Keep an eye on your hands: on the role of visual mechanisms in processing of haptic space

The present paper reviews research on a haptic orientation processing. Central is a task in which a test bar has to be set parallel to a reference bar at another location. Introducing a delay between inspecting the reference bar and setting the test bar leads to a surprising improvement. Moreover, offering visual background information also elevates performance. Interestingly, (congenitally) blind individuals do not or to a weaker extent show the improvement with time, while in parallel to this, they appear to benefit less from spatial imagery processing. Together this strongly points to an important role for visual processing mechanisms in the perception of haptic inputs

Comparison of the haptic and visual deviations in a parallelity task

Deviations in both haptic and visual spatial experiments are thought to be caused by a biasing influence of an egocentric reference frame. The strength of this influence is strongly participant-dependent. By using a parallelity test, it is studied whether this strength is modality-independent. In both haptic and visual conditions, large, systematic and participant-dependent deviations were found. However, although the correlation between the haptic and visual deviations was significant, the explained variance due to a common factor was only 20%. Therefore, the degree to which a participant is “egocentric” depends on modality and possibly even more generally, on experimental condition

Cross-modal visuo-haptic mental rotation: comparing objects between senses

The simple experience of a coherent percept while looking and touching an object conceals an intriguing issue: different senses encode and compare information in different modality-specific reference frames. We addressed this problem in a cross-modal visuo-haptic mental rotation task. Two objects in various orientations were presented at the same spatial location, one visually and one haptically. Participants had to identify the objects as same or different. The relative angle between viewing direction and hand orientation was manipulated (Aligned versus Orthogonal). In an additional condition (Delay), a temporal delay was introduced between haptic and visual explorations while the viewing direction and the hand orientation were orthogonal to each other. Whereas the phase shift of the response time function was close to 0° in the Aligned condition, we observed a consistent phase shift in the hand’s direction in the Orthogonal condition. A phase shift, although reduced, was also found in the Delay condition. Counterintuitively, these results mean that seen and touched objects do not need to be physically aligned for optimal performance to occur. The present results suggest that the information about an object is acquired in separate visual and hand-centered reference frames, which directly influence each other and which combine in a time-dependent manner

The haptic perception of spatial orientations

This review examines the isotropy of the perception of spatial orientations in the haptic system. It shows the existence of an oblique effect (i.e., a better perception of vertical and horizontal orientations than oblique orientations) in a spatial plane intrinsic to the haptic system, determined by the gravitational cues and the cognitive resources and defined in a subjective frame of reference. Similar results are observed from infancy to adulthood. In 3D space, the haptic processing of orientations is also anisotropic and seems to use both egocentric and allocentric cues. Taken together, these results revealed that the haptic oblique effect occurs when the sensory motor traces associated with exploratory movement are represented more abstractly at a cognitive level

Tactual perception: a review of experimental variables and procedures

This paper reviews literature on tactual perception. Throughout this review we will highlight some of the most relevant variables in touch literature: interaction between touch and other senses; type of stimuli, from abstract stimuli such as vibrations, to two- and three-dimensional stimuli, also considering concrete stimuli such as the relation between familiar and unfamiliar stimuli or the haptic perception of faces; type of participants, separating studies with blind participants, studies with children and adults, and an analysis of sex differences in performance; and finally, type of tactile exploration, considering conditions of active and passive touch, the relevance of movement in touch and the relation between exploration and time. This review intends to present an organised overview of the main variables in touch experiments, attending to the main findings described in literature, to guide the design of future works on tactual perception and memory.This work was funded by the Portuguese “Foundation for Science and Technology” through PhD scholarship SFRH/BD/35918/2007

