Tactile memory in sighted and blind observers: the influence of orientation and rate of presentation

Sighted, early blind, and late blind subjects attempted to identify numerals or number sequences printed on their palms. The numerals were either upright, or inverted, or rotated perpendicular to the arm axis. Stimulus rotation degraded recognition in the early blind subjects, suggesting the influence of experience with visual frames of reference. Slower rates of presentation with upright number sequences improved recall in both sighted and blind observers. An experiment on tactual-visual braille recognition in the sighted observers showed that tilt degraded pattern identification, but visual guidance of the fingertip and ballpoint minimized this loss. A further experiment was performed to distinguish between visual imagery and visual frame of reference explanations of the visual guidance effect on recognition of rotated braille. Subjects explored upright or tilted braille characters while viewing only a light emitting diode on the exploratory fingertip. Sight of scanning movements did not aid pattern recognition with tilt. The results indicate that the benefits of visual guidance on recognition of tilted patterns were probably due to frame of reference information. It is concluded that spatial reference information may aid tactile memory in the sighted and late blind, since the early blind performed at a lower level in the retention task. It is proposed that visual imagery may only explain the superiority of the sighted and late blind when familiar stimuli are studied.     

Picture and pattern perception in the sighted and the blind: the advantage of the late blind

Two experiments are reported on the contribution of visual experience to tactile perception. In the first experiment, sighted, congenitally blind, and late blind individuals made tactual matches to tangible embossed shapes. In the second experiment, the same subjects attempted tactile identification of raised-line drawings. The three groups did not differ in the accuracy of shape matching, but both groups of blind subjects were much faster than the sighted. Late blind observers were far better than the sighted or congenitally blind at tactile picture identification. Four of the twelve pictures were correctly identified by most of the late blind subjects. The sighted and congenitally blind performed at comparable levels in picture naming. There was no evidence that visual experience alone aided the sighted in the tactile task under investigation, since they performed no better than did the early blind. The superiority of the late blind suggests that visual exposure to drawings and the rules of pictorial representation may help tactile picture identification when combined with a history of tactual experience.     

Effect of visual experience on iocational judgements after perspective change in small-scale space

Congenitally blind, late blind and blindfold sighted adults overleamed an object-array within a square frame by touch, and judged, facing the midpoint of the frame, the near/far/left/right locations of objects from sides and diagonally from corners. One-half were first guided to points (A-condition), the rest were first asked to imagine themselves as being at points (I-condition). Group and condition did not, but group and observation point did, interact. Lack of visual experience added to RTs and total times and increased errors especially at diagonal stations. Congenitally blind subjects differed from both late blind and blindfold sighted subjects. However, a section of the congenitally blind subjects attained the level of blindfold sighted subjects. The sequence A-I speeded up judgements in all groups. Group did not interact with size of space. Congenitally blind subjects reportedly resorted to holistic representations, but had specific limitations in using them at diagonal stations. Orientation skills of the congenitally blind in far space could be improved by practising perspective taking in near space.     

The haptic oblique effect in the perception of rod orientation by blind adults

The haptic perception of vertical, horizontal, +45° oblique, and +135° oblique orientations was studied in completely blind adults. The purpose was to determine whether the variations of the gravitational cues provided by the arm-hand system during scanning would affect the manifestation of the oblique effect (lower performance in oblique orientations than in vertical-horizontal ones) as they did in blindfolded sighted people (Gentaz & Hatwell, 1996). In blindfolded sighted adults, the oblique effect was reduced or absent when the magnitude of gravitational cues was decreased. If visual experience participated in the haptic oblique effect, we should observe no oblique effect in early blind subjects in the conditions of manual exploration where late blind and blindfolded sighted manifest this effect. The magnitude of gravitational cues was therefore varied by changing gravity constraints, whereas the variability of these cues was varied by changing the plane in which the task was performed: horizontal (low variability) and frontal (high variability). Early and late blind adults were asked to explore haptically a rod and then to reproduce its orientation ipsilateraUy in one of two exploratory conditions in each plane. In the horizontal plane, the oblique effect was absent, whatever the gravity constraints, in both groups (early and late blind subjects). In the frontal plane, the oblique effect was present, whatever the gravity constraints, in both groups. Taken together, these results showed that, in blind people, the variability of gravitational cues played a role in the haptic oblique effect; no effect of previous visual experience was observed.     

Movement cues and body orientation in recall of locations by blind and sighted children

Experiment 1 tested blind children's recall of locations with repeated and changed recall movements under normal and out-of-line body-to-target orientation. Changed movements produced target undershooting and inaccurate path-keeping by the older blind, particularly for horizontal directions. Errors by the younger blind depended more on body orientation.

