d together in a specific order, because different words can be written with the same letters. The present research had two aims: first, to clarify the cerebral stages of processing that lead to invariant word recognition, and second, to examine whether those stages can proceed in the absence of consciousness. In literate adults, an extended strip of the left fusiform gyrus activates whenever visual words are presented (Cohen et al., 2000; Cohen et al., 2002; Nobre, Allison, & McCarthy, 1994). This region, which has been termed the Visual Word Form Area (VWFA), is responsive only to written words, not to spoken words (Dehaene, Le Clec'H, Poline, Le Bihan, & Cohen, 2002). Its lesioning results in a severe word identification impairment, pure alexia, which is restricted to the visual modality (Leff et al., 2001). Thus, it is a plausible candidate for the neural basis of invariant visual word recognition. To further specify the nature of word coding in the VWFA, we used the priming metho

& Recent evidence has suggested that the human occipitotemporal region comprises several subregions, each sensitive to a distinct processing level of visual words. To further explore the functional architecture of visual word recognition, we employed a subliminal priming method with functional magnetic resonance imaging (fMRI) during semantic judgments of words presented in two different Japanese scripts, Kanji and Kana. Each target word was preceded by a subliminal presentation of either the same or a different word, and in the same or a different script. Behaviorally, word repetition produced significant priming regardless of whether the words were presented in the same or different script. At the neural level, this cross-script priming was associated with repetition suppression in the left inferior temporal cortex

Introduction: the challenge of a science of consciousness Understanding consciousness has become the ultimate intellectual challenge of this new millennium. Even if philosophers now accept the notion that it is a "real , natural, biological phenomenon literally located in the brain" (Revonsuo, 2001), a view in harmony with the neuroscientist conception that "consciousness is entirely caused by neurobiological processes and realized in brain structures" (Changeux, 1983; Crick, 1994; Edelman, 1989), the real issue becomes: how to elaborate a science of consciousness? This challenging problem raises two questions. A first one is how to empirically define experimental paradigms in order to delineate a relevant and ultimately causal relationship between subjective phenomena and objective measurements of neural activity. Cognitive psychologists have now defined a variety of minimal experimental protocols which allow a fair comparison between conscious and non-conscious processing of informa

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Causal role of prefrontal cortex in the threshold for access to consciousness

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www.elsevier.com/locate/concog 2 Motion-induced blindness does not affect the formation 3 of negative afterimages 4 Constanze Hofstoetter a,*

7 figures, 54 references

The mammalian visual system includes numerous brain areas that are profusely interconnected. With few exceptions, these connections are reciprocal. Anatomical feedback connections in general outnumber feedforward connections, leading to widespread speculation that feedback connections play a critical role in visual awareness. However, evidence from physiological experiments suggests that feedback plays a modulatory role, rather than a driving role. Here we discuss theoretical constraints on the significance of feedback’s anatomical numerical advantage, and we describe theoretical limits on feedback’s potential physiological impact. These restrictions confine the potential role of feedback in visual awareness and rule out some extant models of visual awareness that require a fundamental role of feedback. We propose that the central role of feedback is to maintain visuospatial attention, rather than visual awareness. Our conclusions highlight the critical need for experiments and models of visual awareness that control for the effects of attention. As a matter of clarity in this chapter: by “visual awareness ” or “visibility”, we mean the conscious perception that a stimulus is visible. Thus for the purposes of this discussion, we use the terms visual awareness, visibility, and consciousness interchangeably. Anatomical observations of feedback in the visual system The visual areas of the brain are interconnected in a complex pattern of feedforward, lateral, and feedback pathways (Felleman & Van Essen, 1991). Feedback connections are ubiquitous throughout the cortex, and subcortical regions in ascending hierarchical pathways also receive a large amount of feedback from cortical areas (Erisir, Van Horn, &

Consciousness is considered one of the ‘final frontiers ’ in modern science. The phenomenon seems to escape all attempts to scientific reduction, and some philosphers argue that we may never be able to reveal its true nature. During the last decades, the subject has been taken up by neuroscientists, trying to find the ‘neural correlates of consciousness ’ (the NCC). It seems, however, that this is not solving the riddle in any real sense. What would we learn about consciousness if we knew what neurons or brain structures are involved? I think the answer lies in taking a different approach than finding the NCC. Our starting point should be neuroscience itself, not consciousness (which is rather ill-defined anyhow). I have devised a hypothesis about how phenomena like visually guided behavior, visual attention, visual memory and conscious visual experience might emerge from different neural mechanisms. This hypothesis can be tested (and further refined) with experiments using awake behaving monkeys and human subjects, doing electrophysiological recordings and electrical and pharmacological manipulations, as well as brain imaging (fMRI / EEG) experiments. If supported by these experiments, this hypothesis will reveal that consciousness is not what we think it is now. It is different from attention, working memory, reportability, or ‘thinking’. In