Florence Gaunet

Representation of space in blind persons : Vision as a spatial sense ?

Some researchers of studies of the incidence of early visual experience on spatial abilities have demonstrated profound spatial deficits in early blind participants, whereas others have not found evidence of deleterious effects of early visual deprivation. The aims of this article are to (a) consider the theoretical background of these studies, (b) take stock of the divergent data, and (c) propose new means of investigation. The authors examine the reasons why vision plays a critical role in spatial cognition. They review the literature data. They also review the factors that could account for the discrepant data and the effects of lack of early visual experience on brain functioning. They propose that the study of strategies is a valuable option to obtain insight into early blind persons spatial impairment.

Early visual experience affects memorization and spatial representation of proprioceptive targets

FIVE subjects who had been blind from an early age and five age-matched blindfolded sighted subjects were engaged in a spatial memory task. Locations to be memorized were presented on a sagittal plane by passive positioning of the left index finger. A go signal for matching the target location with the right index finger was provided 0 or 8 s after left hand positioning. Constant errors in amplitude and direction of movement and pointing distribution observed after the longer delay differed across groups. Pointing variability was higher in the blindfolded sighted group. In addition, the main axis of pointing distributions obtained in the blindfolded sighted group were aligned with the target array for the 8 s but not the 0 s delay.1 By contrast, the main axis tended to be aligned with movement direction for blind subjects for both delays. These results suggest that memorizing a proprioceptively defined target may involve distinct spatial representations according to delay and to early visual experience.

Exploring the functional specifications of a localized wayfinding verbal aid for blind pedestrians: simple and structured urban areas

We propose functional specifications for a localized verbal wayfinding aid for blind pedestrians, in simple and structured urban areas. A user-centered design approach, that is, the analyses of route descriptions produced by blind pedestrians, allowed first to evidence verbal guidance rules and then to elaborate route descriptions of unfamiliar paths; their efficiency was confirmed. We found that specific database features are streets, sidewalks, crosswalks, and intersections and that guidance functions consist of a combination of orientation and localization, goal location, intersection, crosswalks, and warning information as well as of progression, crossing, orientation, and route-ending instructions; they have to be provided between 5 to 10 meters before an intersection, after crossing, at middle block, and after entering a street. Last, verbal guidance is possible in simple and structured urban areas, with no localization aid, and is optimal within 5 meters precision. The outcomes and limits of the requirements of the navigational aid evidenced are discussed.

Early-Blind Subjects' Spatial Abilities in the Locomotor Space: Exploratory Strategies and Reaction-to-Change Performance

The present study was aimed at analysing the effect of the lack of visual experience in the human subject in detecting the rearrangement of objects after a free exploration in the locomotor space. Exploratory patterns and performance levels were recorded. Distance processing was affected by early blindness. The early-blind groups patterns of exploration differed significantly from those of the visually experienced groups. Significant correlations were found between the performance level and the use of systematic patterns of exploration but not with individual features. These data are discussed in the light of the importance of early vision on the development of spatial cognition.

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

Congenially 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.

Early-blind subjects' spatial representation of manipulatory space : exploratory strategies and reaction to change

The present study was aimed at analysing the effects of a lack of visual experience in human subjects on the detection and identification of a spatial change brought about to a configuration of objects displayed in manipulatory space. Exploratory patterns and performance levels were recorded. Learning effects were observed in different types of change and condition of presentation only in the early-blind and blindfolded sighted groups, but not in the late-blind group. Early blindness affected both exploratory patterns and performance levels. In addition, significant correlations were found between performance level and the use of systematic patterns of exploration. These data are discussed in relation with the importance of early vision during the development of spatial cognition.

Verbal guidance rules for a localized wayfinding aid intended for blind-pedestrians in urban areas

Automatic wayfinding verbal aids for blind pedestrians in simple and structured urban areas are claimed to rely on specific database features and guidance functions (i.e., instructions and spatial information provided at specific places). This paper reports an experiment in which these requirements for such areas, and for complex and unstructured urban areas, were tested by 7 cane- and 3 dog-users. Very few hesitations and errors along with the need for few modifications of the verbal guidance rules and for a one-meter localization device for traversing crosswalks were found. Further research issues for designing a localized verbal navigational aid are also presented (i.e., extension/diversification of the population and gradual introduction of the interface).

Pointing with the left and right hands in congenitally blind children

Congenitally blind and blindfolded sighted children at ages of 6, 8, 10 and 12 years performed a pointing task with their left and right index fingers at an array of three targets on a touch screen to immediate (0 s) and delayed (4 s) instructions. Accuracy was greater for immediate than delayed pointing and there was an effect of delay for the orientation of the main axis of the pointing distribution in both groups, indicating distinct spatial representations with development such as ego- and allocentric frames of reference, respectively. The pointing responses of the blind covered less surface area indicating better overall accuracy as compared to the sighted blindfolded. The hands differed for four of the six precision and accuracy parameters. The right hand performed better and seemed relatively contextually oriented, whereas the responses of the left hand were closer to the body and egocentrically oriented. The elongation of the scatter of the pointing responses was greater for the boys and more allocentrically oriented, indicating gender differences in spatial representation. The study provides a first evidence of ego- and allocentric spatial frames of reference in congenitally blind children and an ability to point at targets with the left and right hands in the total absence of vision.

When facing an unfamiliar person, pet dogs present social referencing based on their owners' direction of movement alone

When confronted with an unfamiliar object, dogs, Canis familiaris, engage in social referencing, i.e. synchronizing their reaction with that of their owner. The question of whether, like infants, they do so when confronted with an unfamiliar person, has not yet been studied. We tested the reactions of 72 pet dogs (36 shepherds and 36 molossoids) that were confronted with an unfamiliar person who approached them in a neutral manner. The dogs owners were instructed to behave in one of three ways towards the stranger: stay still, approach or retreat. The dogs performed referential looks and gaze alternations between the experimenter and their owner. In the retreat condition, the dogs looked at the stranger significantly sooner and took significantly more time before first contact with the stranger compared to the approach condition. Moreover, in the retreat condition the dogs interacted more with their owners compared to other conditions. Additionally, sex had an effect on dogs behaviours, with males looking towards their owner for information less than females. Breed also influenced dogs reactions, with molossoid dogs behaving more independently than shepherd dogs. This study shows that pet dogs use social referencing with their owner in an approach paradigm involving a stranger. These findings provide evidence of similar processes in dogs with their owners and human infants with caregivers, and suggest a new way to manage dogs reactions in public places.

Pointing at targets by children with congenital and transient blindness

The study investigated pointing at memorized targets in reachable space in congenitally blind (CB) and blindfolded sighted (BS) children (6, 8, 10 and 12xa0years; ten children in each group). The target locations were presented on a sagittal plane by passive positioning of the left index finger. A go signal for matching the target location with the right index finger was provided 0 or 4xa0s after demonstration. An age effect was found only for absolute distance errors and the surface area of pointing was smaller for the CB children. Results indicate that early visual experience and age are not predictive factors for pointing in children. The delay was an important factor at all ages and for both groups, indicating distinct spatial representations such as egocentric and allocentric frames of reference, for immediate and delayed pointing, respectively. Therefore, the CB like the BS children are able to use both ego- and allocentric frames of reference.