INDIVIDUAL AND INTERINDIVIDUAL DIFFERENCES IN BINOCULAR RETINAL RIVALRY IN MAN

In a group of 12 male and female subjects of ages between 18 and 45 years the alternation frequency of binocular retinal rivalry (BRR) has been found to change depending upon the durations of the periods for which the target is fixated, and of the intercalated resting time. Analysis of variance indicated significant inter-individual differences in level of mean frequency and in rate of increase.     

Hierarchy of cortical responses underlying binocular rivalry

During binocular rivalry, physical stimulation is dissociated from conscious visual awareness. Human brain imaging reveals a tight linkage between the neural events in human primary visual cortex (V1) and the dynamics of perceptual waves during transitions in dominance during binocular rivalry. Here, we report results from experiments in which observers' attention was diverted from the rival stimuli, implying that: competition between two rival stimuli involves neural circuits in V1, and attention is crucial for the consequences of this neural competition to advance to higher visual areas and promote perceptual waves.     

Noise-induced alternations in an attractor network model of perceptual bistability

When a stimulus supports two distinct interpretations, perception alternates in an irregular manner between them. What causes the bistable perceptual switches remains an open question. Most existing models assume that switches arise from a slow fatiguing process, such as adaptation or synaptic depression. We develop a new, attractor-based framework in which alternations are induced by noise and are absent without it. Our model goes beyond previous energy-based conceptualizations of perceptual bistability by constructing a neurally plausible attractor model that is implemented in both firing rate mean-field and spiking cell-based networks. The model accounts for known properties of bistable perceptual phenomena, most notably the increase in alternation rate with stimulation strength observed in binocular rivalry. Furthermore, it makes a novel prediction about the effect of changing stimulus strength on the activity levels of the dominant and suppressed neural populations, a prediction that could be tested with functional MRI or electrophysiological recordings. The neural architecture derived from the energy-based model readily generalizes to several competing populations, providing a natural extension for multistability phenomena.     

Slow binocular rivalry in bipolar disorder

BACKGROUND: The rate of binocular rivalry has been reported to be slower in subjects with bipolar disorder than in controls when tested with drifting, vertical and horizontal gratings of high spatial frequency. METHOD: Here we assess the rate of binocular rivalry with stationary, vertical and horizontal gratings of low spatial frequency in 30 subjects with bipolar disorder, 30 age- and sex-matched controls, 18 subjects with schizophrenia and 18 subjects with major depression. Along with rivalry rate, the predominance of each of the rivaling images was assessed, as was the distribution of normalized rivalry intervals. RESULTS: The bipolar group demonstrated significantly slower rivalry than the control, schizophrenia and major depression groups. The schizophrenia and major depression groups did not differ significantly from the control group. Predominance values did not differ according to diagnosis and the distribution of normalized rivalry intervals was well described by a gamma function in all groups. CONCLUSIONS: The results provide further evidence that binocular rivalry is slow in bipolar disorder and demonstrate that rivalry predominance and the distribution of normalized rivalry intervals are not abnormal in bipolar disorder. It is also shown by comparison with previous work, that high strength stimuli more effectively distinguish bipolar from control subjects than low strength stimuli. The data on schizophrenia and major depression suggest the need for large-scale specificity trials. Further study is also required to assess genetic and pathophysiological factors as well as the potential effects of state, medication, and clinical and biological subtypes.     

Traveling waves of activity in primary visual cortex during binocular rivalry

When the two eyes view large, dissimilar patterns that induce binocular rivalry, alternating waves of visibility are experienced as one pattern sweeps the other out of conscious awareness. Here we combine psychophysics with functional magnetic resonance imaging to show tight linkage between dynamics of perceptual waves during rivalry and neural events in human primary visual cortex (V1).     

Neural correlates of binocular rivalry in the human lateral geniculate nucleus

When dissimilar images are presented to the two eyes, they compete for perceptual dominance so that only one image is visible at a time while the other one is suppressed. Neural correlates of such binocular rivalry have been found at multiple stages of visual processing, including striate and extrastriate visual cortex. However, little is known about the role of subcortical processing during binocular rivalry. Here we used fMRI to measure neural activity in the human LGN while subjects viewed contrast-modulated gratings presented dichoptically. Neural activity in the LGN correlated strongly with the subjects' reported percepts, such that activity increased when a high-contrast grating was perceived and decreased when a low-contrast grating was perceived. Our results provide evidence for a functional role of the LGN in binocular rivalry and suggest that the LGN, traditionally viewed as the gateway to the visual cortex, may be an early gatekeeper of visual awareness.     

