Encoding of spatial patterns using electrotactile stimulation via a multi‐pad electrode placed on the torso

Abstract

Background Tactile stimulation can be used to convey information to a user in different scenarios while avoiding overloading other senses. Tactile messages can be transmitted as spatial patterns, potentially allowing for a high information throughput. The aim of the present study was to design and test different encoding schemes to determine the best approach for conveying spatial patterns. Methods Encoding schemes with simultaneous (SIM) and sequential pad activation (SEQ) were evaluated, including four SEQ variants designed to potentially facilitate the recognition. In SEQ‐col and SEQ‐row, the column and row of the activated pad were signified using different frequencies, while SEQ‐all and SEQ‐all‐fast included the activation of all pads where those belonging to the pattern were indicated by changes in frequency (ON pads). The success rate (SR) of the pattern identification and the response time were quantified in 15 participants who recognized 20 patterns delivered through a 3 × 2 pad matrix placed on the lateral torso. Results SIM was not a feasible method to present the patterns (median, 15%; IQR, 5%). The SR improved with SEQ (median, 60%; IQR, 20%) and further increased with additional cues, particularly with SEQ‐row (median, 78.3%; IQR, 23.3%) and SEQ‐all (median, 96.7%; IQR, 5%). Importantly, the stimulation time of SEQ‐all could be decreased without a substantial drop in accuracy (SEQ‐all‐fast: median, 89.2%; IQR, 19.2%). Conclusions The spatiotemporal stimulation with sequential activation of all pads (SEQ‐all) seems to be the method of choice when conveying tactile messages as spatial patterns. This is an important outcome for increasing the information bandwidth of communication through the tactile channel.

Electrotactile Communication via Matrix Electrode Placed on the Torso Using Fast Calibration, and Static vs. Dynamic Encoding

“…During the spatial recognition test ( Figure 5 a), the pads facing the ventral side of the torso were on average better recognized compared to the pads facing the dorsal side (SR: 83.3% vs. 79.3%), which agrees with the findings in the literature that the ventral side of the torso is more sensitive and accurate [ 39 , 54 ]. The side of the body (i.e., front or back) was rarely misinterpreted, and most errors were made along the vertical axis of the electrode.…”

“…The electrode was designed based on the project requirements. The preliminary psychometric evaluation of this system confirmed that this design choice was suitable for the application of interest [ 54 , 55 , 56 ]. The electrode design considered six smaller circle-shaped pads and two larger pads with rounded rectangle shape ( Figure 1 ).…”

“…These techniques have been used to increase the recognizability of the information presented in the form of Chinese and English characters [ 51 , 52 ], shapes [ 53 ], and military hand signs [ 49 ]. In our recent publication several methods for the dynamic presentation of the spatial patterns have been tested with promising results [ 54 ]. However, such dynamic encoding has not been directly compared to a static single pad encoding, which is the simplest approach to convey information.…”

Improving electrotactile communication with a multi‐pad electrode under cognitive load

“…17 This placement was a specific requirement of first responders to minimize potential interference with gear (e.g., backpacks, face masks, and armbands) and movement. 17,22 The electrode comprised six circle-shaped active pads arranged in a 3 × 2 pad matrix and two rectangular active pads with rounded corners, each of them surrounded by a reference pad forming eight concentric pad pairs (Figure 1A).…”

“…10,17 In addition, the system could convey many messages with high reliability by encoding the information using a spatiotemporal approach with sequential activation of pads. 22 However, the proposed method was tested while subjects were fully focused on interpreting electrotactile stimulation, whereas the envisioned application of the system (i.e., first responders) implies that information is delivered in situations where the user divides his/her attention across several tasks. 10 Although studies have shown that haptic communication suffers from lower performance when performing concomitant tasks, there is not much literature on how to optimize haptic communication during multitasking.…”