Relation of visual evoked potentials to the integral characteristics of cognitive activity in 8- to 9-year-old children

Amplitude and temporal parameters of evoked potentials (EPs) in response to a checkerboard pattern, picture of a house, the Russian word "dom", meaning house, combination of letters "DMO" and a number of other stimuli, correlated with indices of the verbal, nonverbal, and general intelligence as well as with those of the cognitive style "field dependence-independence". Maximum number of statistically significant correlations was found in the course of comparison of integrative cognitive characteristics and parameters of EPs to stimuli with increased semantic complexity. No interhemispheric differences were found in the character of interrelations between cognitive characteristics and parameters of EPs to verbal and spatially structured stimuli.     

On the mechanisms underlying appearance of responses to movement,directional sensitivity and velocity tuning of the cat's striate cortical neurons

The responses to moving and stationary stimuli of 27 cat's striate cortical units were studied. Two stationary light bars located in different parts of the receptive field were used. The order of presentation and the time-interval between the stimuli varied; so, the presentation of a pair of stationary stimuli was an analogue of a moving stimulus.It was shown that responses occurred in neurons previously unresponsive to stationary stimuli when two stationary stimuli were presented successively in certain order. In the direction-sensitive units an asymmetry of the temporal course of the inhibitory processes was observed. The inhibitory zone located on the side of the preferred direction of movement was characterized by an early inhibitory phase followed by a phase of disinhibition and by a second inhibitory phase. For the inhibitory zone located on the side of the null direction no disinhibitory phase was demonstrated.The significance of the spatial and temporal characteristics of the receptive field for the appearance of responses to movement, the directional sensitivity and the velocity tuning in striate neurons is discussed.     

Comparison of sensitivity to first- and second-order local motion in 5-year-olds and adults

We compared sensitivity to first- versus second-order motion in 5-year-olds and adults tested with stimuli moving at slower (1.5 degrees s(-1)) and faster (6 degrees s(-1)) velocities. Amplitude modulation thresholds were measured for the discrimination of the direction of motion (up vs. down) for luminance-modulated (first-order) and contrast-modulated (second-order) horizontal sine-wave gratings. At the slower velocity (1.5 degrees s(-1)), the differences in threshold between 5-year-olds and adults were small but significant for both first- and second-order stimuli (0.02 and 0.05 log units worse than adults' thresholds, respectively). However, at the faster velocity (6 degrees s(-1)), the differences in threshold between the children and adults were 8 times greater for second-order motion than for first-order motion. Specifically, children's thresholds were 0.16 log units worse than those of adults for second-order motion compared to only 0.02 log units worse for first-order motion. The different pattern of results for first-order and second-order motion at the faster velocity (6 degrees s(-1)) is consistent with models positing different mechanisms for the two types of motion and suggests that those mechanisms mature at different rates.     

The auditory aftereffects of radial sound source motion with different velocities

Auditory aftereffects were evaluated after short adaptation to radial sound source motion with different velocities. Approach and withdrawal of the sound source were simulated by means of rhythmical noise (from 20 Hz to 20 kHz) impulse sequences with an arising or diminishing amplitude. They were presented to an anechoic chamber through two loudspeakers placed at 1.1 and 4.5 m from the listener. The adapting stimulus velocities were 0.68, 3.43, 6.92, and 9.97 m/s with an adaptation duration of 5 s. At all motion velocities, the aftereffect manifested itself in divergence of psychometric functions upon approaching and withdrawing of adaptors. The direction of function displacements was opposite to that of the adaptor motion. Three parameters reflecting alteration of perception after motion adaptation were determined and compared with control data: the evaluation of stationary test stimuli; the velocity of moving test signal at the point of subjective equality (perceptually unmoving point); and the percentage of responses after averaging over all test signals. These parameters of auditory radial motion aftereffect similarly changed with the adaptor velocity. They demonstrated a significant effect at slow motion (0.68 and 3.43 m/s) and a small effect at a quick motion (6.92 and 9.97 m/s).     

