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J T Petersik

Publications and source records attributed to J T Petersik.

18 recordsLinked to original sources
PubMed1991

Effects of adaptation to apparent movement on recovery of structure from motion.

Past work on the recovery of three-dimensional structure from dynamic two-dimensional images has led to inconsistent conclusions regarding the contributions of the short-range and long-range motion processes. In the present experiments, subjects adapted to displays (either four lines or 50 randomly positioned pixels) whose spatiotemporal parameters were chosen to favor either the short-range or long-range process. Adaptation periods were followed by test displays that simulated the rotation of a four-pixel random object about the vertical gamma-axis. The dependent measure was the angle of rotation between successive frames of the rotation display at which percepts of three-dimensional structure broke down. Both the original data and derived measures based on best-fitting polynomials showed small but consistent effects: Compared to control conditions, adaptation to short-range motion reduced the angle at which percepts of structure broke down; adaptation to long-range motion increased them. It is suggested that both low-level (i.e. short-range) and high-level (long-range) processes contribute to the recovery of structure from motion.

Adaptation, Ocular↗
PubMed1991

Comments on Cavanagh and Mather (1989): coming up short (and long)

Cavanagh and Mather (1989) reviewed literature concerning the possible distinction between short- and long-range processes in motion perception and concluded that the distinction cannot be supported. Instead, they proposed that motion perception be considered on the basis of detectors for first-order (luminance, color) and second-order (first-order motion, texture, stereo) stimulus attributes. They supported their position with studies of motion based on second-order stimuli. The present paper contends that when experiments permitting the investigation of both processes in the same display are included and when criteria are examined in their totality rather than one-by-one, the original short-range/long-range distinction can be retained. Furthermore, it is argued that the first-order/second-order distinction does not represent a theoretical advancement and that studies of second-order motion can be interpreted in terms of the older distinction. It is concluded that the short-range/long-range distinction is useful and should not be abandoned.

Adaptation, Ocular↗
PubMed1991

Perception of three-dimensional angular rotation.

In three experiments, difference thresholds (dLs) and points of subjective equality (PSEs) for three-dimensional (3-D) rotation simulations were examined. In the first experiment, observers compared pairs of simulated spheres that rotated in polar projection and that differed in their structure (points plotted in the volume vs. on the surface), axis of rotation (vertical, y, vs. horizontal, x), and magnitude of rotation (20 degrees-70 degrees). DLs were lowest (7%) when points were on the surface and when at least one sphere rotated around the y-axis and varied with changes in the independent variables. PSEs were closest to objective equality when points were on the surface of both spheres and when both spheres rotated about the x-axis. In the second experiment, subjects provided direct estimates of the rotations of the same spheres. Results suggested a reasonable agreement between PSEs for the indirect-scaling and direct-estimate procedures. The third experiment varied sphere diameter (and therefore mean linear velocity of stimulus elements) and showed that although rotation judgments are biased by mean linear velocity, they are not likely to be made solely on the basis of that information. These and past results suggest a model whereby recovery of structure is conducted by low-level motion-detecting mechanisms, whereas rotation (and other) judgments are based on a higher level representation.

Acceleration↗
PubMed1990

Auditory sensitivity and tone-sequence reproduction in oral contraceptive users and nonusers.

In two stages spanning a single academic year, 10 women using oral contraceptives and 11 not using oral contraceptives were tested on their auditory threshold sensitivity to six frequencies (250, 750, 1500, 3000, 6000, and 8000 Hz) as a function of phases of the menstrual cycle. 11 women (5 users and 6 nonusers) were also tested on their ability to reproduce successively longer tone sequences. Results showed that there was little variation due to phase of the menstrual cycle, with the exception that oral contraceptive users showed lower relative thresholds at low frequencies during the postmenstrual phase. Over-all, oral contraceptive users had higher absolute and relative thresholds than nonusers, except at 3000 Hz. Although not statistically significant, results on the tone-reproduction test showed an enhanced ability to reproduce tones during the premenstrual phase for women using oral contraceptives. Results are discussed in relation to previous findings.

Adult↗
PubMed1990

Global cooperativity of the short-range process in apparent movement: evidence obtained with contour-containing stimuli.

