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Biomedical subjects

N Yakimoff

Publications and source records attributed to N Yakimoff.

At least 37 records · Page 2Linked to original sources
PubMed1987

A linear model for the response time in motion prediction.

A linear relationship was found to exist between the response time and the concealment time in motion extrapolation experiments. It follows that the subjects performance is characterized by the two parameters of the linear relationship rather than by the error in determining the position of the occluded moving stimulus. These two parameters can be manipulated separetely by specific changes in the experimental arrangement. A suggestion is made that one of the parameters is connected with velocity estimation, while the other with internal organization and execution of the motor response.

Humans↗
PubMed1987

Estimating the duration of briefly presented physiognomic stimuli.

The influence of complex stimuli which are supposed to induce different attitude and emotional effects in the observer on short time interval perception was studied. It is concluded that emotional and/or aesthetical factors do not interfere with short time interval perception.

Esthetics↗
PubMed1987

Spatial frequency, contrast and duration estimation.

Duration estimation of square-wave gratings presented for "short" (up to 150 ms) and "long" (above 190 ms) time intervals was studied. The spatial frequency (SF) of the gratings with equal mean luminance and contrast 85% varied from 0.7 to 12 c/deg. Duration estimates were assessed by the method of magnitude estimation. For brief presentations only the duration of high SF gratings was subjectively shorter than the duration of low SF gratings. It was shown that the apparent contrast of the square-wave gratings decreased with the increase of SF. In an experiment on duration estimation of patterns of different contrast it was demonstrated that duration estimates increased with increasing contrast for short presentations only. The apparent contrast of the gratings covarying with SF was supposed to underlie SF influence on short duration estimation. The assumption about different mechanisms operating in short and long duration perception was supported by the results.

Analysis of Variance↗
PubMed1987

Determination of the threshold of simultaneity and temporal order using the "step-ladder" method.

The article considers the sensitivity of the mechanisms for perceiving simultaneity and temporal order. A method similar to the psychophysical "staircase" method is used for determining the thresholds of the perception of simultaneity and temporal order. The simultaneity and temporal order thresholds are measured for two levels of visual adaptation of the subjects. Two clearly distinguishable thresholds are established: simultaneity threshold and temporal order threshold. The threshold values for simultaneity and temporal order are preserved, irrespective of the adaptation level, which suggests that the general illumination does not affect the mechanisms for perceiving simultaneity and temporal order.

Adaptation, Ocular↗
PubMed1987

In search of paintings influence on time judgement.

The influence of paintings on short time interval perception was studied. Three methods for time estimation were tested: direct scaling and two modifications of the method of reproduction – with and without simultaneous presentation of the painting whose duration was, reproduced. The results show that short time interval perception is influenced by such complex stimuli as paintings. The motor reproduction with simultaneous presentation of the visual stimulus was the most effective in revealing the influence of paintings on short time interval perception.

Art↗
PubMed1986

Mechanisms and asymmetries in visual perception of simultaneity and temporal order.

Temporally overlapping, spatially separated visual stimuli were used for studying perception of simultaneity and temporal order. Pairs of flashes each of 100 ms duration were presented with stimulus onset asynchronies of 0, 30, 50, and 70 ms. Three spatial arrangements of flash presentation were tested: both flashes were presented foveally; one flash was presented foveally and the other at 8 deg in the left visual hemifield; one flash was presented foveally and the other at 8 deg in the right visual hemifield. Onset asynchronies of 30 and 50 ms were not sufficient for correct identification of temporal order although the flashes were not perceived as simultaneous. Analysis of the response distributions suggests the existence of two-independent mechanisms for evaluating temporal interrelations: one for detecting simultaneity and the other for identifying temporal order. A better detection of simultaneity was found when synchronous flashes were presented together with pairs of flashes separated by larger onset asynchronies. Reading habits may explain only part of the left-right asymmetries of the response distributions. The possible lateralization of the two suggested mechanisms within the cerebral hemispheres is discussed.

Adult↗
PubMed1986

Perceived orientation of contour quadrangles.

One hundred subjects ranked the apparent tilt of ten quadrangles. A scale of perceived orientation was derived from a pair-comparison treatment of these data. The main characteristic determining estimated orientation of the quadrangles was the axis from which the sum of the squared distances to each point of the figure was minimal (the LS-axis). Judgements were also influenced by the orientation of an 'axis of balance', which ran through the centre of gravity and the lowermost apex of the quadrangle. Quadrangles with parallel LS-axes were systematically judged as differently tilted according to the difference in the orientation of their axes of balance. Both the LS-axis and the axis of balance are physical characteristics of an object that are of great importance for the optimal control of human action through vision.

Gravitation↗
PubMed1985

Extrapolation of horizontal motion to linear targets of different orientation.

In a motion extrapolation task the subjects were asked to press a button at the moment of the imaginary impact between a concealed moving stimulus and a stationary target-line intersecting with the extension of motion trajectory. Horizontal motion of constant velocity was used. The target-line had two possible orientations: vertical and tilted at an angle of 30 degrees with respect to the moving stimulus trajectory. Four extrapolation distances subtending 4.5, 6.0, 7.5, and 9.0 degs of visual angle were used. The target-line was presented 2 s before the disappearance of the moving stimulus. Target-line position and orientation were chosen at random. Four out of five subjects were significantly faster in predicting the impact between the moving stimulus and the tilted target-line. The results are compared to data obtained in line-segment extrapolation experiments and the existence of a common mechanism for spatial extrapolation in static and dynamic conditions is discussed.

Adolescent↗
PubMed1984

Influence of the target delay and duration on the prediction of a moving stimulus future position.

