An analysis of the McKee phonetic inventory for grade three.

Thesis (Ed.M.)--Boston Universit

Human cones appear to adapt at low light levels: Measurements on the red—green detection mechanism

AbstractRecent physiological evidence suggests that cones do not light adapt at low light levels. To assess whether adaptation is cone-selective at low light levels, the red-green detection mechanism was isolated. Thresholds were measured with a large test flash, which stimulated the L and M cones in different fixed amplitude ratios, on different colored adapting fields. Thresholds were plotted in L and M cone contrast coordinates. The red-green mechanism responded to an equally-weighted difference of L and M cone contrast on each colored field, demonstrating equivalent, Weberian adaptation of the L and M cone signals. The L and M cone signals independently adapted for illuminance levels as low as 60 effective trolands (e.g. M-cone trolands. Since this adaptation is entirely selective to cone type, it suggests that the cones themselves light-adapt. The red-green detection contour on reddish fields was displaced further out from the origin of the cone contrast coordinates, revealing an additional sensitivity loss at a subsequent, spectrally-opponent site. This second-site effect may arise from a net “red” or “green” signal that represents the degree to which the L and M cones are differently hyperpolarized by the steady, colored adapting field. Such differential hyperpolarization is compatible with equivalent, Weberian adaptation of the L and M cones

The Effects of Luminance Boundaries on Color Perception

The luminance and red-green chromatic detection mechanisms respond to, respectively, the sum and difference of the long-wave (L) and middle-wave (M) zone contrast signals. The most-detectable stimulus is not a small patch of luminance drifting grating, as suggested by others, but rather a small, foveal red-green chromatic flash. Even at the smallest test size examined, 2.3\u27 diameter, the red-green mechanism i~s more sensitive than the luminance mechanism, which has profound implication for visual physiology. When a suprathreshold luminance flash (a pedestal) occurs coincidentally with a red-green chromatic flash, detection of color is facilitated ~2-fold, regardless of spot size, as shown by forced-choice results, and this constant facilitation contrasts with the much larger facilitation reported earlier for small flashes. The lack of chromatic masking by suprathreshold luminance pedestals supports the view of separable luminance and red-green detectors. Isolation of the red-green mechanism with large test flashes on different colored backgrounds showed that the red-green mechanism responds to an equally-weighted difference of L and M cone contrast on each background. Even for fields as low as 400 trolands, sensitivity is controlled by cone-selective adaptation (as well as second-site adaptation), which is surprising in view of recent physiological recordings suggesting that light adaptation in cones is insignificant below 2000 trolands. Motion mechanisms receiving L and M cone signals were studied with 1 cpd, flickering and drifting gratings. At low velocity, a spectrally-opponent (SPO) motion mechanism is more sensitive than the luminance (LUM) mechanism, which summates L and M signals. The SPO mechanism has equal L and M contrast weights at low velocity but is L-cone dominated at intermediate and high velocity, whereas the LUM mechanism shows the reverse pattern of weights. The SPO motion mechanism appears distinct frown a red-green hue mechanism, for the latter has balanced L and M inputs at all temporal frequencies. The two motion mechanisms can be distinguished by the relative phase shifts of the L and M inputs: large shifts are seen for the LUM mechanism at intermediate frequency (4-9 Hz), where SPO shows very little shifts

Ueber das Auftreten von Xanthin im Harn

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The photopigment bleaching hypothesis of complementary after-images: A psychophysical test

Normal observers color-adapted simultaneously to two spatially distinct sequences of light stimulation, equivalent in their bleaching effects but complementary to one another in hue. Following the adapting period, observers reported on the color appearance of the two adjacent after-images seen against a neutral background. The nonequivalence of the two after-images argues against the explanation of complementary after-images based on photopigment bleaching; in addition, the fact that the two after-images are mutually complementary further restricts the class of (neural) adaptation hypotheses.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/34030/1/0000307.pd

Draft Genome Sequence of the Phenazine-Producing \u3ci\u3ePseudomonas fluorescens\u3c/i\u3e Strain 2-79

Pseudomonas fluorescens strain 2-79, a natural isolate of the rhizosphere of wheat (Triticum aestivum L.), possesses antagonistic potential toward several fungal pathogens. We report the draft genome sequnce of strain 2-79, which comprises 5,674 protein-coding sequences

Malignant Myoepithelioma of the Palate: A Case Report with Review of the Clinicopathological Characteristics