Mismatch negativity as a characteristic of the distinguishing locating capacity of the human auditory system

Mismatch negativity has been studied under the conditions of dichotic stimulation by deviant stimuli that either changed their azimuth from zero to 4.5°, 13.5°, and 22.5° or moved with small velocities from the head midline to one of the ears. The reference stimuli were located along the head midline. Our experiments have shown that both a discontinuous increase in the azimuth and an increase in the velocity of moving stimuli are accompanied by an increase in the amplitude of mismatch negativity. This process is more pronounced in the cases of (1) an instantaneous change in the deviant azimuth compared to its movement, (2) a longer duration of the deviant sound, (3) action of the deviant in the right hemisphere, and (4) the frontal derivation. The correlations of changes in the mismatch negativity with psychophysical data on the resolution of the human auditory system are considered.     

Forecast ability of the auditory system during perception of gradually or abruptly moving short sound images

The ability to localize endpoints of sound image trajectories was studied in comparison with stationary sound image positions. Sound images moved either gradually or abruptly to the left or right from the head midline. Different types of sound image movement were simulated by manipulating the interaural time delay. Subjects were asked to estimate the position of the virtual sound source, using the graphic tablet. It was revealed that the perceived endpoints of the moving sound image trajectories, like stationary stimulus positions, depended on the interaural time delay. The perceived endpoints of the moving sound images simulated by stimuli with the final interaural time delay lower than 200 micros were displaced further from the head midline as compared to stationary stimuli of the same interaural time delays. This forward displacement of the perceived position of the moving target can be considered as "representational momentum" and can be explained by mental extrapolation of the dynamic information, which is necessary for successive sensorimotor coordination. For interaural time delays above 400 micros, final positions of gradually and abruptly moving sound sources were closer to the head midline than corresponding stationary sound image position. When comparing the results of both duration conditions, it was shown that in case of longer stimuli the endpoints of gradually moving sound images were lateralized further from the head midline for interaural time delays above 400 micros.     

不同运动速度下人眼的阈上调制特性

本文报道了在光栅的三种恒定运动速度(0°/S,10°/S,30°/S)下,阈值对比敏感度函数CSF(V)和阈上对比度比配函数CMF(V,C)的测试数据.计算机拟合结果表明,在各个不同的恒定运动速度下,人眼的阈上对比度比配函数CMF(V,C)和阈值对比敏感度函数CSF(V),可以由静止目标的阈值对比敏感函数CSF近似地预测出来.本文给出了预测方法的数学描述及有关经验公式.     

Effect of fast moving stimuli and saccadic eye movements on cell activity in visual areas V1 and V2 of behaving monkeys

Extracellular recordings were carried out in the visual cortex of behaving monkeys trained on a fixation/detection task, during which a target light was displayed stationary or suddenly moving on a tangent translucent screen. The responses of visual cortical cells to fast moving stimuli during steady fixation and those obtained during rapid eye movements (saccades) which moved their receptive field across a stationary stimulus, were studied. Areas V1 and V2 were explored. When tested with rapidly moving stimuli (500 deg/sec) during steady fixation, neurons in each area behaved in almost the same way. About one fourth of them were activated, the remainder showing either no response (little more than a half of them) or a reduction of the spontaneous firing rate. In both areas, some of the neurons activated during steady fixation did not respond or responded very weakly during eye motion at saccadic velocity (500 +/- 50 deg/sec). Neurons of this type, which we refer to as 'real motion' cells, could somehow contribute to the maintenance of visual stability during the execution of large eye movements.     

Representation of moving stimuli by somatosensory neurons.

The findings obtained in neurophysiological and psychophysical investigations using tactile stimuli that move at constant velocity across the skin are reviewed. For certain neurons in the postcentral gyrus of the cerebral cortex (S-I) of macaque monkeys, direction of stimulus motion is a "trigger feature" i.e., moving tactile stimuli evoke vigorous discharge activity in these neurons only if the stimuli are moved in a particular direction across the receptive field. This directional selectivity is maximal when stimulus velocity is between 5 and 50 cm/sec, and falls off rapidly at lower or higher velocities. The capacity for human subjects to correctly identify the direction of stimulus motion on the skin exhibits a similar dependence on stimulus velocity. The similar effects of velocity on neural and psychophysical measures of directional sensitivity support the idea that direction of stimulus motion on the skin can only be recognized if the moving stimulus optimally activates the group of S-I neurons for which that directions of simulus motion is the trigger feature.     

