Relation between flicker fusion threshold and retinal positions

The critical flicker frequencies (CFF) were determined for various locations on the retina. Under the conditions in which pupil size varies little with target luminance and size for a retinal location, two findings were obtained. First, the relation between the CFF value and the retinal location depends basically upon the density distribution of the receptor cells (cones and rods) on the retina. Second, when a large test field is employed, the peripheral area shows a maximal CFF value. These characteristics are explicable in terms of the retinal structure and by assuming some functions for it.     

The fusion frequency of flicker in the central and peripheral field with photopic levels of surround luminance

Flicker-fusion frequencies have been measured against a photopic level of surround luminance in the four quadrants of the visual field and the critical fusion frequences (c.f.f.s.) taken in direct vision compared with those determined at 15° and 35° in the periphery. The central c.f.f.s. of 47 subjects exceeded the peripheral values only in just over half of all the quadrants tested, although smaller differential thresholds were given almost without exception in the centre than in the periphery by the same observers and under similar conditions on a test of brightness discrimination. Likewise higher central than peripheral c.f.f.s. were recorded in the great majority of all quadrants when determinations were made against a dark surround. The contrasting types of flicker response observed against the photopic ground were shown to be relatively reproducible, and the same pattern was as a rule found in at least three quadrants of any one visual field. It was ascertained that the different patterns might result from a reciprocal shift of fusion frequencies either in central or peripheral vision.

Interpretations of the higher peripheral c.f.f.s which adduce the effect of accentuated pupillary constriction with central stimulation mere contra-indicated since such patterns of flicker perception survive after the photopupillary reflex has been abolished. Some evidence was, however, forthcoming for the view that peripheral fusion frequencies tend to exceed central values when the test object is larger than about 1·5° in angular size and more intense than the surround. It was suggested that the contrasting types of flicker response might be related to individual differences in the effect that stimulus size has on the flicker pattern.     

An electroluminescent lamp device for critical flicker fusion and apparent motion

A circuit that uses electroluminescent lamps as light sources for the study of critical flicker fusion (CFF) and apparent motion phenomena is described. The technique involves the modulation of a 2- KH z exciting current with a multivibrator-formed pulse adjustable over a suitable range of frequencies. Components are readily available from commercial sources.     

Frequency thresholds for two-flash flicker and critical flicker: Why they differ

The minimum interval detectable between two successive flashes is longer than the minimum interval detectable when many flashes are viewed. The probability summation hypothesis is suggested to explain the difference. For a given flash duration, the minimum interval detectable decreases as a function of the number of flashes, n, until n equals about 8 or 10; further increases in n cause no further changes in this interval. Of the total decrease in the interval, from n=2 to n=99, about 90% is explained by the probability summation hypothesis.     

Attention-capturing properties of high frequency luminance flicker: Implications for brake light conspicuity

In two experiments, the authors studied the effect of high frequency luminance flicker on reaction time in a simulated driving task. In Experiment 1, 24 research participants performing a primary simulated driving task were required to apply the brake pedal as quickly as possible following the activation of a red light somewhere in their field of vision. The red lights were displayed in one of two ways, (a) with 20 Hz luminance flicker and (b) continuous (no flicker), and presented at three eccentricities, 10°, 45° and 80°. Results showed that the light with 20 Hz flicker was more attention-capturing than the continuous light, but that the effect of 20 Hz flicker on reaction time was not influenced by eccentricity of presentation. The second experiment was identical to the first except that the primary simulated driving task was considerably more attention demanding. Under this higher workload, the light with 20 Hz flicker again proved to be more attention-capturing than the continuous light, and to a greater extent than in Experiment 1. In Experiment 2, there also appeared to be tendency for the light with 20 Hz flicker to be more effective at greater eccentricities. Implications for brake light conspicuity and rear-end collision avoidance are discussed.     

