Contrast Sensitivity for Letter and Grating Targets under Various Stimulus Conditions

Herse, Peter; Bedell, Harold E.

doi:10.1097/00006324-198911000-00009

Cited by 59 publications

(36 citation statements)

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“…Due to the extrafoveal fall-off in photoreceptor density, visibility of a visual target decreases rapidly with foveal eccentricity as small as a few minutes of arc, as measured by contrast sensitivity or letter acuity (Herse and Bedell 1989;Ludvigh 1941). Thus, position error decreases visibility.…”

Section: Introductionmentioning

confidence: 99%

The Main Sequence of Saccades Optimizes Speed-accuracy Trade-off

2006

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In primates, it is well known that there is a consistent relationship between the duration, peak velocity and amplitude of saccadic eye movements, known as the 'main sequence'. The reason why such a stereotyped relationship evolved is unknown. We propose that a fundamental constraint on the deployment of foveal vision lies in the motor system that is perturbed by signaldependent noise on the motor command. This noise imposes a compromise between the speed and accuracy of an eye movement. We propose that saccade trajectories have evolved to optimize a trade-off between the accuracy and duration of the movement. Taking a semi-analytical approach we use Pontryagin's minimum principle to show that there is an optimal trajectory for a given amplitude and duration; and that there is an optimal duration for a given amplitude. It follows that the peak velocity is also fixed for a given amplitude. These predictions are in good agreement with observed saccade trajectories and the main sequence. Moreover, this model predicts a small saccadic dead-zone in which it is better to stay eccentric of target than make a saccade onto target. We conclude that the main sequence has evolved as a strategy to optimize the trade-off between accuracy and speed.

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Section: Introductionmentioning

confidence: 99%

The Main Sequence of Saccades Optimizes Speed-accuracy Trade-off

2006

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“…Ho & Bilton (1986) concurred with the choice of 10% contrast for a lowcontrast chart which would find utility in clinical practise, and speculated that acuity might deteriorate substantially for figure-ground contrasts Ͻ10%: the present results now confirm this latter point. Herse & Bedell (1989) considered that reduced-contrast letter stimuli would prove especially useful for the quantification of visual performance under conditions where acuity was unstable or variable due to diffusive (as distinct from refractive) blur: for example, in the presence of corneal oedema or lenticular opacity. A standalone reducing-contrast chart of economical design has been devised by Pelli et al (1988) for such clinical applications.…”

Section: Discussionmentioning

confidence: 99%

The influence of level and polarity of figure‐ground contrast on vision

Pointer¹

2001

Acta Ophthalmologica Scandinavica

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ABSTRACT.Purpose: To document the effect upon human foveal vision of changes in the level and polarity of figure-ground contrast under photopic controlled test conditions, with particular emphasis on performance at low contrast levels. Methods: Using a forced-choice psychophysical paradigm, threshold acuity estimates were derived at 9 discrete levels over a near-3 octave contrast range for Landolt ring-type stimuli of either positive or negative polarity. Data were obtained under binocular conditions from 10 young adults, each wearing their optimum low myopic spectacle correction. Results: Visual acuity declined linearly with reducing stimulus contrast, the deterioration increasing substantially at ∞10% figure-ground contrast regardless of stimulus polarity. Performance was slightly (but not statistically significantly) better for positive contrast stimuli. Conclusion: Irrespective of contrast polarity, a reduction in stimulus figureground contrast ∞10% produces an accelerated decrement in photopic foveal vision compared to the performance at levels Ͼ10%. Some clinical and practical implications of this outcome are considered with regard to the examination of patients with normal and compromised visual function.

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“…The precision of laser ablation of corneal tissue versus manual incisions held the promise of more accurate outcomes with less fluctuation of refraction [17][18][19]. Studies of refractive outcomes have shown an improvement in the accuracy and stability of laser procedures such as PRK over RK [20][21][22][23][24][25][26][27][28].…”

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“…How well these tests provide results that correspond to performance on grating tests of contrast sensitivity is important if results are to be comparable. For foveal best-corrected vision, Herse and Bedell (1989) found that the contrast sensitivity for letter and grating targets of corresponding spatial frequencies is highly correlated [19]. …”

Section: !mentioning

confidence: 99%

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Corneal Shape and Visual Performance After Keratorefractive Surgery

Pol¹

2002

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Contrast Sensitivity for Letter and Grating Targets under Various Stimulus Conditions

Cited by 59 publications

References 0 publications

The Main Sequence of Saccades Optimizes Speed-accuracy Trade-off

The Main Sequence of Saccades Optimizes Speed-accuracy Trade-off

The influence of level and polarity of figure‐ground contrast on vision

Corneal Shape and Visual Performance After Keratorefractive Surgery

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