Representations of space based on haptic input

Abstract

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).