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Visual Processes (visual + process)
Selected AbstractsColor constancy from invariant wavelength ratios: I. The empirical spectral mechanismCOLOR RESEARCH & APPLICATION, Issue 3 2008Ralph W. PridmoreArticle first published online: 10 APR 200 Abstract The wavelengths of several constant hues over four illuminants (D95, D65, D50, A) are derived from several sets of published data. In the plane of wavelength and reciprocal illuminant color temperature (MK,1), the wavelengths of constant hues plot straight approximately parallel lines whose mean slope is about 87°. Parallel lines give invariant wavelength ratios, hence constant hues in this plane are near-invariant wavelength ratios across illuminants. As recently demonstrated, the complementary wavelengths to a constant hue (across illuminants) represent the complementary constant hue; these complementary wavelengths also plot a near-parallel line to the first constant hue. To confirm and further define the constant slope of these lines, it is shown that complementary wavelength pairs, per CIE data, can only plot parallel straight lines at the angle of 87° ± 1. In summary, near-parallel sloping lines represent constant hues at near-invariant wavelength ratios. This mechanism of color constancy is shown to relate to the well-known theory of relational color constancy from invariant cone-excitation ratios. In the visual process, the latter ratios are presumably the source of the former (invariant wavelength ratios). © 2008 Wiley Periodicals, Inc. Col Res Appl, 33, 238,249, 2008 [source] High-frequency gamma oscillations coexist with low-frequency gamma oscillations in the rat visual cortex in vitroEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 8 2010Olaleke O. Oke Abstract Synchronization of neuronal activity in the visual cortex at low (30,70 Hz) and high gamma band frequencies (> 70 Hz) has been associated with distinct visual processes, but mechanisms underlying high-frequency gamma oscillations remain unknown. In rat visual cortex slices, kainate and carbachol induce high-frequency gamma oscillations (fast-,; peak frequency , 80 Hz at 37°C) that can coexist with low-frequency gamma oscillations (slow-,; peak frequency , 50 Hz at 37°C) in the same column. Current-source density analysis showed that fast-, was associated with rhythmic current sink-source sequences in layer III and slow-, with rhythmic current sink-source sequences in layer V. Fast-, and slow-, were not phase-locked. Slow-, power fluctuations were unrelated to fast-, power fluctuations, but were modulated by the phase of theta (3,8 Hz) oscillations generated in the deep layers. Fast-, was spatially less coherent than slow-,. Fast-, and slow-, were dependent on ,-aminobutyric acid (GABA)A receptors, ,-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors and gap-junctions, their frequencies were reduced by thiopental and were weakly dependent on cycle amplitude. Fast-, and slow-, power were differentially modulated by thiopental and adenosine A1 receptor blockade, and their frequencies were differentially modulated by N -methyl- d -aspartate (NMDA) receptors, GluK1 subunit-containing receptors and persistent sodium currents. Our data indicate that fast-, and slow-, both depend on and are paced by recurrent inhibition, but have distinct pharmacological modulation profiles. The independent co-existence of fast-, and slow-, allows parallel processing of distinct aspects of vision and visual perception. The visual cortex slice provides a novel in vitro model to study cortical high-frequency gamma oscillations. [source] Cognitive control processes during an anticipated switch of taskEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 3 2003G. R. Wylie Abstract For successful negotiation of our environment, humans must be readily able to switch from one task to another. This ability relies on ,executive control' processes and despite extensive efforts to detail the nature of these processes, there is little consensus as to how the brain achieves this critical function. Behavioural studies show that as subjects are given more time to prepare to switch task, performance improves; yet even with the longest preparation intervals, there remains an ineradicable performance cost on switch trials. As such, some elements of the switching process must wait until the stimulus to be acted upon has actually been presented. Here, using the methods of high-density mapping of brain potentials, we show that early visual processes are substantially different on switch trials than on later trials. Our data show that while there is clearly a degree of preparatory processing that occurs prior to a predictable switch of task, some elements of switching are only achieved after the switch stimulus has been presented. Our findings are discussed in the context of a new model of executive control processes that suggests that preparing to switch task may not be a separate (control) process per se, but rather, the beginning of a competition between the potentially relevant tasks, a competition that is ultimately resolved during the switch trial. [source] How does the color influence figure and shape formation, grouping, numerousness and reading?OPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 5 2010The role of chromatic wholeness, fragmentation Abstract In this work it is suggested that color induces phenomenal wholeness, part-whole organization and fragmentation. The phenomenal wholeness subsumes the set of its main attributes: homogeneity, continuity, univocality, belongingness, and oneness. If color induces wholeness, it can also induce fragmentation. Therefore, in order to understand the role played by color within the process of part-whole organization, color is used both as a wholeness and as a fragmentation tool, thus operating synergistically or antagonistically with other wholeness processes. Therefore, color is expected to influence figure-ground segregation, grouping, shape formation and other visual processes that are related to the phenomenal wholeness. The purpose of this study is to rate the influence of color in inducing whole and part-whole organization and, consequently, in determining the perception of figure-ground segregation, grouping, shape formation, numerousness evaluation and time reading. We manipulated experimental conditions by using equiluminant colors to favor or break (parcel-out) the wholeness of objects like geometrical composite figures and words. The results demonstrated that color is aimed, among other psychological and biological purposes, at: (1) relating each chromatic component of an object, thus favoring the emergence of the whole object; (2) eliciting a part-whole organization, whose components are interdependent; (3) eliciting fragments and then breaking up the whole and favoring the emergence of single components. Wholeness, part-whole organization and fragmentation can be considered as three further purposes of color. [source] Historical perspective: Neurological advances from studies of war injuries and illnesses,ANNALS OF NEUROLOGY, Issue 4 2009Douglas J. Lanska MD Early in the 20th century during the Russo-Japanese War and World War I (WWI), some of the most important, lasting contributions to clinical neurology were descriptive clinical studies, especially those concerning war-related peripheral nerve disorders (eg, Hoffmann-Tinel sign, Guillain-Barré-Strohl syndrome [GBS]) and occipital bullet wounds (eg, the retinal projection on the cortex by Inouye and later by Holmes and Lister, and the functional partitioning of visual processes in the occipital cortex by Riddoch), but there were also other important descriptive studies concerning war-related aphasia, cerebellar injuries, and spinal cord injuries (eg, cerebellar injuries by Holmes, and autonomic dysreflexia by Head and Riddoch). Later progress, during and shortly after World War II (WWII), included major progress in understanding the pathophysiology of traumatic brain injuries by Denny-Brown, Russell, and Holbourn, pioneering accident injury studies by Cairns and Holbourn, promulgation of helmets to prevent motorcycle injuries by Cairns, development of comprehensive multidisciplinary neurorehabilitation by Rusk, and development of spinal cord injury care by Munro, Guttman, and Bors. These studies and developments were possible only because of the large number of cases that allowed individual physicians the opportunity to collect, collate, and synthesize observations of numerous cases in a short span of time. Such studies also required dedicated, disciplined, and knowledgeable investigators who made the most out of their opportunities to systematically assess large numbers of seriously ill and injured soldiers under stressful and often overtly dangerous situations. Ann Neurol 2009;66:444,459 [source] | ||||||||||