Multistage model for binocular rivalry

Binocular rivalry is the alternating perception that occurs when incompatible stimuli are presented to the two eyes: one monocular stimulus dominates vision and then the other stimulus dominates, with a perceptual switch occurring every few seconds. There is a need for a binocular rivalry model that accounts for both well-established results on the timing of dominance intervals and for more recent evidence on the distributed neural processing of rivalry. The model for binocular rivalry developed here consists of four parallel visual channels, two driven by the left eye and two by the right. Each channel consists of several consecutive processing stages representing successively higher cortical levels, with mutual inhibition between the channels at each stage. All stages are architecturally identical. With n the number of stages, the model is implemented as 4n nonlinear differential equations using a total of eight parameters. Despite the simplicity of its architecture, the model accounts for a variety of experimental observations: 1) the increasing depth of rivalry at higher cortical areas, as shown in electrophysiological, imaging, and psychophysical experiments; 2) the unimodal probability density of dominance durations, where the mode is less than the mean; 3) the lack of correlation between successive dominance durations; 4) the effect of interocular stimulus differences on dominance duration; and 5) eye suppression, as opposed to feature suppression. The model is potentially applicable to issues of visual processing more general than binocular rivalry.     

Binocular rivalry in half-occluded region is weakened by eye movement

To investigate the effect of eye movement on suppression of binocular rivalry in the half-occluded region, which is the monocular region made by occlusion, the amount of binocular rivalry in the half-occluded region was measured in the eye movement condition and the fixating condition. In the eye movement condition, the observer moved their eyes between the occluder and the occluded object. In the fixating condition, the observers fixated the occluder (the fixating-the-occluder condition) or the occluded object (the fixating-the-occluded-object condition). Following facts were found: (a) the amount of binocular rivalry in the half-occluded region reduced more in the eye movement condition than in the two fixating conditions, (b) there was no significant difference in the amount of binocular rivalry in the half-occluded region between the two fixating conditions. These results suggested that eye movement is one of the factors to suppress binocular rivalry in the half-occluded region in natural viewing situations.     

Role of mutual inhibition in binocular rivalry

Binocular rivalry is a phenomenon that occurs when a different image is presented to each eye. The observer generally perceives just one image at a time, with perceptual switches occurring every few seconds. A natural assumption is that this perceptual mutual exclusivity is achieved via mutual inhibition between populations of neurons that encode for either percept. Theoretical models that incorporate mutual inhibition have been largely successful at capturing experimental features of rivalry, including Levelt's propositions, which characterize perceptual dominance durations as a function of image contrasts. However, basic mutual inhibition models do not fully comply with Levelt's fourth proposition, which states that percepts alternate faster as the stimulus contrasts to both eyes are increased simultaneously. This theory-experiment discrepancy has been taken as evidence against the role of mutual inhibition for binocular rivalry. Here, we show how various biophysically plausible modifications to mutual inhibition models can resolve this problem.     

Spatio-temporal dynamics of the visual system revealed in binocular rivalry

From the evolutionary viewpoint, animals need to monitor the surrounding environment and capture salient features, such as motion, for survival. The visual system is highly developed for monitoring a wide area of visual field and capturing such salient features. In humans and primates, there is a wide binocular field, suggesting a necessity of integrating the images from the two eyes. Binocular rivalry [R. Blake, A neural theory of binocular rivalry, Psychol. Rev. 96 (1989) 145-167; R. Blake, N.K. Logothetis, Visual competition, Nat. Rev. Neurosci. 3 (2002) 13-21], where incompatible inputs from the two eyes compete to emerge in the subject's visual percept, has been shown to exhibit highly adaptive behavior [I. Kovacs, T.V. Parathomas, M. Yang, A. Feher, When the brain changes its mind: interocular grouping during binocular rivalry. Proc. Natl. Acad. Sci. U.S.A. 93 (1996) 15508-15511; N.K. Logothetis, Single units and conscious vision, Philos. Trans. R. Soc. Lond. B. Biol. Sci. 353 (1998) 1801-1818]. Here we investigated the spatio-temporal dynamics of the ocular dominance pattern in binocular rivalry under conditions where conflicting salient features were presented in a temporally varying manner. We found a striking example of the detailed structure of the dominance wave propagation, by using a spatio-temporal sampling method. The data show in detail the ability of the visual system to dynamically adapt to the changing stimuli in the context of the massively parallel visual field. We show by model prediction that the globally coherent dominance change in the presence of multiple stimuli can be explained by a mechanism based on local saliency comparison.     