The effects of size changes on haptic object recognition

Two experiments examined the effects of size changes on haptic object recognition. In Experiment 1, participants named one of three exemplars (a standard-size-and-shape, different-size, or different-shape exemplar) of 36 categories of real, familiar objects. They then performed an old/new recognition task on the basis of object identity for the standard exemplars of all 36 objects. Half of the participants performed both blocks visually; the other half performed both blocks haptically. The participants were able to efficiently name unusually sized objects haptically, consistent with previous findings of good recognition of small-scale models of stimuli (Lawson, in press). However, performance was impaired for both visual and haptic old/new recognition when objects changed size or shape between blocks. In Experiment 2, participants performed a short-term haptic shapematching task using 3-D plastic models of familiar objects, and as in Experiment 1, a cost emerged for ignoring the irrelevant size change. Like its visual counterpart, haptic object recognition incurs a significant but modest cost for generalizing across size changes. © 2009 The Psychonomic Society, Inc

Representations of space based on haptic input

The present thesis focused on the representations of grasping space based on haptic input. We aimed at identifying their characteristics, and the underlying neurocognitive processes and mechanisms. To this end, we studied the systematic distortions in performance on several orientation perception tasks, and identified some of the circumstances under which they occur. In addition to examining performance of blindfolded sighted participants on several tasks (Chapters 2, 3 and 4), we looked at differences between specific groups. Performances by the early blind, the late blind and the sighted were compared in Chapters 5 and 6. In Chapter 7 differences between male and female performances were examined. We found that systematic biases in egocentric referencing are responsible for the systematic deviations in haptic tasks requiring the representation of orientation. Importantly, it seems that these deviations can be traced back to the employment of one particular egocentric reference frame: the hand. The extent of misalignment of hand orientation with the body’s midsagittal plane was found to be related to the size of the deviation (Chapter 3). In addition, the deviations all seem to result from biases in perception; complementary deviation patterns of performance on a verbal judgment and an orientation production task suggested that also in tasks that require a motor response the deviations do not result from egocentric reference frames involved in the actual rotation of the bar (Chapter 7). However, the impact of hand orientation on haptic orientation perception appeared to depend highly on the precise task characteristics (Chapters 2, 3, 4, 5 and 7). Temporal manipulations (Chapters 2 and 3), orienting direction (Chapter 4) and the extent to which a task stimulates specific processes like (mental) allocentric frame employment and (visuo)spatial imagery (Chapters 3, 4, 5, 7), appeared to have direct consequences for the size of the deviation. Basically, the findings suggest that the more allocentric reference frame employment and mental imagery is stimulated, the smaller the deviations in haptic orientation perception. With respect to orienting, we found that, in parallel-setting orienting towards the reference bar enhanced performance. In addition to task characteristics, we found that the visual status and sex of the observer, as well as hand use affected haptic spatial performance. Also the effects of visual status seem to depend on task characteristics. Chapter 5 suggested that visual experience becomes increasingly important in haptic orientation perception tasks that stimulate allocentric reference frame employment. Furthermore, Chapter 6 suggested that visual experience becomes increasingly important if tasks address more explicit spatial knowledge. With respect to sex differences, we can conclude that, in general, males outperform females on allocentric haptic orientation tasks (Chapter 7). Interestingly, we found specific sex differences with respect to hand use; male’s left hand performance was better than males right hand performance, and than female performance in general. This suggests that haptic spatial integration mechanisms in males may be more lateralized than in women (i.e., located mainly in the right hemisphere)

Effects of hand orientation and delay on the verbal judgment of haptically perceived orientation

We examined the haptic perception of orientations of a single bar throughout the horizontal plane using a verbal response: participants were to assign a number of minutes to the orientation of a bar defined with respect to the stimulus table. Performance was found to be systematically biased. Deviations were consistent with, yet much smaller than, those resulting from haptic motor matching tasks. The size and direction of the deviations were found to correlate with hand orientation, and not to depend on spatial location per se, suggesting a role for hand-centred reference frames in biasing performance. Delaying the response by 10 s led to a small improvement only of right-hand perceptions, indicating different hemispheric involvement in processes involved in retaining and/or recoding of haptic orientation information. Also the haptic oblique effect was found with the current verbal response. Importantly, it was affected neither by hand orientation nor by delay, suggesting that the oblique effect is independent of the aforementioned deviations in orientation perception