Applying Incongruent Visual-Tactile Stimuli during Object Transfer with Vibro-Tactile Feedback

Summary

We present a protocol to apply incongruent visual-tactile stimuli during an object transfer task. Specifically, during block transfers, performed while the hand is hidden, a virtual presentation of the block shows random occurrences of false block drops. The protocol also describes adding vibrotactile feedback while performing the motor task.

Abstract

The application of incongruent sensory signals that involves disrupted tactile feedback is rarely explored, specifically with the presence of vibrotactile feedback (VTF). This protocol aims to test the effect of VTF on the response to incongruent visual-tactile stimuli. The tactile feedback is acquired by grasping a block and moving it across a partition. The visual feedback is a real-time virtual presentation of the moving block, acquired using a motion capture system. The congruent feedback is the reliable presentation of the movement of the block, so that the subject feels that the block is grasped and see it move along with the path of the hand. The incongruent feedback appears as the movement of the block diverts from the actual movement path, so that it seems to drop from the hand when it is actually still held by the subject, thereby contradicting the tactile feedback. Twenty subjects (age 30.2 ± 16.3) repeated 16 block transfers, while their hand was hidden. These were repeated with VTF and without VTF (total of 32 block transfers). Incongruent stimuli were presented randomly twice within the 16 repetitions in each condition (with and without VTF). Each subject was asked to rate the difficulty level of performing the task with and without the VTF. There were no statistically significant differences in the length of the hand paths and durations between transfers recorded with congruent and incongruent visual-tactile signals – with and without the VTF. The perceived difficulty level of performing the task with the VTF significantly correlated with the normalized path length of the block with VTF (r = 0.675, p = 0.002). This setup is used to quantify the additive or reductive value of VTF during motor function that involves incongruent visual-tactile stimuli. Possible applications are prosthetics design, smart sport-wear, or any other garments that incorporate VTF.

Introduction

Illusions are exploitations of the limitations of our senses, as we mistakenly perceive information that deviates from objective reality. Our perceptual inference is based on our experience in interpreting sensory data and on the calculation of our brain of the most reliable estimate of reality in the presence of ambiguous sensory input¹.

A sub-category in the research of illusions is one that combines incongruent sensory signals. The illusion that results from incongruent sensory signals originates from the constant multisensory integration performed by our brain. While there are numerous studies concerning incongru....

Protocol

The following protocol follows the guidelines of human research ethics committee of the university. See Table of Materials for reference to the commercial products.

NOTE: After receiving approval of the university ethics committee, 20 healthy individuals (7 males and 13 females, mean and standard deviation [SD] of age 30.2 ± 16.3 years) were recruited. Each subject read and signed an informed consent form pretrial. Inclusion criteria were right-handed individuals aged 18 or above. Exclusion criteria were any neurological or orthopaedic impairment affecting the upper extremities or uncorrected sight impairment. The subj....

Results

We used the described technique to test the three hypotheses that when moving an object from one place to another using virtual visual feedback: (i) the path and duration of the object’s transfer motion will increase when incongruent visual-tactile stimuli is presented; (ii) this change will increase when incongruent visual-tactile stimuli is presented and VTF is activated on the moving arm; and (iii) a positive correlation will be found between the perceived difficulty level of performing the task with the VTF act.......

Discussion

In this study, a protocol that quantifies the effect of adding VTF on the object transfer kinematics in the presence of incongruent visual-tactile stimuli was presented. To the best of our knowledge, this is the only protocol available to test the effect of VTF on the response to incongruent visual-tactile stimuli. The several critical steps involved in the application of incongruent visual-tactile stimuli during object transfer with VTF include the following: attaching the VTF system to the subject, activating the VTF, .......

Materials

Name	Company	Catalog Number	Comments
3D printer	Makerbot		https://www.makerbot.com/
Box and Blocks test	Sammons Preston		https://www.performancehealth.com/box-and-blocks-test
Flexiforce sensors (1lb)	Tekscan Inc.		https://www.tekscan.com/force-sensors
JASP	JASP Team		https://jasp-stats.org/
Labview	National Instruments		http://www.ni.com/en-us/shop/labview/labview-details.html
Micro Arduino	Arduino LLC		https://store.arduino.cc/arduino-micro
Motion capture system	Qualisys		https://www.qualisys.com
Shaftless vibration motor	Pololu		https://www.pololu.com/product/1638
SPSS	IBM		https://www.ibm.com/analytics/spss-statistics-software