Alterations to foveal crowding with microsaccade preparation.

Visual stimuli presented around the time of a saccade have been shown to be perceived differently by the visual system, including a reduction in the harmful impact of flankers (crowding). However, whether the effects observed are due strictly to crowding remains controversial, and the effects have only been measured with large saccades in peripheral vision. Here we investigate how crowded stimuli placed 20 arc minutes from the center of gaze are affected by an upcoming microsaccade. The stimulus consisted of a rotated T of size 6.25 arcminutes that was either unflanked, surrounded by four flankers (Experiment 1), or surrounded by two flankers that were positioned either radially or tangentially (Experiments 2 and 3). In 80 % of trials, subjects made voluntary microsaccades to the target when cued, and in the remaining 20 % of the trials subjects continued to maintain fixation. In Experiments 1 and 2, subjects were required to saccade to the same location as the target, while in Experiment 3 subjects saccaded to a different location âˆ¼ 20 arc min to the upper left of the target. Thus, we provide evidence for two separable pre-saccadic benefits for crowded parafoveal targets: one isotropizes the crowding zone for stimuli presented 200 to 125 ms before microsaccadic onset, and another provides a benefit exclusively for microsaccade targets surrounded by tangential flankers in the presence of imminent microsaccades. Two possible mechanisms are attentional enhancement and predictive remapping of receptive fields, respectively.

Microsaccadic correlates of covert attention and crowding.

Spatial crowding occurs when an object is cluttered among other objects in space and is a ubiquitous factor affecting object recognition in the peripheral visual field. Crowding is typically tested by presenting crowded stimuli at an eccentric location while having observers fixate at a point in space. However, even during fixation, our eyes are not perfectly steady but instead make small-scale eye movements (microsaccades) that have recently been suggested to be affected by shifts in attentional allocation. In the current study, we monitored microsaccadic behavior (a possible attentional correlate) to understand naturally occurring shifts in attention that occur following the presentation of a crowded stimulus. A tracking scanning laser ophthalmoscope (TSLO) was used to image the right eye of each observer during a psychophysical task. The stimuli consisted of Sloan numbers (0-9) presented briefly, either unflanked or surrounded by Sloan numbers at one of four nominal spacings. The extent of crowding was found to decrease by 26% on trials with the presence of incongruent microsaccades (proposed to suggest attentional capture). These findings complement the existing body of literature on the beneficial impact of explicit shifts of spatial attention to the location of a crowded stimulus.

Asymmetries of reading eye movements in simulated central vision loss.

Patients with central vision loss are forced to use an eccentric retinal location as a substitute for the fovea, called a preferred retinal locus, or PRL. Clinical studies have shown that patients habitually choose a PRL located either to the left, and/or below the scotoma in the visual field. The position to the right of the scotoma is almost never chosen, even though this would be theoretically more suitable for reading, since the scotoma no longer blocks the upcoming text. In the current study, we tested whether this asymmetry may have an oculomotor basis. Six normally sighted subjects viewed page-like text with a simulated scotoma, identifying embedded numbers in "words" comprising random letters. Subjects trained and tested with three different artificial PRL ("pseudo-PRL," or pPRL) locations: inferior, to the right, or to the left of the scotoma. After several training blocks for each pPRL position, subjects were found to produce reliable oculomotor control. Both reading speed and eye movement characteristics reproduced observations from traditional paradigms such as page-mode reading and RSVP for an advantage for an inferior pPRL. While left and right positions resulted in similar reading speeds, we observed that a right pPRL caused excessively large saccades and more direction switches, exhibiting a zig-zag pattern that developed spontaneously. Thus, we propose that patients' typical avoidance of pPRL positions to the right of their scotoma could have an oculomotor component: the erratic eye motion might potentially negate the perceptual benefit that this pPRL would offer.

Formalin dab, the effective way of treating haemorrhagic radiation proctitis: a randomized trial from a tertiary care hospital in South India.

AIM: Chronic radiation proctitis with bleeding is a common problem encountered following radiotherapy for pelvic malignancy. Sucralfate-steroid enema and formalin dab are two common nonsurgical treatments. A randomized trial was conducted to compare the efficacy of these two methods. METHOD: This was a prospective randomized controlled trial conducted in the Jawaharlal Institute of Postgraduate Medical Education & Research (JIPMER) from August 2005 to May 2007. One-hundred and two patients with chronic radiation proctitis, presenting as rectal bleeding after radiotherapy for carcinoma of the cervix, were recruited and randomly allocated into two treatment groups: Group 1, formalin dab; and Group 2, sucralfate-steroid retention enema. The mean age of the patients was 51.3 ± 5.1 years. The mean interval between the end of radiotherapy and the onset of bleeding was 12.3 ± 3.5 months. Symptom score and sigmoidoscopic grade were assessed before, and at 1 month after, treatment. RESULTS: Ninety per cent of patients in Group 1 and 74.5% of patients in Group 2 responded to treatment (P = 0.038). In spite of having a higher median symptom score before treatment, patients in Group 1 demonstrated a marked decrease in symptom score after treatment compared with patients in Group 2 and the difference once again was statistically significant (P = 0.000). Similarly, the median sigmoidoscopic grade was significantly lower for patients in Group 1 compared with patients in Group 2 after treatment (P = 0.000). There were no specific treatment-related complications in either group. CONCLUSIONS: Formalin (4%) dab is superior to sucralfate-steroid retention enema for treatment of chronic haemorrhagic radiation proctitis.