Experiment 2 tested blindfolded sighted children under the same conditions, with four forms of coding instructions. The sighted showed no effect of body orientation, but changed movements had similar effects on target localization as for the older blind, regardless of instructions. Different forms of instructions affected bias from movement directions in near and far sectors of the display differently, and instructions to code by reference to the shape of the display surround eliminated the differences.

It was argued that blind and sighted children use extent and direction cues from the positioning movement in locating targets, and that these are not automatic effects but result from children's assessment of the informational conditions.     

Haptic orientation perception benefits from visual experience: evidence from early-blind, late-blind, and sighted people

Early-blind, late-blind, and blindfolded sighted participants were presented with two haptic allocentric spatial tasks: a parallel-setting task, in an immediate and a 10-sec delay condition, and a task in which the orientation of a single bar was judged verbally. With respect to deviation size, the data suggest that mental visual processing filled a beneficial role in both tasks. In the parallel-setting task, the early blind performed more variably and showed no improvement with delay, whereas the late blind did improve, but less than the sighted did. In the verbal judgment task, both early- and late-blind participants displayed larger deviations than the sighted controls. Differences between the groups were absent or much weaker with respect to the haptic oblique effect, a finding that reinforces the view that this effect is not of visual origin. The role of visual processing mechanisms and visual experience in haptic spatial tasks is discussed.     

Evaluation of the attentional capacities and working memory of early and late blind persons

Although attentional processes and working memory seem to be significantly involved in the daily activities (particularly during navigating) of persons who are blind and who use these abilities to compensate for their lack of vision, few studies have investigated these mechanisms in this population. The aim of this study is to evaluate the selective, sustained and divided attention, attentional inhibition and switching and working memory of blind persons. Early blind, late blind and sighted participants completed neuropsychological tests that were designed or adapted to be achievable in the absence of vision. The results revealed that the early blind participants outperformed the sighted ones in selective, sustained and divided attention and working memory tests, and the late blind participants outperformed the sighted participants in selective, sustained and divided attention. However, no differences were found between the blind groups and the sighted group in the attentional inhibition and switching tests. Furthermore, no differences were found between the early and late blind participants in this set of tests. These results suggest that early and late blind persons can compensate for the lack of vision by an enhancement of the attentional and working memory capacities.     

Perspective taking, pictures, and the blind

Congenitally blind, late blind, and blindfolded sighted controls attempted a Piagetian perspective-taking (three-mountain) task. Piaget used the term perspective to mean point of view (Piaget & Inhelder, 1967, p. 210), and the present usage does not imply linear perspective. Subjects used raised-line drawings to depict alternative points of view of an array of three geometric solid forms (cube, cone, and ball). They then identified the point of view of raised-line drawings. The effect of visual status on accuracy was nonsignificant for both response measures. Using alternating vision of the array and drawings, sighted subjects in a control condition performed like the congenitally blind. However, congenitally blind individuals did require more time than the other subjects for the perspective-taking task. In an additional experiment, no difference was found between the three groups in the accuracy or speed of tactile shape matching. The results suggest that visual imagery and visual experience are not necessary for tactile perspective taking.     

Mechanisms in the haptic horizontal-vertical illusion: Evidence from sighted and blind subjects

The haptic horizontal-vertical illusion was studied in two experiments. In Experiment 1, the illusion was relatively weak in sighted subjects and depended on stimulus size and the nature of the figure, that is, whether the pattern was an inverted-T or L shape. Experiment 2 compared early blind and late blind subjects. The illusion was present for an inverted-T figure but absent for an L figure in late blind subjects. However, the early blind subjects treated both the L and T figures as similar and showed the illusion to both. These results support the idea that visual experience may alter haptic judgments in sighted and late blind subjects.     

Late‐ but not early‐onset blindness impairs the development of audio‐haptic multisensory integration

Integrating different senses to reduce sensory uncertainty and increase perceptual precision can have an important compensatory function for individuals with visual impairment and blindness. However, how visual impairment and blindness impact the development of optimal multisensory integration in the remaining senses is currently unknown. Here we first examined how audio‐haptic integration develops and changes across the life span in 92 sighted (blindfolded) individuals between 7 and 70 years of age. We used a child‐friendly task in which participants had to discriminate different object sizes by touching them and/or listening to them. We assessed whether audio‐haptic performance resulted in a reduction of perceptual uncertainty compared to auditory‐only and haptic‐only performance as predicted by maximum‐likelihood estimation model. We then compared how this ability develops in 28 children and adults with different levels of visual experience, focussing on low‐vision individuals and blind individuals that lost their sight at different ages during development. Our results show that in sighted individuals, adult‐like audio‐haptic integration develops around 13–15 years of age, and remains stable until late adulthood. While early‐blind individuals, even at the youngest ages, integrate audio‐haptic information in an optimal fashion, late‐blind individuals do not. Optimal integration in low‐vision individuals follows a similar developmental trajectory as that of sighted individuals. These findings demonstrate that visual experience is not necessary for optimal audio‐haptic integration to emerge, but that consistency of sensory information across development is key for the functional outcome of optimal multisensory integration.     