Previous research has demonstrated that the short-range process in apparent movement, as studied with random-dot cinematograms, exhibits global cooperativity; that is, computations performed by local elements interact nonlinearly and are pooled. Other research using displays containing extended contours has implicated the short-range process, but has never demonstrated global cooperativity. In the first of four experiments, it was shown that under certain conditions of presentation, a short-range motion percept exhibiting apparent global cooperativity can be obtained when collections of randomly located contours are rotated about the center of a display, despite the fact that the displacement of peripheral contours falls outside the normal limit of the short-range process. Experiments 2-4 were conducted to provide further evidence that the observed motion is short-range (i.e., it can be disrupted by illuminating the interstimulus interval or with dichoptic viewing) and that the percept is globally cooperative (i.e., masking the center of the display, where separations between corresponding elements across frames are smallest, results in a decline in the frequency of reports of the short-range percept). Control observations suggest that the effect produced with masks was not due to a decrease in the number of elements in the display. The argument that the display exhibits a short-range process with global cooperativity is further developed.

Adult↗
PubMed1990

The effects of position cues on the appearance of stimulus elements in a bistable apparent movement display.

A modified version of the Ternus display was used to assess the relative effects of element position cues on reports of group and end-to-end movement. In this display, two rows of stimulus elements are joined by connecting lines. In one version of the display, the connecting lines remain stationary across frames, facilitating the interpretation that the associated stimulus elements also remain stationary. In another version of the display, one end of the connecting lines shifts horizontally from frame to fame, facilitating the interpretation that the associated stimulus elements have also shifted. The experiment showed that when the connecting lines remain stationary, reports of end-to-end movement increase, regardless of the interstimulus interval (ISI) at which the frames alternate. When the connecting lines shift, reports of group movement increase, regardless of ISI. Theoretical interpretations of the results involving both relatively low-level motion signals and higher order perceptual influences are considered.

Attention↗
PubMed1987

Dependence of apparent movement of a subjective figure on the perceptual fate of inducing elements.

In a series of demonstrations, two stimulus frames that contained subjective figures were alternated. It is shown that the perception of apparent movement of a subjective figure depends upon the configuration of the inducing stimuli and whether or not conditions of presentation favor the short-range or long-range process in apparent movement. Those conditions that favor the long-range process result in global apparent movement of the subjective figure. However, those conditions that favor the short-range process may prevent apparent movement of the subjective figure, or may result in a kind of apparent movement that is qualitatively different from that seen when similar physical contours are alternated. These results are interpreted in terms of the assumed differences between the short-range and long-range processes.

Form Perception↗
PubMed1987

Preliminary findings suggesting cyclic changes in visual contrast sensitivity during the menstrual cycle.

Visual contrast thresholds to both stationary and moving gratings of three spatial frequencies (2, 4, and 16 cyc/deg) were measured over a 32-day period in two women displaying normal menstrual cycles and in two noncycling control subjects. The time-series data of each subject in each condition were Fourier analyzed and the resulting amplitude spectra showed differences between the two sets of subjects. The spectra of the control subjects were relatively flat, whereas those of the experimental subjects showed a number of peaks at several harmonics (periods). Conservative significance tests suggested that the peaks in the spectra of the cycling women were larger than might be expected by chance. The data also suggested that changes in sensitivity were greatest for 4-cyc/deg gratings, those nearest the peak of the normal contrast sensitivity function.

Adult↗
PubMed1987

Contrast requirements for picture recognition: converging evidence for a spatial frequency hypothesis.

Based upon perceptual studies, the present hypothesis was that different ranges of spatial-frequency information constitute different sources of information for recognition memory. In Experiment 1, 40 subjects were tested with sets of focused and unfocused pictures as inspection and test stimuli. In addition to reporting whether each test picture was believed to be a member of the inspection set or a novel picture, each subject was allowed to adjust the contrast of the stimulus until such a judgment could be made. In Experiment 2, subjects made similar judgments when inspection or test stimuli were flickered (perceptually enhancing low spatial frequencies) or unflickered. Results from both studies were consistent with the experimental hypothesis. Other studies were reviewed, which, together with the present data, lend converging evidence to the spatial-frequency hypothesis.

Attention↗
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↗