Mechanism of directional selectivity of neurons with complex receptive fields in the cat visual cortex

Spatio-temporal interactions within complex receptive fields in the cat visual cortex were investigated by sequential presentation of two stationary stimuli. When two stimuli were presented in phase (on-on or off-off) in the order corresponding to preferred direction of movement, facilitation or weak inhibition of the response to the second stimulus was observed, whereas if it corresponded to zero direction of movement, the response was strongly inhibited. In the case of stimulation out of phase (on-off or off-on), in the order corresponding to the preferred direction of movement, considerable inhibition of the response to the second stimulus was observed, whereas in the opposite order, facilitation or weak inhibition was observed. The strength of interaction between different parts of the field depended on the distance between them and the duration of the interval between stimuli. Directional selectivity of "complex" neurons is thus ensured by asymmetry of spatio-temporal interactions between receptive field inputs of the same type. Interactions between inputs of different types, arising when a multiedge stimulus (bar, grating) can be used by the visual system to distinguish an object from the background and to assess changes in size of objects and the relative velocity of their movement.V. Kapsukas State University, Vilnius. Translated from Neirofiziologiya, Vol. 16, No. 4, pp. 505–512, July–August, 1984.     

Dependence of Subjective Traverse Length on Velocity of Moving Tactile Stimuli

Two series of experiments were performed to assess the effects of stimulus velocity on human subjects' perception of the distance traversed by a moving tactile stimulus. In all experiments, constant-velocity stimuli were applied to the dorsal surface of the left forearm; velocities ranging between 1.0 and 256 cm/sec were used. In some experiments the stimuli moved from distal to proximal over the skin, and in others they moved from proximal to distal. The length of skin contacted by the moving stimulus was defined by a plate having an aperture of 4.0 × 0.5 cm.

In the first series of experiments, subjects were required to compare the distance traversed by a test stimulus delivered 2 sec after a standard stimulus, and also to report the on-locus and the off-locus of the brushing stimulus. In the second series of experiments, the subjects rated the perceived distance on the skin using a free-magnitude-estimation procedure. The data from both series of experiments defined the same relationship between stimulus velocity and perceived stimulus distance. More specifically, although the length of skin contacted by the stimulus was the same at all velocities, subjects' estimates of stimulus distance decreased with increasing stimulus velocity. In addition, the function relating estimates of stimulus distance to velocity was flat for velocities between 5 and 20 cm/sec, but possessed an appreciable negative slope at lower and higher velocities.

It is interesting that the plateau of the relationship between perceived stimulus distance and velocity occurred within the range of velocities that human subjects employ to scan textured surfaces; it also corresponded precisely with the range of stimulus velocities at which the directional sensitivity of somatosensory cortical neurons and human subjects is optimal.     

Auditory motion aftereffects of approaching and withdrawing sound sources

Auditory motion aftereffects of approaching and withdrawing sound sources were investigated in the free field. The approaching and withdrawing of a sound source were simulated by means of differently directed changes in the amplitude of impulses of broadband noise (from 20 Hz to 20 kHz) through two loudspeakers placed 1.1 and 4.5 m away from the listener. Presentation of the adapting approaching and withdrawing stimuli changed the perception of test signals following them: a stationary test signal was perceived by listeners as moving in the direction opposite to one of the movement of the adapting stimulus, whereas a test stimulus slowly moving in same direction as the adapting signal was perceived as stationary. The specific features of the auditory aftereffect of signals moving in a radial direction were similar to those of sound sources moving in a horizontal plane.     

