PLOS Biology has a most interesting article from Stanislas Dehaene‘s group on the neurodynamics of conscious experience. The researchers studied brain activation using EEG, while subjects rated visually presented stimuli on a scale from unseen to clearly seen. It was found that conscious experience of a stimulus was related to the engagement of a widespread network involving the frontal, parietal and temporal cortices.

SCR note: It is mentioning a recent study using fMRI (Christensen et al. 2006) provided comparable results, and adding two factors; (1) the conscious experience of a visual stimulus involved activation of both thalami, and (2) subjects consistently rated some experiences as vague, i.e., as “detected but not identified”. This experience was associated with both lower activation in those regions involved in conscious experience, and unique activation of additional regions, including some prefrontal regions.

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Melloni et al. have recently demonstrated, in the Journal of Neuroscience, that neural synchrony in the gamma range between distal rain regions is important for conscious perception. The authors say about their work that “the access to conscious perception is the early transient global increase of phase synchrony of oscillatory activity in the gamma frequency range”

Here we link to the article and some related works.

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Abstract of Attention and consciousness: two distinct brain processes, in TRENDS in Cognitive Sciences.

The close relationship between attention and consciousness has led many scholars to conflate these processes. This article summarizes psychophysical evidence, arguing that top-down attention and consciousness are distinct phenomena that need not occur together and that can be manipulated using distinct paradigms. Subjects can become conscious of an isolated object or the gist of a scene despite the near absence of top-down attention; conversely, subjects can attend to perceptually invisible objects. Furthermore, top-down attention and consciousness can have opposing effects. Such dissociations are easier to understand when the different functions of these two processes are considered. Untangling their tight relationship is necessary for the scientific elucidation of consciousness and its material substrate.

For full access to this paper, click here.

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As if it was not bad enough to suffer from a brain injury following such as stroke, many sufferers of injury to visual areas also report experiences of hallucinations.

Interestingly, these reports should not necessarily be understood as the result of neuropathology or as unimportant symptoms, but rather as the result of functional reorganization – aka plasticity – of the neural underpinnings of visual perception.

Visual hallucinations during spontaneous and training-induced visual field recovery

D.A. Poggel et al.

Neuropsychologia
Volume 45, Issue 11, 2007, Pages 2598-2607

Visual hallucinations after post-geniculate visual system lesions were shown to be associated with spontaneous recovery of visual functions. We investigated the occurrence of hallucinations during spontaneous recovery and additionally tested whether hallucinations were re-instated in a phase of vision restoration therapy (VRT). Nineteen patients with post-geniculate lesions and homonymous visual loss participated in a prospective study, and 121 patients with various lesions were included in a retrospective study using a questionnaire including verbal descriptions as well as drawings of hallucinations experienced by the patients. In both samples, visual-field size was determined before and after 6 months of VRT. Many patients in both groups experienced post-lesion hallucinations (mostly colors, objects, motion) which subsided after spontaneous recovery of visual functions (increase of visual field size, recovery of more complex visual function) was ended. Hallucinations re-emerged during training. However, the majority of patients reported simple, unformed visual hallucinations (uncolored phosphenes, spots, flashes), especially when visual field recovery was most intense. Hallucinations were mainly found in patients with large shifts of the visual field border. They occurred in blind areas, particularly in areas of residual vision where recovery was predominantly observed. Hallucinations may reflect functional recovery in partially lesioned brain areas. While the colored/formed hallucinations during spontaneous recovery may represent non-specific activation of higher visual areas, the simple, unformed training-related hallucinations may indicate recovery in the primary visual cortex during treatment. Hallucinations should not generally be discarded as pathological or unimportant symptoms, but they may be functional indicators of visual system plasticity.

ScienceDirect

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Abstract of Early Neural Correlates of Conscious Somatosensory Perception, in the Journal of Neuroscience.

The cortical processing of consciously perceived and unperceived somatosensory stimuli is thought to be identical during the first 100 –120 ms after stimulus onset. Thereafter, the electrophysiological correlates of conscious perception have been shown to be reflected in the N1 component of the evoked response as well as in later (_200 ms) nonstimulus-locked _-band (28 –50 Hz) oscillatory activity. To evaluate more specifically the time course and correlation of neuronal oscillations with conscious perception, we recorded neuromagnetic responses to threshold-intensity somatosensory stimuli. We show here that cortical broadband activities phase locked to the subsequently perceived stimuli in somatosensory, frontal, and parietal regions as early as 30 –70 ms from stimulus onset, whereas the phase locking to the unperceived stimuli was weak and primarily restricted to somatosensory regions. Such stimulus locking also preceded the perceived stimuli, indicating that the phase of ongoing cortical activities biases subsequent perception. Furthermore, the data show that the stimulus locking was present in the _- (4–8 Hz), _- (8 –14 Hz), _- (14 –28 Hz), and _- (28–40 Hz) frequency bands, of which the widespread _-band component was dominant for the consciously perceived stimuli but virtually unobservable for the unperceived stimuli. Our results show that the neural correlates of conscious perception are already found during the earliest stages of cortical processing from 30 to 150 ms after stimulus onset and suggest that _-frequency-band oscillations have a role in the neural mechanisms of sensory awareness.

