Haptic scanning of braille cells by low- and high-proficiency blind readers.

A cell-by-cell analysis of finger movements of blind braille readers was conducted to separate, catalogue, and measure the components of scanning movements across braille cells as a function of reading proficiency. Particular attention was paid to the hypothesis that low- and high-proficiency readers could be differentiated by scanning differences on cells over which the finger paused. On cells containing pauses, high-proficiency readers paused for significantly longer durations than did low-proficiency readers, and left-finger pause duration was longer than right-finger pause duration. High-proficiency readers paused on fewer cells with the right finger than did low-proficiency readers. Finger speed (time to traverse a cell independent of pauses and direction changes and expressed in cells per second) was unaffected by reading proficiency. Left-finger speed was faster than right-finger speed, and backward scanning was faster than forward scanning. High-proficiency readers scanned almost twice as many cells with two hands as did low-proficiency readers. These results confirm earlier reports of the superiority of bimanual reading, and suggest that the two hands may perform different functions, allowing pausing for rescanning to occur simultaneously with reading new material.

Eliminating the haptic oblique effect: influence of scanning incongruity and prior knowledge of the standards.

Although the oblique effect has been conceptualized as a purely visual phenomenon, recent studies report its occurrence in a haptic matching task and present the hypothesis that differences in haptic orientational sensitivity might be responsible for the results. The possibility that procedural variables could be responsible was investigated. Specifically, the effect of prior knowledge of the stimulus orientation standards and of use of bilateral haptic exploration of standard and comparison orientations was examined. The results indicate that the reported oblique effect is reduced either when subjects are not informed which orientations will be tested, or when a unilateral matching procedure instead of a bilateral one is used. When both conditions are combined, the haptic oblique effect is eliminated. It is concluded that this particular manifestation of the oblique effect is not related to haptic sensitivity, but stems from the use of well-established imagery as referent for a match (imagery for oblique stimulus orientations is inferior) and the inherently different scanning patterns required in bilateral exploration of obliques (percepts of standard and comparison obliques will be necessarily different).

Effect of modality-specific experience on visual and haptic judgment of orientation.

Although the 'oblique effect' (poorer performance on oblique orientations as compared to performance on vertical and horizontal orientations) is generally understood as a strictly visual phenomenon, a haptic oblique effect occurs for blindfolded subjects required to set a stimulus rod by hand. Because oblique effects are often attributed to the observer's experience with a predominantly horizontal and vertical environment, we assessed the effect of visual and haptic experience by providing subjects with modality-specific inspection periods to familiarize them with the more poorly judged obliques. Oblique error was significantly reduced in magnitude for judgments made by the modality of experience, and for judgments made across modalities. Rate of improvement, consistency of transfer, and the subjective reports of subjects indicate that this haptic oblique effect is more strongly influenced by visual experience and imagery than by haptic experience. It need not be interpreted as an effect based on factors intrinsic to the haptic modality.

Haptic equivalence matching of curvature by nonretarded and mentally retarded blind and sighted persons.

Retarded and nonretarded blind subjects were compared on haptic curvature matching tasks that varied in difficulty. All subjects' accuracy decreased with increasing task difficulty. Accuracy of nonretarded subjects did not differ as a function of visual status. Blind retarded subjects were more accurate than were sighted retarded subjects. The data were discussed in terms of haptic information-gathering experience.

Haptic-visual shape matching by mentally retarded children: exploratory activity and complexity effects.

The accuracy of nonretarded persons in shape matching within and across vision and touch improves with development, and matching by eye is usually better than is matching by hand. The pattern is less clear with mentally retarded children, however. In the present experiment we compared haptic and visual matching of retarded and nonretarded children at different developmental levels, while systematically observing variables known to have developmentally linked effects on task accuracy, including stimulus complexity and haptic exploratory search style. The results showed that accuracy depended on both stimulus complexity, modality, and mental age, regardless of whether or not children were retarded. The selection of haptic search styles also depended on these factors but, in addition, was influenced by intellectual status of the children.

Figure embeddedness as a function of the orientation embedding-field contours.

The 'oblique effect' was studied with the use of an embedded-figures task in which the percentage of contextual or embedding contours aligned in the same orientations as those comprising the hidden forms was systematically varied. For hidden forms comprised either of horizontal and vertical contours, or of oblique (45 degree and 135 degree) contours, search times increased markedly as the percentage of aligned contextual contours increased. Although the rate at which embeddedness increased was the same for both orientations, search times were consistently greater for locating obliquely oriented targets (p less than 0.05), and search time variance was significantly greater (p less than 0.025) on trials in which the hidden form was oblique. The results suggest that the laws of organization governing embeddedness apply equally to oblique and horizontal-vertical orientations, but perceptual processing of oblique orientations is poorer. The relationship between search time and aligned contour is discussed in terms of the dual processes of extraction and synthesis in visual search.

The effect of stimulus duration and monocular viewing on the "oblique effect" in peripheral vision.

Luminance thresholds were obtained for narrow bars of light in vertical, horizontal and oblique orientations. From 5 degrees to 60 degrees into the periphery, a small but significant elevation in threshold was found for stimuli in oblique orientations. The monocularly obtained data replicate an earlier report using binocular presentations and a stimulus duration of 100 msec. When exposure time was 10 msec or 500 msec, this effect of orientation broke down. Theoretical implications are discussed.