Learning to differentiate microintervals of time using verbal feedback

Reaction time (RT) and the number of correct estimations of time microintervals (10 and 180 ms) between two visual stimuli were recorded in healthy subjects. It has been shown that 10 ms interval is better estimated when the stimuli are presented in the right visual field, i.e. when they are addressed directly to the left hemisphere. At the same time the number of correct estimations of 180 ms interval is greater and their RT is less when the stimuli are addressed directly to the right hemisphere. This points to different hemispheric mechanisms of time microintervals estimation. Study of the influence of different forms of verbal reinforcement on this learning has shown that after positive reinforcement (the word "good") the number of correct estimations is on average by 10% greater than after negative reinforcement (the word "error"). This may be connected with such processes as isolation and identification of erroneous reaction.     

Lateralization of visuo-spatial function during masking in healthy subjects and in patients with chronic alcoholism

In healthy subjects and patients with chronic alcoholism, the ability to construct in mind geometric figures in conditions of masking was studied by means of recording the number of correct decisions, the reaction time and evoked cortical electrical activity. It has been found that solution of visual-spatial task of mentally constructing geometric figures is accomplished better if a figure-standard can be formed from the presented fragments. During solution of the visual-spatial task in norm the reaction time is shorter if the information comes "directly" to the right hemisphere. Such interhemispheric differences are not observed at chronic alcoholic intoxication. In patients with chronic alcoholism the late components of EPs N200 and P300 developed with a longer latency and lesser amplitude than in healthy subjects. The greatest depression of cortical activity is observed in the right hemisphere.     

Unimanual Reaction Time during Comparison of Lateralized Verbal Stimuli: the Features of Interhemispheric Interactions Related to Subjects' Gender

Reaction time (RT) and number of correct responses to letter stimuli were measured in 49 male and 47 female subjects under conditions of crossed and uncrossed lateralization of a pair of stimuli and the hand that performed motor reaction. Gender differences were detected on the basis of RT in the hemispheric organization when a task was performed. Males reacted more rapidly to the stimuli presented in the right visual field, while females demonstrated no lateral effects. There was a significant difference in the case of the males' right hand between crossed and uncrossed lateralization of visual stimuli, which exceeded that in the females and in the case of the males' left hand. There were no gender differences in the number of correct responses. When motor response was performed by either hand, the number of correct responses was significantly higher when the stimuli were presented in the right visual field.     

The role of feedback in the dynamics of functional asymmetry of brain hemispheres in man

Reaction time, number of correct evaluations of time microintervals, and P300 wave were studied in healthy adult subjects. The role is shown of feedback stimuli in training of a subject to discriminate short intervals and in changes of interhemispheric functional relations. These relations change in the course of training as a result of lateralized activation of the left hemisphere. Training with informative feedback is more efficient in the left hemisphere. The right hemisphere in lesser extent than the left one is subject to correcting influence of the feedback. In this sense the former is more autonomous.     

Asymmetry of the cerebral hemispheres during comparison of paired visual stimuli

In conditions of tachistoscopic presentation of visual stimuli, healthy (male and female) right-handed subjects carried out a paired comparison of the stimuli presented unilaterally and in the center of the visual field. In case of recognition of images of words and objects, the number of correct answers and motor reaction time usually did not significantly differ at two interstimuli intervals (1 and 10 s). In comparing images of faces, there also were no differences by the number of reactions, and the reaction time was less at the intervals of 1 s. The left hemisphere dominated at the identification of words and female faces, the right one--at the recognition of male faces. When the right visual field was stimulated images of various classes were recognized more differentially than at the stimulation of the left visual field. The male subjects had more prominent interhemispheric differences than the females. The increase of the interstimuli interval from 1 to 10 s brought to a weakening of the functional interhemispheric asymmetry and decreasing of the differences between the male and female subjects. The obtained data show that in the processes connected with short-time memory, functional interhemispheric asymmetry is basically formed at the initial stages of the information processing.     

Solution of visuo-spatial tasks during masking

The images of two fragments of simple geometrical figures (square, triangle, etc.) were successively presented to healthy adult subjects in the left and right visual fields with the interval of 20, 80 and 380 ms; the subjects had to compare them mentally and decide whether they formed a geometrical figure. The correctness of reaction was controlled by a computer which lightened on the screen the word "correct" or "error". The number of correct decisions was significantly greater in response to the stimuli, forming a regular figure and increased with the increase of interstimuli interval. At the interval of 120 ms, when no regular figure could be formed from two fragments, the number of correct decisions was greater if the stimuli were presented in the left visual field. The reaction time did not depend on the hemisphere to which information was addressed; it was less in response to the stimuli forming a regular figure, and became shorter with the increase of the interstimuli interval.     

