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Ausbildung kortikaler Repräsentationen, die der langfristigen perzeptuellen Bahnung (Priming) zugrunde liegen: Die Rolle von Verarbeitungseffizienz, Aufmerksamkeit, neuronaler Selektivität und Markmalsverlust

Subject Area Clinical Neurology; Neurosurgery and Neuroradiology
Term from 2008 to 2011
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 44294592
 
Final Report Year 2017

Final Report Abstract

Perceptual priming is a capability by which memory left in the brain by a prior event influences current perception. For example, words and objects encountered in the recent past are perceived more accurately and faster than words and objects not recently encountered, and ambiguous stimuli are more likely to receive a perceptual interpretation that conforms to a perceptual interpretation adopted in the recent past. Thus, memory "greases the wheels" of perception. Perceptual priming is a critical memory capability because it plays a strong role in creating intelligent, adaptive, behaviour—but it has particularly attracted interest because it sometimes appears to occur in the absence of conscious recollection of the prior event whose influence is revealed in current behaviour. For example, patients with amnesia caused by brain damage sometimes show intact perceptual priming, while being unable to remember anything about the past event that caused the priming. A key goal in cognitive neuroscience has, therefore, been to investigate the brain mechanisms underlying perceptual priming, and the extent to which these differ from the brain mechanisms underlying conscious recollection. This DFG project was designed to provide further critical information on this issue. Prior to the project, much research in cognitive neuroscience had focussed on the neural processes that happen at the time when perceptual priming occurs, that is, at the very time when perception is facilitated by a past event—in cognitive neuroscience terms, neural processes at retrieval. A typical finding is that the facilitating influence on perceptual performance, as revealed in behavioural measures, is accompanied by a decreased neural response, a phenomenon sometimes called neural repetition suppression. In past work, the principal investigator and his colleagues at the University of Magdeburg had shown that these repetition-related neural response decreases truly relate to perceptual priming in the absence of conscious recollection—even in normal healthy human participants. Much less investigated prior to the project were the neural processes that occur at the time when memory traces are laid down in the brain that lead to later perceptual priming—in cognitive neuroscience terms, neural processes at encoding. The principal investigator and colleagues had conducted some pioneering work on this issue and had uncovered preliminary evidence that encoding events relating to later perceptual priming occur in the brain before encoding events relating to later conscious recollection, and that these priming-related events occur in neural pathways that are involved in the identification of external stimuli, and not in neural pathways that are typically associated with laying down memory traces that support later conscious recollection. They also uncovered fascinating initial evidence that different kinds of attention to stimuli during encoding might be involved in laying down neural memory traces for later priming as compared with neural memory traces for later conscious recollection. The current project was designed to provide more conclusive evidence, using evolutions of the behavioural techniques that had been developed to study memory encoding and retrieval in the prior research. At retrieval (i.e., the memory test), research participants were asked to identify (name) rapidly flashed words, which made identification difficult. Some of these words had been encountered before in the experiment during another task (i.e., the encoding task), and others had not, allowing assessment of priming at test—an identification-advantage for old over new words. For each identified word, participants had to indicate whether they remembered having encountered the word earlier in the experiment, allowing assessment of conscious recollection. Words were classified as identified and remembered (R), identified but not remembered (primed, P), or not identified at all (nonID). Brain responses during the encoding task measured by functional magnetic resonance imaging (fMRI) were then seperated according to the later fate of the word at test. The researchers discovered striking evidence for two neural networks in the brain supporting later priming and later conscious recollection, respectively, the former consisting of dorsal prefrontal and ventral posterior parietal areas, and the latter consisting of of ventral prefrontal and dorsal posterior parietal areas. These networks pointed to two different kinds of attention that might be involved at encoding: Attention to the perceptual characteristics of the word (i.e., appearance), versus attention to the conceptual characteristics of the word (i.e., meaning). In follow-up work, the researchers confirmed this hypothesis by manipulating attention at encoding, to involve either attention to perceptual characterics or attention to conceptual characteristics. The same two memory networks were revealed, relating to later perceptual priming and to later conscious recollection, respectively. In addition to elucidating the basic mechanisms of memory formation, these results could have considerable relevance to understanding neurological conditions involving impaired priming.

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