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PubMed1959

Fusion of complex flicker.

Brown and Forsyth have recently performed a flicker-fusion experiment showing clearly that there is more to flicker than meets the eye. This report presents an analysis of their results which indicates the likelihood that at fusion threshold all but one of the Fourier components of their presentation are imperceptible.

Flicker Fusion↗
PubMed2005

Critical flicker frequency in migraine. A controlled study in patients without prophylactic therapy.

The critical flicker frequencies (CFF) of individuals with migraine with and without aura were determined and compared to those of normal controls. Twenty-six migraine patients, 12 with aura and 14 without aura and 30 healthy controls were included. Migraineurs were tested during a migraine-free period, through both the continuous flicker method (CFM) and the forced choice method (FCM). Migraineurs presented a mean flickering fusion threshold lower than healthy controls with the CFM (40.45 vs. 44.33, respectively; P = 0.019) and with the FCM (34.16 Hz vs. 38.5 Hz, respectively, P = 0.019). Both groups of migraineurs had significantly lower thresholds as compared to controls, migraineurs with aura presenting the lowest thresholds for the fusion of flickering (P = 0.008 and P = 0.0001 with the CFM and the FCM, respectively). Results confirmed and extended previous observations of abnormal flicker fusion thresholds in migraineurs. We hypothesize that this finding might be related to a shorter cortical stimulation silent period.

Adult↗
PubMed1975

Psychomotor skills related to driving after intramuscular administration of diazepam and meperidine.

Psychomotor skills related to driving and the ability to discriminate the fusion of flickering light were measured in a double-blind cross-over fashion in 11 healthy volunteers before, and 1, 3, 5, and 7 hours after, intramuscular injection of saline solution, 10 mg diazepam, or 75 mg meperidine. The late effects of meperidine were tested in five other subjects 12 and 24 hours after the injection. The effects of diazepam were the most harmful to coordinative and reactive skills, which were significantly impaired for as long as 5 hours. Meperidine impaired reactive skills for as long as 3 hours and flicker-fusion discrimination and coordinative skills for as long as 12 hours. It is concluded that patients should not drive or operate machinery for at least 7 hours after receiving 10 mg diazepam intramuscularly and for 24 hours after receiving 75 mg meperidine intramuscularly.

Adult↗
PubMed1995

The effect of nitrous oxide on the performance of psychomotor tests. A dose-response study.

The effect of different nitrous oxide concentrations on the performance of psychomotor tests (inspection time, tapping frequency, critical flicker fusion, picture memory and time sense) was investigated in seven healthy volunteers. The results show a dose-related impairment of memory, a reduction in tapping frequency and an increase in inspection time. A paradoxical increase in critical flicker-fusion threshold was observed. There was no effect on critical fusion-flicker threshold or time sense. Recovery was incomplete for memory tests performed 20 min after withdrawal of nitrous oxide. Subjective effects persisted for several hours.

Adult↗
PubMed1968

The sensations produced by electrical stimulation of the visual cortex.

1. An array of radio receivers, connected to electrodes in contact with the occipital pole of the right cerebral hemisphere, has been implanted into a 52-year-old blind patient. By giving appropriate radio signals, the patient can be caused to experience sensations of light (;phosphenes') in the left half of the visual field.2. The sensation caused by stimulation through a single electrode is commonly a single very small spot of white light at a constant position in the visual field; but for some electrodes it is two or several such spots, or a small cloud.3. For weak stimuli the map of the visual field on the cortex agrees roughly with the classical maps of Holmes and others derived from war wounds. With stronger stimuli, additional phosphenes appear; these follow a map that is roughly the classical map inverted about the horizontal meridian.4. The phosphenes produced by stimulation through electrodes 2.4 mm apart can be easily distinguished. By stimulation through several electrodes simultaneously, the patient can be caused to see predictable simple patterns.5. The effects of the duration and frequency of stimulating pulses on the threshold have been explored.6. For cortical phosphenes there is no sharp flicker fusion frequency, and probably no flicker fusion frequency at all.7. During voluntary eye movements, the phosphenes move with the eyes. During vestibular reflex eye movements they remain fixed in space.8. Phosphenes ordinarily cease immediately when stimulation ceases, but after strong stimulation they sometimes persist for up to 2 min.9. Our findings strongly suggest that it will be possible, by improving our prototype, to make a useful prosthesis.

Accommodation, Ocular↗
PubMed1976

Residual effects and skills related to driving after a single oral administration of diazepam, medazepam or lorazepam.

Psychomotor skills and visual functions related to driving were measured double-blind cross-over in ten healthy volunteers before, and 1,3,5 and 7 h after a single oral administration of diazepam (10mg), medazepam (15 mg) or lorazepam (2.5 mg). The late effects of lorazepam were tested in seven other subjects 12 and 24 h after the administration. Lorazepam impaired almost all the measured skills more (P less than 0.05 to 0.001) than diazepam, medizepam or the placebo. The lorazepam impairment of reactive skills and flicker fusion discrimination remained statistically significant (P less than 0.05) for as long as 12 h. Medazepam impaired only reactive skills and flicker fusion, the latter remaining impaired (P less than 0.05) for as long a 5 h after the administration. The magnitude and duration of the effects of diazepam were intermediate between those of lorazepam and medazepam. Diazepam impaired perceptual speed and reactive and co-ordinative skills as well as flicker fusion discrimination and visual parameters related to driving. Slight impairments in performance were measurable for up to 5 h after administration but at 7 h the results resembled those measured after the placebo. The lack of alterations in adaptation to darkness, sensitivity to brightness or visual discrimination ability in bright counterlight at a time when flicker fusion discrimination was severely depressed suggests that an impaired ability to discriminate flickering light is of no or little clinical significance to driving ability. It is concluded that patients receiving a 2.5 mg dose of lorazepam should not drive or operate machinery for 24 h after the administration. After diazepam (10 mg) or medazepam (15 mg) patients should refrain from driving or participating inskilled performances for only 5 to 7 hours.

Adult↗
PubMed1992

Anxiogenic effects of caffeine in patients with anxiety disorders.

The effects on measures of anxiety from two doses of oral caffeine (250 and 500 mg) and placebo were compared in 12 patients with generalized anxiety disorder (GAD), 12 patients with panic disorder, and 12 normal subjects. Caffeine produced significantly less decrease in electroencephalographic alpha wave activity, greater decrease in N1-P2 auditory evoked potential amplitude, and greater increased in skin conductance level, systolic and diastolic blood pressure, critical fusion flicker frequency, and self-ratings of anxiety and sweating in patients with GAD than in normal patients. Patients with panic disorder showed different reactivity than normal patients did with respect to electroencephalographic alpha waves, N2 latency, N2-P2 auditory evoked potential amplitude, and physical tiredness but were less reactive than patients with GAD on several variables. It is concluded that patients with GAD are abnormally sensitive to caffeine and that the data support the view that panic disorder is a separable disorder from GAD.

Alpha Rhythm↗