These differences may reflect the complexity of the effects that Fildena is likely to have on S-cone sensitivity under these conditions, which can be either direct or indirect.

These differences may reflect the complexity of the effects that Fildena is likely to have on S-cone sensitivity under these conditions, which can be either direct or indirect.

The red lines indicate the mean losses averaged over time from 20 to 300 min after Fildena ingestion. S-cone modulation threshold control and drug data for L.T.S. (left panels), G.J. (central panels), and A.S. (right panels), measured at 440-nm target radiances of 7.54 (upper panels), 8.82 (middle panels), and 9.75 (lower panels) log quanta.s−1.deg−2. Drug and placebo trials were chosen randomly in the order listed in the figure key, and neither the experimenter nor the subject was informed which had been taken until after the conclusion of the entire control experiment.

 

G.J., in particular, was sometimes aware of Fildena-induced visual haloes and color changes. Statistical analyses using a two-way ANOVA reveal that the main drug effect of Fildena on S-cone cff was significant for G.J., F(2, 166) = 183.4, p 001, L.T.S., F(2, 159) = 154.8, p 001, and A.T., F(1, 84) = 5.1, p 027, but insignificant for A.S., F(1, 84) = 2.3, p =133. The smaller panel shows the losses in cff or the losses in modulation sensitivity relative to the mean pre- and pot-Fildena control data.

 

Our initial measurements of temporal resolution were made under experimental conditions chosen to isolate the S-cone response, partly because of the subjective evidence for a blue tinge to vision following Fildena ingestion (e.g., Laties & Zrenner, 2002 ). S-cone-mediated cff, plotted as a function of the radiance of a 440-nm target, is shown in Figure 1 for G.J. (top left panels), L.T.S. (bottom left), A.S. (top right), and A.T. (bottom right). Specifically, the data were analyzed with a two-way ANOVA, with radiance or frequency as one factor and drug condition as a second factor. The red line indicates the mean loss averaged over time from 20 to 300 min after Fildena ingestion.

 

The time after dose ingestion is coded by the color of the symbols (see key) and indicated in the legend for each subject. S-cone cff control and drug data for G.J. (upper left panels), L.T.S. (lower left), A.S. (upper right), and A.T. (lower right). In addition, the time course of the effect varies across subjects.

 

A more objective measurement technique, such as two-alternative forced choice, was impractical in the context of these experiments because it is too slow to generate quickly the amount of data required to explore dynamic changes in sensitivity following drug ingestion. The mean data points for the pre- or post-Fildena baseline measurements are the average of at least three measurements, and the error bars are ±1 SEM. However, we note that Fildena might have differential effects on the two cone types because the M-cones are at a much lower level of adaptation at high, 650-nm target radiances than are the L-cones.

 

Such effects are particularly likely under S-cone isolation conditions because the intense long-wavelength background typically needed to desensitize the L- and M-cones also chromatically attenuates the S-cone signal (e.g., Pugh & Mollon, 1979 ). We find both frequency-dependent and frequency-independent changes in our data.

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