Abilities and strategies of blind and sighted subjects in visuo-spatial imagery

An active visuo-spatial memory task was used in order to determine the characteristics of mental imagery in subjects with and without visual experience. Subjects were instructed to generate a mental representation of verbally presented 2D patterns that were placed in a grid and to indicate how many pattern elements were in corresponding positions in the two halves of the grid according to a specific grid axis (vertical or horizontal). Unexpectedly, results showed a similar performance in early blind, late blind and sighted subjects. However, subjects' debriefing showed that the three groups used different strategies. The sighted and the late blind subjects took advantage of a visuo-spatial strategy. They generated a mental image of the matrix and they simplified this image to maintain only the relevant information in memory. In contrast, the early blind subjects encoded each pattern element by its location in a (X,Y) coordinate system without visual representation. This indicates that both early and late blind subjects are able to perform an active visuo-spatial imagery task as well as sighted subjects although they use different strategies.     

Smell and taste function in the visually impaired

Surprisingly few quantitative studies have addressed the question of whether visually impaired individuals evidence, perhaps in compensation for their loss of vision, increased acuteness in their other senses. In this experiment we sought to determine whether blind subjects outperform sighted subjects on a number of basic tests of chemosensory function. Over 50 blind and 75 sighted subjects were administered the following olfactory and gustatory tests: the University of Pennsylvania Smell Identification Test (UPSIT); a 16-item odor discrimination test; and a suprathreshold taste test in which measures of taste-quality identification and ratings of the perceived intensity and pleasantness of sucrose, citric acid, sodium chloride, and caffeine were obtained. In addition, 39 blind subjects and 77 sighted subjects were administered a single staircase phenyl ethyl alcohol (PEA) odor detection threshold test. Twenty-three of the sighted subjects were employed by the Philadelphia Water Department and trained to serve on its water quality evaluation panel. The primary findings of the study were that (a) the blind subjects did not outperform sighted subjects on any test of chemosensory function and (b) the trained subjects significantly outperformed the other two groups on the odor detection, odor discrimination, and taste identification tests, and nearly outperformed the blind subjects on the UPSIT. The citric acid concentrations received larger pleasantness ratings from the trained panel members than from the blind subjects, whose ratings did not differ significantly from those of the untrained sighted subjects. Overall, the data imply that blindness, per se, has little influence on chemosensory function and add further support to the notion that specialized training enhances performance on a number of chemosensory tasks.     

Journeying beyond classical somatosensory cortex.

Visual cortical areas are involved in a variety of somatosensory tasks in the sighted, including tactile perception of two-dimensional patterns and motion, and haptic perception of three-dimensional objects. It is still unresolved whether visual imagery or modality-independent representations can better explain such cross-modal recruitment. However, these explanations are not necessarily in conflict with each other and might both be true, if imagery processes can access modality-independent representations. Greater visual cortical engagement in blind compared to sighted people is commonplace during language tasks, and also seems to occur during processing of tactile spatial information. Such engagement is even greater in the congenitally blind compared to the late blind, indicative of enhanced cross-modal plasticity during early development. At the other extreme, short-term visual deprivation of the normally sighted also leads to cross-modal plasticity. Altogether, the boundaries between sensory modalities appear to be flexible rather than immutable.     

盲生错误记忆和真实记忆研究

错误记忆指的是人们会回忆或再认那些没有出现过的事件。目前,针对错误记忆的研究多集中于视力正常的人群。国外近年来有针对视障人群错误记忆的研究认为,在听觉学习情境中视障成人有更好的真实记忆和更低的错误记忆。目前对于盲生的错误记忆特征尚缺乏研究。而盲文摸读作为视障人群重要的学习方式,其对视障人群的真实记忆和错误记忆的影响尚未有研究者关注。本研究以初中盲生和视力正常学生作为研究对象,采用DRM范式,发现被试采用阅读学习(盲生摸读盲文,视力正常学生阅读屏幕文字)和听觉学习两种学习方式下,都发现被试身上存在稳定的错误记忆;盲生的错误记忆显著低于视力正常学生。在摸读学习方式下,盲生真实记忆好于听觉学习方式。     

