Transitions between central and peripheral vision create spatial/temporal distortions: a hypothesis concerning the perceived break of the curveball

Background

The human visual system does not treat all parts of an image equally: the central segments of an image, which fall on the fovea, are processed with a higher resolution than the segments that fall in the visual periphery. Even though the differences between foveal and peripheral resolution are large, these differences do not usually disrupt our perception of seamless visual space. Here we examine a motion stimulus in which the shift from foveal to peripheral viewing creates a dramatic spatial/temporal discontinuity.

Methodology/Principal Findings

The stimulus consists of a descending disk (global motion) with an internal moving grating (local motion). When observers view the disk centrally, they perceive both global and local motion (i.e., observers see the disk''s vertical descent and the internal spinning). When observers view the disk peripherally, the internal portion appears stationary, and the disk appears to descend at an angle. The angle of perceived descent increases as the observer views the stimulus from further in the periphery. We examine the first- and second-order information content in the display with the use of a three-dimensional Fourier analysis and show how our results can be used to describe perceived spatial/temporal discontinuities in real-world situations.

Conclusions/Significance

The perceived shift of the disk''s direction in the periphery is consistent with a model in which foveal processing separates first- and second-order motion information while peripheral processing integrates first- and second-order motion information. We argue that the perceived distortion may influence real-world visual observations. To this end, we present a hypothesis and analysis of the perception of the curveball and rising fastball in the sport of baseball. The curveball is a physically measurable phenomenon: the imbalance of forces created by the ball''s spin causes the ball to deviate from a straight line and to follow a smooth parabolic path. However, the curveball is also a perceptual puzzle because batters often report that the flight of the ball undergoes a dramatic and nearly discontinuous shift in position as the ball nears home plate. We suggest that the perception of a discontinuous shift in position results from differences between foveal and peripheral processing.     

Extracellular High Mobility Group Box-1 (HMGB1) Inhibits Enterocyte Migration via Activation of Toll-like Receptor-4 and Increased Cell-Matrix Adhesiveness

Toll-like receptor-4 (TLR4) is the receptor for bacterial lipopolysaccharide, yet it may also respond to a variety of endogenous molecules. Necrotizing enterocolitis (NEC) is the leading cause of death from gastrointestinal disease in newborn infants and is characterized by intestinal mucosal destruction and impaired enterocyte migration due to increased TLR4 signaling on enterocytes. The endogenous ligands for TLR4 that lead to impaired enterocyte migration remain unknown. High mobility group box-1 (HMGB1) is a DNA-binding protein that is released from injured cells during inflammation. We thus hypothesize that extracellular HMGB1 inhibits enterocyte migration via activation of TLR4 and sought to define the pathways involved. We now demonstrate that murine and human NEC are associated with increased intestinal HMGB1 expression, that serum HMGB1 is increased in murine NEC, and that HMGB1 inhibits enterocyte migration in vitro and in vivo in a TLR4-dependent manner. This finding was unique to enterocytes as HMGB1 enhanced migration of inflammatory cells in vitro and in vivo. In seeking to understand the mechanisms involved, TLR4-dependent HMGB1 signaling increased RhoA activation in enterocytes, increased phosphorylation of focal adhesion kinase, and increased phosphorylation of cofilin, resulting in increased stress fibers and focal adhesions. Using single cell force traction microscopy, the net effect of HMGB1 signaling was a TLR4-dependent increase in cell force adhesion, accounting for the impaired enterocyte migration. These findings demonstrate a novel pathway by which TLR4 activation by HMGB1 delays mucosal repair and suggest a novel potential therapeutic target in the amelioration of intestinal inflammatory diseases like NEC.     

