Memory processing of spatial order as transmitted by auditory information in the absence of visual cues

Two experiments were conducted concerning spatial order recall when spatial information is transmitted by auditory stimuli. Temporal order either was congruent with spatial order or was independent of spatial order. In Experiment 1, the comparisons were among normally or partially sighted subjects allowed to look, normally sighted subjects who were blindfolded, and blind children. The main findings were a superiority of the sighted subjects allowed to look (that is, to support auditory information with visual cues) and a smaller advantage for the sighted-but-blindfolded subjects, relative to the blind group. In Experiment 2, normally sighted adults (either seeing or blindfolded) and blind adults were tested. Surprisingly, the blind were not worse than the sighted in this study. Subsequent interviews and detailed analysis of errors suggested that the blind coded spatial information kinesthetically. These indirect analyses also suggested that whereas spatial order was coded temporally in the sighted, it was controlled by both temporal and spatial factors in the blind and blindfolded subjects.     

Tactual picture recognition in congenitally blind and sighted children

Three experiments were carried out to investigate tactual processing of two-dimensional raised line drawings by blind and blindfolded sighted children. The results showed an unexpected but consistent pattern indicating that the introduction of ‘meaning’ facilitated the performance of the blindfolded sighted children but caused a relative decline in the performance of the congenitally blind. A general lack of evidence distinguishing between recognition of objects that had or had not been directly experienced through touch suggested that the internal spatial representations of objects depended not only on perceptual information but also on knowledge derived from other sources.     

Structural properties of spatial representations in blind people: Scanning images constructed from haptic exploration or from locomotion in a 3-D audio virtual environment

When people scan mental images, their response times increase linearly with increases in the distance to be scanned, which is generally taken as reflecting the fact that their internal representations incorporate the metric properties of the corresponding objects. In view of this finding, we investigated the structural properties of spatial mental images created from nonvisual sources in three groups (blindfolded sighted, late blind, and congenitally blind). In Experiment 1, blindfolded sighted and late blind participants created metrically accurate spatial representations of a small-scale spatial configuration under both verbal and haptic learning conditions. In Experiment 2, late and congenitally blind participants generated accurate spatial mental images after both verbal and locomotor learning of a full-scale navigable space (created by an immersive audio virtual reality system), whereas blindfolded sighted participants were selectively impaired in their ability to generate precise spatial representations from locomotor experience. These results attest that in the context of a permanent lack of sight, encoding spatial information on the basis of the most reliable currently functional system (the sensorimotor system) is crucial for building a metrically accurate representation of a spatial environment. The results also highlight the potential of spatialized audio-rendering technology for exploring the spatial representations of visually impaired participants.     

Visual experience is not necessary for efficient survey spatial cognition: Evidence from blindness

This study investigated whether the lack of visual experience affects the ability to create spatial inferential representations of the survey type. We compared the performance of persons with congenital blindness and that of blindfolded sighted persons on four survey representation-based tasks (Experiment 1). Results showed that persons with blindness performed better than blindfolded sighted controls. We repeated the same tests introducing a third group of persons with late blindness (Experiment 2). This last group performed better than blindfolded sighted participants, whereas differences between participants with late and congenital blindness were nonsignificant. The present findings are compatible with results of other studies, which found that when visual perception is lacking, skill in gathering environmental spatial information provided by nonvisual modalities may contribute to a proper spatial encoding. It is concluded that, although it cannot be asserted that total lack of visual experience incurs no cost, our findings are further evidence that visual experience is not a necessary condition for the development of spatial inferential complex representations.     

Visual experience is not necessary for efficient survey spatial cognition: evidence from blindness

This study investigated whether the lack of visual experience affects the ability to create spatial inferential representations of the survey type. We compared the performance of persons with congenital blindness and that of blindfolded sighted persons on four survey representation-based tasks (Experiment 1). Results showed that persons with blindness performed better than blindfolded sighted controls. We repeated the same tests introducing a third group of persons with late blindness (Experiment 2). This last group performed better than blindfolded sighted participants, whereas differences between participants with late and congenital blindness were nonsignificant. The present findings are compatible with results of other studies, which found that when visual perception is lacking, skill in gathering environmental spatial information provided by nonvisual modalities may contribute to a proper spatial encoding. It is concluded that, although it cannot be asserted that total lack of visual experience incurs no cost, our findings are further evidence that visual experience is not a necessary condition for the development of spatial inferential complex representations.     

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.     

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.     

