Kinesthetic Aftereffects are in the Hands, Not in Phenomenal Space

Adaptation aftereffects reveal that tactile distance is a basic somatosensory feature

The stage at which processing of tactile distance occurs is still debated. We addressed this issue by implementing an adaptation-aftereffect paradigm with passive touch. We demonstrated the presence of a strong aftereffect, induced by the simultaneous presentation of pairs of tactile stimuli. After adaptation to two different distances, one on each hand, participants systematically perceived a subsequent stimulus delivered to the hand adapted to the smaller distance as being larger. We further investigated the nature of the aftereffects, demonstrating that they are orientation- and skin-region-specific, occur even when just one hand is adapted, do not transfer either contralaterally or across the palm and dorsum, and are defined in a skin-centered, rather than an external, reference frame. These characteristics of tactile distance aftereffects are similar to those of low-level visual aftereffects, supporting the idea that distance perception arises at early stages of tactile processing.

Haptic adaptation to slant: No transfer between exploration modes

Human touch is an inherently active sense: to estimate an object's shape humans often move their hand across its surface. This way the object is sampled both in a serial (sampling different parts of the object across time) and parallel fashion (sampling using different parts of the hand simultaneously). Both the serial (moving a single finger) and parallel (static contact with the entire hand) exploration modes provide reliable and similar global shape information, suggesting the possibility that this information is shared early in the sensory cortex. In contrast, we here show the opposite. Using an adaptation-and-transfer paradigm, a change in haptic perception was induced by slant-adaptation using either the serial or parallel exploration mode. A unified shape-based coding would predict that this would equally affect perception using other exploration modes. However, we found that adaptation-induced perceptual changes did not transfer between exploration modes. Instead, serial and parallel exploration components adapted simultaneously, but to different kinaesthetic aspects of exploration behaviour rather than object-shape per se. These results indicate that a potential combination of information from different exploration modes can only occur at down-stream cortical processing stages, at which adaptation is no longer effective.

Influence of shape on the haptic size aftereffect

Recently, we showed a strong haptic size aftereffect by means of a size bisection task: after adaptation to a large sphere, subsequently grasped smaller test spheres felt even smaller, and vice versa. In the current study, we questioned whether the strength of this aftereffect depends on shape. In four experimental conditions, we determined the aftereffect after adaptation to spheres and tetrahedra and subsequent testing also with spheres and tetrahedra. The results showed a clear influence of shape: the haptic aftereffect was much stronger if adaptation and test stimuli were identical in shape than if their shapes were different. Therefore, it would be more appropriate to term such aftereffects haptic shape-size aftereffects, as size alone could not be the determining factor. This influence of shape suggests that higher cortical areas are involved in this aftereffect and that it cannot be due to adaptation of peripheral receptors. An additional finding is that the geometric property or combination of properties participants use in the haptic size bisection task varies widely over participants, although participants themselves are quite consistent.

Investigation into the origin of the haptic aftereffect of curved surfaces

In haptics, the perceived (phenomenal) flatness of a surface is strongly influenced by a previous surface which has been statically touched. The mechanisms underlying this haptic aftereffect of curved surfaces are investigated. It is shown that the representation of curvature abstracted from the sense of touch, ie a high-level representation, is not affected during the aftereffect. This is concluded because: (1) the aftereffect does not exhibit intermanual transfer; (2) the way in which two successive surfaces are touched can influence the magnitude of the aftereffect; and (3) it is not necessary to touch a surface-active muscular contraction can also result in a shift of the phenomenal flatness. Furthermore, it is suggested that the physiological process involved in the aftereffect is a central process, ie it is located in the brain but it is distinct for each hemisphere. This is supported by the findings that: (1) the decay rate of the aftereffect is not influenced by the degree of peripheral stimulation during the decay; and (2) the aftereffect does not transfer from the adapted hand to the unadapted hand.

Studies of movement aftereffects

213 Ss participated in 4 experiments designed to identify relationships between figural aftereffects elicited by hand, limb, and total body movements. The measures obtained were reliable and highly task specific.