Photovoltage of rods and cones in the macaque retina

Schneeweis, David M.; Schnapf, Julie L.

doi:10.1126/science.7754386

Cited by 300 publications

(308 citation statements)

References 11 publications

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“…In salamander retina, the dark resting potential of rods averages −44 mV whereas the cone resting potential is slightly more depolarized (−39 mV) (Thoreson et al, 2003b). In primate retina, rod dark membrane potentials were found to be more positive (−37 mV) than cone membrane potentials (−46 mV) (Schneeweis and Schnapf, 1995).…”

Section: Relationship Between Membrane Potential and Calcium Influxmentioning

confidence: 95%

“…In the cone circuit, noise is reduced by utilizing desensitized AMPA/KA receptors (De Vries and Schwartz, 1999). Voltage noise in amphibian, but not mammalian rod is reduced by rod-rod coupling (Krizaj et al, 1998;Schneeweis and Schnapf, 1995), but this does not greatly diminish the noisy Ca 2+ signals arising from stochastic openings of single calcium channels. Pooling of noisy signals through integration within the OFF bipolar cell dendrites, however, does occur in all vertebrate retinas.…”

Section: Relation Of Synaptic Release To the Underlying Light-evoked mentioning

confidence: 99%

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Synaptic transmission at retinal ribbon synapses

Heidelberger

Thoreson

Witkovsky

2005

Progress in Retinal and Eye Research

208

231

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The molecular organization of ribbon synapses in photoreceptors and ON bipolar cells is reviewed in relation to the process of neurotransmitter release. The interactions between ribbon synapseassociated proteins, synaptic vesicle fusion machinery and the voltage-gated calcium channels that gate transmitter release at ribbon synapses are discussed in relation to the process of synaptic vesicle exocytosis. We describe structural and mechanistic specializations that permit the ON bipolar cell to release transmitter at a much higher rate than the photoreceptor does, under in vivo conditions. We also consider the modulation of exocytosis at photoreceptor synapses, with an emphasis on the regulation of calcium channels.

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Section: Relationship Between Membrane Potential and Calcium Influxmentioning

confidence: 95%

Section: Relation Of Synaptic Release To the Underlying Light-evoked mentioning

confidence: 99%

Synaptic transmission at retinal ribbon synapses

Heidelberger

Thoreson

Witkovsky

2005

Progress in Retinal and Eye Research

208

231

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show abstract

“…Posteriormente, la señal RGB es corregida para reducir la dependencia de la luminancia; la corrección que se utilizada proviene de la ley de Michaelis-Menten [18], la cual modela la adaptación de la visión humana ante los cambios de iluminación. Las nuevas componentes, notadas por (Rc, Gc, Bc), son calculadas como se muestra en la ecuación (2), donde L(x,y) es la luminancia del píxel (x,y) y a, b son parámetros de corrección con valores ajustados heurísticamente en a=0,4 y b=0, 8, …”

Section: Algoritmo De Seguimiento Automático Del Labiounclassified

Sistema audiovisual para reconocimiento de comandos

Ceballos

Serna

Prieto

et al. 2011

Ingeniare. Rev. chil. ing.

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RESUMENSe presenta el desarrollo de un sistema automático de reconocimiento audiovisual del habla enfocado en el reconocimiento de comandos. La representación del audio se realizó mediante los coeficientes cepstrales de Mel y las primeras dos derivadas temporales. Para la caracterización del vídeo se hizo seguimiento automático de características visuales de alto nivel a través de toda la secuencia. Para la inicialización automática del algoritmo se emplearon transformaciones de color y contornos activos con información de flujo del vector gradiente ("GVF snakes") sobre la región labial, mientras que para el seguimiento se usaron medidas de similitud entre vecindarios y restricciones morfológicas definidas en el estándar MPEG-4. Inicialmente, se presenta el diseño del sistema de reconocimiento automático del habla, empleando únicamente información de audio (ASR), mediante Modelos Ocultos de Markov (HMMs) y un enfoque de palabra aislada; posteriormente, se muestra el diseño de los sistemas empleando únicamente características de vídeo (VSR), y empleando características de audio y vídeo combinadas (AVSR). Al final se comparan los resultados de los tres sistemas para una base de datos propia en español y francés, y se muestra la influencia del ruido acústico, mostrando que el sistema de AVSR es más robusto que ASR y VSR.Palabras clave: Reconocimiento audiovisual del habla, modelo oculto de Markov (HMM), coeficientes de Mel, contorno activo, pseudotono, estándar MPEG-4, puntos FAPs, seguimiento de características. ABSTRACT We present the development of an automatic audiovisual speech recognition system focused on the recognition of commands. Signal audio representation was done using Mel cepstral coefficients and their first and second order time derivatives. In order to characterize the video signal, a set of high-level visual features was tracked throughout the sequences. Automatic initialization of the algorithm was performed using color transformations and active contour models based on Gradient Vector Flow (GVF

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“…Studies of the inner segment properties of all vertebrate photoreceptors examined to date suggest that such conductance mechanisms would be present in cat cones (e.g. Brown & Pinto, 1974;Bader et al, 1979Bader et al, , 1982Attwell et al, 1982;Corey et al, 1984;Hestrin, 1987;Maricq & Korenbrot, 1988, 1990Barnes & Hille, 1989;Yagi & MacLeish, 1994;Schneeweis & Schnapf, 1995;Demontis et al, 1999), so the necessary anatomical and biophysical substrates for the center expansion are present (Fig. 6).…”

Section: Retinal Circuitrymentioning

confidence: 99%

Spatiotemporal integration of light by the cat X-cell center under photopic and scotopic conditions

Troy

Bohnsack²,

Chen³

et al. 2005

Vis Neurosci

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Visual responses to stimulation at high temporal frequency are generally considered to result from signals that avoid light adaptive gain adjustment, simply reflecting linear summation of luminance. Under conditions of high photopic illuminance, the center of the receptive field of the cat X-cell has been shown to expand in size when stimulated at high temporal frequency, raising the possibility that there is spatiotemporal interaction in luminance summation. Here we show that this expansion maintains constant the product of the center's luminance summing area and the temporal period of luminance modulation, implying that spatial and temporal integration of luminance can be traded for one another by the X-cell center. As such the X-cell has a spatiotemporal window for luminance integration that fuses the classical concepts of a spatial window of luminance integration (Ricco's Law) with a temporal window of luminance integration (Bloch's Law). We were interested to determine whether this tradeoff between spatial and temporal summation of luminance occurs also at lower light levels, where the temporal-frequency bandwidth of the X-cell is narrower. We found that it does not. Center radius does not expand with temporal frequency under either low photopic or scotopic conditions. These results are discussed within the context of the known retinal circuitry that underlies the X-cell center for photopic and scotopic conditions.

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Photovoltage of rods and cones in the macaque retina

Cited by 300 publications

References 11 publications

Synaptic transmission at retinal ribbon synapses

Synaptic transmission at retinal ribbon synapses

Sistema audiovisual para reconocimiento de comandos

Spatiotemporal integration of light by the cat X-cell center under photopic and scotopic conditions

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