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| Barboni,M.T.S.; Gomes,B.D.; Souza,G.S.; Rodrigues,A.R.; Ventura,D.F.; Silveira,L.C.L.. |
| The purpose of the present study was to measure contrast sensitivity to equiluminant gratings using steady-state visual evoked cortical potential (ssVECP) and psychophysics. Six healthy volunteers were evaluated with ssVECPs and psychophysics. The visual stimuli were red-green or blue-yellow horizontal sinusoidal gratings, 5° × 5°, 34.3 cd/m2 mean luminance, presented at 6 Hz. Eight spatial frequencies from 0.2 to 8 cpd were used, each presented at 8 contrast levels. Contrast threshold was obtained by extrapolating second harmonic amplitude values to zero. Psychophysical contrast thresholds were measured using stimuli at 6 Hz and static presentation. Contrast sensitivity was calculated as the inverse function of the pooled cone contrast threshold. ssVECP... |
| Tipo: Info:eu-repo/semantics/article |
Palavras-chave: Contrast sensitivity; Color vision; Steady-state visual evoked cortical potential; Visual thresholds; Spatial vision; Psychophysics. |
| Ano: 2013 |
URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-879X2013000200154 |
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| Simas,M.L.B.; Santos,N.A.. |
| We measured human contrast sensitivity to radial frequencies modulated by cylindrical (Jo) and spherical (j o) Bessel profiles. We also measured responses to profiles of j o, j1, j2, j4, j8, and j16. Functions were measured three times by at least three of eight observers using a forced-choice method. The results conform to our expectations that sensitivity would be higher for cylindrical profiles. We also observed that contrast sensitivity is increased with the j n order for n greater than zero, having distinct orderly effects at the low and high frequency ends. For n = 0, 1, 2, and 4 sensitivity tended to occur around 0.8-1.0 cpd while for n = 8 and 16 it seemed to shift gradually to 0.8-3.0 cpd. We interpret these results as being consistent with the... |
| Tipo: Info:eu-repo/semantics/article |
Palavras-chave: Spatial frequency; Angular frequency; Polar gratings; Face perception; Contrast sensitivity. |
| Ano: 2002 |
URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-879X2002001100014 |
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| Rodrigues,A.R.; Souza,C.R.B.; Braga,A.M.; Rodrigues,P.S.S.; Silveira,A.T.; Damin,E.T.B.; Côrtes,M.I.T.; Castro,A.J.O.; Mello,G.A.; Vieira,J.L.F.; Pinheiro,M.C.N.; Ventura,D.F.; Silveira,L.C.L.. |
| We measured visual performance in achromatic and chromatic spatial tasks of mercury-exposed subjects and compared the results with norms obtained from healthy individuals of similar age. Data were obtained for a group of 28 mercury-exposed subjects, comprising 20 Amazonian gold miners, 2 inhabitants of Amazonian riverside communities, and 6 laboratory technicians, who asked for medical care. Statistical norms were generated by testing healthy control subjects divided into three age groups. The performance of a substantial proportion of the mercury-exposed subjects was below the norms in all of these tasks. Eleven of 20 subjects (55%) performed below the norms in the achromatic contrast sensitivity task. The mercury-exposed subjects also had lower red-green... |
| Tipo: Info:eu-repo/semantics/article |
Palavras-chave: Mercury exposure; Mercury toxicity; Contrast sensitivity; Color vision; Visual dysfunction; Amazon riverside communities. |
| Ano: 2007 |
URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-879X2007000300018 |
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| Simas,M.L.B.; Nogueira,R.M.T.B.L.; Santos,N.A.. |
| An assumption commonly made in the study of visual perception is that the lower the contrast threshold for a given stimulus, the more sensitive and selective will be the mechanism that processes it. On the basis of this consideration, we investigated contrast thresholds for two classes of stimuli: sine-wave gratings and radial frequency stimuli (i.e., j0 targets or stimuli modulated by spherical Bessel functions). Employing a suprathreshold summation method, we measured the selectivity of spatial and radial frequency filters using either sine-wave gratings or j0 target contrast profiles at either 1 or 4 cycles per degree of visual angle (cpd), as the test frequencies. Thus, in a forced-choice trial, observers chose between a background spatial (or radial)... |
| Tipo: Info:eu-repo/semantics/article |
Palavras-chave: Sine-wave gratings; Spatial frequency; Radial frequency; Bessel functions; Multiple channels; Contrast sensitivity. |
| Ano: 2005 |
URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-879X2005000300013 |
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| This study compares contrast thresholds for sinewave gratings, or spatial frequencies (1/CSF) with contrast thresholds for angular frequencies (1/aCSF) and for radial frequencies, or J0 targets (1/rCSF). Observers had to differentiate between one of these frequency stimuli and a stimulus at mean luminance within a forced-choice procedure. All measurements were made with the same equipment, methods and subjects. Our results show higher sensitivity to, or lower thresholds for, angular frequencies when compared to either sinewave gratings or J0 targets. Contrast values in arbitrary units, in the lower threshold range for angular frequencies, were about half those required to differentiate sinewave gratings from mean luminance in its most sensitive range |
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Palavras-chave: Spatial frequency; CSF; J0 targets; Angular frequency; Contrast sensitivity; Contrast thresholds. |
| Ano: 1997 |
URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-879X1997000500010 |
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