Reaction time to motion onset of luminance and chromatic gratings is determined by perceived speed

We measured reaction times for detecting motion onset for sinusoidal gratings whose contrast was modulated in either luminance or chromaticity, for various drift rates and contrasts. In general, reaction times to chromatic gratings were slower than to luminance gratings of matched cone contrast, but the difference in response depended critically on both contrast and speed. At high image speeds there was virtually no difference, whereas at low speeds, the difference was pronounced, especially at low contrasts. At high image speeds there was little dependence of reaction times on contrast (for either luminance or colour), whereas at low speeds the dependence was greater, particularly for chromatic stimuli. This pattern of results is reminiscent of those found for apparent speed of drifting luminance and chromatic gratings. We verified the effects of contrast on perceived speed, and went on to show that the effects of contrast on reaction times are totally predictable by the perceived speed of the stimuli, as if it were perceived rather than physical speed that determined reaction times. Our results support that idea of separate systems for fast and slow motion (with separate channels for luminance and colour at slower speeds), and further suggest that apparent speed and reaction times may be determined at a similar stage of motion analysis.     

"White matter atrophy, ventricular dilation, and intellectual functioning following traumatic brain injury": Correction.

Reports an error in the original article by S. C. Johnson et al (Neuropsychology, 1994[July], Vol 8[3], 301–315). On page 309, Figure 2 was printed upside down. Figures are provided in the correct position. (The following abstract of this article originally appeared in record 1994-38110-001.) Examined the role in traumatic brain injury (TBI) of injury severity measured by the Glasgow Coma Scale (GCS), white matter atrophy identified by various magnetic resonance imaging (MRI) morphometric techniques, and postinjury intellectual functioning measured with the Wechsler Adult Intelligence Scale—Revised (WAIS—R). MR images of 31 female and 33 male TBI patients were used to calculate corpus callosum (CC) areas, ventricular volumes (estimates of white matter loss), and parenchymal volumes. Results indicated that the men were on the average more severely injured, as indicated by significantly lower GCS scores. CC size correlated significantly with the ventricle-to-brain ratio (VBR), but no significant correlations were found between CC size and WAIS—R scores. Significant correlations were found for men only between VBR and Performance IQ and between VBR and the Digit Symbol subtest of the WAIS—R. Implications for the roles of white matter atrophy and intellectual functioning in TBI are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The planning jungle

Papua New Guinea is a country with more than its fair share of geographical and cultural problems. In order to unify the nation in some way, a comprehensive development programme is essential, as is a system for planning and monitoring the resources. A culture that finds stone tools more natural than steel is unlikely to make a success of a PERT system on a mainframe computer, but a computer of some considerable capacity is needed to facilitate the necessary flow of information. The paper discusses the problems, the thought-processes undertaken in reaching a solution and the lessons learned.     

SqFreeEVAL: An (almost) optimal real-root isolation algorithm

Let f be a univariate polynomial with real coefficients, f∈R[X]. Subdivision algorithms based on algebraic techniques (e.g., Sturm or Descartes methods) are widely used for isolating the real roots of f in a given interval. In this paper, we consider a simple subdivision algorithm whose primitives are purely numerical (e.g., function evaluation). The complexity of this algorithm is adaptive because the algorithm makes decisions based on local data. The complexity analysis of adaptive algorithms (and this algorithm in particular) is a new challenge for computer science. In this paper, we compute the size of the subdivision tree for the SqFreeEVAL algorithm.The SqFreeEVAL algorithm is an evaluation-based numerical algorithm which is well-known in several communities. The algorithm itself is simple, but prior attempts to compute its complexity have proven to be quite technical and have yielded sub-optimal results. Our main result is a simple O(d(L+lnd)) bound on the size of the subdivision tree for the SqFreeEVAL algorithm on the benchmark problem of isolating all real roots of an integer polynomial f of degree d and whose coefficients can be written with at most L bits.Our proof uses two amortization-based techniques: first, we use the algebraic amortization technique of the standard Mahler-Davenport root bounds to interpret the integral in terms of d and L. Second, we use a continuous amortization technique based on an integral to bound the size of the subdivision tree. This paper is the first to use the novel analysis technique of continuous amortization to derive state of the art complexity bounds.     