Movement learning of free flying honeybees

Summary Free flying honeybees were conditioned to moving black and white stripe patterns. Bees learn rapidly to distinguish the direction of movement in the vertical and horizontal plane.After being trained to a moving pattern bees do not discriminate the moving alternative from a stationary one. There is no significant velocity discrimination for patterns moving in the same direction.For vertical movements there are clear asymmetries in the spontaneous choice preference and in the learning curves for patterns moving upward or downward.After bees are trained to a stationary pattern they can discriminate it from an upward moving alternative. Learning curves involving movement are generally biphasic, suggesting different adaptive systems depending on the number of rewards.The flight pattern of bees which are trained to movement changes during the process of learning. At the beginning of the learning procedure bees reveal an optokinetic response to the moving patterns, this response is strongly reduced after a number of rewards on a moving pattern.     

Electrophysiologic analysis of the process of recognizing target and non-target stimuli in healthy and oligophrenic children

In an automatized experiment, with a computer on line, amplitude-temporal parameters of evoked potentials (EPs) to purposive and non-purposive stimuli (digits), were analyzed in normal and mental retarded children. At unilateral stimuli presentation to the left or right visual half-fields EPs were recorded simultaneously in projection, TPO, parietal and central areas of the left and right hemispheres. It has been shown that in normal children, differential involvement of projection and associative structures in the analysis of sensory information takes place in both hemispheres. The amplitudes of most EP components in the range of 100-400 ms to the purposive stimuli are higher than to the non-purposive ones. Considerable similarity of EPs developing in response to ipsi- and contralateral stimulations of visual fields ("direct" and "transmitted" EP) is observed. In mental retarded children significant changes are revealed in intra- and interhemisphere organization of the process of perception of purposive and non-purposive stimuli. In the right hemisphere structures there are no differential EP reactions to the two types of stimuli. Significant, in comparison with the norm, prolongation of the latencies of most EP components is noted, especially in the structures of the left hemisphere, to the purposive stimuli. In the process of perception, changes are seen of the integration of functions of both hemispheres. The totality of disturbances of systemic brain organization at perceptive activity in mental retarded children may reflect neurophysiological mechanisms of mental deficiency.     

Random movement pattern of the sea urchin Strongylocentrotus droebachiensis

We describe the fine-scale movement of the sea urchin Strongylocentrotus droebachiensis based on analyses of video recordings of undisturbed individuals in the two habitats which mainly differed in food availability, urchin barrens and grazing front. Urchin activity decreased as urchin density increased. Individuals alternated between moving and being stationary and their behaviour did not appear to be affected by either current velocity (within the range from 0 to 15 cm s^− 1) and temperature (2.3 to 6.0 °C). Movement of individuals at each location was compared to that predicted by a random walk model. Mean move length (linear distance between two stationary periods), turning angle and net squared displacement were calculated for each individual. The distribution of turning angles was uniform at each location and there was no evidence of a relationship between urchin density and either move length or urchin velocity. The random model predicted a higher dispersal rate at locations with low urchin densities, such as barrens habitats. However, the movement was sometimes greater or less than predicted by the model, suggesting the influence of local environmental factors. The deviation of individual paths from the model revealed that urchins can be stationary or adopt a local (displacement less than random), random or directional movement. The net daily distance displaced on the barrens, predicted by a random walk model, was similar to the observed movement recorded in our previous study of tagged urchins at one site, but less than that observed at a second site. We postulate that the random dispersal of urchins allows individuals on barrens to reach the kelp zone where food is more abundant although the time required to reach the kelp zone may be considerable (months to years). Urchins decrease their rate of dispersal once they reach the kelp zone so that they likely remain close to this abundant food sources for long periods.     

Discrimination and scaling of velocity of stimulus motion across the skin

The capacity of human subjects to discriminate and to scale the velocity of tactile brushing stimuli was assessed. Signal detection and classical psychophysical techniques were employed to estimate the Weber fraction over a wide range of velocities (from 1.5 to 140 cm/sec). In addition, free magnitude estimates of (1) the velocity and (2) the duration of moving tactile stimuli were obtained. It was found that human capacity to discriminate stimuli delivered to a 4 to 6-cm chord of skin on the dorsal forearm and differing in velocity remains grossly constant over the range of velocities tested and is relatively poor (i.e., the Weber fraction = 0.2-0.25). A simple power function (exponent = 0.6) satisfactorily describes the psychophysical relation (1) between the perceived and actual velocity and (2) between the perceived and actual duration of these stimuli. Since a direct proportionality between the reciprocal of a subject's estimate of duration and his or her estimate of velocity was observed, it is suggested that these two sensory attributes may reflect the operation of a neural mechanism sensitive to the duration of stimulation. Moreover, the data are inconsistent with the hypothesis that the subjects computed estimates of mean velocity from the ratio of perceived distance to perceived duration.     