Flow cytometric estimation of DNA and RNA content in intact cells stained with Hoechst 33342 and pyronin Y

The addition of RNA content estimation to flow cytometric measurement of DNA content provides valuable information concerning cells' transitions between quiescent and proliferative states. Equilibrium staining methods employing acridine orange have been used for DNA/RNA content measurement but are difficult to apply to intact cells and impractical for use in conjunction with fluorescent antibodies or ligands for demonstration of cell surface structures. I have used a combination of Hoechst 33342 (HO342) and pyronin Y (PY) to stain intact cells for DNA/RNA content estimation with a dual source flow cytometer using UV and blue-green or green excitation, measuring HO342 fluorescence at 430--470 nm and PY fluorescence at 590--650 nm. Results obtained with cultured cells and stimulated lymphocytes are in good agreement with those obtained using acridine orange for DNA/RNA staining; about half of the PY fluorescence can be removed from ethanol-fixed cells stained with HO342 and PY by RNAse digestion. The HO342/PY method can be combined with fluorescein immunofluorescence for detection of cell surface markers. HO342 can be combined with other tricyclic heteroaromatic dyes for DNA/RNA estimation; the combination of HO342 and oxazine 1 can be excited in a dual source instrument using a mercury arc lamp and a helium-neon laser. The staining procedure is simple; cells in medium are incubated with 5 microM HO342 at 37 degrees C for 45 min, 5 microM PY (or oxazine 1) is then added and cells are analyzed without washing after an additional 45 min incubation. Suitability of these dye combinations for vital cell staining and sorting remains to be determined.     

E2A-HLF-mediated cell transformation requires both the trans-activation domains of E2A and the leucine zipper dimerization domain of HLF.

The E2A-HLF fusion gene, formed by the t(17;19)(q22;p13) translocation in childhood acute pro-B-cell leukemia, encodes a hybrid protein that contains the paired trans-activation domains of E2A (E12/E47) linked to the basic region/leucine zipper DNA-binding and dimerization domain of hepatic leukemia factor (HLF). To assess the transforming potential of this novel gene, we introduced it into NIH 3T3 murine fibroblasts by using an expression vector that also contained the neomycin resistance gene. Cells selected for resistance to the neomycin analog G418 formed aberrant colonies in monolayer cultures, marked by increased cell density and altered morphology. Transfected cells also grew readily in soft agar, producing colonies whose sizes correlated with E2A-HLF expression levels. Subclones expanded from colonies with high levels of the protein reproducibly formed tumors in nude mice and grew to higher plateau-phase cell densities in reduced-serum conditions than did parental NIH 3T3 cells. By contrast, NIH 3T3 cells expressing mutant E2A-HLF proteins that lacked either of the bipartite E2A trans-activation domains or the HLF leucine zipper domain failed to show oncogenic properties, including anchorage-independent cell growth. Thus, both of the E2A trans-activation motifs and the HLF leucine zipper dimerization domain are essential for the transforming potential of the chimeric E2A-HLF protein, suggesting a model in which aberrant regulation of the expression pattern of downstream target genes contributes to leukemogenesis.     

Biocontrol evaluation of extracts and a major component,clusianone, from Clusia fluminensis Planch. & Triana against Aedes aegypti

Studies evaluated the effects of hexanic extracts from the fruits and flowers ofClusia fluminensis and the main component of the flower extract, a purified benzophenone (clusianone), against Aedes aegypti. The treatment of larvae with the crude fruit or flower extracts from C. fluminensis did not affect the survival ofAe. aegypti (50 mg/L), however, the flower extracts significantly delayed development of Ae. aegypti. In contrast, the clusianone (50 mg/L) isolate from the flower extract, representing 54.85% of this sample composition, showed a highly significant inhibition of survival, killing 93.3% of the larvae and completely blocking development of Ae. aegypti. The results showed, for the first time, high activity of clusianone against Ae. aegypti that both killed and inhibited mosquito development. Therefore, clusianone has potential for development as a biopesticide for controlling insect vectors of tropical diseases. Future work will elucidate the mode of action of clusianone isolated from C. fluminensis.     

