Temporal contrast sensitivity and cortical magnification

Virsu, Veijo; Rovamo, Jyrki; Laurinen, Pentti; Näsänen, Risto

doi:10.1016/0042-6989(82)90087-6

Cited by 133 publications

(65 citation statements)

References 23 publications

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“…In the normal adult visual system, contrast sensitivity to a moving bar is maximized at p ≈ 3 deg/s for a bar width of 1 degree, but this increases to p ≈ 10 deg/s for a width of 3 degrees [10]. For low spatial frequency gratings (0.75 cyc/deg), [11] reported a considerable increase in p with foveal eccentricity from˜8 deg/s at the fovea to˜20 deg/s at 7.5 deg. Thus, substantial values for p are not improbable, but it is difficult to 'guesstimate' p for an abnormal visual system (and in infancy!).…”

Section: Discussionmentioning

confidence: 99%

“…Psychophysics has demonstrated that sensitivity to a spatial frequency is maximal at some non-zero image speed, where the optimal speed varies inversely with spatial frequency. Thus, high spatial frequencies (as mediated via the central retina) require very low drift speeds, whereas low spatial frequencies require more moderate speeds to induce maximal visual contrast [10][11][12].…”

Section: Non-veridical Velocity Tuningmentioning

confidence: 99%

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A Distal Model of Congenital Nystagmus as Nonlinear Adaptive Oscillations

Harris

Berry

2006

Nonlinear Dyn

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Abstract. Congenital nystagmus (CN) is an incurable pathological spontaneous oscillation of the eyes with an onset in the first few months of life. The pathophysiology of CN is mysterious. There is no consistent neurological abnormality, but the majority of patients have a wide range of unrelated congenital visual abnormalities affecting either the cornea, lens, retina or optic nerve. In this theoretical study, we show that these eye oscillations could develop as an adaptive response to maximize visual contrast with poor foveal function in the infant visuomotor system, at a time of peak neural plasticity. We argue that in a visual system with abnormally poor high spatial frequency sensitivity, image contrast is not only maintained by keeping the image on the fovea (or its remnant) but also by some degree of image motion. Using the calculus of variations, we show that the optimal trade-off between these conflicting goals is to generate oscillatory eye movements with increasing velocity waveforms, as seen in real CN. When we include a stochastic component to the start of each epoch (quick-phase inaccuracy) various observed waveforms (including pseudo-cycloid) emerge as optimal strategies. Using the delay embedding technique, we find a low fractional dimension as reported in real data. We further show that, if a velocity command-based pre-motor circuitry (neural integrator) is harnessed to generate these waveforms, the emergence of a null region is inevitable. We conclude that CN could emerge paradoxically as an 'optimal' adaptive response in the infant visual system during an early critical period. This can explain why CN does not emerge later in life and why CN is so refractory to treatment. It also implies that any therapeutic intervention would need to be very early in life.

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Section: Discussionmentioning

confidence: 99%

Section: Non-veridical Velocity Tuningmentioning

confidence: 99%

A Distal Model of Congenital Nystagmus as Nonlinear Adaptive Oscillations

Harris

Berry

2006

Nonlinear Dyn

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“…75 The tCSF decreases globally with increasing eccentricity, although again the maximum does not change its position. 76 However, unlike visual acuity, higher CFF values are found outside the fovea at scotopic levels. 77 …”

Section: Spatial Frequency (Cpd) Visual Eccentricity (Deg)mentioning

confidence: 99%

“…eccentricity increases (Figure 20, centre), but all curves collapse to a single one if velocity is measured in mm of cortex per second instead of degrees per second (Figure 20, right). 76 It follows, therefore, that the visual cortex is not just spatially homogeneous, but is also homogeneous in the spatio-temporal domain: a single spatio-temporal CSF characterizes the behaviour of the whole cortex.…”

Section: Figure 16mentioning

confidence: 99%

Spatio-temporal Contrast Sensitivity in the Cardinal Directions of the Colour Space. A Review

Dı́ez-Ajenjo

Capilla

2010

Journal of Optometry

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We review the psychophysics of the spatio-temporal contrast sensitivity in the cardinal directions of the colour space and their correlation with those neural characteristics of the visual system that limit the ability to perform contrast detection or pattern-resolution tasks. We focus our attention particularly on the influence of luminance level, spatial extent and spatial location of the stimuli -factors that determine the characteristics of the physiological mechanisms underlying detection. Optical factors do obviously play a role, but we will refer to them only briefly. Contrast sensitivity measurements are often used in clinical practice as a method to detect, at their early stages, a variety of pathologies affecting the visual system, but their usefulness is very limited due to several reasons. We suggest some considerations about stimuli characteristics that should be taken into account in order to improve the performance of this kind of measurement. RESUMENSe revisa la psicofísica sobre la sensibilidad al contraste con patrones espacio-temporales en las direcciones cardinales del espacio de color y su relación con las características neuronales del sistema visual que limitan la habilidad para realizar una tarea de detección de contraste o de resolución de patrones. La atención se centra especialmente en la influencia del nivel de luminancia, el tamaño y la localización espacial de los estímulos, en la medida que estos son los factores más importantes que determinan las características de los mecanismos fisiológicos que median la detección. Obviamente, los factores ópti-cos también juegan un papel en el conjunto del sistema visual, pero nos referiremos a ellos sólo brevemente. Las medidas de sensibilidad al contraste son a menudo usadas en clínica como método para detectar, en un estado temprano, una amplia variedad de patologías del sistema visual, pero su utilidad en la práctica es bastante limitada por diferentes razones. Sugerimos que ciertas consideraciones sobre los estímulos deberían ser tenidas en cuenta si se quiere mejorar las prestaciones actuales de este tipo de medidas. (J Optom 2010;3:2-19 ©2010 Consejo General de Colegios de Ópticos-Optometristas de España) PALABRAS CLAVE: sensibilidad al contraste; patrones espacio-temporales; espacio de color; direcciones cardinales; caminos visuales. INTRODUCTIONDuring the last three decades, the possibility of early detection of a variety of pathologies affecting the visual system by means of the measurement of spatial and temporal contrast sensitivity functions -CSFs-has been thoroughly explored. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] (Burr D, et al. IOVS 2003;44: ARVO E-Abstract 3193). It has been shown, however, that the usefulness of these functions is rather limited in practice, for several reasons. In the first place, measurements are often limited to the fovea, whilst anatomical damage and functional loss frequently begin outside this region [see, for example, F. Rowe's book 17 ]. In fact, different perimetry technique...

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“…This may be because the spatial summation process that enhances peripheral contrast sensitivity at the cost of spatial resolution (Green, 1970;Thibos, Cheney, & Walsh, 1987;Virsu, Rovamo, Laurinen, & Näsänen, 1982;Wang et al, 1997) is compromised by the increase in temporal frequency of the stimulus. Because central vision does not rely on summation in the same way as peripheral vision, the effect of increasing temporal frequency is not as severe.…”

Section: Experiments 2: An Examination Of the Basis For The Reversal: mentioning

confidence: 99%