Blindness enhances tactile acuity and haptic 3-D shape discrimination

This study compared the sensory and perceptual abilities of the blind and sighted. The 32 participants were required to perform two tasks: tactile grating orientation discrimination (to determine tactile acuity) and haptic three-dimensional (3-D) shape discrimination. The results indicated that the blind outperformed their sighted counterparts (individually matched for both age and sex) on both tactile tasks. The improvements in tactile acuity that accompanied blindness occurred for all blind groups (congenital, early, and late). However, the improvements in haptic 3-D shape discrimination only occurred for the early-onset and late-onset blindness groups; the performance of the congenitally blind was no better than that of the sighted controls. The results of the present study demonstrate that blindness does lead to an enhancement of tactile abilities, but they also suggest that early visual experience may play a role in facilitating haptic 3-D shape discrimination.     

Spatial representation by blind and sighted children

Spatial representation by 72 blind and blindfolded sighted children between the ages of 6 and 11 was tested in two experiments by mental rotation of a raised line under conditions of clockwise varied directions.Experiment 1 showed that the two groups were well matched on tactual recognition and scored equally badly on matching displays to their own mentally rotated position.Experiment 2 found the sighted superior in recall tests. There was a highly significant interaction between sighted status and degree of rotation. Degree of rotation affected only the blind. Their scores were significantly lower for rotating to oblique and to the far orthogonal directions than to near orthogonal test positions. On near orthogonals the blind did not differ from the sighted.Age was a main effect, but it did not interact with any other variable. Older blind children whose visual experience dated from before the age of 6 were superior to congenitally blind subjects, but not differentially more so on oblique directions.The results were discussed in relation to hypotheses about the nature of spatial representation and strategies by children whose prior experience derived from vision or from touch and movement.     

Numerical estimation in blind subjects: evidence of the impact of blindness and its following experience

Vision was for a long time considered to be essential in the elaboration of the semantic numerical representation. However, early visual deprivation does not seem to preclude the development of a spatial continuum oriented from left to right to represent numbers (J. Castronovo & X. Seron, 2007; D. Szücs & V. Csépe, 2005). The authors investigated the impact of blindness and its following experience on a 3rd property of the mental number line: its obedience to Weber's law. A group of blind subjects and a group of sighted subjects were submitted to 2 numerical estimation tasks: (a) a keypress estimation task and (b) an auditory events estimation task. Blind and sighted subjects' performance obeyed Weber's law. However, blind subjects demonstrated better numerical estimation abilities than did sighted subjects, especially in contexts involving proprioception, indicating the existence of better mapping abilities between the symbolic representations of numbers and their corresponding magnitude representations, obeying Weber's law (e.g., J. S. Lipton & E. Spelke, 2005). These findings suggest that blindness and its following experience with numbers might result in better accuracy in numerical processing.     

Subitizing in congenitally blind adults

We investigated the role of vision in tactile enumeration within and outside the subitizing range. Congenitally blind and sighted (blindfolded) participants were asked to enumerate quickly and accurately the number of fingers stimulated. Both groups of participants enumerated one to three fingers quickly and accurately but were much slower and less accurate with four to nine fingers. Within the subitizing range, blind participants performed no differently from both sighted (blindfolded) and sighted-seeing participants. Outside of the subitizing range, blind and sighted-seeing participants showed better performance than did sighted-blindfolded participants, suggesting that lack of access to the predominant sensory modality does affect performance. Together, these findings further support the claim that subitizing is a general perceptual mechanism and demonstrate that vision is not necessary for the development of the subitizing mechanism.     

The role of head movements in the discrimination of 2-D shape by blind echolocation experts

Similar to certain bats and dolphins, some blind humans can use sound echoes to perceive their silent surroundings. By producing an auditory signal (e.g., a tongue click) and listening to the returning echoes, these individuals can obtain information about their environment, such as the size, distance, and density of objects. Past research has also hinted at the possibility that blind individuals may be able to use echolocation to gather information about 2-D surface shape, with definite results pending. Thus, here we investigated people’s ability to use echolocation to identify the 2-D shape (contour) of objects. We also investigated the role played by head movements—that is, exploratory movements of the head while echolocating—because anecdotal evidence suggests that head movements might be beneficial for shape identification. To this end, we compared the performance of six expert echolocators to that of ten blind nonecholocators and ten blindfolded sighted controls in a shape identification task, with and without head movements. We found that the expert echolocators could use echoes to determine the shapes of the objects with exceptional accuracy when they were allowed to make head movements, but that their performance dropped to chance level when they had to remain still. Neither blind nor blindfolded sighted controls performed above chance, regardless of head movements. Our results show not only that experts can use echolocation to successfully identify 2-D shape, but also that head movements made while echolocating are necessary for the correct identification of 2-D shape.