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Biomedical subjects

J T Petersik

Publications and source records attributed to J T Petersik.

At least 37 records · Page 2Linked to original sources
PubMed1984

A three-dimensional motion aftereffect produced by prolonged adaptation to a rotation simulation.

After adaptation to a perspective simulation of a square plane rotating in depth, an ambiguous rotation simulation (ie one containing no perspective information) appears to rotate in the direction opposite that of adaptation. The strength of this three-dimensional motion aftereffect (MAE) is proportional to the amount of perspective available in the adaptation display and, in the dark, decays to about 75% of its initial strength within about 546 s. The nature of the testing situation and a control experiment suggest that the three-dimensional MAE is not caused by retinal adaptation of two-dimensional directionally selective mechanisms.

Adaptation, Physiological↗
PubMed1984

Evidence for color-contingent organizational aftereffects.

An effort was made to produce negative organizational aftereffects in response to a perceptually ambiguous stimulus that can be seen as a cube in either of two orientations. 6 subjects were adapted to alternative disambiguated versions of the ambiguous cube, shown either in green or magenta light. When tested with the ambiguous figure shown in either green or magenta light, 5 subjects showed negative aftereffects while one subject showed a positive aftereffect. The aftereffects showed an average change in preferred organization of 25%. The results are interpreted in terms of both cognitive and hard-wired processes.

Adult↗
PubMed1983

Failure to find an absolute retinal limit of a putative short-range process in apparent motion.

Previous studies of apparent movement have concluded that the short-range process does not operate when stimulus displacements exceed 15-20' arc. In the present experiments, we studied a bistable apparent-movement display, one of whose perceptual organizations is mediated by short-range process. In both experiments it was found that the perceptual organization mediated by the short-range process could be made dominant at stimulus displacements well in excess of the proposed spatial limit, provided the stimulus elements were made larger. It is concluded that the spatial limit of the short-range process is a relative, not absolute, one. Current knowledge regarding the short-range process is reviewed, and an hypothesis regarding the functional utility of the short-range process in compensating for the effects of small eye tremors is advanced.

Adolescent↗
PubMed1982

Perception of eye scans with the Müller-Lyer stimuli: evidence for filter theory.

Ginsburg's filter theory successfully accounts for the perceptual distortions perceived in a wide range of illusions and bistable phenomena. Essentially, the theory proposes that illusory distortions are the natural consequence of low-pass spatial filtering (based upon the human modulation transfer function) of the physical stimulus. With regard to the Müller-Lyer illusion, predictions based upon filter theory and human scan-path data are in accord. However, data linking filter theory's predictions regarding perceptual experiences associated with the illusion to the eye-scan results have been missing. In the present experiment subjects provided subjective estimations of their own eye scans while viewing each of the following stimuli: the fins-out member of the Müller-Lyer illusion, the fins-in member of the Müller-Lyer illusion, and a finless horizontal line (variations of each stimulus consisted of one, two, and three line segments). The analysis of these data supported three predictions that were derived from filter theory. Potential problems facing filter theory are also addressed.

Adolescent↗
PubMed1981

High fundamental spatial frequencies and edges have different perceptual consequences in the 'group/end-to-end' movement phenomenon.

A subject viewing two alternating frames, each containing, say, three vertical stripes in a horizontal row, displaced laterally by one cycle in one frame with respect to the others, perceives either the three stripes moving left-right-left in unison (group movement) or one stripe moving from one end of the display to the other and the two overlapping stripes stationary (end-to-end movement). At suitable temporal parameters of presentation (frame duration, interstimulus interval) the perception of the display is bistable. Experiments have shown that the relative strengths of these alternative movement sensations depend upon the fundamental spatial frequency of the display and upon stimulus waveform. Square-wave stimuli, which have energy at high spatial frequencies, had effects opposite to those produced by increases in fundamental spatial frequency. Amblyopes differed from normal viewers only in the perception of the square-wave stimuli.

Amblyopia↗
PubMed1981

A new bistable motion illusion based upon 'kinetic optical occlusion'.

