The utilization of external and movement cues in simple spatial tasks by blind and sighted children

Models of Sensory Deprivation: The Nature/Nurture Dichotomy and Spatial Representation in the Blind

It is argued that models of sensory deprivation often depend on a nativist versus empiricist dichotomy which has little basis in empirical fact. Fallacies about the nature of abilities and learning and about the interaction between sense modalities which follow from the dichotomy are examined in relation to explanations of spatial development in the blind. It is suggested that interactions between cognitive and perceptual factors need to be taken into account in order to explain the effects of sensory deprivation more adequately.

Movement Imagery in Young and Congenitally Blind Children: Mental Practice without Visuo-spatial Information

The study explored whether young children and congenitally totally blind children show mental practice effects for blind movements which cross the body midline. Experiment 1 tested blindfolded sighted children, with a mean age of 7 years and 11 months, on recall of a linear movement. Prior to recall, subjects either had to perform, or to imagine irrelevant (larger/smaller/same) movements. Irrelevant movements produced significant bias (CE/Constant Errors), whether carried out or imaged, although bias from imagined movements was smaller. The VE (variance/consistency) scores improved with (actual and mental) rehearsal. Articulatory suppression during delays had no effect. Experiment 2 used the same paradigm to test three groups of congenitally totally blind children with respective mean Mental Ages (MA) of 10 years and 7 months, 13 years and 7 months, and 16 years and 4 months, based on IO scores on the Williams Intelligence Test (1956) for visually handicapped children. Irrelevant movements during delays produced bias (CE) in recall, whether the movements were carried out or imagined, although bias was smaller in imagery conditions. The (CE) bias effects did not interact with MA. Mental Age interacted significantly with Delay Tasks in VE scores. The lowest MA group was less efficient (more variable) than the others, particularly in (actual and imagined) rehearsal. Articulatory suppression had no effect. The results suggest that young children can show mental practice effects in the absence of current visual cues, and that visuospatial imagery is not a necessary condition, because imagined movements also biased recall by the congenitally totally blind. It was argued that movement as well as cognitive factors can be involved in mental practice effects, and that the nature of mediation depends on the available information.

Are there relationships among different spatial skills of individuals with blindness?

The aim of this study was to detect the possible relationships between various spatial skills of individuals with blindness. Twenty-eight individuals with blindness participated in five experiments that examined the body knowledge, laterality, directionality, perspective-taking, spatial coding of the near space and spatial knowledge of the far space. According to the results a positive correlation between body knowledge and directionality has emerged. Moreover, body knowledge and spatial coding of near space are found to be predictors of perspective-taking, while directionality and perspective-taking are found to be predictors of spatial coding of near space, and directionality and perspective-taking predictors of spatial knowledge of far space. This finding suggest that future studies should seriously take into account the possibility that the development of a certain skill could in fact be the result of the development of another skill/s. Moreover, the findings support the notion that a delay in the development of a spatial skill may not necessarily be a result of the visual impairment itself but of the incomplete development of another spatial skill.

Accuracy and Coordination of Spatial Frames of Reference during the Exploration of Virtual Maps: Interest for Orientation and Mobility of Blind People?

Even if their spatial reasoning capabilities remain quite similar to those of sighted people, blind people encounter difficulties in getting distant information from their surroundings. Thus, whole body displacements, tactile map consultations, or auditory solutions are needed to establish physical contacts with their environment. Therefore, the accuracy of nonvisual spatial representations heavily relies upon the efficiency of exploration strategies and the ability to coordinate egocentric and allocentric spatial frames of reference. This study aims to better understand the mechanisms of this coordination without vision by analyzing cartographic exploration strategies and assessing their influence on mental spatial representations. Six blind sailors were immersed within a virtual haptic and auditory maritime environment. They were required to learn the layout of the map. Their movements were recorded and we identified some exploration strategies. Then they had to estimate the directions of six particular seamarks in aligned and misaligned situations. Better accuracy and coordination were obtained when participants used the “central point of reference” strategy. Our discussion relative to the articulation between geometric enduring representations and salient transient perceptions provides implications on map reading techniques and on mobility and orientation programs for blind people.

