3,208 research outputs found

    Studying feature specific mechanisms of the human visual system

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    What are the current limits of our knowledge of brain activity underlying vision and can I further this knowledge? In this thesis, I explore this basic question. I focus on those aspects of visual input that can be described as basic features of visual perception. Examples include orientation, color, direction of motion and spatial frequency. However, understanding how humans visually perceive the external world is closely related with the study of attention. Attention, that is, the selection of some aspects of the environment over others, is one of the most intensively studied areas in experimental psychology, yet its neural mechanisms remain largely elusive. This thesis focuses on three distinct topics at the border of feature specific visual perception and feature-specific visual attention. First, in a series of studies, I explore the influence of heightened attentional demand to a central task to feature-specific neural processing in the ignored periphery. I discover that heightened attentional demand does not influence feature-specific representations in early visual cortices. Second, I investigate the influence of feature-based attention on neural processing of early visual cortices. At the same time, I also probe the influence of a behavioral decision to deploy feature-specific attention in the imminent future. I find that feature-based attention operates independent of other types of attention. Additionally, results indicate that a behavioral decision to deploy feature-based attention alone, without visual stimulation present, is able to modulate neural activity in early visual cortices. Third, I examine the more complex feature of facial gender and where in the brain gender discrimination might receive neural processing. I find that, in an established network of face-selective brain areas, facial gender is represented in nearly all areas of that network. Finally, I discuss all findings in the light of the current state of research, for their scientific significance and for future research opportunities

    Outcome contingency selectively affects the neural coding of outcomes but not of tasks

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    Value-based decision-making is ubiquitous in every-day life, and critically depends on the contingency between choices and their outcomes. Only if outcomes are contingent on our choices can we make meaningful value-based decisions. Here, we investigate the effect of outcome contingency on the neural coding of rewards and tasks. Participants performed a reversal-learning paradigm in which reward outcomes were contingent on trial-by-trial choices, and performed a ‘free choice’ paradigm in which rewards were random and not contingent on choices. We hypothesized that contingent outcomes enhance the neural coding of rewards and tasks, which was tested using multivariate pattern analysis of fMRI data. Reward outcomes were encoded in a large network including the striatum, dmPFC and parietal cortex, and these representations were indeed amplified for contingent rewards. Tasks were encoded in the dmPFC at the time of decision-making, and in parietal cortex in a subsequent maintenance phase. We found no evidence for contingency-dependent modulations of task signals, demonstrating highly similar coding across contingency conditions. Our findings suggest selective effects of contingency on reward coding only, and further highlight the role of dmPFC and parietal cortex in value-based decision-making, as these were the only regions strongly involved in both reward and task coding

    Distributed networks for auditory memory differentially contribute to recall precision

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    Re-directing attention to objects in working memory can enhance their representational fidelity. However, how this attentional enhancement of memory representations is implemented across distinct, sensory and cognitive-control brain network is unspecified. The present fMRI experiment leverages psychophysical modelling and multivariate auditory-pattern decoding as behavioral and neural proxies of mnemonic fidelity. Listeners performed an auditory syllable pitch-discrimination task and received retro-active cues to selectively attend to a to-be-probed syllable in memory. Accompanied by increased neural activation in fronto-parietal and cingulo-opercular networks, valid retro-cues yielded faster and more perceptually sensitive responses in recalling acoustic detail of memorized syllables. Information about the cued auditory object was decodable from hemodynamic response patterns in superior temporal sulcus (STS), fronto-parietal, and sensorimotor regions. However, among these regions retaining auditory memory objects, neural fidelity in the left STS and its enhancement through attention-to-memory best predicted individuals’ gain in auditory memory recall precision. Our results demonstrate how functionally discrete brain regions differentially contribute to the attentional enhancement of memory representations

    Paying attention to working memory: similarities in the spatial distribution of attention in mental and physical space

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    Selective attention is not limited to information that is physically present in the external world, but can also operate on mental representations in the internal world. However, it is not known whether mechanisms of attentional selection in mental space operate in a similar fashion as in physical space. We studied the spatial distribution of attention for items in physical and in mental space by comparing how successfully distracters were rejected at varying distances from the attended location. The results indicate very similar distribution characteristics of spatial attention in physical and mental space. Specifically, we found that performance monotonically improved with increasing distracter distance relative to the attended location suggesting that distracter confusability is particularly pronounced for nearby distracters relative to further away distracters. The present findings suggest that mental representations preserve their spatial configuration in working memory, and that similar mechanistic principles underlie selective attention in physical and mental space

    The cognitive neuroscience of visual working memory

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    Visual working memory allows us to temporarily maintain and manipulate visual information in order to solve a task. The study of the brain mechanisms underlying this function began more than half a century ago, with Scoville and Milner’s (1957) seminal discoveries with amnesic patients. This timely collection of papers brings together diverse perspectives on the cognitive neuroscience of visual working memory from multiple fields that have traditionally been fairly disjointed: human neuroimaging, electrophysiological, behavioural and animal lesion studies, investigating both the developing and the adult brain
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