A display was devised for the purpose of studying the information afforded by kinetic optical occlusion (the progressive erasure and replacement of static elements within a display). A microcomputer generated a series of equally spaced light bars on a dark background. The first bar on the left was suddenly blanked and, after a pause of variable duration (an interblank interval, or IBI), was replaced. As the first bar was replaced, the second bar in the series was blanked, and so on, until each bar in the pattern had been blanked and replaced. Depending upon the duration of the IBI, this display gave rise to one of two alternative percepts: the observer either saw movement of a dark shadow 'in front of' the pattern of bars (with IBIs approximately less than 50 ms) or he saw right-to-left stroboscopic movement of successive bars (with IBIs approximately greater than 85 ms). At some intermediate IBI (the transition IBI) the display was bistable. A two-bar variant of the original display was also studied and found to be bistable under appropriate conditions. In a series of experiments it was found that the transition IBI for the original display did not depend upon whether the observer was tracking the sequence of events or fixating a stationary point in the display. The transition IBI was an increasing function of spatial frequency above about 3 cycles deg-1, and depended upon whether the display was focused or optically blurred. Empirically determined transition IBIs correspond well to estimates of the integration times of visual mechanisms studied in other paradigms.

Eye Movements↗
PubMed1980

The effects of spatial and temporal factors on the perception of stroboscopic rotation simulations.

In the present two experiments subjects viewed discontinuous, i.e. stroboscopic, simulations of a transparent sphere partially filled with randomly positioned luminous dots and rotating about the y axis in depth. Over a range of stimulus conditions, such simulations elicited coherent sensations of continuous rotation and internal volume of the sphere. By manipulating both spatial and temporal variables in the simulations, it was attempted to define the boundary conditions for which corresponding elements of a simulation are perceptually paired from frame to frame to yield coherent sensations of rotation and depth. The results indicated that the process that matches or pairs corresponding elements in a three-dimensional simulation cannot be identified with the process that matches corresponding elements in similar two-dimensional displays. Furthermore, temporal factors influenced the perception of these simulations more than did spatial factors, and rotation-judgment accuracy and perceived depth were different functions of temporal frequency. Over a range of temporal frequencies, such three-dimensional simulations are apparently processes in a manner similar to that in which objects undergoing real motion are processed.

Depth Perception↗
PubMed1979

Optical defocusing reverses perceptual organization.

At a certain point during the defocusing of a reversible figure, the organization of the figure reversed unexpectedly, and the reversal seemed more abrupt than a spontaneous reversal. The critical point is approximately constant over time for a given subject, and a similar point occurs during refocusing. This phenomenon is discussed in terms of inhibition between competing neural structures.

Fixation, Ocular↗
PubMed1978

Apparent movement of successively generated subjective figures.

In the present studies a pair of random-dot frames was constructed so that two areas in the first frame (f1) were correlated with two areas in the second frame (f2). The alternation of the pair of frames (an f1--f2 sequence) gave rise to two subjective figures. When two pairs of randomdot frames (an f1--f2 sequence and an f3--f4 sequence), each of which produced two subjective figures in different locations, were thmeselves alternated, the subjective figures from the f1--f2 sequence interacted with the subjective figures from the f3--f4 sequence to produce apparent movement. With any one of the four general kinds of displays which we constructed, subjects usually perceived only one of two types of subjective-figure movement. The type of movement that was perceived with a given display depended primarily upon the degree of change (across the interval between an f1--f2 and an f3--f4 sequence) of the internal structure of the successively generated subjective figures. Relative intensity differences between the subjective figures and their backgrounds influenced the type of apparent movement seen, whereas variations in the density of elements in a display did not. We tentatively propose a two-stage model to explain the apparent movement of the subjective figures: the first stage is assumed to generate the subjective figures by means of a cross-correlation of the intensity distributions of the two frames within an f1--f2 sequence and within an f3--f4 sequence; on the basis of inputs from the first stage, the second stage generates apparent movement signals for the subjective figures.

Discrimination, Psychological↗
PubMed1978

Possible role of transient and sustained visual mechanisms in the determination of similarity judgments.

Two studies examined the role played by transient and sustained visual mechanisms in the determination of similarity judgments produced in response to pairs of geometrical stimuli. In two experiments, subjects were trained to attend to two dimensions of a set of stimuli and to assign similarity ratings with respect to those two dimensions only. An INDSCAL multidimensional scaling analysis of the subsequent similarity ratings showed that subjects emphasized global blob, or low spatial frequency-dependent, dimensions of the stimuli when they were presented for brief durations (20 msec.), irrespective of the dimensions to which the subjects and had been trained to attend. This finding suggested that low spatial frequency selective transient mechanisms dominated the perceptual processes which underlie the similarity judgments. When the stimulus duration was raised to 50 msec. so that sustained mechanisms could also make a signficicant contribution to the perceptual processes underlying the similarity judgments, subjects emphasized only those dimensions on which they had been trained. The implications of the present findings for the concepts of selective attention and automatic activation were discussed.

Attention↗