The role of preschoolers' social understanding in evaluating the informativeness of causal interventions

Preschoolers use information from interventions, namely intentional actions, to make causal inferences. We asked whether children consider some interventions to be more informative than others based on two components of an actor’s knowledge state: whether an actor possesses causal knowledge, and whether an actor is allowed to use their knowledge in a given situation. Three- and four-year-olds saw a novel toy that activated in the presence of certain objects. Two actors, one knowledgeable about the toy and one ignorant, each tried to activate the toy with an object. In Experiment 1, either the actors chose objects or the child chose for them. In Experiment 2, the actors chose objects blindfolded. Objects were always placed on the toy simultaneously, and thus were equally associated with the effect. Preschoolers’ causal inferences favored the knowledgeable actor’s object only when he was allowed to choose it (Experiment 1). Thus, children consider both personal and situational constraints on knowledge when evaluating the informativeness of causal interventions.     

Sequential vs simultaneous encoding of spatial information: a comparison between the blind and the sighted

The aim of this research is to assess whether the crucial factor in determining the characteristics of blind people's spatial mental images is concerned with the visual impairment per se or the processing style that the dominant perceptual modalities used to acquire spatial information impose, i.e. simultaneous (vision) vs sequential (kinaesthesis). Participants were asked to learn six positions in a large parking area via movement alone (congenitally blind, adventitiously blind, blindfolded sighted) or with vision plus movement (simultaneous sighted, sequential sighted), and then to mentally scan between positions in the path. The crucial manipulation concerned the sequential sighted group. Their visual exploration was made sequential by putting visual obstacles within the pathway in such a way that they could not see simultaneously the positions along the pathway. The results revealed a significant time/distance linear relation in all tested groups. However, the linear component was lower in sequential sighted and blind participants, especially congenital. Sequential sighted and congenitally blind participants showed an almost overlapping performance. Differences between groups became evident when mentally scanning farther distances (more than 5m). This threshold effect could be revealing of processing limitations due to the need of integrating and updating spatial information. Overall, the results suggest that the characteristics of the processing style rather than the visual impairment per se affect blind people's spatial mental images.     

Blind children recognizing tactile pictures respond like sighted children given guidance in exploration

Theory of tactile pictures argues that untrained blind subjects can recognize raised, outline pictures. It contends the blind person’s knowledge of the shapes of common objects is like that of the sighted, and the blind person’s pictorial abilities use the same principles as the sighted person’s. To test this theory, blind children (aged 8–13) and blindfolded age-matched sighted children were asked to identify raised-line drawings of common objects. Their performances were correlated. In addition, the blind children identified more than sighted children exploring the pictures actively, but the same number of pictures as sighted children who were given passive, guided exploration. We argue blind and sighted children use the same principles to identify the pictures, but the blind have superior exploration skills. The differences in the effects of exploration skills on recognition scores are minimized when the sighted children are given guidance, since the sighted children then have efficient contact with the displays, and the performance of the sighted and the blind is then governed by the same principles, without one group benefitting from advantages in exploration skills.     

Imagery in the congenitally blind: how visual are visual images?

Three experiments compared congenitally blind and sighted adults and children on tasks presumed to involve visual imagery in memory. In all three, the blind subjects' performances were remarkably similar to the sighted. The first two experiments examined Paivio's (1971) modality-specific imagery hypothesis. Experiment 1 used a paired-associate task with words whose referents were high in either visual or auditory imagery. The blind, like the sighted, recalled more high-visual-imagery pairs than any others. Experiment 2 used a free-recall task for words grouped according to modality-specific attributes, such as color and sound. The blind performed as well as the sighted on words grouped by color. In fact, the only consistent deficit in both experiments occurred for the sighted in recall of words whose referents are primarily auditory. These results challenge Paivio's theory and suggest either (a) that the visual imagery used by the sighted is no more facilitating than the abstract semantic representations used by the blind or (b) that the sighted are not using visual imagery. Experiment 3 used Neisser and Kerr's (1973) imaging task. Subjects formed images of scenes in which target objects were described as either visible in the picture plane or concealed by another object and thus not visible. On an incidental recall test for the target objects, the blind, like the sighted, recalled more pictorial than concealed targets. This finding suggests that the haptic images of the blind maintain occlusion just as the visual images of the sighted do.     