Climate impacts on transocean dispersal and habitat in gray whales from the Pleistocene to 2100

Arctic animals face dramatic habitat alteration due to ongoing climate change. Understanding how such species have responded to past glacial cycles can help us forecast their response to today's changing climate. Gray whales are among those marine species likely to be strongly affected by Arctic climate change, but a thorough analysis of past climate impacts on this species has been complicated by lack of information about an extinct population in the Atlantic. While little is known about the history of Atlantic gray whales or their relationship to the extant Pacific population, the extirpation of the Atlantic population during historical times has been attributed to whaling. We used a combination of ancient and modern DNA, radiocarbon dating and predictive habitat modelling to better understand the distribution of gray whales during the Pleistocene and Holocene. Our results reveal that dispersal between the Pacific and Atlantic was climate dependent and occurred both during the Pleistocene prior to the last glacial period and the early Holocene immediately following the opening of the Bering Strait. Genetic diversity in the Atlantic declined over an extended interval that predates the period of intensive commercial whaling, indicating this decline may have been precipitated by Holocene climate or other ecological causes. These first genetic data for Atlantic gray whales, particularly when combined with predictive habitat models for the year 2100, suggest that two recent sightings of gray whales in the Atlantic may represent the beginning of the expansion of this species' habitat beyond its currently realized range.     

Dexamethasone and estrogen regulate Xenopus laevis albumin mRNA levels

The regulation of albumin mRNA levels by steroid hormones was examined in a primary Xenopus liver culture system. In the absence of exogenous steroid hormone, albumin mRNA levels declined rapidly in culture. Dexamethasone is required for preservation of albumin mRNA levels in culture and effects a greater than 10 fold induction of albumin mRNA in cultures maintained in steroid hormone-free medium. Estrogen can override the effect of dexamethasone and elicits a decline of greater than 80% in albumin mRNA levels. Our cDNA clones of the mRNAs encoding the two 74,000 dalton and one 72,000 dalton cellular albumins allowed us to show that all three albumin mRNAs were down regulated by estrogen.     

Longitudinal roentgencephalometric study of the growth of the New Zealand white rabbit: cumulative and biweekly incremental growth rates for skull and mandible

A longitudinal roentgencephalometric study of the New Zealand white rabbit has documented postnatal skull and mandible growth from 2 to 34 weeks of age. Dorsoventral and lateral radiographs were performed using a specially constructed restrainer that allowed for standardized films and did not require the use of anesthesia. Assessments from 17 male and 12 female rabbits at biweekly intervals documented cumulative growth as well as biweekly incremental growth. Indices reported here include skull length, interzygomatic width, intercondylar width, and mandibular length. Mean skull length at 2 weeks was 54% of that at 34 weeks, and by 16 weeks 91% of adult skull length was achieved. Mean interzygomatic width at 2 weeks was 60% of that at 34 weeks, and by 16 weeks 91% of adult male and 94% of adult female widths were achieved. Mean mandibular length at 2 weeks was 47% of that at 34 weeks, and by age 16 weeks 90% of adult length was achieved. Mean intercondylar width at 2 weeks was 57% of that at 34 weeks, and by 16 weeks 89% of adult male and 93% of adult female widths were achieved. Biweekly increments decreased continually from 2 weeks of age on for all indices.     

Palmitoyl-coenzyme A synthetase. Mechanism of reaction

The mechanism of long-chain fatty acid activation catalysed by highly purified microsomal palmitoyl-CoA synthetase was investigated. The kinetics of the overall reaction were found to conform to the Bi Uni Uni Bi Ping Pong mechanism. (18)O was transferred from [(18)O]palmitate to AMP and palmitoyl-CoA exclusively. The enzyme intermediate formed appeared to consist of enzyme-bound palmitate; this formation occurred only in the presence of ATP. However, the involvement of palmitoyl-AMP in the reaction catalysed by the purified enzyme has proved difficult to establish.