Perceptual grouping of strip dot patterns.

Grouping of one-dimensional (strip) dot patterns was investigated, using an adjustment procedure to evaluate the distance (adjusted gap) at which two patterns appear to merge in a single strip. The size of the patterns had only a scaling effect on the adjusted gap. The adjusted gap and the variance of the estimates were influenced by the number of dots and the regularity (similarity, symmetry) of the patterns in the pair.

Different mechanisms may underlie the performance in relative localization tasks.

Two different groups of subjects had to adjust two-dimensional stimuli, differing in size, shape and type (dot patterns or irregular contour figures), within a reference circle. The two groups performed under two different instructions. The first instruction stressed matching the centres of the stimulus and the circle, while the second required simply positioning the test stimulus in the middle of the reference circle.

Vasopressin- and oxytocin-immunoreactive nerve cells in the aging rat hypothalamus.

Immunohistochemistry and morphometry were used to study the age-related changes in the vasopressin (AVP) and oxytocin (OXT) nerve cells in the paraventricular (PVN), supraoptic (SON) and suprachiasmatic (SCN) nuclei of 3-, 11- and 28-month-old rats. The results showed a statistically significant reduction in the mean number of AVP cells in the PVN, SON and SCN, and of OXT cells in the PVN with advancing age. Different age-related changes in the mean size of the immunoreactive cells were found in the three nuclei: a significant and transitory increase in the AVP and OXT cell sizes in the PVN, a tendency towards increasing the AVP and OXT cell sizes in the SON, and a significant and gradual decrease in the AVP cell size in the SCN.

Perceived location of two-dimensional patterns.

The study attempted to test the possibility that the center of gravity of two-dimensional patterns is the cue used by a human observer for their localization. Four experiments were carried out. The first, using a matching procedure, required the localization of the center of irregular dot patterns, contour and filled polygons which varied in size and orientation.

The relative roles of vertices and sides in determining perceptual centres within shapes.

In the main experiment, subjects estimated the centre of five polygons in three variants: whole contour, only sides, or only corners. The perceived centre was closer to the area barycentre than to any other mathematical centre. Errors decreased as the number of sides of the figures increased.

[The accuracy of saccadic eye movements is associated with their horizontal and vertical direction].

Electro-oculagraphic, photo-oculographic, and magnetoelectro-oculographic methods were used to study and to compare the accuracy of 10 degrees saccadic movements of the eyes in dependence on their direction to the right, to the left, upwards and downwards. Leftward saccades in right-handers and rightward saccades in left-handers proved to be more accurate compared to saccades in the opposite direction. This finding may be related to the functional asymmetry of the cerebral hemispheres.

Perceptual constancy during ocular pursuit: a quantitative estimation procedure.

Perceptual constancy of visual motion is usually described as the degree of correspondence between physical and perceived characteristics of motion in the external world. To study it, one has to assess the relationship between physical motion, its retinal image, and its perception. We describe a quantitative estimation procedure for a measure K denoting the degree of perceptual constancy of background target motions noncollinear to the eye movements during ocular pursuit.

Matching the orientation of dot patterns with real, interpolated, and extrapolated lines.

The perception of the orientation of random-dot patterns was studied using four different matching tasks. Homogeneous, elongated patterns and patterns containing Moiré effects were used. One of the tasks implied linear extrapolation and two others implied linear interpolation of the matching line.

Selective directional sensitivity in visual motion perception.

We present two experiments demonstrating that: (i) the latency of perception of the position of a small visual target moving towards the fovea is shorter than that of the same target moving away from the fovea; (ii) the reaction time (RT) to onset of motion of the same type of target is also shorter when it moves towards the fovea; and (iii) the RT to onset of motion away from the fovea may be shorter when larger, textured stimuli are employed. The relation of the findings to the existence of two systems for visual motion information processing and to recent neurophysiological findings is discussed.

Models for the perception of orientation in random dot patterns.

The aim of this paper is to summarize and to compare some known mathematical models of orientation perception in random dot patterns and to propose new solutions of this question. The model adequacy is judged from the previously obtained experimental results. Apart from the models based on some simple function of the coordinates of dots forming a pattern, also models derived from the so-called image function of the pattern are analysed.

Perceiving the center of irregular contour quadrangles.

This investigation examined how subjects perceived and localized the centers of irregular quadrangles. Five contour figures in four orientations were used. Seventeen subjects localized the centers of the figures in each orientation, three times.

Errors in estimating the orientation of dot patterns.

The error in estimating the orientation of a dot pattern was measured as the difference between the orientation of the least-squared-distances line (LS-line) of the pattern and the orientation of a line adjusted by the subject to match the perceived orientation of the pattern. Analysis of the mean errors (averaged over ten subjects) obtained for one hundred patterns confirmed that the orientation of the LS-line represents the orientation of elongated dot-patterns. It is shown that estimated orientation was systematically biased towards the nearest 45 degrees oblique meridian.

Is the 45 degrees-oblique a third dominant direction?

Vertical and horizontal are widely accepted as dominant directions or norms of visual orientation in the frontoparallel plane. They are supposed to cause a normalization effect consisting in the apparent rotation of a tilted straight line towards the nearest dominant direction. The evidence for tilt normalization towards the vertical or horizontal visual meridia is indirect.

Adaptation of suprathreshold contrast and luminance stimuli.

The temporal and spatial properties of the difference in perceived contrast and brightness of two suprathreshold stimuli presented successively in different retinal locations were determined. Stimulus onset asynchrony (SOA) was varied and the perceived contrast or brightness of the first stimulus (S1) was measured as a function of SOA by matching the contrast or luminance of the second stimulus (S2) to that of S1. The two stimuli overlapped in time for 200 ms to allow the comparison to be made.

Estimating the duration of gratings under masking and nonmasking conditions.

Previous research has shown that the subjective duration of very short time intervals decreases with the increase of spatial frequency (SF) and this effect is supposed to be mediated by an early peripheral component of the persistence process called "retinal persistence". As the retinal components of persistence are very likely to be erased by a mask, we suggest that if retinal persistence underlies SF influence on duration estimation, the introduction of a mask would make subjective duration independent of SF. This inference was tested estimating the duration of presentation of square-wave gratings of equal mean luminance and contrast (85%) and of varying SF under two conditions: with and without a mask.

Influence of local orientation cues on estimating the tilt of two-dimensional patterns.

Ten subjects estimated the orientation of elongated random patterns composed of dots or short line segments. The estimated overall orientation of the patterns was influenced by the local orientation of the composing lines. Thus, when they formed an angle of 5.

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.

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.

On visual orientation of dot patterns.

Two-dimensional normally distributed random dot patterns were used in two experiments on visual orientation estimation. In the first experiment the patterns differed in their sample correlation and in dot number. In the second one the number of dots was maintained constant but the patterns were generated as a superposition of two normally distributed orthogonal sets composed of different number of dots.

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.

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.

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.