The impact of vision in spatial coding

The aim of this study is to examine the performance in coding and representing of near-space in relation to vision status (blindness vs. normal vision) and sensory modality (touch vs. vision). Forty-eight children and teenagers participated. Sixteen of the participants were totally blind or had only light perception, 16 were blindfolded sighted individuals, and 16 were non-blindfolded sighted individuals. Participants were given eight different object patterns in different arrays and were asked to code and represent each of them. The results suggest that vision influences performance in spatial coding and spatial representation of near space. However, there was no statistically significant difference between participants with blindness who used the most effective haptic strategy and blindfolded sighted participants. Thus, the significance of haptic strategies is highlighted.

Prior visual experience, and perception and memory of shape in people with total blindness

The aim of this study was to explore the role of prior visual experience for tactile differentiation of object shapes. The study investigated whether people who lost their vision later in life were able to identify and recognize object shapes more accurately and faster than those who were blind from their birth. Four experiments were conducted. The first two were concerned with tactile shape differentiation, the second two with shape recognition. The hypotheses were only partially confirmed. The ‘late’ blind participants distinguished shapes more accurately than the congenitally blind (particularly in ‘simple’ perception tasks). This finding may suggest that people who have prior visual experience use an allocentric strategy when visualizing object shapes in their imagery. The ‘late’ blind participants performed the tasks more slowly than those who were congenitally blind. This may be explained by the complexity of the task, the time needed to create an allocentric representation, and discrepancy in the tactile experiences between the congenitally and late blind groups. A number of implications for further research are outlined.

Differences between early-blind, late-blind, and blindfolded-sighted people in haptic spatial-configuration learning and resulting memory traces

The roles of visual and haptic experience in different aspects of haptic processing of objects in peripersonal space are examined. In three trials, early-blind, late-blind, and blindfolded-sighted individuals had to match ten shapes haptically to the cut-outs in a board as fast as possible. Both blind groups were much faster than the sighted in all three trials. All three groups improved considerably from trial to trial. In particular, the sighted group showed a strong improvement from the first to the second trial. While superiority of the blind remained for speeded matching after rotation of the stimulus frame, coordinate positional-memory scores in a non-speeded free-recall trial showed no significant differences between the groups. Moreover, when assessed with a verbal response, categorical spatial-memory appeared strongest in the late-blind group. The role of haptic and visual experience thus appears to depend on the task aspect tested.

Effects of visual deprivation on space representation: immediate and delayed pointing toward memorised proprioceptive targets

Congenitally blind, late-blind, and blindfolded-sighted participants performed a pointing task at proximal memorised proprioceptive targets. The locations to be memorised were presented on a sagittal plane by passively positioning the left index finger. A 'go' signal for matching the target location with the right index finger was given 0 or 8 s after left-hand demonstration. Absolute distance errors were smaller in the blind groups, with both delays pooled together; signed distance and direction errors were underestimated with the longer delay, and were overestimated by blind groups, whereas the blindfolded-sighted group underestimated them. Elongation of the scatters was stretched but not affected by delay or group. The surface scatter was greater with the longer delay; and orientation of the main axis of the pointing ellipses shows the use of an egocentric frame of reference by the congenitally blind group for both delays, the use of egocentric (0 s) and exocentric (8 s) frame of reference by the blindfolded-sighted group, with the late-blind group using an intermediate frame of reference for both delays. Therefore, early and late visual-deprivation effects are distinguished from transient visual-deprivation effects as long-term deprivation leads to increased capabilities (absolute distance estimations), unaltered organisation (for surface and elongation), and altered organisation (amplitude and direction estimations, orientation of pointing distribution) of the spatial representation with proprioception. Besides providing an extensive exploration of pointing ability and mechanisms in the visually deprived population, the results show that cross-modal plasticity applies not only to neural bases but extends to spatial behaviour.

