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Timothy Petersik
  • Ripon, Wisconsin, United States

Timothy Petersik

Ripon College, Psychology, Faculty Member
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... more
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.
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... more
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 random-dot frames (an f1-f2 sequence and an f3-f4 sequence), each of which produced two subjective figures in different locations, were themselves 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.
Researchers often assume a critical band of spatial frequencies is required for face recognition. Also, many studies have not measured the contrast required for recognition. On Day 1, observers viewed high-pass-filtered (HP),... more
Researchers often assume a critical band of spatial frequencies is required for face recognition. Also, many studies have not measured the contrast required for recognition. On Day 1, observers viewed high-pass-filtered (HP), low-pass-filtered (LP), or unfiltered (UF) faces. On Day 2, they viewed a variety of faces, some of which were LP filtered, HP filtered, and UF. Observers adjusted contrast until they achieved both detection and recognition. Observers were most accurate and sensitive when filtered faces agreed in spatial-frequency content across days. Faces differing in spatial-frequency content were least well recognized. Unfiltered faces always fell between the 2 extremes. Observers generally used less contrast to recognize unfiltered than filtered faces. Correspondence of information between inspection and testing seemed more important than any particular range of frequencies.
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... more
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.
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... more
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.
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 other, perceives either the three stripes moving left-right-left... more
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 other, 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.
Observers viewed a screen on which a number of patches containing horizontally moving pixels were presented. Target patches consisted of pixels whose motion simulated the rotation of a cylinder around its Y-axis; distractors, of pixels... more
Observers viewed a screen on which a number of patches containing horizontally moving pixels were presented. Target patches consisted of pixels whose motion simulated the rotation of a cylinder around its Y-axis; distractors, of pixels whose motion was linear. The task was to assess whether a display contained a target patch. Exp. 1 showed that the superposition of the displays with drifting sine-wave gratings interfered with rotation detection in a spatial- and temporal-frequency specific manner. In Exp. 2, dichoptic presentation greatly reduced the interference of the drifting gratings. It is argued on various grounds that the process(es) responsible for the detection and discrimination of rotating structure in depth exists at a low level of the visual system.
Apparent movement occurs when stimulus figures are presented at different spatial locations at different times. In the present studies, the periodicity of the background upon which stimuli were presented was manipulated. Subjects viewed a... more
Apparent movement occurs when stimulus figures are presented at different spatial locations at different times. In the present studies, the periodicity of the background upon which stimuli were presented was manipulated. Subjects viewed a bistable movement display presented on a background consisting of a variable-frequency grating. The type of movement perceived varied systematically with the spatial frequency of the background, suggesting that more than the target stimuli are processed in the generation of apparent movement.
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... more
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.
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... more
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.
Odic and Pratt (2008, Perception, 37, 1790–1804) proposed that the type of movement seen in the bistable Ternus display depends on the elements' temporal summation of contrast relative to the background. To test this theory,... more
Odic and Pratt (2008, Perception, 37, 1790–1804) proposed that the type of movement seen in the bistable Ternus display depends on the elements' temporal summation of contrast relative to the background. To test this theory, participants viewed a flicker-defined Ternus display where the elements had no temporal summation of contrast. Participants also viewed a luminance-defined control condition. Five interstimulus intervals (ISIs) (0, 20, 40, 60, and 80 ms) and two stimulus durations (SDs) (200 and 400 ms) were used in each condition. If temporal summation of contrast does not influence perceived group and end-to-end movement in flicker-defined forms, it was expected that the frequency of their reports would be equal to those in the luminance- defined control condition at the same ISIs and SDs. As predicted, the main effect of condition was not significant and participants reported both percepts at expected rates in both conditions, contrary to the predictions of Odic and Pratt...
Abstract. The Ternus effect involves a multi-element stimulus that can lead to either of two different percepts of apparent movement depending upon a variety of stimulus conditions. Since Ternus's 1926 discussion of this phenomenon,... more
Abstract. The Ternus effect involves a multi-element stimulus that can lead to either of two different percepts of apparent movement depending upon a variety of stimulus conditions. Since Ternus's 1926 discussion of this phenomenon, many researchers have attempted to explain it. We examine the history of explanations of the Ternus effect and show that they have evolved to contemporary theoretical positions that are very similar to Ternus's own ideas. Additionally, we describe a new experiment showing that theoretical positions that emphasize element grouping and element identity within groups can predict the effects of certain stimulus manipulations on the Ternus effect. 1 Introduction and
Abstract : Five well-practiced observers set detection and identification contrast thresholds for Snellen-letter stimuli of different sizes (i.e., fundamental spatial frequencies) under the following conditions: moving (three velocities)... more
