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.     

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.     

Task-irrelevant visual motion and flicker attenuate the attentional blink

Our reduced ability to correctly report two sequentially presented targets is seen in the robust effect known as the attentional blink (AB; Raymond, Shapiro, & Arnell, 1992). One recent report (Olivers & Nieuwenhuis, 2005) strikingly reveals the AB to be virtually abolished when non-task-demanding music occurs in the background. The authors suggest that a diffuse attentional state is the mediating factor. Here, we seek to broaden the finding’s generality by determining if task-irrelevant visual motion and flicker also attenuate the AB. In our experiments, the AB task was presented together with a background field of moving dots that could moveaway from ortoward the central AB task, or flicker. In the control condition, the dots remained static. The AB was attenuated—though to different degrees—in all experimental conditions, but not in the static condition. Our findings add to the generality of the previous conclusions, and we emphasize an account based on the overallocation of attention.     

Effects of flicker rate, complexity, and color combinations of Chinese characters and backgrounds on visual search performance with varying flicker types

This study investigated the effects of number of strokes in Chinese characters, flicker rate, flicker type, and character/background color combination on search performance. 37 participants ages 14 to 18 years were randomly assigned to each flicker-type condition. The search field contained 36 characters arranged in a 6 x 6 matrix. Participants were asked to search for the target characters among the surrounding distractors and count how many target characters were displayed in the search array. Analysis indicated that the character/background color combination significantly affected search times. The color combinations of white/purple and white/green yielded search times greater than those for black/white and black/yellow combinations. A significant effect for flicker type on search time was also identified. Rotating characters facilitated search time, compared with twinkling ones. The number of strokes and the flicker rates also had positive effects on search performances. For flicker rate, the search accuracy for 0.5 Hz was greater than that for 1.0 Hz, and the latter was also greater than that for 2.0 Hz. Results are applicable to web advertisement designs containing dynamic characters, in terms of how to best capture readers' attention by various means of dynamic character presentation.     

Perceptual grouping based on temporal structure: Impact of subliminal flicker and visual transients

In two experiments we examined the perceived grouping of grids of equidistant dots, which are rapidly modulated over time so that alternate rows or columns are presented out of phase. In Experiment 1, we report that observers were able to group the grids consistent with the temporal modulation reliably, even at contrasts/frequencies for which flicker was not detectable. Moreover, flicker thresholds decreased with stimulus duration, whilst grouping thresholds did not change. In Experiment 2, we examined the impact of visual transients, by measuring performance when, either a mask or a contrast ramp was presented before and after the stimulus. Performance dropped substantially for both conditions, but remained significantly above chance. The results are discussed in relation to the role of temporal correlations in stimulus modulations and visual transients in grouping.     

Changes in critical flicker frequency during prolonged visual deprivation

Subjects were tested on the critical flicker frequency during a 1-week period of visual deprivation (either homogeneous illumination or darkness). Deprived subjects showed no significant differences from a confined control group. Results were discussed in relation to previous research, Schultz’s theory of “sensoristasis” and Sharpless’ revision of the “law of denervation.”     

Two channels for flicker in the human visual system

The human visual system contains a large number of narrowly-tuned spatial-frequency-specific channels. Does it contain an analogous set of channels tuned to a narrow range of temporal frequency? On the basis of data gathered with the use of a threshold elevation technique it is argued that human sensitivity to flicker can be accounted for by assuming the existence of just two filters, one a low-pass filter peaking gently at around 6 Hz and one a band-pass filter peaking at around 9 Hz. Similar data gathered from studies of interocular transfer suggest that at least some of the mechanisms involved are binocular, rather than being purely monocular as has previously been suggested.     

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.     

Time perception and the internal clock: Effects of visual flicker on the temporal oscillator

Abstract

Our ability to estimate time intervals has sometimes been attributed to a biological source of temporal information. A model for a temporal oscillator that provides such information has recently been described (Treisman, Faulkner, Naish & Brogan, 1990). This predicts that an imposed stimulus rhythm at certain frequencies may interfere with the temporal oscillator so as to alter its frequency. This interference would cause perturbations in temporal judgements at certain frequencies of the imposed rhythm. The pattern of interference would depend on the frequency at which the temporal oscillator runs, and so would contain information about the oscillator frequency. Evidence for such a pattern was found when auditory clicks at different rates were presented concurrently with time intervals whose durations subjects estimated. The present study examines whether a similar interference pattern can be obtained if visual flicker is substituted for auditory clicks. On each trial, flicker was presented at a rate between 2.5 and 17.5 Hz, concurrently with a time interval to be estimated. A pattern of increased estimates at some rates and decreased estimates at others was obtained. This pattern showed similarities to interference patterns obtained using auditory clicks. This provides evidence that the entrainment of the internal clock predicted by the model can also be produced by visual inputs. Other theoretical implications are discussed.