Jerome D. Tietz

Absolute motion parallax and the specific distance tendency

In the absence of definitive cues’to distance, the perceived distance of an object will be in error in the direction of the object appearing at a distance of about 2 m from O. This tendency to perceive an object at a relatively near distance is termed the specific distance tendency (Gogel. 1969). Also, it has been found that an error in perceiving the distance of an object will result in an apparent movement of the object when the head is moved (Hay & Sawyer. 1969; Wallach, Yablick. & Smith. 1972). From these two results, it was expected that the direction of trie apparent movement of a stationary point of light resulting from head movement would vary predictably as a function of the physical distance of the point of light from O. This expectation was confirmed in an experiment in which both the perceived motion and perceived distance of the point of light were measured. The consequences of the study for the role of motion parallax in the perception of distance and for the reafference principle in the perception of object motion with head motion are discussed

A geographical information system for a GPS based personal guidance system

This paper describes the process of building a GIS for use in real time by blind travellers. Initially the components of a Personal Guidance System (PGS) for blind pedestrians are outlined. The location finding and database components of the system are then elaborated. Next follows a discussion of the environmental features likely to be used by blind travellers, and a discussion of the different path following and environmental learning modes that can be activated in the system. Developments such as personalizing the system and accounting for veering are also presented. Finally, possible competing schemes and problems related to the GIS component are examined.

Personal guidance system for the visually impaired

We outline the design for a navigation system for the visually impaired and describe the progress we have made toward such a system. Our long-term goal is for a portable, self-contained system that will allow visually impaired individuals to travel through familiar and unfamiliar environments without the assistance of guides. The system, as it exists now, consists of the following functional components: (1) a means of determining the travelers position and orientation in space, (2) a Geographic Information System comprising a detailed database of the surrounding environment and functions for automatic route planning and for selecting the database information desired by the user, and (3) the user interface.

Image capture: simulation of sensor responses from hyperspectral images

This paper describes the design and performance of an image capture simulator. The general model underlying the simulator assumes that the image capture device contains multiple classes of sensors with different spectral sensitivities and that each sensor responds in a known way to irradiance over most of its operating range. The input to the simulator is a set of narrow-band images of the scene taken with a custom-designed hyperspectral camera system. The parameters for the simulator are the number of sensor classes, the sensor spectral sensitivities, the noise statistics and number of quantization levels for each sensor class, the spatial arrangement of the sensors and the exposure duration. The output of the simulator is the raw image data that would have been acquired by the simulated image capture device. To test the simulator, we acquired images of the same scene both with the hyperspectral camera and with a calibrated Kodak DCS-200 digital color camera. We used the simulator to predict the DCS-200 output from the hyperspectral data. The agreement between simulated and acquired images validated the image capture response model and our simulator implementation. We believe the simulator will provide a useful tool for understanding the effect of varying the design parameters of an image capture device.

A comparison of oculomotor and motion parallax cues of egocentric distance

Abstract Using the head motion procedure, the apparent distance of a point of light in an otherwise dark visual field was measured under conditions in which oculomotor cues (accommodation, convergence) and absolute motion parallax were varied together and separately. It was concluded that absolute motion parallax is almost as effective a cue to distance as are oculomotor cues from monocular observation, but is not as effective as oculomotor cues from binocular observation. Evidence was also presented that the null adjustment method, used in conjunction with the head motion procedure, provides an unbiased measure of apparent distance.

The effect of perceived distance on perceived movement

Equations were developed to predict the apparent motion of a physically stationary object resulting from head movement as a function of errors in the perceived distances of the object or of its parts. These equations, which specify the apparent motion in terms of relative and common components, were applied to the results of two experiments. In the experiments, the perceived slant of an object was varied with respect to its physical slant by means of perspective cues. In Experiment I, O reported the apparent motion and apparent distance of each end of the object independently. The results are consistent with the equations in terms of apparent relative motion, but not in terms of apparent common motion. The latter results are attributed to the tendency for apparent relative motion to dominate apparent common motion when both are present simultaneously. In Experiment II, a direct report of apparent relative motion (in this case, apparent rotation) was obtained for illusory slants of a physically frontoparallel object. It was found that apparent rotations in the predicted direction occurred as a result of head motion, even though under these conditions no rotary motion was present on the retina.

Determinants ofthe perception of sagittal motion

This study examines the change in the perceived distance of an object in three-dimensional space when the object andlor the observer’s head is moved along the line of sight (sagittal motion) as a function of the perceived absolute (egocentric) distance of the object and the perceived motion of the head. To analyze the processes involved, two situations, labeled A and B, were used in four experiments. In Situation A, the observer was stationary and the perceived motion of the object was measured as the object was moved toward and away from the observer. In Situation B, the same visual information regarding the changing perceived egocentric distance between the observer and object was provided as in Situation A, but part or all of the change in visual egocentric distance was produced by the sagittal motion of the observer’s head. A comparison of the perceived motion of the object in the two situations was used to measure the compensation in the perception of the motion of the object as a result of the headmotion. Compensation was often clearly incomplete, and errors were often made in the perception of the motion of the stimulus object. A theory is proposed, which identifies the relation between the changes in the perceived egocentric distance of the object and the tandem motion of the object resulting from the perceived motion of the head to be the significant factor in the perception of the sagittal motion of the stimulus object in Situation B.

Adjacency and attention as determiners of perceived motion

Abstract Motion induction was investigated as a function of depth adjacency and attention. Moving induction objects producing opposing induction effects in a test object were presented simultaneously at different distances in the visual field with the apparent distance of the test object varied relative to the induction objects. In agreement with the adjacency principle, it was found that separating the test and induction object in apparent depth decreased the induction effect. Instructions to attend to one and to ignore the other induction object while looking at the test object clearly modified the induction effect and accounted for about half of the total effect produced by depth adjacency. The results are discussed in terms of the measurement of attention and the ability to perceptually organize the visual world.

Eye fixation and attention as modifiers of perceived distance.

An error in the perceived distance of a physically stationary object results in an apparent horizontal motion of the object if the head is moved horizontally. Procedures have been developed to use this apparent motion to measure the apparent distance of the object. Research also has indicated that the apparent distance of an object will tend to be displaced toward the distance at which the eyes are fixated. In the present study head-motion procedures were used to measure the effect of eye fixation and attention upon the apparent distance of a point of light in two experiments. Substantial errors in perceived distance occurred in the predicted direction as a function of fixation distance. Attending to an object at a distance other than the distance of the fixated point of light had a much less effect upon the apparent distance of the point. It is concluded that the apparent concomitant motion which occurs in a variety of situations as a function of the distance of fixation indicates that substantial errors in perceived distance are common in most environments.

Relative cues and absolute distance perception

It is possible, in theory, for the simultaneous occurrence of several different relative cues of distances to increase the veridicality of the perception of absolute distance. To test whether this actually occurs, a three-dimensional display was viewed monocularly while moving the head laterally, under conditions in which some error in perceived absolute distance was expected. The perceived absolute distance of the display was measured with the number of relative cues of distance within the display varied. No systematic reduction was found in the error in perceived absolute distance as a consequence of the variation in the number of relative cues. The study provides no evidence that the potential source of absolute distance information provided by relative cues is utilized by the visual system.