Abstract : Five well-practiced observers set detection and identification contrast thresholds for Snellen-letter stimuli of different sizes (i.e., fundamental spatial frequencies) under the following conditions: moving (three velocities) vs. stationary, six rotations in the picture plane, and flickering (five temporal frequencies). The subjects contrast sensitivities for Snellen-letter stimuli were also compared to their contrast sensitivity functions (CSFs) for both static and moving sinusoidal gratings. In a final experiment, subjects adapted to stationary spatial-frequency gratings and set contrast thresholds for letter stimuli.
Two bistable apparent-movement displays (i.e. ones that generate two qualitatively different kinds of movement percepts under different conditions) were compared. They were designed to be as similar as possible spatially, and were studied... more
Two bistable apparent-movement displays (i.e. ones that generate two qualitatively different kinds of movement percepts under different conditions) were compared. They were designed to be as similar as possible spatially, and were studied with identical stimulus manipulations to see whether changes in balance between their bistable percepts would be similar. Results show that the two displays had different response characteristics to the same stimulus manipulations. Two models of motion perception that have previously predicted at least one kind of bistable apparent motion were considered in terms of how well they address the current data. As yet, neither model has been shown to predict the motion states and bistable behavior of the two displays studied here. It is concluded that results of the type described here (specifically, differences in the psychophysical functions yielded by two structurally similar but qualitatively different bistable displays) present a challenge for theories of motion perception.
Four experiments and controls were run in order to determine the ability of the visual system to detect slight changes in three-dimensional (3D) rotating stimuli in comparison to two-dimensional (2D) controls. A small number of observers... more
Four experiments and controls were run in order to determine the ability of the visual system to detect slight changes in three-dimensional (3D) rotating stimuli in comparison to two-dimensional (2D) controls. A small number of observers (between 5 and 8) viewed computerized displays of pixel-defined transparent rotating spheres or circular patches of pixels drifting linearly in opposite directions. Halfway through the circuit of rotation a letter was briefly displayed and the rotation continued with some change introduced. Our results showed that for horizontal shifts of the stimulus on the X-axis, changes in the axis of rotation, and additions/deletions of pixels, observers were better at detecting the changes associated with 3D motion than 2D motion. There was no good 2D control for approaching and receding stimuli, but on the basis of other results it was concluded that 3D movement had no advantage. It is suggested that rotation in 3D is more readily monitored by the visual syst...
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... more
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.
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... more
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.
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... more
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.
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... more
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.
Observers viewed a screen on which a number of patches containing horizontally moving pixels were presented. Target patches consisted of pixels whose motion simulated the rotation of a cylinder around its Y-axis; distractors, of pixels... more
Observers viewed a screen on which a number of patches containing horizontally moving pixels were presented. Target patches consisted of pixels whose motion simulated the rotation of a cylinder around its Y-axis; distractors, of pixels whose motion was linear. The task was to assess whether a display contained a target patch. Exp. 1 showed that the superposition of the displays with drifting sine-wave gratings interfered with rotation detection in a spatial- and temporal-frequency specific manner. In Exp. 2, dichoptic presentation greatly reduced the interference of the drifting gratings. It is argued on various grounds that the process(es) responsible for the detection and discrimination of rotating structure in depth exists at a low level of the visual system.
Visual and haptic perceptions of the two-dimensional size of square stimuli were compared using cross-modal, intramodal, and bimodal matching tasks. In a repeated-measures factorial design, 12 women participated in five matching tasks... more
Visual and haptic perceptions of the two-dimensional size of square stimuli were compared using cross-modal, intramodal, and bimodal matching tasks. In a repeated-measures factorial design, 12 women participated in five matching tasks involving various combinations of vision and haptic touch; five sizes of standard squares were matched with a comparison range of 10 squares during each task. Analysis showed that, for stimuli with side lengths of .75 in. and smaller, matching accuracy was superior when vision was used during the matching task regardless of the modality used during inspection. When haptic touch was used in the matching task, accuracy was better when vision had been used during inspection than when it bad not. These results were consistent with those of previous studies comparing size perception by vision and other forms of touch. The over-all relationship between matched size and inspected size was best accounted for by a third-order polynomial function.
The spatial structure of the background upon which figures engage in apparent movement has been a neglected variable in research. In this pilot study, the presence of a sine-wave-grating as background had a strong influence on the quality... more
The spatial structure of the background upon which figures engage in apparent movement has been a neglected variable in research. In this pilot study, the presence of a sine-wave-grating as background had a strong influence on the quality of apparent movement that was perceived by 3 observers.

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