Visual gnosis is the“ cognitive” stage of processing when the percept is identified/recognized.Closely related to visual gnosis (recognition) is attention. Attention is the perceptual selectivity that allows the choice of what is relevant and ignoring what is irrelevant. Gnosis implies both the recognition and the full awareness (consciousness) of the object and its meaning. The visual system is modular with each module sub-serving a specific function and operating via a distributed network with“ essential nodes” (Zeki2001) or“ crucial nodal points” (Celesia&Brigell1999). How is the process of gnosis understood within our model of visual organization? The ventral pathways processing is constituted by a hierarchy of sequential featureselective neuronal populations of increasing complexity; each level representing a particular feature (color, orientation, etc.) with higher level concepts represented in higher hierarchy areas (inferior-medial temporal cortex) with feed-forward and feed-back to hippocampus, parietal and frontal cortices. A similar hierarchical construct applies to the dorsal pathways with early levels representing spatial location and motion, and with higher concepts represented in parietal lobes. This dichotomy is not absolute and there are several connections between the two systems and intermediate cortical areas (placed between the temporal and parietal lobes) that have uncertain function.Acquired cerebral achromatopsia (failure to recognize colors) and prosopagnosia (failure to recognize faces) are classical deficit related to lesions of the higher hierarchy areas of the ventral pathways (inferior temporal cortex). A kinetopsia(failure to recognize motion)represents the classic deficit related to lesions ofthe dorsal pathways (specifically areas MT/MST). Visual attention disorders such as Balint's syndrome, visual neglect and simultagnosia, are complex perceptual deficits difficult to attribute to specific cortical locations.An unresolved question is how the initial analysis by specialized channels and modules is integrated together into a single percept. If color, orientation, motion etc. are represented in separate modules there must be a point when these features are reintegrated into a unified representation. This feature integration represents the unsolved binding problem.The other related controversy is how much conscious perception and storage of a visual stimulus is limited to specific cortical structures and what portion is distributed over a diffuse network?

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Psychological time needs to be considered separately from physical time. Indeed, some studies including our own on crossmodal“ chronostasis” effect indicate that psychological clock is not united nor single in the brain. A variety of backward perceptual phenomena, including the classical effects such as backward masking well as our new findings such as the flash-lag and the generalized flash-lag effects, strongly argue for some postdictive process. While some of our own TMS findings have qualitatively similar implications, I will attempt to dissociate several different claims that are crudely categorized as postdiction.

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Alzheimer's disease(AD)is a neurodegenerative disease characterized by memory impairment and progressive cognitive decline. Currently AD is the most common cause to dementia, and its prevalence may rea ch up to 25% among elderly subjects older than 80 years of age. In addition to damaged high level cog nitive functions, electroencephalography-studies have showed impairment of early brain processing in AD. Magnetoencephalography(MEG), which offers excellent spatial and milliseconds temporal resolution, is ideal tool to study noninvasively cortical activity. We have shown with MEG that parallel auditory processing between the hemispheres underlying stimulus detection is selectively delayed in Parkinson's disease, AD and that delayed auditory processing correlates with cognitive decline in AD. Results of pharmacological studies with scopolamine, which temporarily blocks cholinergic receptors in the brain, indicate that auditory processing and spontaneous activity are modulated by the cholinergic system. Sensitivity to cholinergic modulation appears to be age-related in the auditory system. MEG results also indicate damaged auditory processing in Down syndrome(DS), which is characterized by mental retardation, and cholinergic damage similar to AD. Slowing of spontaneous brain activity is a common finding in AD progression. Present MEG-studies suggest altered oscillation activity in AD and in mild cognitive impairment(MCI), which often precedes dementia, compared with normal aging. Thus MEG might offer additional information to make a diagnosis between AD and MCI. Due to recent software development, MEG is now suitable to patients who have implanted deep brain stimulation(DBS)device. Our recent results tentatively suggest that DBS modulates somatosensory processing in PD. In conclusion, MEG appears to be a useful tool to study human brain activity in aging, neurodegenerative diseases, and even mental retardation.

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There are several studies showing the hedonics of odor affects human brain responses. In preceding studies, however, the hedonics of odor was decided by experimenters'settings, not by participants'own ratings. This might be one reason of disagreement of activated brain areas among preceding studies. Thus, in this study, the odor stimulations were grouped into one of three conditions, pleasant, neutral and unpleasant conditions, based on participants'own ratings, and then brain responses revealed by fMRI were analyzed and compared based on these conditions. Activation was clearly detected in the insula and the cingulate cortex during odor stimulations that participants evaluated as unpleasant, and in the cingulate cortex during odor stimulation that the participants evaluated as pleasant. It is suggested that the inconsistency of activated brain areas in previous studies may have been caused by individual differences in the evaluation of odor hedonics.

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