External and body-centered frames of reference in spatial memory: Evidence from touch

The study reports independent effects of external and body-centered reference cues on spatial coding of an irregular sequence of haptic locations. The aim was to investigate the nature of spatial coding by using a modality that does not provide distal cues routinely. Our method isolates and combines body-centered and external spatial reference cues for irregularly placed locations, scanned along a raised-line route. Disrupting body-centered reference for the locations, by orienting the map differently to the body in the test phase than in the presentation phase, doubled errors in positioning the locations along the route in recall. Adding external reference, by giving instructions to use a surrounding frame for reference when body-centered coding was disrupted, reduced errors to near baseline (no-rotation) levels. Adding external reference cues to intact (not displaced) body-centered reference halved errors, as compared with the baseline. The results are consistent with the hypothesis that accurate spatial coding is determined by the congruence of potential reference cues from diverse sources. The new findings suggest that external and body-centered reference cues have independent additive effects on spatial coding. The sequence of locations had a significant effect in all the reference conditions, suggesting the additional use of fortuitous but distinctive local touch cues on the route. The discussion considers theoretical and practical implications of the results.

Development of anticipatory orienting strategies during locomotor tasks in children

Some basic problems related to the development of goal-directed locomotion in humans are reviewed here. A preliminary study is presented which was aimed at investigating the emergence of anticipatory head orienting strategies during goal-directed locomotion in children. Eight children ranging from 3.5 to 8 years had to walk along a 90 degrees right corner trajectory to reach a goal, both in light and in darkness. The instantaneous orientation in space of the head, trunk, hips and left foot antero/posterior axes was computed by means of an ELITE four-TV camera, 100 Hz system. The results showed that predictive head orienting movements can occur also in the youngest children. The head starts to rotate toward the goal before the corner point of the trajectory is reached. In children, the head peak rotation coincides with the trajectory corner while in adults the peak is attained before. In children, the walking speed is largely decreased in darkness. The results suggest that feedforward control of goal-directed locomotion appears very early in gait development and becomes increasingly important afterwards.

Haptic discrimination of bilateral symmetry in 2-dimensional and 3-dimensional unfamiliar displays

In five experiments, we tested the accuracy and sensitivity of the haptic system in detecting bilateral symmetry of raised-line shapes (Experiments 1 and 2) and unfamiliar 3-D objects (Experiments 3-5) under different time constraints and different modes of exploration. Touch was moderately accurate for detecting this property in raised displays. Experiment 1 showed that asymmetric judgments were systematically more accurate than were symmetric judgements with scanning by one finger. Experiments 2 confirmed the results of Experiment 1 but also showed that bimanual exploration facilitated processing of symmetric shapes without improving asymmetric detections. Bimanual exploration of 3-D objects was very accurate and significantly facilitated processing of symmetric objects under different time constraints (Experiment 3). Unimanual exploration did not differ from bimanual exploration (Experiment 4), but restricting hand movements to one enclosure reduced performance significantly (Experiment 5). Spatial reference information, signal detection measures, and hand movements in processing bilateral symmetry by touch are discussed.

Mental rotation of a tactile layout by young visually impaired children

Mental rotation tasks have been used to probe the mental imagery both of sighted and of visually impaired people. People who have been blind since birth display a response pattern which is qualitatively similar to that of sighted people but tend to respond more slowly or with a higher error rate. It has been suggested that visually impaired people code the stimulus and its (or their own) motion in a different way from sighted people-in particular, congenitally blind people may ignore the external reference framework provided by the stimulus and surrounding objects, and instead use body-centred or movement-based coding systems. What has not been considered before is the relationship between different strategies for tactually exploring the stimulus and the response pattern of congenitally blind participants. Congenitally blind and partially sighted children were tested for their ability to learn and recall a layout of tactile symbols. Children explored layouts of one, three, or five shapes which they then attempted to reproduce. On half the trials there was a short pause between exploring and reproducing the layouts. In an aligned condition children reproduced the array from the same position at which they had explored it; in a rotated condition children were asked to move 90 degrees round the table between exploring and reproducing the layout. Both congenitally blind and partially sighted children were less accurate in the rotated condition than in the aligned condition. Five distinct strategies used by the children in learning the layout were identified. These strategies interacted with both visual status and age. We suggest that the use of strategies, rather than visual status or chronological age, accounts for differences in performances between children.