Sociability/impulsivity and attenuated dopaminergic arousal: critical flicker/fusion frequency and procedural learning

Two experiments examined the interaction of sociability (Soc) and impulsivity (Imp) components of extraversion and reduced dopamine activity (by haloperidol) on critical flicker/fusion frequency change scores (ACFFT) and procedural learning. In double-blind designs, subjects received either haloperidol (5 mg) or placebo; Soc and Imp were randomly sampled. In Experiment 1, Drug × Imp, and Drug × Imp × Soc interactions were found on ΔCFFT; in Experiment 2, a drug × Soc interaction was found on procedural learning. In both experiments, introverts seemed over-aroused under placebo (putatively due to the medical context), more optimally aroused under haloperidol; for procedural learning, extraverts seemed more optimally aroused under placebo, less optimally aroused under haloperidol. These data indicate that both Soc and Imp mediate the effects of arousal; Drug × Imp effects my conceal joint effects of Soc × Imp; and that Soc shows more consistent effects than Imp. These data complement a previous study of Soc/Imp and caffeine-induced arousal (Corr, Pickering & Gray, 1995), and lend support to H. J. Eysenck's (1967) arousal model of Extraversion.     

Effects of fasting on visual flicker fusion

Two experiments are reported which investigated the effects of fasting on visual flicker fusion (VFF). In Exp. 1 the VFF of 40 undergraduate students, 20 men and 20 women, whose mean age was 22.5 yr., was measured in nonfasting conditions 1 to 2 weeks before and in fasting conditions during the Muslim fasting month of Ramadan. In Exp. 2 the VFF of a comparable group of 15 men and 15 women, whose mean age was 23.2 yr., was measured in a different month in both fasting and nonfasting conditions. Subjects were assigned randomly to these two conditions. Analysis shows that fasting reduced VFF significantly in both experiments. This finding indicates that fasting is likely to reduce perceptual sensitivity. The results were explained in terms of fatigue and physical exhaustion effects produced by fasting.     

The age deficit on photopic counterphase flicker: contrast, spatial frequency, and luminance effects.

This study evaluated the contribution of reduced contrast sensitivity and retinal illuminance to the age-related deficit on the temporal resolution of suprathreshold spatial stimuli. The discrimination of counterphase flicker was measured in optimally refracted young and elderly observers for sinusoidal gratings of three spatial frequencies (1, 4, and 8 cycles per degree) at three contrast levels (0.11, 0.33, and 0.66). Age deficits in flicker discrimination at the two higher contrast levels and at the two lower spatial frequencies were unrelated to observer contrast sensitivity. Flicker discrimination of young observers who carried out the task through .5 ND filters to simulate a two-thirds reduction of retinal illuminance in the older eye, was similar to that of the elderly observers. An age-related reduction in retinal luminance appears to be a major determinant of the age-related spatiotemporal deficit at suprathreshold contrast levels, although neural factors may also be involved.     

Relative area and relative luminance combine to anchor surface lightness values

The anchoring of lightness perception was tested in simple visual fields composed of only two regions by placing observers inside opaque acrylic hemispheres. Both side-by-side and center/surround configurations were tested. The results, which undermine Gilchrist and Bonato’s (1995) recent claim that surrounds tend to appear white, indicate that anchoring involves both relative luminance and relative area. As long as the area of the darker region is equal to or smaller than the area of the lighter region, relative area plays no role in anchoring. Only relative luminance controls anchoring: The lighter region appears white, and the darker region is perceived relative to that value. When the area of the darker region becomes greater than that of the lighter region, relative area begins to playa role. As the darker region becomes larger and relative area shifts from the lighter region to the darker region, the appearance of the darker region moves toward white and the appearance of lighter region moves toward luminosity. This hitherto unrecognized rule is consistent with almost all of the many previous reports of area effects in lightness and brightness. This in turn suggests that a wide range of earlier work on area effects in brightness induction, lightness contrast, lightness assimilation, and luminosity perception can be understood in terms of a few simple rules of anchoring.     

Probability summation model for heterochromatic luminance additivity failure at absolute visual threshold

Vos and Wabraven recently derived a new set of foveal primaries. These primaries, in conjunction with the revised zone fluctuation theory of color vision, account for more psychophysical color vision data than any other model to date. The new primaries depend heavily on Abney’s law, and their success has been challenged by Guth’s observations of additivity failure at absolute threshold. The present paper develops a probability summation model which accounts for threshold additivity failure within the framework of Vos’s and Walraven’s assumptions.