Hemispheric lateralization of visuo-spatial function in man

Two parts of a geometrical figure are consecutively presented to healthy adult subjects in the left and right visual fields; the subjects have to compare them mentally and to decide whether these parts form a standard figure or not. Correctness of the reaction is controlled by a computer which lights up on the screen the words "good" or "error". The number of correct decisions of this visual-spatial task does not depend on the hemisphere to which information is addressed. The reaction time is substantially shorter if the information comes "directly" to the right hemisphere. Due to better training in the left hemisphere interhemispheric difference in reaction time gradually disappears in repeated tests. Training to mental "constructing" takes place only in the tests following positive feedback stimulus. Analysis of amplitude-temporal parameters of P300 wave shows that at correct decision of the visual-spatial task the level of activation in the right hemisphere is higher than in the left one.     

The hemispheric lateralization of the recognition of noisy visual stimuli in man

At tachistoscopic unilateral presentation of noisy visual stimuli and application of "yes-no" method in man predominance was found of the right hemisphere by the number and "yes" reaction time and of the left hemisphere by the number of responses "no". At verbal mnemic load preceding the presentation of visual patterns the left hemisphere asymmetry was observed by the number of "yes" responses and reactions time of both types. FMA was more clearly expressed in men in the first case and in women--in the second one. In more difficult conditions of recognition of several types of patterns, FMA was noticed mainly in women: initial left hemisphere advantage during the increase of the disturbance was changed to the right hemispheric one and appeared again. Preferential participation of the right hemisphere in singling out of the visual signal from noise is supposed. Possibility of the left hemispheric asymmetry manifestation was determined by the specificity and complexity of the visual task, by the level of the disturbance, presentation of competitive task and sexual composition of the group.     

Effect of music on motor reaction time and interhemispheric relations

Influence of music on motor reaction time (RT) was studied. Warning and triggering stimuli were presented either in the left or in the right visual fields. RT was recorded when playing classical or variety music; control sessions were not accompanied by music. Music shortened RT, and its stimulating effect was the stronger the longer were the initial RTs without music. The influence of variety music was more effective than of the classic one. RT was shortened more when the triggering stimulus was presented in the left visual field. This phenomenon is considered to be an evidence of predominant influence of music on the right cerebral hemisphere due to greater activation from emotional structures.     

Hemispheric interaction in man during perception of visual stimuli]

Averaged evoked potentials (AEP) to verbal (letters) and nonverbal (random shapes) stimuli exposed in the left and right visual fields were registered in healthy subjects with normal vision. Analysis of the later AEP latencies pointed to asymmetry in the temporal parameters of the interhemispheric interaction. The late AEP latency is shorter in the right hemisphere than in the left hemisphere. The difference is more pronounced in responses to nonverbal stimuli. The earlier development of the evoked potential in the right hemisphere (or the later one in the left hemisphere) accounts for the interhemispheric difference in the temporal parameters of the late AEP components. Comparison of the latency of the component P300 to verbal and nonverbal stimuli presented in the ipsilateral or the contralateral visual fields reveals a transfer of the results of the cortical processing of visual information in the course of interhemispheric interaction.     

Lateralization of visual perception of letters during reverse masking

Identification by healthy subjects of single letters in conditions of backward masking was studied at lateralized presentation of stimuli. Both at dichoptic and unilateral presentations, the letters are identified better if they are presented in the left visual field, i.e. addressed "directly" to the right hemisphere. It is suggested that the data obtained result from the specificity of hemispheres' cooperation under difficult conditions of visual-spatial stage of information processing.     

Dynamics of the formation, reproduction and recognition of trace conditioned reflexes to positive and negative stimuli

The dynamics of formation, reproduction, and recognition of trace conditioned reflexes to positive and differentiation stimuli was studied on subjects of 15-17 years old. Formation and reproduction of such reflexes was found to occur under a close interaction of both levels of the higher nervous activity--recognized and unrecognized levels. Recognized reactions prevailed on unrecognized ones in cases of involvement of active attention. On the basis of this fact, the formation and reproduction of trace conditioned reflexes to positive stimuli has been supposed to occur with an active participation of the left hemisphere. The right hemisphere apparently plays a leading role in formation and reproduction of trace conditioned reflexes to differention stimuli to which the attention of the subjects was not fixed.     

Changes in the latencies of motor responses to visual stimuli presented with musical accompaniment

The effects of music with specific intensity on the latencies of the left or right hand motor responses to visual stimuli have been studied. When the latency of the initial motor response is more than 400 ms, the music accompaniment decreases the latency of the motor response of the left hand. It is supposed that the decrease in the mean latency of the left hand response in subjects who are not professional musicians is related to the activation effect of music on the right hemisphere. Music has no effect when the initial motor responses have shorter latencies.     

Hemispheric specialization in dogs for processing different acoustic stimuli

Considerable experimental evidence shows that functional cerebral asymmetries are widespread in animals. Activity of the right cerebral hemisphere has been associated with responses to novel stimuli and the expression of intense emotions, such as aggression, escape behaviour and fear. The left hemisphere uses learned patterns and responds to familiar stimuli. Although such lateralization has been studied mainly for visual responses, there is evidence in primates that auditory perception is lateralized and that vocal communication depends on differential processing by the hemispheres. The aim of the present work was to investigate whether dogs use different hemispheres to process different acoustic stimuli by presenting them with playbacks of a thunderstorm and their species-typical vocalizations. The results revealed that dogs usually process their species-typical vocalizations using the left hemisphere and the thunderstorm sounds using the right hemisphere. Nevertheless, conspecific vocalizations are not always processed by the left hemisphere, since the right hemisphere is used for processing vocalizations when they elicit intense emotion, including fear. These findings suggest that the specialisation of the left hemisphere for intraspecific communication is more ancient that previously thought, and so is specialisation of the right hemisphere for intense emotions.     

