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.     

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.     

Reference light source for luminance and illuminance photometry

The rationale for a constant source of both luminance and illuminance to check photometer calibration is discussed. The inexpensive construction of such a reference source is described, together with some performance data.     

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.     

Seeing the light: Adapting luminance reveals low-level visual processes in the attentional blink

It is widely assumed that high-level visual processes subserve the attentional blink (AB). Recent evidence from studies of visual masking during the AB that were designed to directly test the contributions of high-level masking effects, however, have failed to provide empirical support for this position. The implication is that low-level visual processes are crucial to the AB. We tested this idea by manipulating adapting luminance in a standard AB paradigm. Consistent with the involvement of low-level neural mechanisms, the AB effect interacted with adapting luminance such that an AB was revealed only under photopic (light adapted) viewing conditions.     

Sociability/impulsivity and caffeine-induced arousal: Critical flicker/fusion frequency and procedural learning

The influence of sociability/impulsivity in caffeine-induced arousal effects was investigated in two separate experiments: Experiment 1 examined critical flicker/fusion frequency change scores (ΔCFFT) in 60 subjects; and Experiment 2 investigated procedural learning in 30 subjects. In the two experiments, subjects received either caffeine citrate (500 mg) or placebo. The pattern of results was consistent across both studies:(1) a strong interactive effect of sociability (as measured by the EPQ extraversion scale) by caffeine/placebo which showed that (a) subjects low in sociability showed the greatest increase in ACFFT and learned most under placebo, while the reverse was true under caffeine; (b) subjects high in sociability, showed no increase in ΔCFFT and learned least under placebo, while the reverse was true under caffeine; and (2) in neither experiment did impulsivity (as measured by the EPS impulsiveness scale) significantly interact with caffeine/placebo. The results are consistent with Eysenck's (The Biological Basis of Personality, 1967) theory of personality in suggesting that subjects low in sociability are highly arousable under low-arousal (placebo) but over-aroused under high-arousal (caffeine), with the reverse pattern of effects holding for subjects high in sociability. The implications of these data for the respective roles of sociability and impulsivity components of extraversion in arousal-mediated performance 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.