Antioxidant reactions of α-tocopherolhydroquinone

α-Tocopherolhydroquinone (TQH₂) is a product of α-tocopherol oxidation/reduction that exerts antioxidant effects in biological systems. TQH₂ inhibited autoxidation of methyl linoleate initiated by peroxyl radicals derived from thermolysis of 2,2′-azobis(2,4-dimethylvaleronitrile) in acetonitrile. TQH₂ oxidation yielded α-tocopherolquinone (TQ) as a major product and 2,3-epoxy-α-tocopherolquinone and 5,6-epoxy-α-tocopherolquinone as minor products. Each TQH₂ consumed approximately two peroxyl radicals in the course of the oxidation. The data suggest that TQH₂ scavenges peroxyl radicals primarily by electron transfer to form TQ and secondarily by addition-elimination to form the epoxyquinones.     

Large receptive fields for optic flow detection in humans

We used a psychophysical summation technique to study the properties of detectors tuned to radial, circular and translational motion, and to determine the spatial extent of their receptive fields. Signal-to-noise motion thresholds were measured for patterns curtailed spatially in various ways. Sensitivity for radial, circular and translational motion increased with stimulus area at a rate predicted by an ideal integrator. When sectors of noise were added to the stimulus, sensitivity decreased at a rate consistent with an ideal integrator. Summation was tested for large annular stimuli, and shown to hold up to 70 degrees in some cases, suggesting very large receptive fields for this type of motion (consistent with the physiology of neurones in the dorsal region of the medial superior temporal area (MSTd)). This is a far greater area than observed for summation of contrast sensitivity to gratings (Anderson SJ and Burr DC, Vis Res 1987;29:621-635, and to this type of stimuli (Morrone MC, Burr DC and Vaina LM, Nature 1995;376:507-509, consistent with the suggestion that the two techniques examine different levels of motion analysis.     

Cloning and characterization of a maize cDNA encoding phytoene desaturase, an enzyme of the carotenoid biosynthetic pathway

The work presents the results of researches of binding and degradation of 125I-Insulin by erythrocyte receptors in the patients with essential hypertension and healthy patients after glucose intake. In order to obtain full representation of the pattern of changes the serum IRI and glucose concentrations were assayed. Binding and degradation of 125I-Insulin by erythrocyte receptors were determined with the method described by Gambhir (1977), modified by the authors. The modification consisted in usage of constant concentrations of iodized insulin (0.9 pg/0.1 ml) and bovine insulin (2.4 I.U./0.1 ml). Before administration of glucose and in 30, 60 and 120 minutes after, venous blood was collected from ulnar vein. All examined persons were in sitting position during the trial of glucose intake. Obtained results show, that blood insulin level in the patients with essential hypertension is statistically significantly higher than in healthy persons of similar anthropometric characteristics. Binding of 125I-Insulin to erythrocyte receptors in fasting state is statistically significantly lower. Degradation after glucose intake in the patients shows decreasing tendency, while in healthy persons--growing tendency.     

Saponification of wheat straw-g-polyacrylonitrile

Wheat straw-g-polyacrylonitrile (PAN), containing 40% PAN, was saponified with sodium hydroxide and isolated under three sets of saponification and work-up conditions. Each reaction mixture was separated into a water-soluble and a water-insoluble fraction, which were individually analyzed for percentages (by weight) of synthetic polymer (saponified PAN), cellulose, hemicellulose, and lignin. Water solubles amounted to 14–24% of the total product and contained 70–74% synthetic polymer, the remainder being hemicellulose and lignin. Although water-insoluble fractions contained 52–54% saponified PAN, their water absorbencies were low (14–17 g H₂O/g polymer). Treatment of these fractions with the enzyme cellulase converted 55–62% of the total cellulose of glucose.