In a linear-motion prediction study an immobile target with different duration and delay with respect to the onset of the visible motion determined the motion extrapolation distance. The subject's task was to press a key at the moment when the moving stimulus would reach the position of the target if it continued its motion on the screen. The subject's response time was measured between the moment of the moving stimulus disappearance and the moment of key pressing. A linear relationship between the response time and the concealment time was obtained under all experimental conditions. It was demonstrated that the duration of the target did not affect the linear regression equation constants. The delay of the target presentation with respect to the onset of the visible motion was found to influence the free term of the linear relationship. When the target was presented with a great delay (0.56 s before the moving stimulus disappearance) the intercept in the linear relationship significantly decreased. The present results suggest that the organization of the response in the motion prediction conditions influences the temporal characteristics of the subject's performance. This influence is manifested in alternation of the free term in the linear relationship between the response time and concealment time.

Distance Perception↗
PubMed1983

Estimating the orientation of dot patterns presented tachistoscopically.

Human ability for determining the orientation of dot patterns was studied under tachistoscopic presentation. Random dot configurations with a great difference between the line determined by the most distant dots in the configuration and the line for which the sum of the squared distances between each dot of the configuration and this line is minimal were used. These lines determine the "extension" and the "elongation" of the patterns (Yakimoff, 1981). The results have shown that the elongation of a dot pattern is the essential characteristic determining its perceived orientation.

Adult↗
PubMed1982

Scanning open and closed polygons.

The process of selection of target points during voluntary eye movements when contoured polygonal shapes with open and closed angles are observed was analysed in humans by means of an eye recording technique. It has been found for both types of stimuli that the majority of fixation points where located at angles and that the mean value of distribution was found to be more distant from the vertex for acute angles than for obtuse ones. In this respect a difference was found between open and closed contours. In the former case the mean values of fixation point distribution were more distant from the vertex and the dispersion of eye fixation was greater.

Adult↗
PubMed1981

Does assignment of orientation to dot patterns reveal optimization processes in the visual system?

Sixty subjects were tested to assign orientation to ten dot patterns differing in their overall form and the number of dots in the pattern. The patterns were presented in four different positions in the visual field and their orientation was estimated in two ways. It was demonstrated that the assignment of orientation did not depend on the position of the pattern in the visual field as well as on the method of estimation used. A quantitative measure for the elongation of a dot pattern is proposed which correlates with the degree of ambiguity in orientation estimation. The greater the elongation the smaller the standard deviation of the estimates given. The distributions of the estimates for the ten patterns were analyzed. It was shown that they can be presented as superpositions of two or more groups of normally distributed estimates determined by some salient characteristics of the stimuli. Data are discussed from the point of view that assignment of orientation to dot patterns reveals the existence of optimization mechanisms in human brain that extract perceptual invariants from external stimulation.

Adult↗
PubMed1981

Localization of brief visual stimuli during pursuit eye movements.

Experimental findings concerning the properties of the phenomenon of mislocation of brief visual stimuli during smooth eye tracking are described. One of these, which cannot be explained by existing hypotheses, is that under certain conditions the mislocation magnitude tends to have zero or even negative values. A model is developed for explanation of the mislocation phenomenon. It is suggested that localization is based on: (1) information about the current eye position and (2) information about the stimulus locus on the retina. They both arrive at the localization centre with non-zero delays. The mode of information processing in this centre leads to a magnitude of mislocation which is proportional to the difference between the two delays and which could be positive, zero or negative. Factors which influence either delay should also influence the mislocation magnitude.

Discrimination, Psychological↗
PubMed1981

Visio-motor prediction of collision.

Visually presented moving stimuli were used in a collision prediction experiment aimed at revealing the ability of human subjects to estimate the velocity of motion. Spatial extent, velocity and exposure duration of movement were varied so that the correlation between these characteristics of the stimuli was low (about 0.5). The moving stimulus disappeared at a certain place on the screen. By pressing a button the subject had to estimate the moment the stimulus would reach a target in the visual field. A linear dependence between estimated and actual duration of concealed motion was obtained. It is concluded that spatial extent and duration of motion do not influence the performance of the task. Velocity estimation and individual characteristics of the mechanisms controlling the motor response are supposed to determine the linear dependences obtained for all subjects tested.

Accidents↗
PubMed1981

Scaling spatial extent, velocity and duration of motion.

Experiments on magnitude estimation of spatial extent, velocity and duration of 11 moving stimuli which had low correlations between the stimulus attributes revealed psychophysical curves of different slopes and shapes for the three attributes of motion. A psychophysical power function with an exponent almost equal to 1.0 described the magnitude estimation of distance. Deviations in velocity judgments were observed with shortening the spatial extent of motion. Duration estimation determined by moving stimuli was found to differ significantly from the estimation of time intervals of the same range presented with stationary light stimuli (Marinova, Mitrani, Yakimoff, 1980). The results indicate that velocity cannot be regarded as a directly perceived attribute of motion. Distance only seems to be directly perceived.

Distance Perception↗
PubMed1981

Estimating the velocity of briefly presented moving stimuli.

The ability of human subjects to estimate the velocity of briefly presented moving stimuli was studied in a prediction-of-collision experiment. After the disappearance of the moving target the subject had to press a button at the moment the target would reach a predetermined position in the visual field. Four velocities of the moving target were used -6 degrees/s, 10 degrees/s, 14 degrees/s, and 20 degrees/s. For each velocity there were five exposure distances: 0.5, 1.0, 2.0, 3.0 and 4.0 degrees and four concealment distances: 6, 8, 10 and 12 degrees. For the large exposure distances a linear dependence of the response time on the concealment time was observed. This dependence was not linear for exposure durations less than 100 ms. The response time increased in these cases. Despite the common character of the results obtained with different subjects there were clear individual differences most probably due to differences in subjective velocity scales and individual mechanisms of motion extrapolation and organization of motor responses.

Humans↗