Neuronal activity in human primary visual cortex correlates with perception during binocular rivalry

During binocular rivalry, two incompatible monocular images compete for perceptual dominance, with one pattern temporarily suppressed from conscious awareness. We measured fMRI signals in early visual cortex while subjects viewed rival dichoptic images of two different contrasts; the contrast difference served as a 'tag' for the neuronal representations of the two monocular images. Activity in primary visual cortex (V1) increased when subjects perceived the higher contrast pattern and decreased when subjects perceived the lower contrast pattern. These fluctuations in V1 activity during rivalry were about 55% as large as those evoked by alternately presenting the two monocular images without rivalry. The rivalry-related fluctuations in V1 activity were roughly equal to those observed in other visual areas (V2, V3, V3a and V4v). These results challenge the view that the neuronal mechanisms responsible for binocular rivalry occur primarily in later visual areas.     

The Influence of Some Central Nervous Depressants on the Reciprocal Inhibition Between the Two Retinae as Manifested in Retinal Rivalry1

The influence of drugs on retina1 rivalry between a horizontal and a vertical bar was studied with the aim of finding pharmaco-logical agents which might become useful in the treatment of suppression and amblyopia in squint, Amytal, bromural, chloral, ethyl alcohol, phenobarbital and trional can weaken or abolish retinal rivalry. Under the influence of these drugs, completely simultaneous perception of the two dis-parate objects may occur. I n less pronounced cases only a decrease in depth of suppression of the momentarily subjugated image is observed. Together with the decrease in intensity of rivalry the drugs cause a decrease in the frequency of alternation. If, in the normal state, there is an imbalance between the two competing pictures, one of them being dominant more than half of the time, the degree of imbalance usually increases when rivalry is weakened under the influence of the drugs. Morphine in one case caused a marked increase, in two other cases uncertain decreases in rivalry. 3-methyl-5.5-diphenyl-hydan-toin (one case) had no effect on rivalry.     

心理干预在脑梗死后双眼复视患者焦虑中的应用

目的探讨心理干预对脑梗死后双眼复视患者焦虑状态的影响。方法66例脑梗死后双眼复视患者采用Zung焦虑自评量表进行测评，筛选出焦虑标准分1〉50分的患者56例，按单双病历号尾数分成实验组和对照组，对照组按常规实施治疗和护理，实验组在此基础上由专门的医护人员实施心理干预。干预5天后再次进行评估。结果实验组与对照组两组间干预后的焦虑改善率差异有统计学意义（X2=9．970，P〈0．01）。结论心理干预可以明显改善脑梗死后双眼复视患者焦虑状态。     

Psychophysical evidence for two routes to suppression before binocular summation of signals in human vision

Visual mechanisms in primary visual cortex are suppressed by the superposition of gratings perpendicular to their preferred orientations. A clear picture of this process is needed to (i) inform functional architecture of image-processing models, (ii) identify the pathways available to support binocular rivalry, and (iii) generally advance our understanding of early vision. Here we use monoptic sine-wave gratings and cross-orientation masking (XOM) to reveal two cross-oriented suppressive pathways in humans, both of which occur before full binocular summation of signals. One is a within-eye (ipsiocular) pathway that is spatially broadband, immune to contrast adaptation and has a suppressive weight that tends to decrease with stimulus duration. The other pathway operates between the eyes (interocular), is spatially tuned, desensitizes with contrast adaptation and has a suppressive weight that increases with stimulus duration. When cross-oriented masks are presented to both eyes, masking is enhanced or diminished for conditions in which either ipsiocular or interocular pathways dominate masking, respectively. We propose that ipsiocular suppression precedes the influence of interocular suppression and tentatively associate the two effects with the lateral geniculate nucleus (or retina) and the visual cortex respectively. The interocular route is a good candidate for the initial pathway involved in binocular rivalry and predicts that interocular cross-orientation suppression should be found in cortical cells with predominantly ipsiocular drive.     

A neural network of obsessive- compulsive disorder: modelling cognitive disinhibition and neurotransmitter dysfunction

While significant advances have been made in documenting both neurotransmitter and neuropsychological dysfunction in obsessive-compulsive disorder (OCD), there remains a need for theoretical models to account for their relationship. A neural network model of OCD was developed to provide a rigorous simulation of the relationship between the cognitive disinhibition and serotonin/dopamine dysfunction that characterize this disorder. An architecture-specific recurrent neural network of the Elman type was able to model the cognitive disinhibition that is apparent when OCD patients are compared with other anxiety disorder patients on a modified Stroop (Temporal Stroop) test, with OCD patients showing reduced negative priming (shorter reaction times to previously ignored stimuli). Lesions to either the color gain parameter (reflective of serotonergic dysfunction) or to the context gain parameter (reflective of dopaminergic dysfunction) resulted in decreased semantic negative priming. Neural network modelling provides a surprisingly coherent perspective of the psychobiology of OCD, simulating both reduced cognitive disinhibition as well as neurotransmitter dysfunction.     

