Biomedical subjects

Z Pizlo

Publications and source records attributed to Z Pizlo.

8 recordsLinked to original sources

PubMed1995

An exponential pyramid model of the time-course of size processing.

Two prior approaches to size processing are discussed in this paper. The first approach is based on measurements of mental size transformations, the second on measurements of thresholds for size and separation. We first analyze these prior approaches and point out differences among prior models and similarities among prior results. This analysis led to new psychophysical experiments that tested the effect of size, relative precision, and eccentricity on the speed of perceptual processing. Speed was not affected by size, but was affected by relative precision and eccentricity. These new results, along with prior results, are then used to formulate a new model based on an exponential pyramid algorithm. This new model, which uses elements of both traditional approaches, can better account for prior, as well as our new results, on the time-course of size processing.

Algorithms↗

PubMed1995

The function of visual search and memory in sequential looking tasks.

UNLABELLED: Eye and head movements were recorded as unrestrained subjects tapped or only looked at nearby targets. Scanning patterns were the same in both tasks: subjects looked at each target before tapping it; visual search had similar speeds and gaze-shift accuracies. Looking, however, took longer and, unlike tapping, benefitted little from practice. Looking speeded up more than tapping when memory load was reduced: memory was more efficient during tapping. CONCLUSION: eye movements made when only looking are different from those made when tapping. Visual search functions as a separate process, incorporated into both tasks: it can be used to improve performance when memory load is heavy.

Eye Movements↗

PubMed1995

3-D shape perception.

In this paper, we analyze and test three theories of 3-D shape perception: (1) Helmholtizian theory, which assumes that perception of the shape of an object involves reconstructing Euclidean structure of the object (up to size scaling) from the object's retinal image after taking into account the object's orientation relative to the observer, (2) Gibsonian theory, which assumes that shape perception involves invariants (projective or affine) computed directly from the object's retinal image, and (3) perspective invariants theory, which assumes that shape perception involves a new kind of invariants of perspective transformation. Predictions of these three theories were tested in four experiments. In the first experiment, we showed that reliable discrimination between a perspective and nonperspective image of a random polygon is possible even when information only about the contour of the image is present. In the second experiment, we showed that discrimination performance did not benefit from the presence of a textured surface, providing information about the 3-D orientation of the polygon, and that the subjects could not reliably discriminate between the 3-D orientation of textured surface and that of a shape. In the third experiment, we compared discrimination for solid shapes that either had flat contours (cuboids) or did not have visible flat contours (cylinders). The discrimination was very reliable in the case of cuboids but not in the case of cylinders. In the fourth experiment, we tested the effectiveness of planar motion in perception of distances and showed that the discrimination threshold was large and similar to thresholds when other cues to 3-D orientation were used. All these results support perspective invariants as a model of 3-D shape perception.

Attention↗

PubMed1994

A theory of shape constancy based on perspective invariants.

Shape constancy refers to the phenomenon in which the percept of the shape of a given object remains constant despite changes in the shape of the object's retinal image. The phenomenon of shape constancy is considered from historical, theoretical and empirical perspectives in this paper. First, four prior theories are discussed; specifically, (1) Helmholtzian theory, which assumes that shape constancy is achieved by taking an object's orientation into account, (2) Gestalt theory, which assumes that shape constancy involves a relationship between the perceived shape and perceived orientation of an object, (3) Gibsonian theory, which assumes that shape constancy is based on projective invariants and (4) multiple view theory, which assumes that shape constancy is achieved by memorizing a large set of different views of the object. It is shown, by an analysis of the prior literature, that none of these theories can actually explain the phenomenon of shape constancy. A new theory, which is based on new perspective invariants of a flat shape, is then proposed. The new Perspective Invariants Theory can account for all prior shape constancy experiments. New experiments, testing predictions of the Perspective Invariants Theory are then described. These experiments showed that: (1) a novel shape can be matched with its single perspective image in the absence of depth cues, (2) perceptual processing of shape is impaired when the range of possible values of tilt is wide, (3) perceptual processing of shape is not affected by the width of the range of possible values of slant. These results support predictions of Perspective Invariants Theory.

Algorithms↗

PubMed1994

Is vision metric? Comment on Lappin and Love (1992).

In a recent paper, Lappin and Love (1992) showed that depth judgments, based on planar motion of a stimulus, are remarkably precise. This led them to the conclusion that perception of planar motion allows acquiring metric information about visual space. We show, however, that Lappin and Love's stimuli contained 2-D cues in the frontal plane that could subserve the subject's judgments. This means that high precision in this task does not necessarily imply metric structure of visual space.

Depth Perception↗

PubMed1988

Physiology based simulation model of triangle shape recognition.

The present paper considers the relation between the shape of a triangle and probability of its recognition. An effect of triangle size on perception of its shape is examined in the first experiment. In the second the loci of eye fixations during triangle recognition task are recorded and analysed. A simulation model of the recognition process is proposed. The model is based on two main assumptions: 1. an accuracy of shape processing is related to the cortical magnification factor, 2. a subject's response depends on actual position of eye fixation. The validity of the model is verified by comparing the theoretical and experimental response distributions. Some psycho-physiological implications are then discussed.

Computer Simulation↗

PubMedDate not supplied

Correlations of neuronal spike discharges of VL neurons during spontaneous firing and during the activity evoked by peripheral stimulation.

The temporal relations between simultaneously recorded neurons of the nucleus ventralis lateralis (VL) of cat thalamus were studied. The interaction and the functional connections between individual VL neurons are described. This was achieved with an application of cross correlation techniques. The response patterns of different individual neurons to somatic sensory and photic stimuli were also analyzed. For the purpose of classifying neurons as thalamocortical relay cells (T-C) and non relay cells (N-C) which do not project to the motor sensory cortex antidromic cortical stimulation was used. This stimulation was also used as conditioning one when proceeded peripheral stimuli. To analyze the nonspecific specific interactions upon single neurons conditioning photic stimuli were applied. The results show that T-C neurons are antidromically excited from a wide cortical areas and that the functional interaction between T-C neurons is mediated by a shared input from common sources. It is further postulated that N-C cells interposed between relay neurons subserve the functions of gating units modifying the neuronal network of lateral ventral nucleus of the thalamus.

Action Potentials↗

PubMedDate not supplied

When push comes to shove: compensation for passive perturbation of the head during natural gaze shifts.

The effects of passive displacements to the head delivered by an abrupt push to the upper body were studied in human subjects during gaze shifts to nearby targets while the head was completely unrestrained. Accurate measurements of gaze were obtained via the Maryland Revolving Field Monitor, used to measure head and eye rotations unconfounded with translations, and by an acoustic ranging system, used to measure head translations. Compensation for head perturbations was quite good, with gaze errors much the same as gaze errors in the absence of the push. Compensation along one or both meridians was achieved by means of the vestibulo-ocular response in many of the gaze shifts. The results suggest an impressive ability to coordinate head and eye movements during natural gaze shifts, carried out by one or more different kinds of compensatory systems that the subject can access at will or according to task demands.

Eye Movements↗