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A J Pantle

Publications and source records attributed to A J Pantle.

11 recordsLinked to original sources
PubMed2001

Direction-specific changes of sensitivity after brief apparent motion stimuli.

Direction-specific losses in sensitivity were found for a test grating which was superimposed on a stationary contrast pedestal and which moved either in the same or opposite direction as a prior biasing stimulus. Three types of biasing stimuli were employed: a grating swept through 270 degrees in 45 degrees steps, a single 90 degrees step of a grating, and a single 90 degrees step of a grating which contained a blank IFI and whose perceived direction was reversed. For the biasing sweep and the single 90 degrees step, the response of directionally selective mechanisms (directional motion energy) is greatest for the direction which corresponds to the actual physical displacement of the stimulus. For the biasing step with an IFI, the response is maximum for the opposite direction. For all three types of biasing stimuli, directional sensitivity for a test stimulus was reduced most when it moved in the biasing direction, i.e. the direction which produced the strongest signal in directionally selective mechanisms. Unlike the effects of the same types of biasing stimuli on the perceived direction of a suprathreshold 180 degrees step of a grating [Pinkus, A., & Pantle, A. (1997). Probing motion signals with a priming paradigm. Vision Research, 37, 541-52; Pantle, A., Gallogly, D.P., & Piehler, O.C. (2000). Direction biasing by brief apparent motion stimuli. Vision Research, 40, 1979-91], all the direction-specific losses of sensitivity can be explained by changes in the response characteristics of directionally selective mechanisms.

Contrast Sensitivity↗
PubMed2000

Direction biasing by brief apparent motion stimuli.

The perceived direction of a motion step (probe stimulus) can be influenced by an earlier motion step or a brief motion sweep containing a series of steps (biasing stimulus). Depending upon experimental conditions, the biasing of the direction of the probe step (a phase shift of 180 degrees +/-Phi) by a biasing stimulus which precedes it by approximately 250 ms can either increase (positive filter biasing) or decrease (negative filter biasing) the tendency to see the probe move in the biasing direction as computed with a motion filter with a biphasic temporal impulse response. In a series of experiments it was found that biasing motions traversing 90 degrees of phase angle in fewer than six steps in less than 100 ms produced positive filter biasing. Also, biasing of the probe direction could be dissociated from the consciously reported direction of the biasing stimulus, and it did not occur when the probe preceded rather than followed the biasing stimulus. A biasing sweep containing more than six steps traversing 90 degrees or a sweep traversing 270 degrees produced negative filter biasing. Perceptual fusion of the steps of the sweep was not a necessary condition for obtaining negative filter biasing. In general, the negative filter biasing effects were found to be the most pervasive for the conditions investigated, and they are suggestive of a direction-specific, adaptation-like (gain-control) process in first-order motion filters. The exception to the negative biasing rule was found only with biasing stimuli which were short in duration or distance spanned.

Humans↗
PubMed1998

Viewer-centered temporal biasing of 3-D rotation percepts.

The perceived direction of rotation of a 3-D cloud of dots can be biased by a prior rotation (Jiang, Pantle, and Mark, 1998 Perception & Psychophysics 60 275-286). In a series of experiments, it is shown that the temporal rotation bias is reversed by a 180 degrees change of head orientation between two rotation sequences; i.e. the perceived direction of rotation reverses for the second of two sequences when head orientation is changed. The bias is, therefore, viewer-centered. Perceptual reversals are not obtained when the orientation of the head is changed and returned to its original position between rotation sequences. It was also found that the viewer-centered bias combined additively with viewer-independent near-far luminance information. Finally, the bias was manifest when 3-D depth was re-established, but not maintained, between rotation sequences. A model, in descriptive and flowchart forms, is used to explain the integration of world-centered information and a viewer-centered temporal bias on the presence/absence of perceptual reversals of the rotating virtual sphere. In the model, the temporal bias is the result of the coupling of depth values to persisting 2-D retinal motion signals.

Computer Graphics↗
PubMed1998

Visual inertia of rotating 3-D objects.

Five experiments were designed to determine whether a rotating, transparent 3-D cloud of dots (simulated sphere) could influence the perceived direction of rotation of a subsequent sphere. Experiment 1 established conditions under which the direction of rotation of a virtual sphere was perceived unambiguously. When a near-far luminance difference and perspective depth cues were present, observers consistently saw the sphere rotate in the intended direction. In Experiment 2, a near-far luminance difference was used to create an unambiguous rotation sequence that was followed by a directionally ambiguous rotation sequence that lacked both the near-far luminance cue and the perspective cue. Observers consistently saw the second sequence as rotating in the same direction as the first, indicating the presence of 3-D visual inertia. Experiment 3 showed that 3-D visual inertia was sufficiently powerful to bias the perceived direction of a rotation sequence made unambiguous by a near-far luminance cue. Experiment 5 showed that 3-D visual inertia could be obtained using an occlusion depth cue to create an unambiguous inertia-inducing sequence. Finally, Experiments 2, 4, and 5 all revealed a fast-decay phase of inertia that lasted for approximately 800 msec, followed by an asymptotic phase that lasted for periods as long as 1,600 msec. The implications of these findings are examined with respect to motion mechanisms of 3-D visual inertia.

Contrast Sensitivity↗
PubMed1983

Temporal determinants of spatial sine-wave masking.

A temporal forced-choice procedure was used to measure the contrast threshold for a sinusoidal test grating (spatial frequency - f) superimposed upon a sinusoidal background or masking grating (spatial frequency = 3f). The spatial contrast of the background grating was varied, and threshold measurements were made at each of a number of background contrasts to describe a threshold versus masking contrast (tvc) function. Tvc functions were obtained when the background and test grating contrasts were, independently of each other, held steady (0 Hz) or modulated at 5 Hz. The changes of temporal modulation frequency affected the slopes of the tvc functions. In some cases the tve functions for steady and flickering test gratings crossed one another. The changes of slope suggest, and the crossovers imply, that some steady and flickering patterns are detected by separate visual mechanisms.

Form Perception↗
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↗