Serotonergic systems associated with arousal and vigilance behaviors following administration of anxiogenic drugs

Serotonergic systems play important roles in modulating behavioral arousal, including behavioral arousal and vigilance associated with anxiety states. To further our understanding of the neural systems associated with increases in anxiety states, we investigated the effects of multiple anxiogenic drugs on topographically organized subpopulations of serotonergic neurons using double immunohistochemical staining for c-Fos and tryptophan hydroxylase combined with topographical analysis of the rat dorsal raphe nucleus (DR). Anxiogenic drugs with diverse pharmacological properties including the adenosine receptor antagonist caffeine, the serotonin 5-HT2A/2C receptor agonist m-chlorophenyl piperazine (mCPP), the alpha2-adrenoreceptor antagonist yohimbine, and the benzodiazepine receptor partial inverse agonist N-methyl-beta-carboline-3-carboxamide (FG-7142) induced increases in behavioral arousal and vigilance behaviors consistent with an increase in anxiety state. In addition, these anxiogenic drugs, excluding yohimbine, had convergent actions on an anatomically-defined subset of serotonergic neurons within the middle and caudal, dorsal subdivision of the DR. High resolution topographical analysis revealed that at the mid-rostrocaudal level, caffeine and FG-7142 had convergent effects on c-Fos expression in serotonergic neurons that were restricted to a previously undefined region, which we have named the shell region of the dorsal part of the dorsal raphe nucleus (DRDSh), that overlaps the anatomical border between the dorsal part of the dorsal raphe nucleus, the ventral part of the dorsal raphe nucleus (DRV), and the ventrolateral part of the dorsal raphe nucleus (DRVL). Retrograde tracing methods revealed that DRDSh contains large numbers of neurons projecting to the basolateral amygdaloid nucleus, a forebrain structure important for emotional appraisal and modulation of anxiety-related physiological and behavioral responses. Together these findings support the hypothesis that there is a functional topographical organization in the DR and are consistent with the hypothesis that anxiogenic drugs have selective actions on a subpopulation of serotonergic neurons projecting to a distributed central autonomic and emotional motor control system regulating anxiety states and anxiety-related physiological and behavioral responses.     

Functional and neuronal binocularity in kittens raised with rapidly alternating monocular occlusion

1. In order to determine the degree of synchrony of binocular activation required for the development of binocularity we reared 11 kittens with rapidly alternating monocular occlusion. Alternating occlusion was achieved with microprocessor-controlled electrooptic solid-state shutters, which were fitted to individually moulded goggles. The intervals of alternating occlusion were varied from 50 to 1,000 ms. Two normally reared kittens and three kittens that were reared with the shutters operating synchronously with open/close intervals of 50/50 ms, 200/200 ms, and 400/100 ms, respectively, were used as controls. Toward the end of the critical period we examined the kittens' ability for binocular depth discrimination and tested binocular luminance summation of the pupillary light reflex. Single-cell recordings were made from the visual cortex in order to determine the percentages of binocularly excitable neurons. 2. There was a good correlation between the degree of asynchrony of binocular experience, the impairment of depth discrimination, and the percentage of binocular neurons. Kittens reared with alternation rates of 200, 330, and 400 ms, respectively, had developed normal binocularity and were indistinguishable from the controls. Alternation rates of 500 ms or longer prevented the development of normal depth discrimination and luminance summation and resulted in reduced cortical binocularity. 3. A linear relationship between depth discrimination, binocular luminance summation, and percentages of binocular neurons was found. 4. Our findings indicate that an asynchrony of binocular activation of several hundred milliseconds is compatible with the development of normal binocularity in the kitten visual system.     

Filling-in of visual phantoms in the human brain

The constructive nature of perception can be demonstrated under viewing conditions that lead to vivid subjective impressions in the absence of direct input. When a low-contrast moving grating is divided by a large gap, observers report seeing a 'visual phantom' of the real grating extending through the blank gap region. Here, we report fMRI evidence showing that visual phantoms lead to enhanced activity in early visual areas that specifically represent the blank gap region. We found that neural filling-in effects occurred automatically in areas V1 and V2, regardless of where the subject attended. Moreover, when phantom-inducing gratings were paired with competing stimuli in a binocular rivalry display, subjects reported spontaneous fluctuations in conscious perception of the phantom accompanied by tightly coupled changes in early visual activity. Our results indicate that phantom visual experiences are closely linked to automatic filling-in of activity at the earliest stages of cortical processing.