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I Hadani

Publications and source records attributed to I Hadani.

9 recordsLinked to original sources
PubMed1997

A simple integrative method for presenting head-contingent motion parallax and disparity cues on intel x86 processor-based machines.

Rogers and Graham (1979) developed a system to show that head-movement-contingent motion parallax produces monocular depth perception in random dot patterns. Their display system comprised an oscilloscope driven by function generators or a special graphics board that triggered the X and Y deflection of the raster scan signal. Replication of this system required costly hardware that is no longer on the market. In this paper the Rogers-Graham method is reproduced with an Intel processor based IBM PC compatible machine with no additional hardware cost. An adapted joystick sampled through the standard game-port can serve as a provisional head-movement sensor. Monitor resolution for displaying motion is effectively enhanced 16 times by the use of anti-aliasing, enabling the display of thousands of random dots in real-time with a refresh rate of 60 Hz or above. A color monitor enables the use of the anaglyph method, thus combining stereoscopic and monocular parallax on a single display without the loss of speed. The power of this system is demonstrated by a psychophysical measurement in which subjects nulled head-movement-contingent illusory parallax, evoked by a static stereogram, with real parallax. The amount of real parallax required to null the illusory stereoscopic parallax monotonically increased with disparity.

Computer Terminals↗
PubMed1994

Two metric solutions to three-dimensional reconstruction for an eye in pure rotations.

A problem in space perception concerns how a mobile observer acquires information about the structure of objects. Earlier research derived the optic-flow equations for an eye undergoing pure rotations. It was suggested that, by utilizing three points and two views, one can recover the distance of points and the motion parameters. The radius of the eyeball was the metric unit. Yet the common view regards this problem as indeterminate. We derived a unique solution in the discrete case, which required three points and two views. However, when we observed a single bright point, a substantial amount of visual stability existed. We therefore derived a solution in the differential approach for a single point, which is based on a distinction that we made between mathematical and visual points. Both solutions were checked with a computer simulation and were found to be accurate, supporting the space perception in navigation (SPIN) theory.

Computer Simulation↗
PubMed1989

Stereopsis impairment during smooth pursuit eye tracking.

Coherent motion of random dot pattern across a stationary stereograting at 1-5.5 deg/s causes an impairment in perceiving the stereograting which is associated with optokinetic nystagmus. This study was aimed towards understanding the cause of the impairment. We tested two alternative hypotheses: (1) that the impairment is caused by efferent-afferent interactions and (2) that it is due to a temporal integration process, the effect of which is expressed at the temporal resolution limit of the stereoscopic mechanism to disparity alternation. The first hypothesis was rejected on the basis of modified displays and experimental conditions which clearly showed that in these displays stereopsis was not impaired in the presence of optokinetic nystagmus. In testing the second hypothesis, we first determined, for the original display, the threshold values of spatial frequency and angular velocity at which stereopsis ceased. We found for these values spatial frequency x angular velocity = 7.2 cycles/s, i.e., a constant limiting alternation rate for all angular velocity values tested. The averaging effect at the critical alternation rate was demonstrated by bisecting the display, each part having a different disparity value. The perceived depth levels of the two parts were different and are in accordance with an averaging process explanation. It is, therefore, argued that the cause of the impairment is a temporal integration process which averages the alternating disparity values of the moving dots.

Attention↗
PubMed1984

The effects of exposure duration and luminance on the 3-dot hyperacuity task.

The 3-dot hyperacuity task was given to two subjects under three experimental paradigms: constant luminance, constant energy and constant duration. Hyperacuity was obtained under conditions (3 dots, 2 msec exposure) which rule out any significant temporal or spatial averaging. There was a clear threshold decrease in the constant luminance paradigm as exposure duration increased, no significant variations in threshold with the constant energy paradigm, as exposure duration varied and a U-shaped function in the constant exposure duration paradigm as luminance varied. It is concluded that what limits performance, at least for short exposure durations, is the total energy of the stimulus. The implications of the present results to the static and dynamic approaches to hyperacuity are discussed.

Humans↗
PubMed1980

Visual stability and space perception in monocular vision: mathematical model.

A deterministic model for monocular space perception is presented. According to the model, retinal luminance changes due to involuntary eye movements are detected and locally analyzed to yield the angular velocity of each image point. The stable three-dimensional spatial coordinates of viewed objects are then reconstructed using a method of infinitesimal transformations. The extraction of the movement (parallax) field from the optical flow is represented by a set of differential equations, the derivation of which is based on the conservation of energy principle. The relation of the model to retinal neurophysiology and to various aspects of visual space perception is discussed.

Depth Perception↗
PubMedDate not supplied

The SPIN theory--a navigational approach to space perception.

A fundamental problem in the study of spatial orientation concerns how a mobile observer navigates in space on the basis of retinal and extraretinal signals while obtaining the perceptual constancies of position size and shape across head and eye movements. This problem was dealt with by the inferential, direct perception, and computational approaches, yet it is not fully understood. In theory, the above constancies could be obtained from retinal information if the absolute distance is known. However, the common view is that the problem can be determined only up to a scalar in the velocity vector, providing only relative depth. This paper is a theoretical one. It elaborates on an original mathematical theory for space perception (SPIN theory) which suggests that mental representation of objects is exocentric rather than egocentric. The theory postulates absolute (metric) depth perception and shows its mathematical feasibility. It regards space perception as a navigational process that combines retinal and extraretinal signals in a manner that enables continuous phenomenological experience of time invariant (exocentric) representation across fixations and saccades. The theory considers the Listing and Donders' laws of eye movement, as well as the vestibulo-ocular reflex, and suggests some newly driven theological conjectures for them.

Computer Simulation↗