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Using double silent substitution, it is possible to generate L-cone and M-cone isolating electroretinograms~ERGs! on a CRT. A major limitation of the technique is that the depth of modulation of cone classes is limited by the restricted luminance of the phosphors and their spectral overlap. To address this problem we have ported the technique to a four-color LED Ganzfeld stimulus~Diagnosis ColorDome!. This allows higher retinal illuminances, higher contrasts, and triple silent substitution. With careful control over the retinal area stimulated, we show that the same data can be recorded from both CRT and LED stimuli when luminance, size and cone contrast are kept constant. Importantly, the different temporal profiles of the two devices do not influence the ERG amplitude and phase plots. We present data over a much wider range of luminances~up to about 10000 trolands! and contrasts with the LED stimulator than previously reported with CRT screens. We conclude that the close resemblance between data obtained with an LED stimulator and with a CRT screen indicate that the differences have a purely physiological origin.

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Purpose To study abnormal dark adaptation (DA) in aging and macular degeneration (AMD) using a new technique that measures DA at two retinal locations by using a dual stimulus. To establish whether there are localized regions of impaired rod function, especially the rate of the rod‐mediated recovery (S2) as it has been previously suggested Methods Dual arc‐shaped white stimuli were presented on a black CRT monitor at locations 6º and 11º of eccentricity in the inferior visual fiel. Recovery of sensitivity to the two stimuli was measured concurrently using the method of adjustment, following a bleaching exposure of at least 30%. The dynamic range of the CRT was expanded using ND filters. DA curves were obtained after fitting the data by non‐linear regression to a seven‐parameter model. Three groups of observers (young, older and AMD) were tested to detrmine any differences between them and the effect of the testing location, focusing on parameters α (rod‐cone break) and S2 (slope of the post‐ α phase of rod recovery) Results Both stimuli produced matched cone recovery curves within each group. Comparing groups (young vs. older) and (older vs. AMD), we found significant differences in the two DA parameters studied here. Regarding the AMD group, we found a trend in both parameters to be more affected at 6º than at 11º, however, these differences were not significant Conclusion This technique has shown to be sensitive to detect changes in rod recovery in AMD patients compared to healthy subjects and allows the measurement of DA in two retinal locations simultaneously. It may help in the early diagnosis and monitoring of degenerative diseases of the macula, which are increasingly common

Simple reaction times (RTs) are a useful measure of supra-threshold information processing. This chapter examines how the metric used to scale coloured stimuli influences the variation in RT with chromaticity. The variation of simple RT with chromaticity appears to be strongly dependent upon the extent to which stimulus activates either the L/M or S/(L+M) colour opponent mechanism. The dominant influence of these two mechanisms suggests that pre-cortical as opposed to cortical colour processing has a strong influence on the RT to chromatic isoluminant stimuli.