The importance of alignment in blind subjects' use of tactual maps

An experiment was conducted to test for the presence of alignment effects (previously found in sighted map users) in blind and visually impaired subjects using tactual maps. The term 'alignment effects' refers to the fact that when points represented as further up on a map do not correspond to points forward from the user in the environment, errors in the directional judgments made by subjects are greatly increased. The results show that alignment effects do exist in blind and visually impaired map users. Blind subjects encoded maps using the 'up equals forward' rule, and demonstrated some similarity to sighted subjects in the types of errors made. There was also some indication of improved performance over repeated trials. Differences between blind and sighted subjects were also found and were tentatively attributed to visual experience with object transformations and/or representational variables. Subject background variables were also investigated and some relationships between background of the subject and performance were drawn.     

Psychophysical functions for active tactual discrimination of line width by blind children

Two psychophysical experiments were conducted on active tactual discrimination of line width using the method of constant stimuli with blind subjects. In Experiment I, 93 subjects made single judgments over each of five standards between 0.04 and 0.12 in. In Experiment II, 6 subjects were tested repeatedly over seven standards between 0.04 and 0.50 in. Over the range of standards common to both experiments, the Weber fractions decreased as the width of the standard increased. For two larger standards (0.25 and .50 in.), the Weber fractions approached asymptote and then increased respectively suggesting a U-shaped function. No differences in accuracy of discrimination were found between males vs. females, age groupings, or grade groupings.     

Shape correlates of visual and tactual size judgments: A contrast with complexity

Pattern correlates of perceived size were studied by obtaining category judgments of the size of 100 random forms from 40 Ss who explored the forms visually and 40 Ss who explored them factually. Comparison of the modalities and contrasts with perceived complexity were made via intercorrelations of judgments and latencies, multiple regression analyses using factored form dimensions, and correlations with original form measures. By holding area of the forms constant, it was shown that perceived size can be related to characteristics of shape.     

Visual and tactual form complexity:A psychophysical approach to perceptual equivalence

Equivalence of two modalities for processing form-complexity information was investigated by obtaining category judgments of the complexity of 100 random forms from 40 Ss who explored the forms visually and 40 Ss who explored them tactually. Intercorrelations of judgments and multiple regression analyses with form measures indicate that information was used in the same fashion independent of input modality. Latencies were interpreted as reflecting information gaining and processing capabilities.     

Effects of tactual and phonological similarity on the recall of Braille letters by blind children.

Forty-eight severly blind children, able to cope with set-sizes of two and three, four, five or six serial items were tested on probed recall of Braille letters they could either name or discriminate, when the letters were (1) dissimilar in tactual characteristics and name sounds, (2) similar in feel, but different in name sound, and (3) dissimilar in feel but similar in name sound. Results showed that tactual similarity produced recall decrements by subjects able to be tested under set-sizes of up to five items, while phonological similarity produced recall decrements by subjects testable under set-sizes of five and six items. It was argued that tactual information survives perception and affects recall, and that blind children can encode tactual inputs either tactually or verbally, but that this probably depends upon different processes.     

Expanding the tactual field of view

Can tactual information be acquired simultaneously by several different fingers? Blind and sighted Ss were asked to scan vertical displays of braille (consisting of either one or two dots) with the index and middle fingers on each hand-using one, two, or four fingers at the same time. Stimuli were recognized most rapidly when the displays were scanned by two fingers on different hands and least rapidly when two fingers on the same hand were used; performance was similar with one finger and with four fingers. The results indicated some parallel perceptual processing of the inputs to the two hands and mutual interference in processing inputs from fingers on the same hand.     

Lack of evidence for a tactual Poggendorff illusion

Lucca, Dellantonio, and Riggio (1986) reported large distortions in a tactual analogue of the visual Poggendorff illusion. They also reported large effects in the direction opposite to the visual illusion, which they termed "inversions." However, their evidence for such effects is questionable; they used what we consider to be inappropriate measurement and analysis procedures. In attempting to replicate their experiment, and in conducting four additional experiments, we found no evidence at all for their alleged tactual analogue of the visual Poggendorff effect. Instead, we demonstrated that "inversions" are likely due to the use of a raised stimulus display that causes artifactual mistracking, which is totally unrelated to normal mechanisms of alignment judgment. We also discuss the possible role of intersensory factors in the generation of tactual illusions.     

