The abstraction and generalization of dot patterns

The Ss were trained on patterns representing different levels of distortion and transferred to test trials containing the old training patterns, the prototype patterns, and new distortions. Training on low levels of distortion consistently produced superior performance on all test patterns except the most distorted ones. The results also showed that the prototypes and low distortion-level test patterns of meaningful concepts were identified more often than prototypes and low distortion-level test patterns of meaningless concepts but the reverse was true for highly distorted test patterns. Training with patterns whose average dot positions corresponded to the original positions of the dots in the prototypes and to two different levels of distortion of training patterns did not facilitate transfer of any abstractions formed.     

Comparison of matching and drawing in the perception of shape at various intelligence levels

The Pennsylvania State University, University Park, Pennsylvania 16802 The tendency toward shape constancy was investigated using both the traditional matching technique of Thouless and free-hand drawing of the stimulus object. Data were obtained for college students and for institutionalized feebleminded Ss at three levels of intelligence. The previous observation that Ss of higher intelligence level produce a lower tendency toward shape constancy, as measured by the matching method, was confirmed. With the drawing method, the same trend was observed but the differences among groups were exaggerated. The sensitivity of measures of perceived shape to experimental as well as nonexperimental variables is discussed.     

Cross-cultural and educational aspects of the Ponzo perspective illusion

The magnitude of the Ponzo illusion was determined for two groups of Ugandans, university students and villagers. For the university population, increase in the depth cues in which the illusion was embedded produced an increase in illusion magnitude similar to that observed among students in an American university. For the villagers, however, no illusion was observed for any of the stimulus conditions. Since the environmental ecology of the two groups was similar, the lack of illusion among the villagers cannot be attributed to differential past history of exposure to depth cues. Rather it is hypothesized that responses to two-dimensional stimuli are determined by both depth and flatness cues, and that the responses of the uneducated observers were determined primarily by flatness cues.     

Laser optometer incorporating the Badal principle

The refractive state of the eye can be accurately determined while performing a visual task by introducing the diverged beam of a laser, reflected from a moving drum, into the visual field. The direction of the apparent motion of the resultant interference pattern is a direct indicator of refractive state. By incorporation of the Badal principle into the optical system, a measurement can be completed within approximately 30 sec. The advantage of this method over other techniques is that it permits evaluation of refractive state but does not itself influehce the magnitude of accommodation. A number of applications of this principle are cited.     

The effect of feedback on luminance thresholds for peripherally presented stimuli

The effect of a central task on peripheral vision was determined by obtaining absolute luminance thresholds for peripherally presented stimuli. A competing central task was provided by interrupting the fixation light and requiring the S to reilluminate it. Data were obtained over five sessions, with feedback information provided on each trial. Thresholds were highest for the initial session and declined as a function of practice. The magnitude of the change depended upon the interruption rate. When central and peripheral stimuli compete for attention, priority is given initially to the central task, but, with practice, the differences are reduced.     

Evidence for the persistence of visual guidance information

An earlier study from our laboratory provided initial support for the hypothesis that information facilitating visual guidance persists in the absence of retinal stimulation. The present study supports and extends this hypothesis with three experiments in which visually occluded subjects positioned a point of light at the location of a previously viewed target and also walked in the direction of a previously viewed path. In both tasks, performance was possible following occlusion, and in all cases, performance slowly and significantly decreased with longer durations of occlusion. This decay in performance was gradual and had a “half-life” of greater than 15 sec. Absolute performance was correlated across tasks. The effect of occlusion on absolute error in the localization performance was relatively stable within individuals over a 3-week period. The biological utility of guidance information persistence is discussed along with implications for space constancy, illusions of motion, and problems of disorientation.