Mental imagery,reasoning, and blindness

Although reasoning seems to be inextricably linked to seeing in the “mind's eye”, the evidence is equivocal. In three experiments, sighted, blindfolded sighted, and congenitally totally blind persons solved deductive inferences based on three sorts of relation: (a) visuo-spatial relations that are easy to envisage either visually or spatially, (b) visual relations that are easy to envisage visually but hard to envisage spatially, and (c) control relations that are hard to envisage both visually and spatially. In absolute terms, congenitally totally blind persons performed less accurately and more slowly than the sighted on all such tasks. In relative terms, however, the visual relations in comparison with control relations impeded the reasoning of sighted and blindfolded participants, whereas congenitally totally blind participants performed the same with the different sorts of relation. We conclude that mental images containing visual details that are irrelevant to an inference can even impede the process of reasoning. Persons who are blind from birth—and who thus do not tend to construct visual mental images—are immune to this visual-impedance effect.     

盲人的时间水平方向隐喻的通道特异性

通过2个实验, 考察了感觉通道对盲人的时间水平方向隐喻的影响。实验1发现, 盲人只在动作水平上存在同阅读方向一致的时间水平方向隐喻, 对表征过去的词或句子按左键反应和对表征将来的词或句子按右键反应时更快, 表明盲人用于隐喻时间的空间信息是知觉性的。实验2比较了明眼人可视组被试和明眼人遮眼组被试的时间空间隐喻, 发现明眼人可视组被试只在动作水平上存在时间水平方向隐喻, 明眼人遮眼组被试只在刺激在右侧时呈现才出现动作水平的时间水平方向隐喻。综合分析表明, 盲人和明眼人可视组被试的反应更为接近, 表明盲人的时间空间隐喻未受听觉信息的影响。盲人通过运动通道获得的空间认知代偿了视觉通道信息的缺失。     

Mental imagery, reasoning, and blindness

Although reasoning seems to be inextricably linked to seeing in the “mind's eye”, the evidence is equivocal. In three experiments, sighted, blindfolded sighted, and congenitally totally blind persons solved deductive inferences based on three sorts of relation: (a) visuo-spatial relations that are easy to envisage either visually or spatially, (b) visual relations that are easy to envisage visually but hard to envisage spatially, and (c) control relations that are hard to envisage both visually and spatially. In absolute terms, congenitally totally blind persons performed less accurately and more slowly than the sighted on all such tasks. In relative terms, however, the visual relations in comparison with control relations impeded the reasoning of sighted and blindfolded participants, whereas congenitally totally blind participants performed the same with the different sorts of relation. We conclude that mental images containing visual details that are irrelevant to an inference can even impede the process of reasoning. Persons who are blind from birth—and who thus do not tend to construct visual mental images—are immune to this visual-impedance effect.     

Properties of spatial representations: Data from sighted and blind subjects

Five questions concerning the properties of spatial representations are explored. (1) How accurately does a spatial representation correspond to the true scene? (2) If inaccurate, how does it differ? (3) Are representations of a familiar scene more accurate than those of an unfamiliar one? (4) Do representations of a scene currently in view differ from those retained in memory? (5) Do the representations of the blind have properties comparable to those-of the sighted? Seven sighted and 7 highly mobile blind subjects, all familiar with a room, and 6 sighted subjects unfamiliar with it, were asked to estimate the absolute distances between 10 salient objects in the room. The 14 familiar subjects made their estimates twice: while they were in the room, and while they were remote from it. Regression analyses showed that the estimates of all subjects had strong metric properties, being linearly related to true distance, with a true zero point; and multidimensional scaling showed that all subjects produced distance estimates that could be scaled in two dimensions to closely match the actual locations of the objects. Familiarity had no effect. The effect of location of testing was the same for both the sighted and the blind: all subjects displayed better spatial knowledge when tested in the room; and all subjects underestimated true distance substantially when tested out of the room. The results showed no qualitative differences as a function of blindness, at least for these highly skilled blind travelers.     

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.     

Obstacle Crossing Differences Between Blind and Blindfolded Subjects After Haptic Exploration

Little is known about the ability of blind people to cross obstacles after they have explored haptically their size and position. Long-term absence of vision may affect spatial cognition in the blind while their extensive experience with the use of haptic information for guidance may lead to compensation strategies. Seven blind and 7 sighted participants (with vision available and blindfolded) walked along a flat pathway and crossed an obstacle after a haptic exploration. Blind and blindfolded subjects used different strategies to cross the obstacle. After the first 20 trials the blindfolded subjects reduced the distance between the foot and the obstacle at the toe-off instant, while the blind behaved as the subjects with full vision. Blind and blindfolded participants showed larger foot clearance than participants with vision. At foot landing the hip was more behind the foot in the blindfolded condition, while there were no differences between the blind and the vision conditions. For several parameters of the obstacle crossing task, blind people were more similar to subjects with full vision indicating that the blind subjects were able to compensate for the lack of vision.