Charles F. Reed

Studies of the field-of-view resolution tradeoff in virtual-reality systems

Most virtual-reality systems use LCD-based displays that achieve a large field-of-view at the expense of resolution. A typical display will consist of approximately 86,000 pixels uniformly distributed over an 80-degree by 60-degree image. Thus, each pixel subtends about 13 minutes of arc at the retina; about the same as the resolvable features of the 20/200 line of a Snellen Eye Chart. The low resolution of LCD-based systems limits task performance in some applications. We have examined target-detection performance in a low-resolution virtual world. Our synthesized three-dimensional virtual worlds consisted of target objects that could be positioned at a fixed distance from the viewer, but at random azimuth and constrained elevation. A virtual world could be bounded by chromatic walls or by wire-frame, or it could be unbounded. Viewers scanned these worlds and indicated by appropriate gestures when they had detected the target object. By manipulating the viewers field size and the chromatic and luminance contrast of annuli surrounding the field-of-view, we were able to assess the effect of field size on the detection of virtual objects in low-resolution synthetic worlds.

The measuring function of the first legs of Araneus diadematus Cl.

Spiders deprived of one first leg or two front legs on the same side built webs changed in specific ways and never recovered. Web components were changed from control values to a statistically significant degree as follows: angle regularity and the number of radii decreased, the median central angle increased in size; the number of spiral turns and, in some cases, the spiral regularity decreased; the spiral area decreased relative to frame and central areas; the thread length decreased. No change could be detected in web shape or in the position of the hub. It is concluded that the first leg has a measuring as well as a locomotor function, that the second leg can partly substitute for that measuring function. Web changes following delegging reflect loss of normal adequacy in both of these functions. No evidence of right-left differences in leg function were found. All adaptation to the absence of one or two legs had occurred in the first web after the operation. The variation in control webs and the differential severity in reaction to delegging require evaluation of several animals and many webs; such extensive evaluation is made feasible by computer analysis of an array of points defining a web.

Terrestrial passage theory of the moon illusion.

Theories of the celestial, or moon, illusion have neglected geometric characteristics of movement along and above the surface of the earth. The illusion occurs because the characteristics of terrestrial passage are attributed to celestial passage. In terrestrial passage, the visual angle subtended by an object changes discriminably as an essentially invariant function of elevation above the horizon. In celestial passage, by contrast, change in visual angle is indiscriminable at all elevations. If a terrestrial object gains altitude, its angular subtense fails to follow the expansion projected for an orbital course: Angular diminution or constancy is equivalent to distancing. On the basis of terrestrial projections, a similar failure of celestial objects in successive elevations is also equivalent to distancing. The illusion occurs because of retinal image constancy, not--as traditionally stated--despite it.

Progressive disturbance of spider web geometry caused by two sedative drugs

Abstract The effects of diazepam and phenobarbital upon web-building show a time- and dose-dependency such that—in contrast to man—the action of phenobarbital is stronger than that of diazepam. Within the dose range here employed, the actions of both drugs are similar but have different rates of development. It is well possible, however, that if dose-levels were raised even higher, further differences would be found between the two substances. Both drugs produce significant curtailment of activity and ultimately evidence of imprecision of movement, presumably due to failure in sensory-motor coordination; this becomes apparent in radius construction for both drugs and in spiral placement for phenobarbital. Phenobarbital forces more radical economies of effort at lower dose-levels and earlier times than does diazepam. This curtailment of activity is not the result of potential thread material; at least, measures of gland content under diazepam showed no slowing of glandular synthesis.

The Story of the Drug Web

In the year 1948 Dr. Hans M. Peters, professor of zoology, asked advice from the Pharmacology Department at the University of Tuebingen. He had tried to take movie pictures of spiders during web construction; this usually takes place around 4 o’clock in the morning, a bad hour for the movie crew to work. It was hoped that with the help of stimulant drugs, web building time could be shifted forward. At that time I investigated drugs which attacked primarily central nervous system functions. The use of dextro-amphetamine, strychnine, and morphine was recommended as a first approach to changing the behavior of an animal which had not yet been tried in its reaction to drugs. Dr. Peters soon reported that the experiments had resulted in badly distorted webs, built at the usual time. A movie was taken of a spider building a web under the influence of amphetamine and resulting in a most irregular pattern.

FREE-HAND COPYING OF A GEOMETRIC PATTERN AS A TEST FOR SENSORY-MOTOR DISTURBANCE.

Detailed measurements of freehand copies of a geometric figure were made in order to assess the utility of such drawings for reflecting changes in skilled manual performance. For normal Ss, reliability was satisfactory only for short time-intervals and for certain parameters. However, measures of size of drawings and the placement of spiral lines appeared to show differential sensitivity to stimulant, tranquilizer, and stress conditions.

The solution of hidden-figures: Brightness discrimination and eye movement

Abstract Previous investigation using a statistically-defined display to represent hidden-figures tasks had found brain-injured subjects to show characteristic difficulty in solution, but had implicated a possible role for brightness-discrimination and oculomotor handicaps. These variables are shown not to account for differences between brain-injured and control subjects. A hypothesis regarding the basis of the differences is offered, in which the defect in brain-damaged subjects is sought in the insufficient elaboration of certain central templates during search.

The Silk Glands

The silk glands of the spider are attractive models for study since they are discrete organs which have the sole function of the rapid production of single proteins. Evolution in the Arachnidae has been such as to make the greatest use of silk fibroins. The spider catches its food in a silken web, swathes its prey in a silken bag, and wraps its eggs in a silken cocoon. Wherever the spider goes, it lays a silken thread and throughout its life its contact with the outside world is via its silk.

Specificity of the Web

There exist a number of observations which indicate that the pattern which an adult female Araneus diadematus Cl. spins is characteristic for the species. Comparison of webs of the closely related Araneus diadematus and Araneus sericatus (Figs. 1 and 8) shows a striking similarity in the patterns, while geometric webs of builders only remotely related construct patterns which look quite different. Efforts have been made to trace the history and relationship of species of spiders by means of web Open image in new window Fig. 8 This web of an adult female Araneus sericatus Cl. was built and photographed under the same circumstances as the web in Fig. 1. Note similarities as well as differences in the two webs resemblances under the assumption that a more “primitive”, simple, irregular web was the forerunner of the more elaborate patterns. For a number of reasons such deductions seem at present precipitous, and other approaches such as determining the chemical similarity of silk proteins (see previous chapter) appear to provide a more secure basis for construction of a family tree of web-builders.

The immediacy of the moon illusion

Exception is taken to the conclusion that the terrestrial-passage theory ignores the immediacy of the experience of the moon illusion and is therefore to be rejected. The meaning of immediacy and the definition of the illusion as a horizon enlargement are examined critically. In demonstrating that immediacy is not ignored, the passage theory is restated, with special attention to potential tests of the theory in explaining individual differences and related phenomena.