Effect of Varying Stimulus Conditions on the Flicker-Fusion Threshold When Nitroglycerin or the Cold Pressor Test Was Employed

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Abstract
With specially designed equipment and standardized procedures critical flicker-fusion thresholds (CFF) for each of 3 observers were determined before, during and after administration of sublingual nitro- glycerin, 0.4 mg, and the cold pressor test. The mean and SD of the CFF in cps in groups of 10 determinations were compared. The area and color of the test patch and of the intermittent light pulse form and duration were systematically varied. A summary of the effect of each of the known determinants which acted to increase CFF was as follows: (1) A test patch area subtending 3.5[degree] in contrast to 1[degree] yielded an increase in 72 of 72 comparisons; (2) A square light pulse of longer duration in contrast to a spike pulse of short duration, in 58 of 60 comparisons; (3) White in contrast to red, in 51 of 54 comparisons, white in contrast to blue, in 42 of 42 comparisons, and red in contrast to blue, in 37 of 42 comparisons; (4) Chronological age arranged from youngest to oldest observer, in 50 of 54 comparisons; (5) First 10 of 70 observations in contrast to last 10 of the 70 observations (fatigue effect), 17 of 29 comparisons, i.e., no effect; (6) The CFF "before" compared to the "during" effect of nitroglycerin in 16 of 29 comparisons, i.e., no effect; and (7) "Before" compared to "during" the cold pressor test in 26 out of 27 comparisons. Although there was but little variability in CFF of each trained observer on any given day or during day-to-day observations over some weeks, there was a marked tendency for each observer to sharply alter his mean CFF on one or another day of the series in contrast to his usual mean performance. The basis for such exceptional performances was not found.