A malignant myoepithelioma is one of the rarest salivary gland neoplasms which may either arise de novo or develop within a preexisting pleomorphic adenoma or benign myoepithelioma. The parotid gland is the most common primary site and the palate the most common intra-oral site of occurrence. Herein is present a case of a malignant myoepithelioma arising in the hard palate of a 79-year-old woman. The lesion had been examined by biopsy at another hospital, and diagnosed as a poorly differentiated squamous cell carcinoma. The patient underwent a wide local tumor resection. Examination of the resection specimen showed the characteristic histopathological and immunohistochemical features of a malignant myoepithelioma. Five months after the operation, the patient was well without evidence of recurrence or metastasis

Pupil responses associated with coloured afterimages are mediated by the magno-cellular pathway

Sustained fixation of a bright coloured stimulus will, on extinction of the stimulus and continued steady fixation, induce an afterimage whose colour is complementary to that of the initial stimulus; an effect thought to be caused by fatigue of cones and/or of cone-opponent processes to different colours. However, to date, very little is known about the specific pathway that causes the coloured afterimage. Using isoluminant coloured stimuli recent studies have shown that pupil constriction is induced by onset and offset of the stimulus, the latter being attributed specifically to the subsequent emergence of the coloured afterimage. The aim of the study was to investigate how the offset pupillary constriction is generated in terms of input signals from discrete functional elements of the magno- and/or parvo-cellular pathways, which are known principally to convey, respectively, luminance and colour signals. Changes in pupil size were monitored continuously by digital analysis of an infra-red image of the pupil while observers viewed isoluminant green pulsed, ramped or luminance masked stimuli presented on a computer monitor. It was found that the amplitude of the offset pupillary constriction decreases when a pulsed stimulus is replaced by a temporally ramped stimulus and is eliminated by a luminance mask. These findings indicate for the first time that pupillary constriction associated with a coloured afterimage is mediated by the magno-cellular pathway. © 2003 Elsevier Science Ltd. All rights reserved

Pattern-Sensitive Epilepsy. I: A Demonstration of a Spatial Frequency Selective Epileptic Response to Gratings

Rare individuals suffer epileptic seizures when they view certain images, particularly stripes. Contrast-threshold functions (the ability to see faint stripes of various widths) were determined for two pattern-sensitive brothers, and the epileptogenicity of various patterns was assessed for one of them. Sine wave grating contrast-detection thresholds for the two subjects were essentially normal, with lowest thresholds at approximately 2 cycles/ degree (c/deg). Epileptiform discharges occurred maximally at 5 c/deg with a 1-octave 50% bandwidth. Pattern epileptogenicity was increased by the addition of a third harmonic sine wave grating to its fundamental, but was unaffected by the phase relation of the two gratings. The frequency selectivity of epileptic responsiveness was quantitatively similar to a “spatial frequency channel.” Inhibitory interactions were not present. The findings suggest relations between the phenomena of pattern-sensitive epilepsy and hypothesized spatial frequency channels which merit further exploration. RESUMEN De manera excepcional, hay personas que pueden tener ataques epilÉpticos cuando ven ciertas imÁgenes, particularmente rayas. Se determinaron los umbrales para contrastes (la capacidad de ver rayas de diversas anchuras y muy tenues) en dos hermanos sensibles a patrones y se estableciÓ la epileptogeneidad de di versos patrones en uno de ellos. Los umbrales para contrastes fueron esencialmente normales en los dos sujetos cuando se utilizeÓ una rejilla hecha con ondas sinusoidales, siendo el umbral inferior unos 2 ciclos/ grado (c/deg). Descargas epileptiformes tuvieron lugar de modo mÁximo a 5 c/deg con una amplitud de banda del 50% de una octava. la capacidad epileptogÉnica del partÓn aumentÓ cuando se aÑadiÓ una tercera sinusoide armÓnica a la rejilla base pero esa capacidad no se viÓ alterada por la relaciÓn de fase entre las dos rejillas. La selectividad de la frecuencia de la respuesta epileptogÉnica fue cuantitativamente similar al “canal de frecuencia espacial”. No se observaron interacciones inhibitorias. Los hallazgos sugieren que hay relaciones entre la epilepsyÍa secundaria a patrones visuales y los hipotÉticos canales de frecuencia espacial, lo cual merece mÁs investigaciÓn.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65270/1/j.1528-1157.1980.tb04075.x.pd