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Contrast (vision)

About: Contrast (vision) is a research topic. Over the lifetime, 10379 publications have been published within this topic receiving 221480 citations.


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Journal ArticleDOI
TL;DR: It is suggested that training-induced neuronal contrast gain in area V1 underlies behaviorally determined perceptual contrast sensitivity improvements.

132 citations

Journal ArticleDOI
TL;DR: It is suggested that frequency modulation improves the encoding of a wide range of brightness levels without a loss of spatial resolution.
Abstract: PURPOSE. In an effort to restore functional form vision, epiretinal prostheses that elicit percepts by directly stimulating remaining retinal circuitry were implanted in human subjects with advanced retinitis pigmentosa RP). In this study, manipulating pulse train frequency and amplitude had different effects on the size and brightness of phosphene appearance. METHODS. Experiments were performed on a single subject with severe RP (implanted with a 16-channel epiretinal prosthesis in 2004) on nine individual electrodes. Psychophysical techniques were used to measure both the brightness and size of phosphenes when the biphasic pulse train was varied by either modulating the current amplitude (with constant frequency) or the stimulating frequency (with constant current amplitude). RESULTS. Increasing stimulation frequency always increased brightness, while having a smaller effect on the size of elicited phosphenes. In contrast, increasing stimulation amplitude generally increased both the size and brightness of phosphenes. These experimental findings can be explained by using a simple computational model based on previous psychophysical work and the expected spatial spread of current from a disc electrode. CONCLUSIONS. Given that amplitude and frequency have separable effects on percept size, these findings suggest that frequency modulation improves the encoding of a wide range of brightness levels without a loss of spatial resolution. Future retinal prosthesis designs could benefit from having the flexibility to manipulate pulse train amplitude and frequency independently (clinicaltrials.gov number, NCT00279500). (Invest Ophthalmol Vis Sci. 2012;53:205‐214) DOI:10.1167/iovs.118401

132 citations

Journal ArticleDOI
TL;DR: Responses to moving sinusoidal gratings, whose spatial frequency, velocity, and contrast were varied systematically, indicated that knowledge of one spatial an .d one temporal curve of a cell allows one to calcu late its response to any combination of spatial and temporal frequencies.
Abstract: I. Recordings were obtained from 108 cells near the border of areas 17 and 18 in anesthetized, paralyzed cats. Emphasis was placed on analyzing responses to moving sinusoidal gratings, whose spatial frequency, velocity, and contrast were varied systematically. In the presence of drifting gratings, about 30% of the cells responded with a periodic discharge at virtually all effective spatial and temporal frequencies. These neurons tended to be “simple,” to have very low levels of spontaneous activity, and to have the narrowest spatialand temporal-frequency response functions. Another 30% of the cells responded aperiodically at all but the lowest spatial and temporal frequencies. These cells tended to be “complex” and to have the broadest tuning curves. The remaining cells responded periodically over part of the range of effective frequencies, and could be simple, complex, or intermediate and difficult to classify. 2. For most of the neurons that responded appreciably to both directions of movement at the optimal orientation, the peak frequency (and shape) of spatialand/or temporal-frequency response functions differ by more than 0.3 octave for the two directions of movement. The peak frequency and/or bandwidth of the temporal response function for either direction may also depend on whether there is a pause between movements in the two directions. 3. The response of almost all cells increases linearly with contrast up to a saturation level. The threshold contrast shows little dependence on spatial frequency, but is a function of temporal frequency. The slopes of response-contrast functions are steepest at the optimal spatial or temporal frequencies and diminish at lower or higher frequencies. 4. The peak frequency and shape (bandwidth and high-frequency roll-off) of temporal-frequency response functions do not depend significantly on the spatial frequency used to make the measurement and the converse is true. Accordingly, it is possible to use a spatial-frequency tuning curve measured at fixed temporal frequency and a temporal curve measured at fixed spatial frequency to predict the spatial-frequency tuning curve that is obtained when all spatial frequencies are presented at the same velocity. This implies that knowledge of one spatial an .d one temporal curve of a cell allows one to calcu late its response to any combination of spatial and temporal frequencies. 5. The higher a cell’s best spatial frequency, the lower is the optimal velocity of movement at the best spatial frequency. The equation for the regression line that summarizes this correlation has velocity proportional to spatial frequency raised to the -5/4 power.

132 citations

Journal Article
Eli Peli1, R.B. Goldstein1, G.M. Young1, C.L. Trempe1, Sheldon M. Buzney1 
TL;DR: The capability of two enhancement techniques to improve recognition of images by patients with central scotoma or cataracts was evaluated using image-processing simulations and direct patient testing, and ability to recognize celebrities from enhanced images improved.
Abstract: Digital image enhancement has been proposed as an aid for the visually impaired The capability of two enhancement techniques to improve recognition of images by patients with central scotoma or cataracts was evaluated using image-processing simulations and direct patient testing Enhancements and simulations were based on measurements of contrast sensitivity loss for patients with macular disease Contrast sensitivity loss was measured using Gabor-type localized stimuli and paradigms that are appropriate for analyzing form perception The simulations using the contrast sensitivity data suggested that patients with moderate visual loss (20/70-20/200) may have difficulty recognizing faces and may benefit from enhancement by both of the techniques used Ability to recognize celebrities from enhanced images improved for 39 of the 46 patients tested The improvement was significant (P less than 005) for 16 of the 38 patients with central visual loss and for 3 of 8 patients with anterior segment media opacities tested The simulations suggest that the benefits of image enhancement may be similar or even greater for recognition of other types of images

132 citations

Journal ArticleDOI
TL;DR: The combination of visual acuity, horizontal visual fields, and broad contrast sensitivity criteria was significantly related to increasing crash involvement for drivers aged 66-75 and 76 and over.

131 citations


Performance
Metrics
No. of papers in the topic in previous years
YearPapers
20241
20231,864
20223,760
2021413
2020329
2019354