Short-term serial tactual recall: effects of grouping on tactually probed recall of Braille letters and nonsense shapes by blind children

The study tested the hypothesis that grouping has adverse effects on the recall of tactual shapes but facilitates the recall of tactual letters on the assumption that this depends on different processes. A further question was the relation of grouping to letter recall span (set-size). Tactually probed recall of tactually presented serial nonsense and letter shapes by blind children was tested under grouped and ungrouped conditions. Results showed a highly significant interaction between list type and grouping, and a (smaller) higher order interaction between set size list type and grouping, in the predicted directions. Grouping had adverse effects on nonsense shape recall. Letter recall was better and was facilitated by grouping, except by subjects with poor letter recall spans who were also slow at letter naming. Mental and chronological age were associated with higher scores, but unlike set size, did not relate differentially to letter grouping. It was argued that the form of coding is a factor in determining the nature of processing and in recall efficiency.     

Mental rotation of tactual stimuli

Three experiments involving different angular orientations of tactual shapes were performed. In experiment 1 subjects were timed as they made 'same-different' judgments about two successive rotated shapes. Results showed that no rotation effect is obtained, i.e., reaction times and error percentage do not increase linearly with rotation angle. The same negative results were found in experiment 2, in which subjects were similarly timed while they made mirror-image discriminations. In experiment 3 a single-stimulus paradigm was used and subjects were asked to decide if a rotated stimulus was a 'normal' or 'reversed' version. Reaction times increased linearly with angular departure from the vertical. Therefore, for tactual stimuli too, this study confirms previous results, which suggest that a mental rotation strategy only occurs if it is facilitated by both type of task and type of stimulus. Results also show a significant difference between hands, and between hands and type of response. Implied hemispheric differences are discussed.     

Reference systems and the perception of tactual and haptic orientation

Adult subjects learned to identify bars differing in orientation. The bars were presented either tactually or haptically. In the first experiment, learning was followed by a transfer test with body posture changed by 90 deg. That is, if subjects originally learned with body upright, the transfer test was carried out with body reclined. Results of the transfer test indicated original learning of the tactually presented bars was done with respect to a body reference system and original learning of the haptically presented bars was done with respect to an environmental or gravity based reference system. In the second experiment, learning was followed by a transfer test using both a change of body posture and a change of stimulus modality from tactual to haptic or vice versa. Performance in this transfer test is interpreted in terms of a conceptual mediation hypothesis.     

On the concordance among empirical confusion matrices for visual and tactual letter recognition

In this article, we examine the concordance among 19 empirical confusion matrices for visual and tactual recognition of capital letters of the alphabet. As a measure of concordance, we employed an index based on within-stimulus triads of letters. Unlike correlation measures of agreement that are based on a one-to-one matching of matrix elements, the selected index directly captures the internal structures of the confusion matrices prior to the comparison. Permutation tests revealed statistically significant concordance among 166 of 171 pairs of matrices in the study. Concordance of confusion structure among tactual matrices tended to be somewhat stronger than concordance among the visual matrices.     

Internal consistency reliability of the tactual performance test trials

Internal consistency reliabilities were calculated for the Tactual Performance Test Preferred Hand (n=300), Nonpreferred H and (n=302), and Both Hands (n=314) trials, and Total Time. Reliabilities are reported for the total sample and three groups: normal, undiagnosed patients sent for assessment, and alcoholic persons. The reliability coefficients ranged from .59 to .90.     

The effect of set on the two-point tactual threshold

This experiment studies the influence of set on the two-point tactual threshold. The two-point limen (critical stimulus) was determined along the mid-longitudinal line of both volar and dorsal surfaces of the right forearms of seven university students. Test-stimuli were selected at 3 mm. steps both up and down from each of the critical stimuli. Each of these test-stimuli was presented separately, the critical stimulus being interpolated 30 times in each test of the series. The proportions of two-point and one-point responses to the critical stimulus were then determined again in a control series. It was found that, as the test-stimulus deviated in the positive direction from the critical stimulus, the proportion of two-point responses to the critical stimulus increased, reached a maximum and then began to decline. A similar rise and fall in one-point responses were found in the opposite direction. The results were explained by Adaptation Level Theory.