.The search for the existence of visual perception without awareness is an important topic in the scientific research on human cognition. In the scope of four experiments, the effects of effectively masked primes on choice reactions are analysed. Especially the question whether visual selective attention modulates the effects of these primes was put. The starting point was the experiment of Vorberg, Mattler, Heinecke, Schmidt & Schwarzbach (in prep.). A first own experiment could demonstrate a dissociation between different masking and nearly identical priming functions. Experiment two and three showed the influence of spatial and feature-based visual selective attention on the priming-effects. The effect of multiple prime-features was analysed in experiment four. The data suggest that these priming-effects cannot result from pure activations in specialised brain areas for the processing of single features. There has to be a possibility for the influence of other areas as well. Concluding from all present data, the underlying processes seems to demonstrate a very general mechanism of visual processing in our brain. Exploring the limits and showing the exact anatomical localisation of the effects has to rely on the use of brain-imaging techniques

Increased Volume and Function of Right Auditory Cortex as a Marker for Absolute Pitch

Absolute pitch (AP) perception is the auditory ability to effortlessly recognize the pitch of any given tone without external reference. To study the neural substrates of this rare phenomenon, we developed a novel behavioral test, which excludes memory-based interval recognition and permits quantification of AP proficiency independently of relative pitch cues. AP- and non-AP-possessing musicians were studied with morphological and functional magnetic resonance imaging (fMRI) and magnetoencephalography. Gray matter volume of the right Heschl's gyrus (HG) was highly correlated with AP proficiency. Right-hemispheric auditory evoked fields were increased in the AP group. fMRI revealed an AP-dependent network of right planum temporale, secondary somatosensory, and premotor cortices, as well as left-hemispheric "Broca's” area. We propose the right HG as an anatomical marker of AP and suggest that a right-hemispheric network mediates AP "perception,” whereas pitch "labeling” takes place in the left hemispher

The well‐worn route revisited: Striatal and hippocampal system contributions to familiar route navigation

Classic research has shown a division in the neuroanatomical structures that support flexible (e.g., short‐cutting) and habitual (e.g., familiar route following) navigational behavior, with hippocampal–caudate systems associated with the former and putamen systems with the latter. There is, however, disagreement about whether the neural structures involved in navigation process particular forms of spatial information, such as associations between constellations of cues forming a cognitive map, versus single landmark‐action associations, or alternatively, perform particular reinforcement learning algorithms that allow the use of different spatial strategies, so‐called model‐based (flexible) or model‐free (habitual) forms of learning. We sought to test these theories by asking participants (N = 24) to navigate within a virtual environment through a previously learned, 9‐junction route with distinctive landmarks at each junction while undergoing functional magnetic resonance imaging (fMRI). In a series of probe trials, we distinguished knowledge of individual landmark‐action associations along the route versus knowledge of the correct sequence of landmark‐action associations, either by having absent landmarks, or “out‐of‐sequence” landmarks. Under a map‐based perspective, sequence knowledge would not require hippocampal systems, because there are no constellations of cues available for cognitive map formation. Within a learning‐based model, however, responding based on knowledge of sequence would require hippocampal systems because prior context has to be utilized. We found that hippocampal–caudate systems were more active in probes requiring sequence knowledge, supporting the learning‐based model. However, we also found greater putamen activation in probes where navigation based purely on sequence memory could be planned, supporting models of putamen function that emphasize its role in action sequencing

Individualized and Clinically Derived Stimuli Activate Limbic Structures in Depression: An fMRI Study

In the search for neurobiological correlates of depression, a major finding is hyperactivity in limbic-paralimbic regions. However, results so far have been inconsistent, and the stimuli used are often unspecific to depression. This study explored hemodynamic responses of the brain in patients with depression while processing individualized and clinically derived stimuli.Eighteen unmedicated patients with recurrent major depressive disorder and 17 never-depressed control subjects took part in standardized clinical interviews from which individualized formulations of core interpersonal dysfunction were derived. In the patient group such formulations reflected core themes relating to the onset and maintenance of depression. In controls, formulations reflected a major source of distress. This material was thereafter presented to subjects during functional magnetic resonance imaging (fMRI) assessment.Increased hemodynamic responses in the anterior cingulate cortex, medial frontal gyrus, fusiform gyrus and occipital lobe were observed in both patients and controls when viewing individualized stimuli. Relative to control subjects, patients with depression showed increased hemodynamic responses in limbic-paralimbic and subcortical regions (e.g. amygdala and basal ganglia) but no signal decrease in prefrontal regions.This study provides the first evidence that individualized stimuli derived from standardized clinical interviewing can lead to hemodynamic responses in regions associated with self-referential and emotional processing in both groups and limbic-paralimbic and subcortical structures in individuals with depression. Although the regions with increased responses in patients have been previously reported, this study enhances the ecological value of fMRI findings by applying stimuli that are of personal relevance to each individual's depression

