Tactile facilitation during actual and mere expectation of object reception

Abstract

During reaching and grasping movements tactile processing is typically suppressed. However, during a reception or catching task, the object can still be acquired but without suppressive processes related to movement execution. Rather, tactile information may be facilitated as the object approaches in anticipation of object contact and the utilization of tactile feedback. Therefore, the current study investigated tactile processing during a reception task. Participants sat with their upper limb still as an object travelled to and contacted their fingers. At different points along the object's trajectory and prior to contact, participants were asked to detect tactile stimuli delivered to their index finger. To understand if the expectation of object contact contributed to any modulation in tactile processing, the object stopped prematurely on 20% of trials. Compared to a pre-object movement baseline, relative perceptual thresholds were decreased throughout the object's trajectory, and even when the object stopped prematurely. Further, there was no evidence for modulation when the stimulus was presented shortly before object contact. The former results suggest that tactile processing is facilitated as an object approaches an individual's hand. As well, we purport that the expectation of tactile feedback drives this modulation. Finally, the latter results suggest that peripheral masking may have reduced/abolished any facilitation.

Figure 1

Left Panel: Illustration of the experimental setup. On 80% of the trials the dowel moved 26 cm (i.e., Pre, Early, Middle and Late stimulation trials) and on 20% of the trials the dowel moved 22 cm (i.e., Late-no contact stimulation trials). The stimulus location is depicted on the right index finger in black. Note that electrodes were placed on the dorsal and palmar surface of the base of the index finger. Right Panel: Dowel velocity profiles and stimulation times when the object travelled 26 cm and made contact with the individual (i.e., 80% of trials; top graph) and when the object travelled 22 cm and did not make contact with the individual (i.e., 20% of trials; bottom graph). In all conditions, a 50 ms auditory stimulus served as a warning cue and only one stimulus was presented for each trial. Note that the only difference between the contact and no contact kinematics was the sudden stop and sharp drop off in dowel velocity in the no contact dowel velocity profile.

Figure 2

Left Panel: The statistically significant main effect of Stimulation Time (p < 0.01) for the relative threshold change, based on the Pre object movement condition. The stars on the bottom half of the graph represent a statistically significant difference from 100% at the Early, Middle and Late-nc stimulation times (all p’s < 0.03). The stars on the top half of the graph represent a statistically significant relative threshold change between the Late stimulation time and all other stimulation times (all p’s < 0.01). Right Panel: The relative variability change across Stimulation Time conditions (p = 0.52). Note that the detection variability difference was also relative to the Pre object movement condition. For both panels, grey lines represent individual participants, black dots represent mean values, and error bars represent 95% CIs.