According to the traditional inferential theory of perception, percepts of object motion or stationarity stem from an evaluation of afferent retinal signals (which encode image motion) with the help of extraretinal signals (which encode eye movements). According to direct perception theory, on the other hand, the percepts derive from retinally conveyed information only. Neither view is compatible with a perceptual phenomenon that occurs during visually induced sensations of ego motion (vection). A modified version of inferential theory yields a model in which the concept of extraretinal signals is replaced by that of reference signals, which do not encode how the eyes move in their orbits but how they move in space. Hence reference signals are produced not only during eye movements but also during ego motion (i.e., in response to vestibular stimulation and to retinal image flow, which may induce vection). The present theory describes the interface between self-motion and object-motion percepts. An experimental paradigm that allows quantitative measurement of the magnitude and gain of reference signals and the size of the just noticeable difference (JND) between retinal and reference signals reveals that the distinction between direct and inferential theories largely depends on: (1) a mistaken belief that perceptual veridicality is evidence that extraretinal information is not involved, and (2) a failure to distinguish between (the perception of) absolute object motion in space and relative motion of objects with respect to each other. The model corrects these errors, and provides a new, unified framework for interpreting many phenomena in the field of motion perception.

Motion perception during selfmotion: The direct versus inferential controversy revisited

With the rapid advance of real-time computer graphics, head-mounted displays HMDs have become popular tools for 3D visualization. One of the most promising and challenging future uses of HMDs, however, is in applications where virtual environments enhance rather than replace real environments. In such applications, a virtual image is superimposed on a real image. The unique problem raised by this superimposition is the difficulty that the human visual system may have in integrating information from these two environments. As a starting point to studying the problem of information integration in see-through environments, we investigate the quantification of depth and size perception of virtual objects relative to real objects in combined real and virtual environments. This starting point leads directly to the important issue of system calibration, which must be completed before perceived depth and sizes are measured. Finally, preliminary experimental results on the perceived depth of spatially nonoverlapping real and virtual objects are presented.

Towards Quantifying Depth and Size Perception in 3D Virtual Environments

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.

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

There is a concern about depth perception with night vision goggles (NVGs). We measured judgments involving depth perception in laboratory and field conditions. When participants judged absolute distance, or collision, in a laboratory, results indicated that objects can appear closer with NVGs than with unaided vision, and underestimations of distance were greater with smaller distances. When participants were transported in a car and judged when to turn a vehicle to avoid collision with a simulated wall, there was no difference between goggle and unaided vision. Effects of NVGs on depth perception may be specific to task and viewing conditions.

Depth and Collision Judgment Using Night Vision Goggles

Abnormal depth perception from motion parallax in amblyopic observers.

Night vision goggles are head-mounted, unity-power systems designed to allow the human operator to see and operate at night. Field experience and experimental studies have revealed many drawbacks in conventional designs that impair performance. One major drawback is the poor space perception provided by the goggles. The Hadani et al. [
J. Opt. Soc. Am.70, 
60–
65 (
1980)] model for space perception attributes this drawback to the fact that the conventional designs shift the observer's effective center of perspective ∼15 cm ahead and also predicts the resulting impairments. An innovative redesign is presented in this paper—the corneal lens goggles (CLG)—which brings the effective center of perspective of the goggles to coincide with the center of perspective of the eyes, thus annulling the optical length of the device. Qualitative and quantitative laboratory studies have compared the performance of the CLG and conventional goggles (type AN/PVS-5). These studies have revealed better visual and visual-motor performance with the CLG. The implications to optical design of the Hadani et al. theory and the CLG concept are discussed.

Corneal lens goggles and visual space perception.

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.

Itzhak Hadani

Papers

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

Corneal lens goggles and visual space perception.

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

Computational aspects of motion perception during self-motion