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L. M. Watson, N. C. Strang, V. Manahilov, L. Gilmour; Temporal Modulation Can Improve Visual Performance in Low-Vision Patients. Invest. Ophthalmol. Vis. Sci. 2010;51(13):3633.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate whether contrast sensitivity to gratings of low spatial frequency can be improved by modulating the contrast over time in low vision patients.
8 low vision subjects with Log Mar Acuity ranging from 0.3 to 1.68 were recruited. Subjects participated with informed consent in the study. Subjects all had been clinically diagnosed with age related macular degeneration. Sensitivity was measured using low spatial frequency gratings (0.5c/deg) orientated at 45 or -45 deg from vertical. Threshold contrasts were determined using a one-interval two-alternative forced choice procedure in conjunction with a staircase method. In Experiment 1, grating contrast was reversed sinusoidally in counterphase at temporal frequencies of 0 (non-modulated control), 5, 10 and 20 Hz. In Experiment 2, three types of random grating contrast modulation were used: (1) additive - adding uniform luminance of 3cd/m² to the stimulus luminance profile; (2) divisive - reducing grating luminance by a factor of 10% (3) motion - changing grating phase.
Temporal contrast sensitivity in low vision subjects had a band pass form. In Experiment 1, contrast sensitivity was maximal at 10Hz and reduced at lower and higher temporal frequencies. The mean increase in sensitivity was 0.18 log units. In Experiment 2, random motion and divisive modulations conditions significantly (t-test with Bonferroni correction, p<0.05) increased the sensitivity of the subjects compared to that for stationary gratings. Random motion resulted in a mean increase in sensitivity of 0.25 log units and divisive modulations resulted in a 0.18 log unit increase.
Low vision subjects perceive a world of blurred images which contain mainly low spatial frequencies. This study has shown a band pass temporal contrast sensitivity function for low vision subjects. Therefore modulating the retinal image of low spatial frequencies to the optimal temporal frequency can improve contrast sensitivity to stationary gratings. Random motion and divisive noise improve contrast sensitivity without the tiring repetition of sinusoidal reversal. These parameters can be utilised to develop new types of low vision aids.
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