The haptic 'oblique effect' in children's and adults' perception of orientation

The haptic perception of vertical, horizontal, and diagonal orientations was studied in children (aged 7 and 9 years) and in adults. The purpose was to test the hypothesis that the haptic oblique effect results from the different scanning movements at work when one hand explores an oblique standard and the other hand sets the response rod. In experiment 1, blindfolded subjects reproduced the orientation of a standard rod presented in either the frontal, the horizontal, or the sagittal plane, and this task was achieved either ipsilaterally (the same hand explored the standard and set the response rod) or contralaterally (one hand explored the standard and the other hand set the response rod). Since, in the sagittal plane, scanning movements are analogous when the left and right hands explore oblique orientations, no oblique effect should be observed in this condition if the hypothesis is valid. Moreover, a development effect should be observed, since young children generally rely more on movement coding than do older children and adults. Results did not support these predictions: the same oblique effect appeared in the frontal and the sagittal planes both in the ipsilateral and in the contralateral condition, and the effect of age was not in the direction predicted by the hypothesis. The results were consistent with the hypothesis in the horizontal plane only. Experiments 2 and 3 provided further tests of this hypothesis but both failed to support it. Taken together, the results of these three experiments did not support the assumption and it is suggested that the haptic oblique effect may be linked to the gravitational cues provided by the arm-hand system when it acts in the three spatial planes.

Tactile localisation: the function of active antennal movements in the crayfish Cherax destructor

Video recordings and single frame analysis were used to study the function of the second antennae of crayfish (Cherax destructor) as a sensory system in freely behaving animals. Walking crayfish move their antennae back and forth through horizontal angles of 100 degrees and more, relative to the body long axis. At rest, animals tend to hold their antennae at angular positions between 20 and 50 degrees. Movements of the two antennae are largely independent of each other. Before and during a turn of the body the ipsilateral antenna is moved into the direction of the turn. Solid objects are explored by repeatedly moving the antennae towards and across them. Both seeing and blinded crayfish can locate stationary objects following antennal contact. On antennal contact with a small novel object, a moving animal withdraws its antenna and attacks the object. When the antenna of a blinded crayfish is lightly touched with a brush the animal turns and attacks the point of stimulation. The direction taken and the distance covered during an attack can be correlated with: the angle at which the antenna is held at the moment of contact and the distance along the antennal flagellum at which the stimulus is applied. From behavioural evidence we conclude that crayfish use information about the angular position of their antennae and about the position of stimulated mechanoreceptors along the antennal flagellum to locate objects in their environment. We suggest ways in which an active tactile system-like the crayfish's antennae--could supply animals with information about the three-dimensional layout of their environment.

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.

Memory for Movement in Blind Children

The role of previous visual experience in the reproduction of a criterion movement was examined in sighted, late-blinded, and congenitally blind children. Results showed that the congenitally blind reproduce movements at a low level of accuracy compared with the other two groups. Detailed analysis showed that although the congenitally blind could reproduce the extent of the movement accurately, the movement was poorly reproduced in terms of its orientation to the criterion movement and its orientation from a reference point. The role of prior vision in establishing a frame of reference is discussed.

Self-referent and movement cues in coding spatial location by blind and sighted children

The study tested the hypothesis that movement and self-referent information differ, and that children can use both to code unseen locations. In one experiment blindfolded sighted children made more errors with changed than with unchanged accessing movements, despite unchanged reference conditions. Rotation decreased accuracy further, although most responses were to the correct side. Age did not interact with experimental conditions. In another experiment blind children and matched blindfolded controls were less accurate with changed movements; and rotations were more difficult still. Visual experience, but not age, interacted with conditions. The blind showed significantly more self-reference (responses to the original side in rotations), and were somewhat worse also with changed movements alone but did not differ from controls when movements and references were unchanged. The results support the hypothesis that movement and self-referent information differ. Visuospatial experience and task conditions rather than age seem to determine the extent to which children use either form of information.