Hewitt D. Crane

Accurate two-dimensional eye tracker using first and fourth Purkinje images.

Although a number of devices are currently in use for monitoring eye position, none is both accurate and convenient to use. Methods based on the use of contact lenses can provide high accuracy but have obvious inconveniences. Other techniques—e.g., skin-mounted electrodes, or eyeglass-mounted photoelectric pickups—are relatively convenient, but eye position can be measured to an accuracy of no better than about 0.5° to 1°. A novel eye-tracking instrument has been developed that makes use of two Purkinje images. The instrument operates in the infrared, so that it does not interfere with normal vision; it requires no attachments to the eye; it has a sensitivity and accuracy of about 1 min of arc, and operates over a two-dimensional visual field of 10° to 20° in diameter. The basic principle of the instrument is described, and operating records are shown.

Generation-V dual-Purkinje-image eyetracker

Major advances characterize the Generation-V dual-Purkinje-image (DPI) eyetracker compared with the Generation-III version previously described. These advances include a large reduction in size, major improvements in frequency response and noise level, automatic alignment to a subject, and automatic adjustment for different separation between the visual and optic axes, which can vary considerably from subject to subject. In a number of applications described in the paper, the eyetracker is coupled with other highly specialized optical devices. These applications include accurately stabilizing an image on a subjects retina; accurately simulating a visually dead retinal region (i.e., a scotoma) of arbitrary shape, size, and position; and, for clinical purposes, stabilizing the position of a laser coagulator beam on a patients retina so that the point of contact is unaffected by the patients own eye movements.

Accurate three dimensional eye tracker

A combined optometer and eyetracking instrument has been developed to measure both the dynamic refractive power and the direction of gaze of the same eye. In effect, this instrument measures, as a function of time, the point in 3-D space on which the eye is fixated. Nothing is attached to the subject (patient), who is easily aligned in the device. The measuring wavelength is in the near ir and is invisible. The usable field of the instrument is greater than 20 degrees ; the horizontal and vertical directions of gaze are measured with a noise level and repeatability of about 1 min of arc. The range of the optometer is approximately -4 to +12 diopters; refractive power is measured to about 0.1 diopter. Two instruments may be aligned side by side for tracking both eyes simultaneously. Three-dimensional monocular and binocular eye movement records are shown.

Servo-Controlled Infrared Optometer*

A device is described that provides an electrical signal proportional to the instantaneous refractive power of the human eye. Infrared light illuminates a target whose optical distance from the subject’s eye can be changed rapidly. The position of this target is servo controlled in such a way that it remains conjugate with the retina regardless of changes of the subject’s state of accommodation. The position of the target provides a direct measure of refractive power. The device may be used on an undrugged eye and does not interfere with normal visual tasks.

On seeing reddish green and yellowish blue.

Four color names—red, yellow, green, and blue—can be used singly or combined in pairs to describe all other colors. Orange, for example, can be described as a reddish yellow, cyan as a bluish green, and purple as a reddish blue. Some dyadic color names (such as reddish green and bluish yellow) describe colors that are not normally realizable. By stabilizing the retinal image of the boundary between a pair of red and green stripes (or a pair of yellow and blue stripes) but not their outer edges, however, the entire region can be perceived simultaneously as both red and green (or yellow and blue).

Three-dimensional visual stimulus deflector

A 3-D visual stimulus deflector has been designed so that a subject can view any stimulus pattern or object through it, and the pattern (up to 25 degrees in diameter) can be moved over a range of 40 degrees horizontally and 30 degrees vertically. The optical distance of the object being viewed can be changed over a 15-diopter range, while the brightness and visual angle subtended by the object remain fixed. Further, the observer can view the object through a pupil of any desired shape and transmittance. Horizontal and vertical movements are independent, with time delays of 1 msec and a response range from dc to 200 Hz. Focus change is independent of lateral field motion and has a time delay of 12 msec and a maximum slewing rate of approximately 40 diopters/sec. Two such devices can be aligned side by side in a binocular configuration for independent 3-D control of the fixation of each eye.

Information available In brief tactile presentations

Two experiments investigated characteristics of Immediate recall for brief tactile stimuli applied to the 24 interjoint regions of the fingers of both hands (thumbs excluded) The obtained Immediate-memory span varied from 35 to 7,5 stimulus positions correct after correction for guessing, similar to the results In analogous visual studies, Properties of any hypothetical tactile short-term memory were studied by requiring subjects to report only a specified portion of the stimuli presented, and by varying the time of occurrence of the marker specifying which portion of the stimuli to report, In this partial-report condition, subjects had more stimulus information available at the time of reporting than their immediate memory spans indicated, provided that the stimulus marker occurred within 0.8 sec after stimulus termination, The data suggest that at least for the amount of training employed here, any tactile short-term memory has much less capacity than an analogous visual short-term memory.

Ocular-Focus Stimulator*

Author(s): Cornsweet, TN; Crane, HD | Abstract: The simple instrument described in this letter performs the following function. When it is pointed at any object, test pattern, or other form of visual display, the optical distance between the observer and the object can be changed at will while the brightness and visual angle of the object are invariant. Further, the observer sees the object through a pupil of any desired shape and transmittance.

Tactile perception of sequentially presented spatial patterns

Tactile pattern recognition was studied by presenting pairs of alphabetic shapes in rapid succession at the same anatomical location, the subject being required on each trial to identify bath of the patterns. Experimental variables were the duration of each stimulus and the time between stimuli. Three aspects of the observed interaction were (1) an increase in letter reversals for very short interstimulus intervals; (2) a greater percentage of first-response errors for short-stimulus onset intervals and a greater percentage of second-response errors for long-stimulus onset intervals; and (3) a crossover in the first- and second-response error rates in the range of 100 to 200 msec. after the onset of the first stimulus. These results are consistent with some of the temporal properties of models proposed for analogous visual tasks.

A High-Speed Logic System Using Magnetic Elements and Connecting Wire Only

By introducing geometric variation in the basic magnetic core toroidal structure, new logic design freedom is achieved and effective decoupling is obtained between different windings linking the same element. By proper interconnection such elements may be used to provide unilateral information-flow properties without the use of explicit unilateral devices such as diodes. A practical system to accomplish this is outlined in this paper. The resulting circuits are relatively fast and inexpensive. Magnetic elements and connecting wires only are required. In particular, single-turn windings may be used in the coupling loops. Furthermore, inherent nondestructive read properties allow a great deal of logic facility. Simple shift register structures and logic elements and circuits are described.