Revealing the Functional Neuroanatomy of Intrinsic Alertness Using fMRI: Methodological Peculiarities

Clinical observations and neuroimaging data revealed a right-hemisphere fronto-parietal-thalamic-brainstem network for intrinsic alertness, and additional left fronto-parietal activity during phasic alertness. The primary objective of this fMRI study was to map the functional neuroanatomy of intrinsic alertness as precisely as possible in healthy participants, using a novel assessment paradigm already employed in clinical settings. Both the paradigm and the experimental design were optimized to specifically assess intrinsic alertness, while at the same time controlling for sensory-motor processing. The present results suggest that the processing of intrinsic alertness is accompanied by increased activity within the brainstem, thalamus, anterior cingulate gyrus, right insula, and right parietal cortex. Additionally, we found increased activation in the left hemisphere around the middle frontal gyrus (BA 9), the insula, the supplementary motor area, and the cerebellum. Our results further suggest that rather minute aspects of the experimental design may induce aspects of phasic alertness, which in turn might lead to additional brain activation in left-frontal areas not normally involved in intrinsic alertness. Accordingly, left BA 9 activation may be related to co-activation of the phasic alertness network due to the switch between rest and task conditions functioning as an external warning cue triggering the phasic alertness network. Furthermore, activation of the intrinsic alertness network during fixation blocks due to enhanced expectancy shortly before the switch to the task block might, when subtracted from the task block, lead to diminished activation in the typical right hemisphere intrinsic alertness network. Thus, we cautiously suggest that – as a methodological artifact – left frontal activations might show up due to phasic alertness involvement and intrinsic alertness activations might be weakened due to contrasting with fixation blocks, when assessing the functional neuroanatomy of intrinsic alertness with a block design in fMRI studies

A possible role of prolonged whirling episodes on structural plasticity of the cortical networks and altered vertigo perception:the cortex of Sufi whirling dervishes

Although minutes of a spinning episode may induce vertigo in the healthy human, as a result of a possible perceptional plasticity, Sufi Whirling Dervishes (SWDs) can spin continuously for an hour without a vertigo perception.This unique long term vestibular system stimulation presents a potential human model to clarify the cortical networks underlying the resistance against vertigo. This study, therefore, aimed to investigate the potential structural cortical plasticity in SWDs. Magnetic resonance imaging (MRI) of 10 SWDs and 10 controls were obtained, using a 3T scanner. Cortical thickness in the whole cortex was calculated. Results demonstrated significantly thinner cortical areas for SWD subjects compared with the control group in the hubs of the default mode network (DMN), as well as in the motion perception and discrimination areas including the right dorsolateral prefrontal cortex (DLPFC), the right lingual gyrus and the left visual area 5 (V5)/middle temporal (MT) and the left fusiform gyrus. In conclusion, this is the first report that warrants the potential relationship of the motion/body perception related cortical networks and the prolonged term of whirling ability without vertigo or dizziness

Event Frequency Modulates the Processing of Daily Life Activities in Human Medial Prefrontal Cortex

Event sequence knowledge is necessary to learn, plan, and perform activities of daily life. Clinical observations suggest that the prefrontal cortex (PFC) is crucial for goal-directed behavior such as carrying out plans, controlling a course of actions, or organizing everyday life routines. Functional neuroimaging studies provide further evidence that the PFC is involved in processing event sequence knowledge, with the medial PFC (Brodmann area 10) primarily engaged in mediating predictable event sequences. However, the exact role of the medial PFC in processing event sequence knowledge depending on the frequency of corresponding daily life activities remains obscure. We used event-related functional magnetic resonance imaging while healthy volunteers judged whether event sequences from high- (HF), moderate- (MF), and lowfrequency (LF) daily life activities were correctly ordered. The results demonstrated that different medial PFC subregions were activated depending on frequency. The anterior medial Area 10 was differentially activated for LF and the posterior medial Area 10 for HF activities. We conclude that subregions of the medial PFC are differentially engaged in processing event sequence knowledge depending on how often the activity was reportedly performed in daily life

The myth of upright vision. A psychophysical and functional imaging study of adaptation to inverting spectacles

The adaptation to inverting prisms and mirror spectacles was studied in four subjects over periods of six to ten days. Subjects showed rapid adaptation of visuomotor functions, but did not report return of upright vision. The persistence of the transformed visual image was confirmed by the subjects' perception of shape from shading. No alteration of the retinotopy of early visual cortical areas was seen in the functional magnetic resonance images. These results are discussed in the context of previous claims of upright vision with inverting prisms and mirror spectacles