Adults' spatial scaling of tactile maps: Insights from studying sighted, early and late blind individuals

The current study investigated spatial scaling of tactile maps among blind adults and blindfolded sighted controls. We were specifically interested in identifying spatial scaling strategies as well as effects of different scaling directions (up versus down) on participants' performance. To this aim, we asked late blind participants (with visual memory, Experiment 1) and early blind participants (without visual memory, Experiment 2) as well as sighted blindfolded controls to encode a map including a target and to place a response disc at the same spot on an empty, constant-sized referent space. Maps had five different sizes resulting in five scaling factors (1:3, 1:2, 1:1, 2:1, 3:1), allowing to investigate different scaling directions (up and down) in a single, comprehensive design. Accuracy and speed of learning about the target location as well as responding served as dependent variables. We hypothesized that participants who can use visual mental representations (i.e., late blind and blindfolded sighted participants) may adopt mental transformation scaling strategies. However, our results did not support this hypothesis. At the same time, we predicted the usage of relative distance scaling strategies in early blind participants, which was supported by our findings. Moreover, our results suggested that tactile maps can be scaled as accurately and even faster by blind participants than by sighted participants. Furthermore, irrespective of the visual status, participants of each visual status group gravitated their responses towards the center of the space. Overall, it seems that a lack of visual imagery does not impair early blind adults' spatial scaling ability but causes them to use a different strategy than sighted and late blind individuals.

Effects of using multiple hands and fingers on haptic performance

It remains controversial whether using two hands and multiple fingers provides any perceptual advantage over a single index finger. The present study examines this long-running question in the haptic-exploration literature by applying rigorous, psychophysical, and mathematical modeling techniques. We compared the performance of fourteen blindfolded sighted participants on seven tactile-map tasks using seven finger conditions. All tasks were benefited by multiple fingers, but it varied whether multiple fingers were beneficial on one hand, two hands, or both. Line-tracing tasks were performed faster when two hands were used, but not more than one finger per hand. Local and global search tasks were faster with multiple fingers, but not two hands. Distance comparison tasks were also performed faster with multiple fingers, and sometimes with two hands. Lastly, moving in a straight line was faster with multiple fingers, but was especially difficult with just two index fingers. These results provide empirical evidence that multiple hands and fingers benefit haptic perception, but the benefits are more complex than simply extending the tactile field of 'view'. This analogy between touch and vision fails to account for the autonomous movements and sensations of the fingers, which we show benefit the haptic perceptual system.

Colour, face, and visuospatial imagery abilities in low-vision individuals with visual field deficits

This study investigates to what extent visual perception integrity is necessary for visual mental imagery. Sixteen low-vision participants with severe peripheral visual field loss, 16 with severe central field loss, 6 left brain-damaged patients with right homonymous hemianopia, 6 right brain-damaged patients with left homonymous hemianopia, and 16 normally sighted controls performed perceptual and imagery tasks using colours, faces, and spatial relationships. Results showed that (a) the perceptual and mental image>ry disorders vary according to the type of visual field loss, (b) hemianopics had no more difficulties imagining spatial stimuli in their contralesional hemispace than in their ipsilesional one, and (c) the only hemianopic participant to have perceptual and mental imagery impairments suffered from attentional deficits. Results suggest that (a) visual memory is not definitively established, but rather needs perceptual practice to be maintained, and (b) that visual mental imagery may involve some of the attentional-exploratory mechanisms that are employed in visual behaviour.

A putative model of multisensory object representation

This review surveys the recent literature on visuo-haptic convergence in the perception of object form, with particular reference to the lateral occipital complex (LOC) and the intraparietal sulcus (IPS) and discusses how visual imagery or multisensory representations might underlie this convergence. Drawing on a recent distinction between object- and spatially-based visual imagery, we propose a putative model in which LOtv, a subregion of LOC, contains a modality-independent representation of geometric shape that can be accessed either bottom-up from direct sensory inputs or top-down from frontoparietal regions. We suggest that such access is modulated by object familiarity: spatial imagery may be more important for unfamiliar objects and involve IPS foci in facilitating somatosensory inputs to the LOC; by contrast, object imagery may be more critical for familiar objects, being reflected in prefrontal drive to the LOC.

Vision and touch: multiple or multisensory representations of objects?

The relationship between visually and haptically derived representations of objects is an important question in multisensory processing and, increasingly, in mental representation. We review evidence for the format and properties of these representations, and address possible theoretical models. We explore the relevance of visual imagery processes and highlight areas for further research, including the neglected question of asymmetric performance in the visuo-haptic cross-modal memory paradigm. We conclude that the weight of evidence suggests the existence of a multisensory representation, spatial in format, and flexibly accessible by both bottom-up and top-down inputs, although efficient comparison between modality-specific representations cannot entirely be ruled out.

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.

Does men’s advantage in mental rotation persist when real three-dimensional objects are either felt or seen?

In several spatial tasks in which men outperform women in the processing of visual input, the sex difference has been eliminated in matching contexts limited to haptic input. The present experiment tested whether such contrasting results would be reproduced in a mental rotation task. A standard visual condition involved two-dimensional illustrations of three-dimensional stimuli; in a haptic condition, three-dimensional replicas of these stimuli were only felt; in an additional visual condition, these replicas were seen. The results indicated that, irrespective of condition, men's response times were shorter than women's, although accuracy did not significantly differ according to sex. For both men and women, response times were shorter and accuracy was higher in the standard condition than in the haptic one, the best performances being recorded when full replicas were shown. Self-reported solving strategies also varied as a function of sex and condition. The discussion emphasizes the robustness of men's faster speed in mental rotation. With respect to both speed and accuracy, the demanding sequential processing called for in the haptic setting, relative to the standard condition, is underscored, as is the benefit resulting from easier access to depth cues in the visual context with real three-dimensional objects.

Haptic identification of rotated letters using the left or right hand

The present study investigated the effects of the use of the left and right hands on haptic identification of letters which were presented in either a normal (0 degrees rotation), downward (90 degrees clockwise rotation), upside down (180 degrees rotation), or facing upward (270 degrees rotation) position. Each of the 80 right-handed subjects was given five series of randomly ordered presentations of sets of 8 letters of the alphabet. The subjects were asked to feel and then name each letter correctly as quickly but as accurately as possible. Times showed no effect of hand, but significant effects were found for different sets of letters, degree of rotation and a significant decrease in identification time was observed across the five series. Interactions occurred between hand and rotation as well as set and rotation. Errors showed a significant interaction of hand with degree of rotation; the right was superior at 0 degrees but the left was superior at 90 degrees. The results were discussed in terms of hypotheses of hemisphere function, mental rotation, and stimulus familiarity.