Recognition of halftone and contour figures under their lateralization and masking

Recognition of shape of natural objects was studied during lateralized tachistoscopic presentation and different degree of noise-like ("rain drops") masking in 15 healthy subjects. Two sets of figures were used: halftone and contour ones. In all masking conditions, the mean group data showed a significantly better recognition of contour images by the left hemisphere as compared to the right hemisphere. The probability of correct response decreased with increase in the degree of masking. Contour figures were recognized significantly better than halftone figures. Gender differences in recognition were revealed. Male subjects displayed no hemispheric preference in recognition of both types of stimuli in both masking conditions. Possible neurophysiological mechanisms and functional significance of the findings are discussed.     

The role of the right and left hemispheres in emotional evaluation of visual stimuli

This work is devoted to the analysis of the role of the right and left hemispheres in realization of various parameters of subjective emotional reactions to external stimuli. Experimental study of the evaluation of difficult-to-verbalize visual stimuli, according to the preset emotional valences, showed that damage to the posterior parts of the right hemisphere predominantly impairs evaluation of the emotion valence, and damage to the anterior parts of the left hemisphere impairs discrimination of the modality (quality) of the emotion.     

Interhemispheric asymmetry in rats differentiating figures by size

Motor alimentary conditioned reflex was elaborated in Wistar line rats to presentation of various pairs of figures, those of larger area serving as positive signals. In tests on animals with intact brain and with unilateral hemispheric cortical inactivation, new pairs of figures were used besides basic stimuli. The level of analysis in testing experiment was lower than normal: by 5.6% at intact brain, by 16.4%--at right hemisphere inactivation, by 36.4%--at left hemisphere inactivation. Elimination of the left hemisphere produced prolongation of the conditioned reaction time, signs of frustration and aftereffect. In conditions of right hemisphere inactivation the level of discrimination of figures depended on their specific properties and the side of presentation. Conclusion is made on dominating role of the left hemisphere in analysis of abstract and concrete characteristics of visual stimuli, in control of temporal, spatial and emotional characteristics of reactions in situations when considerable abstraction and distinguishing of generalizing invariant sign "more-less" is necessary for elaboration of the conditioned reflex.     

The effects of simulated microgravity on characteristics of slow presaccadic potentials

The parameters of saccades and presaccadic slow potentials were studied in seven right-handed male volunteers with a dominant right eye before and after exposure to 6-day dry immersion. Visual stimuli were presented using three light diodes, which were located in the center of the visual field (the central fixation stimulus) and 10° to the right and left of it (peripheral stimuli (PSs)). The subjects performed a test with simple saccades to a PS and a test with antisaccades to the point located symmetrically in the opposite visual field. The EEG (19 monopolar leads) and electrooculogram were recorded. To isolate slow potentials, backward EEG averaging was performed, with the moment of switching on the PS serving as a trigger for the averaging. It was found that the characteristics of saccadic eye movements did not substantially change after exposure to immersion. However, both tests revealed a change in topography and a decrease in the amplitude of presaccadic slow negative potentials (PSNPs) during immersion. Characteristically, the focus of presaccadic negativity shifted to the right hemisphere so that the PSNP amplitude sharply decreased in the left and increased in the right hemisphere. A significant decrease in the PSNP amplitude on day 6 of immersion was found in the midline and left-hemispheric frontal and parietal leads. It may be suggested that, because of support unloading and a decrease in proprioceptive input, exposure to microgravity causes a decrease in the activity of the left hemisphere and prefrontal and parietal cortices, initially involved in preparation and realization of motor responses. The activation of the right hemisphere could be of compensatory character.     

Hemispheric participation in the shaping of spatial-motor asymmetry in visual recognition in rats

Asymmetry of movement direction was found in Wistar rats at establishing of motor alimentary conditioned reflex to simultaneously presented visual stimuli. In the course of learning the asymmetry weakened on the whole, but some individuals retained right- or left side preference. The analysis of asymmetry change before and after unilateral cortical inactivation revealed a special role of right hemisphere influences for the formation of right-side preference and of the left hemisphere--for the choice of the left direction. The lack of asymmetry was observed at the presence of the influences from the left hemisphere cortex depressing ipsilateral nigro-striate system and activating the contralateral one. Influences of the cortex of both hemispheres reduce the absolute value of the asymmetry coefficient; the left hemisphere has a special significance for manifestation of temporal asymmetry parameters. Photic interference is a factor modulating the asymmetry. It reduces the right hemisphere activity more than that of the left one; it intensifies right hemisphere influences, contributes to the involvement of the transcallosal conduction channel in the formation of spatial-motor asymmetry.