Disruption of Eye Movements by Ethanol Intoxication Affects Perception of Depth From Motion Parallax

Motion parallax, the ability to recover depth from retinal motion generated by observer translation, is important for visual depth perception. Recent work indicates that the perception of depth from motion parallax relies on the slow eye movement system. It is well known that ethanol intoxication reduces the gain of this system, and this produces the horizontal gaze nystagmus that law enforcement's field sobriety test is intended to reveal. The current study demonstrates that because of its influence on the slow eye movement system, ethanol intoxication impairs the perception of depth from motion parallax. Thresholds in a motion parallax task were significantly increased by acute ethanol intoxication, whereas thresholds for an identical test relying on binocular disparity were unaffected. Perhaps a failure of motion parallax plays a role in alcohol-related driving accidents; because of the effects of alcohol on eye movements, intoxicated drivers may have inaccurate or inadequate information for judging the relative depth of obstacles from motion parallax.

Effects of diazepam on the latency of saccades for luminance and binocular disparity defined stimuli

Saccadic latency is composed of separate sensory and motor processing delays. Therefore, any alteration in the sensory processing should effect the saccadic latency. Because the highest density of benzodiazepine (Bz) binding sites is located in cerebral cortex, sensory processing of stimuli in this cortical area is expected to be substantially effected by administration of Bzs. It is well known that sensory processing of binocular disparity occurs in the cerebral cortical areas and therefore the latency of saccades to stimuli defined by binocular disparity should be substantially affected by Bz intake. In this study, we tested this prediction by comparing the latency of saccadic eye movements for binocular disparity defined stimuli (stereo stimuli) with those for luminance contrast defined stimuli (luminance stimuli), after diazepam or placebo. Eye movements were mainly recorded by use of the magnetic search coil technique, and the study was performed in a randomized, double-blind way. Although diazepam prolonged the latency of saccades for stereo and luminance stimuli, the percentage increases in saccadic latency for the stereo stimuli were significantly larger than those for the luminance stimuli. Saccadic peak velocity, and saccadic amplitude, also significantly decreased after diazepam under conditions of stereo and luminance stimuli. However, there was no significant difference for either saccadic peak velocity or amplitude between the two types of target. The results suggest that the latency of saccades to binocular disparity defined random-dot stimuli could more sensitively reflect the pharmacodynamic effects of Bzs on the cerebral cortex.

Effects of ayahuasca on binocular rivalry with dichoptic stimulus alternation

RATIONALE

During binocular rivalry, two incompatible images are presented to each eye and these monocular stimuli compete for perceptual dominance, with one pattern temporarily suppressed from awareness. One variant of stimulus presentation in binocular rivalry experiments is dichoptic stimulus alternation (DSA), when stimuli are applied to the eyes in rapid reversals. There is preliminary report that in contrast with healthy controls, schizophrenic patients can maintain binocular rivalry even at very high DSA rates.

OBJECTIVE

The study was undertaken to investigate whether binocular rivalry survives high rates of DSA induced by the South American hallucinogenic beverage ayahuasca.

METHODS

Ten individuals who were participating in ayahuasca ceremonials were requested to volunteer for binocular rivalry tests (DSA=0, 3.75, 7.5, 15 and 30 Hz) without and after drinking the brew.

RESULTS

Ingestion of ayahuasca increased mean dominance periods both in standard binocular rivalry conditions (no DSA) and tests with DSA. At higher DSA rates (15 and 30 Hz) the total length of dominance periods was longer on the brew.

CONCLUSION

It is discussed that ayahuasca-induced survival of binocular rivalry at high DSA rates may be related to slow visual processing and increased mean dominance periods may result from hallucinogen-induced alteration of gamma oscillations in the visual pathways.

Reduced binocular depth inversion in regular cannabis users

The binocular depth inversion illusion (BDII) has been shown to be a sensitive measure of impaired visual information processing under conditions including cannabinoid-intoxicated states, alcohol withdrawal, sleep deprivation, and in patients with positive symptoms of schizophrenia. This study assessed whether the BDII could detect subtle cognitive impairment due to regular cannabis use by comparing 10 regular cannabis users and 10 healthy controls from the same community sources, matched for age, sex, and premorbid IQ. Subjects were also compared on measures of executive functioning, memory, and personality. Regular cannabis users were found to have significantly higher BDII scores for inverted images. This was not due to a problem in the primary processing of visual information, as there was no significant difference between the groups for depth perception of normal images. There was no relationship between BDII scores for inverted images and time since last dose, suggesting that the measured impairment of BDII more closely reflected chronic than acute effects of regular cannabis use. There were no significant differences between the groups for other neuropsychological measures of memory or executive function. A positive relationship was found between EPQ-R-psychoticism and cannabis, tobacco, and alcohol use. Cannabis users also used significantly larger amounts of alcohol. However, no relationship was found between BDII scores and drug use other than cannabis or psychoticism. Compared to the other neuropsychological tests used, the BDII appears to be a more sensitive tool for the detection of subtle impairments in visual information processing related to chronic cannabis use.

