Stationary Reference Point Research Articles

Vector analysis and process combination in motion perception.

Experiments are reported supporting an altered explanation of the vector analysis that occurs in certain motion displays discovered by Johansson (1950). What seemed the result of a perceptual vector analysis is ascribed to the outcome of two different, independent stimulus conditions to which such displays can give rise because of external vector analysis. The different stimulus conditions are configurational change on the one hand and one of the subject-relative stimulus conditions on the other. In two of Johansson's displays, conditions for configurational change were altered by adding stationary reference points in the surround of the displays. Veridical perception of the displays resulted in a majority of instances. We also found that the different motions that result from configurational change and from subject-relative stimulation may combine to form unitary perceived motions and that this happens quite frequently under some conditions.

TWO SYSTEMS IN THE DETECTION OF VISUAL MOTION *

Several groups of authors have suggested separate mechanisms for the detection of motion and for the detection of pattern characteristics of the same stimuli [Kulikowski, J. J. and Tolhurst, D. J. (1973) J. Physiol., Lond. 232, 149-163; and King-Smith, P. E. (1978) In Armington, J. C., Krauskopf, J. and Wooten, B. R. (Eds) Visual Psychophysics and Physiology. Academic Press, New York]. Their stimuli were generally in the frequency domain. Bonnet [(1975) Psychologia 18, 35-50; (1977) Perception 6, 491-500; and (1982) In Wertheim, A. H., Wagenaar, W. A. and Leibowitz, H. W. (Eds) Tutorials in Motion Perception. Plenum, London] has developed a conceptual model of motion detection in the space-time domain. Two systems are assumed: a movement-analysing system (MAS) which processes the motion phase of any translation and a displacement-analysing system (DAS) which processes the successive stationary components of the stimulus. These proposed mechanisms are studied in experiments which use three different modes of translation of a single spot: continuous, discrete and stop-go-stop. The first mode should preferentially trigger the MAS, the second mode the DAS, while the stop-go-stop mode is a test mode. The results show that for short exposure times (less than or equal to 180 ms) the velocity thresholds for the continuous mode are greater than for the other two modes. For these durations, thresholds of the continuous mode are not lowered by the availability of stationary reference points. The effects of luminance on the results with the three modes support the basic model.

Diffractographic Techniques for Vibration Measurement

The single slit diffraction phenomenon is shown to be useful as a noncontacting vibration measurement technique. The diffracting slit is formed between the vibrating object and stationary reference point. Little or no mass need be added to the object. Several readout techniques are described as well as a method for determining vibratory data along a line, in which case vibratory amplitude may be determined at all points in one coordinate direction.

Parametric adjustment to a shifting target alternating with saccades to a stationary reference point

The oculomotor system can progressively improve the accuracy of repeated saccades to a target that shifts in midsaccade, by utilizing retinal feedback to diminish the induced error. The present study investigated whether this parametric adjustment compromises S’s ability to fixate the stationary reference point on alternating saccades to the other side of his visual field. Fixation of the reference point on shifting-target runs was sometimes even more accurate than fixation on stationary-target runs. The capacity of the parametric adjustment mechanism to adapt to specific targets was thereby demonstrated.