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In a most interesting paper by Ceri Trevethan, Arash Sahraie and Larry Weiskrantz, it is suggested that blindsight patients are actually superior on certain visual stimulus detection tasks. In this paper, published in Cognition, the authors also provide experimental evidence that this is indeed the case.

The study highlights the neural dynamics that take place in the case of brain damage. While the areas that are damaged have been responsible for a given task (i.e. vision) it is likely that such injury leads to unmasking of previously suppressed functions in adjacent or other connected areas. As such, brain damage might indeed not only lead to reduced functions, but unmasking — and enhancement — of other functions. As in this study,

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So how do we really experience the world around us, and events as they occur? As discrete units of experiences or as one flow of experience. In a recent paper in Psychologial Bulletin authors Jeffrey Sacks and colleagues suggest that we perceive and conceive of activity in terms of discrete events, and that the perception of boundaries between events arises from ongoing perceptual processing. The elaboration of this view and  accompanying consequences are laid out in this paper. Here we link to the abstract as well as the manuscript.

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Pain is one of the most prominent examples of the problem of consciousness: from a subjective point of view we know the experience of pain all too well. Seen from the objective side of pain, the neural processes related to pain are becoming unravelled. But the essential relationship between neural processes going on from the sensation to the experience are much less known.

In a study by Christmann and colleagues, a combination of EEG and fMRI demonstrates how regional brain areas make different contributions — and at different times — to the experience of pain.

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Surgeons have managed to give an amputee not only a prosthetic arm that moves as directed by her thoughts, but also the feeling of touch — albeit in the wrong part of her body.

When Claudia Mitchell presses an area on her chest, where surgeons re-wired the nerves that used to run to her hand, it feels to her as if her fingers are being touched.

The technique opens the door to additional technologies that could one day relay signals from the prosthesis back to the ‘fingers’ on the chest, allowing an amputee to get sensory information such as touch and temperature from their artificial limb.

Mitchell’s success story was revealed in a press conference last year, but now the details have been published: they are reported this week in the Lancet. (from Nature)

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A recent review article explores how we become aware of the (integrated) flavor of food. Abstract: In recent years, progress has been made understanding the neural correlates of consciousness. Experimental and computational data have been largely based on the visual system. Contemporary neurobiological frameworks of consciousness are reviewed, concluding that neural reverberation among forward- and back-projecting neural ensembles across brain areas is a common theme.

In an attempt to extrapolate these concepts to the oral-sensory and olfactory systems involved with multimodal flavor perception, the integration of the sensory information of which into a flavor gestalt has been reviewed elsewhere. The neurocognitive bases of human multimodal food perception: Sensory integration. I reconceptualize the flavor-sensory system by integrating it into a larger neural system termed the Homeostatic Interoceptive System (HIS). This system consists of an oral (taste, oral touch, etc.) and non-oral part (non oral-thermosensation, pain, etc.) which are anatomically and functionally highly similar. Consistent with this new concept and with a large volume of experimental data, I propose that awareness of intraoral food is related to the concomitant reverberant self-sustained activation of a coalition of neuronal subsets in agranular insula and orbitofrontal cortex (affect, hedonics) and agranular insula and perirhinal cortex (food identity), as well as the amygdala (affect and identity) in humans. I further discuss the functional anatomy in relation essential nodes. These formulations are by necessity to some extent speculative.

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Would we hear things differently if we always kept our eyes closed? The answer is yes! The McGurk Effect is a classic illustration of how the spoken sounds we hear are influenced by whether or not we can see the speaker’s lips.

Click here for a great online example of the McGurk Effect. In this online example, we see a person saying (making lip movements for) “GA GA”, but in reality, we are hearing “BA BA”. When these sounds and lip movements are combined, most adults think that they are hearing “DA DA”.

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It’s time for this year’s Illusion Contest.

The 2007 Contest Gala will be held in Sarasota, Florida (Van Wezel Performing Arts Hall) on Saturday, May 12th, 2007, during the week of the Vision Sciences Society (VSS) conference.

The 2006 annual contest, also held in Sarasota, Florida, was a huge success, which drew numerous accolades from attendees as well as international media coverage. The First, Second and Third Prize winners were Max Dursteler (Universitätsspital Zürich, Switzerland), Peter Tse (Dartmouth College, USA), and Gideon Caplovitz & Peter Tse (Dartmouth College, USA). To see the illusions, photo galleries and other highlights from the 2006 contest, go here.

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