A common oscillator for perceptual rivalries?

Perceptual rivalry is an oscillation of conscious experience that takes place despite univarying. if ambiguous, sensory input. Much current interest is focused on the controversy over the neural site of binocular rivalry, a variety of perceptual rivalry for which a number of different cortical regions have been implicated. Debate continues over the relative role of higher levels of processing compared with primary visual cortex and the suggestion that different forms of rivalry involve different cortical areas. Here we show that the temporal pattern of disappearance and reappearance in motion-induced blindness (MIB) (Bonneh et al, 2001 Nature 411 798-801) is highly correlated with the pattern of oscillation reported during binocular rivalry in the same individual. This correlation holds over a wide range of inter-individual variation. Temporal similarity in the two phenomena was strikingly confirmed by the effects of the hallucinogen LSD, which produced the same, extraordinary, pattern of increased rhythmicity in both kinds of perceptual oscillation. Furthermore. MIB demonstrates the two properties previously considered characteristic of binocular rivalry. Namely the distribution of dominance periods can be approximated by a gamma distribution and, in line with Levelt's second proposition of binocular rivalry, predominance of one perceptual phase can be increased through a reduction in the predominance time of the opposing phase. We conclude that (i) MIB is a form of perceptual rivalry, and (ii) there may be a common oscillator responsible for timing aspects of all forms of perceptual rivalry.

Impaired binocular depth inversion in patients with alcohol withdrawal

Binocular depth inversion represents an illusion of visual perception. Such inversion does not occur in all cases, especially when objects with a higher degree of familiarity (e.g. photographs of faces) are displayed. Cognitive factors are assumed to override the binocular disparity cues of stereopsis. We tested the hypothesis that during alcohol withdrawal the human CNS is unable to correct the implausible perceptual hypothesis. Measurements of binocular depth inversion in perception of 3D objects were performed in 10 patients with mild alcohol withdrawal and in 11 healthy volunteers. The binocular depth inversion scores were highly elevated in the patients group in comparison to the healthy volunteers. The data demonstrates a strong impairment of binocular depth inversion in alcohol withdrawal and support the view that alcohol withdrawal may be accompanied by a disorganization of the interaction between sensory input and generation of perceptual hypotheses.

Ingested ethanol and binocular rivalry

PURPOSE

An early study claimed that ethanol ingestion can attenuate binocular rivalry and, in some cases, may produce the phenomenal fusion of normally rivalrous stimuli. The current study examined those claims in an experiment incorporating key controls that were lacking in the earlier study.

METHODS

There were two conditions, one in which observers consumed ethanol and the other in which they consumed a placebo. Observers reported the course of binocular rivalry for several hours after drink consumption using two types of rivalry stimuli, one consisting of a continuously illuminated set of stimuli, the other consisting of dichoptic afterimages.

RESULTS

Ingestion of ethanol resulted in a decrease in rivalry alternation rates, although there was no evidence of phenomenal fusion. Results were essentially identical for both stimulus types.

CONCLUSION

It is suggested that this effect is not caused by ethanol-induced changes in oculomotor mechanisms but may be caused by ethanol-induced decreases in contrast sensitivity.

The effect of ingested alcohol on fusion latency at various viewing distances

Although diplopia is a frequently reported symptom of severe alcohol intoxication, there have been few past attempts to describe in any systematic fashion the specific impact of alcohol on fusion. In the present experiment, fusion latency was assessed for 8 male emmetropes. At the beginning of the alcohol condition, they consumed a drink containing 1.4 ml/kg of 95% ethanol, plus diluent. For the placebo condition, the drink consisted only of diluent. In each condition, fusion latency (the time required to fuse a binocularly visible target) was recorded for targets requiring a magnitude of vergence that varied from +10 through -2 meter angles, in 1-meter-angle steps. It was found that the far point of fusion approached the observer as a direct function of intoxication level. Furthermore, fusion latency increased for optically far and near targets as a systematic function of intoxication, with no effect of alcohol on intermediate targets. The results were consistent with previous findings of alcohol-induced narrowing of vergence range, suggesting that alcohol causes the farthest and nearest distances at which fusion latency is affected to approach an intermediate value. Measurable effects on fusion latency were observed with blood alcohol levels as low as 0.05%-0.06%, considerably below the legal limit for operating a motor vehicle in most states.

The influence of dopamine on spatial vision

Contrast thresholds for, and contrast matches between, stationary gratings of three spatial frequencies (0.5, 2, and 8 c/deg) were measured on eight subjects with a history of schizophrenia, just before, and again two to three days after, a therapeutic injection of depot neuroleptic. The drug enhanced sensitivity at the low, and reduced it at the medium and high spatial frequency. After injection, subjects required more contrast to match the apparent contrast of the high, and less contrast to match that of the low, to that of the medium spatial frequency. Pupillary measurements suggested that these effects were not due to drug-induced changes in pupil size. The results are discussed in terms of the functional role of dopamine in the retina, and a possible application in therapy for amblyopia.