Theoretical study on the electronic states of formylcarbene (HC.CHO) and triplet ketene (H2CCO) and the ultraviolet absorption spectra attributable to these molecules.

The adiabatic energies, vibrational frequencies, and geometries of the ground and excited electronic states of formylcarbene and the triplet electronic states of ketene are calculated employing the state-of-the art ab initio methods. With the help of these calculations, certain ultraviolet (UV) absorption bands observed in the flash photolysis of oxazole and iso-oxazole are assigned to formylcarbene and triplet ketene.

Detection and classification of motor nerve late-wave activity.

The health of peripheral nerves is commonly assessed using nerve conduction studies, in which the nerve is stimulated electrically and the evoked responses are analyzed. In motor nerve studies, important diagnostic information is provided by the late-wave responses, comprised of F-waves, A-waves and repeaters. Computer-based analysis of late-wave activity is challenging due to the random nature and low amplitude of these signals. This paper describes an algorithm for segmenting portions of late-wave activity and classifying the type of evoked response. The algorithm may be used to improve the robustness of computer-based late-wave assessment.

Theoretical study on the ground and excited states of dicyanocarbene (C3N2) and its isomers: a low-temperature matrix emission spectrum attributable to 3-cyano-2H-azirenylidene.

Ab initio calculations are used to characterize the ground and low lying excited electronic states of selected dicyanocarbene (C(3)N(2) or C(CN)2) isomers. Our calculated ground state geometries and the corresponding vibrational frequencies agree well with available experimental and theoretical data, thereby providing the reliability of the predicted quantities. The present calculations are used to identify the possible emitting species for some unidentified emission bands observed in certain low-temperature matrices. It is found that the 1(3)A' --> X(1)A' transition of 3-cyano-2H-azirenylidene, that is, cyclic C(2)N-CN (Figure 1c) satisfactorily explains all of the observed spectral features of these bands.

Theoretical study on the excited states of HCN.

In the flash-photolysis of oxazole, iso-oxazole, and thiozole a transient band system was observed in the region 2500-3050 angstroms. This band system was attributed to a meta-stable form of HCN, i.e., either HNC or triplet HCN. Theoretical investigations have been carried out on the ground and excited states of HCN to characterize this and other experimentally observed transitions. The predicted geometries are compared with the experiment and earlier theoretical calculations. The present calculations show that the band system in the region 2500-3050 A corresponds to the transition 4 3-A' <-- 1 3-A' of HCN.

Multiresolution Gauss-Markov random field models for texture segmentation.

This paper presents multiresolution models for Gauss-Markov random fields (GMRFs) with applications to texture segmentation. Coarser resolution sample fields are obtained by subsampling the sample field at fine resolution. Although the Markov property is lost under such resolution transformation, coarse resolution non-Markov random fields can be effectively approximated by Markov fields. We present two techniques to estimate the GMRF parameters at coarser resolutions from the fine resolution parameters, one by minimizing the Kullback-Leibler distance and another based on local conditional distribution invariance. We also allude to the fact that different GMRF parameters at the fine resolution can result in the same probability measure after subsampling and present the results for first- and second-order cases. We apply this multiresolution model to texture segmentation. Different texture regions in an image are modeled by GMRFs and the associated parameters are assumed to be known. Parameters at lower resolutions are estimated from the fine resolution parameters. The coarsest resolution data is first segmented and the segmentation results are propagated upward to the finer resolution. We use the iterated conditional mode (ICM) minimization at all resolutions. Our experiments with synthetic, Brodatz texture, and real satellite images show that the multiresolution technique results in a better segmentation and requires lesser computation than the single resolution algorithm.

Delineating buildings by grouping lines with MRFs.

Traditionally, Markov random field (MRF) models have been used in low-level image analysis. The article presents an MRF-based scheme to perform object delineation. The proposed edge-based approach involves extracting straight lines from the edge map of an image. Then, an MRF model is used to group these lines to delineate buildings in aerial images.

Exercise recordings for the detection of T wave alternans. Promises and pitfalls.

Despite significant advances in the treatment of sudden cardiac death, many individuals still go untreated because routine clinical tests do not identify them to be at risk. Recently, a study to identify individuals at risk has shown that the presence of T wave alternans (TWA), a fluctuation in T wave morphology occurring on an every-other-beat basis, is an accurate predictor of subsequent ventricular tachyarrhythmic events. T wave alternans as low as a few microvolts was found to be significant in predicting risk. Since TWA is often detectable only at elevated heart rates, the study used atrial pacing to increase the heart rate to approximately 100 beats/min. To make TWA measurement more broadly applicable, the authors have developed a methodology that uses noninvasive physiologic stress to raise the heart rate. A particular challenge was the measurement of TWA during exercise, since the levels of noise during exercise can far exceed the levels of TWA. However, by using special multisegment Hi-Res electrodes (Cambridge Heart, Bedford, MA), noise reduction software, and a spectral method of alternans analysis, the authors have been able to reduce noise and reliably measure microvolt-level alternans. This study presents an overview of the methodology for recording and analyzing microvolt-level TWA during ergometer exercise.