Heterogeneity of neuron populations with complex receptive fields in the cat visual cortex

The selectivity of striate neurons with complex receptive fields to the orientation, direction, and velocity of movement of various stimuli was investigated in unanesthetized and uncurarized cats. On the basis of all characteristics obtained by the study of single-unit responses to a stationary flickering slit, a moving spot of light, and a moving oriented stimulus, four groups of complex neurons were distinguished. The characteristics of group I neurons indicate a mechanism of orientation selectivity in the organization of their receptive fields, group IV neurons have a mechanism of directional selectivity, and neurons of groups II and III possess both mechanisms. The existence of separate neuronal systems coding the orientation and direction of stimulus movement is suggested.V. Kapsukas State University, Vilnius. Translated from Neirofiziologiya, Vol. 11, No. 2, pp. 109–116, March–April, 1979.     

The role of the genotype in the variability of human evoked potentials at different stages of ontogeny]

The determinants of individual differences in visual EPs to stimuli of different type depending on the age of subjects were studied. EPs to flash, checkerboard pattern and some other stimuli with semantic aspect were recorded in three groups of MZ, DZ twins aged 8-9, 10-12, 18-25 years. The heritability of EPs parameters is not ontogenetically stable characteristic. It changes from one age group to another in different way for separate EPs components and parameters depending on their nature, type of stimulus, area of recording. Most of all genotypical influences are manifested in EPs parameters of 10-12 years old subjects, especially the middle latency components from vertex area and latent periods of EPs in comparison with their amplitudes.     

Dynamic Spatial Organization of Receptive Fields of Neurons in the 21a Cortical Area

We studied changes in the spatial parameters of receptive fields (RFs) of visually sensitive neurons in the associative area 21a of the cat cortex under conditions of presentation of moving visual stimuli. The results of experiments demonstrated that these parameters are dynamic and depend, from many aspects, on the pattern of the stimulus used for their estimation. Angular lengths of the horizontal and vertical axes of the RFs measured in the case of movement of the visual stimuli exceeded many times those determined by presentation of stationary blinking stimuli. As is supposed, a visual stimulus, when moving along the field of vision, activates a certain number of the neurons synaptically connected with the examined cell and possessing RFs localized along the movement trajectory. As a result, such integrated activity of the neuronal group can change the excitation threshold and discharge frequency of the studied neuron. It seems probable that correlated directed activation of the neuronal groups represents a significant neurophysiological mechanism providing dynamic modifications of the RF parameters of visually sensitive neurons in the course of processes of visual perception and identification of moving objects within the field of vision.     

Laser light-scattering analysis of protoplasmic streaming in the slime mold Physarum polycephalum

Laser light scattering is shown to be an effective means of obtaining a rapid, objective assessment of dynamic changes in the intact plasmodium of the myxomycete Physarum polycephalum during bidirectional (shuttle) streaming. The motion of material in a 100 mum diameter region of a plasmodial vein was studied by following changes in the autocorrelation function of the fluctuations in the scattered light intensity. The autocorrelation function was recorded at 10 s intervals and analyzed to follow changes in the flow velocity of protoplasm associated with shuttle streaming. Rhythmic velocity changes and a "beating" pattern of velocity maxima were readily observed. In an attempt to locate the site of underlying structural changes in the vein responsible for the changing pattern of flow, the average scattered intensity was separated into components derived from moving and stationary scatterers. Periodic variations in the light intensity due to stationary scatterers are related to the streaming cycle and indicate the occurrence of important structural changes in the vein walls. Two possible interpretations of the data are offered; one involving gross dynamic changes in vein structure, the other involving the formation, contraction, or breakdown of fibrillar material in the vein wall during the streaming cycle.