Visual attention, EEG alpha power and T7-Fz connectivity are implicated in prosthetic hand control and can be optimized through gaze training

J V V Parr,N R Harrison,G Wood,S J Vine,M R Wilson

doi:10.1186/s12984-019-0524-x

Abstract

BackgroundProsthetic hands impose a high cognitive burden on the user that often results in fatigue, frustration and prosthesis rejection. However, efforts to directly measure this burden are sparse and little is known about the mechanisms behind it. There is also a lack of evidence-based training interventions designed to improve prosthesis hand control and reduce the mental effort required to use them. In two experiments, we provide the first direct evaluation of this cognitive burden using measurements of EEG and eye-tracking (Experiment 1), and then explore how a novel visuomotor intervention (gaze training; GT) might alleviate it (Experiment 2).MethodsIn Experiment 1, able-bodied participants (n = 20) lifted and moved a jar, first using their anatomical hand and then using a myoelectric prosthetic hand simulator. In experiment 2, a GT group (n = 12) and a movement training (MT) group (n = 12) trained with the prosthetic hand simulator over three one hour sessions in a picking up coins task, before returning for retention, delayed retention and transfer tests. The GT group received instruction regarding how to use their eyes effectively, while the MT group received movement-related instruction typical in rehabilitation.ResultsExperiment 1 revealed that when using the prosthetic hand, participants performed worse, exhibited spatial and temporal disruptions to visual attention, and exhibited a global decrease in EEG alpha power (8-12 Hz), suggesting increased cognitive effort. Experiment 2 showed that GT was the more effective method for expediting prosthesis learning, optimising visual attention, and lowering conscious control – as indexed by reduced T7-Fz connectivity. Whilst the MT group improved performance, they did not reduce hand-focused visual attention and showed increased conscious movement control. The superior benefits of GT transferred to a more complex tea-making task.ConclusionsThese experiments quantify the visual and cortical mechanisms relating to the cognitive burden experienced during prosthetic hand control. They also evidence the efficacy of a GT intervention that alleviated this burden and promoted better learning and transfer, compared to typical rehabilitation instructions. These findings have theoretical and practical implications for prosthesis rehabilitation, the development of emerging prosthesis technologies and for the general understanding of human-tool interactions.

Highlights

Prosthetic hands impose a high cognitive burden on the user that often results in fatigue, frustration and prosthesis rejection
Parr et al [7] showed that when using a myoelectric prosthetic hand simulator, participants directed a greater amount of visual attention towards the prosthesis and objects being manipulated by it
Pairwise comparisons revealed that Target locking strategy (TLS) was significantly lower during the prosthetic hand condition across both phases, and that for both anatomic and prosthetic hand conditions TLS was lowest during the lifted the jar from the board (Lift) phase (p < .001; Fig. 2a)

Summary

Introduction

Prosthetic hands impose a high cognitive burden on the user that often results in fatigue, frustration and prosthesis rejection. Despite the increasing sophistication of these devices, they still provide less than 50% of the capability of an intact limb [1, 2], impose a high cognitive burden that results in fatigue and frustration [3], and are frequently rejected [4] The nature of this cognitive burden has recently been explored indirectly by examining disruption to visuomotor behaviours during prosthetic hand use [5, 6]. Parr et al [7] showed that when using a myoelectric prosthetic hand simulator, participants directed a greater amount of visual attention towards the prosthesis and objects being manipulated by it This dependency on visual feedback to monitor and correct movements is in contrast to the feed-forward (target-focused) strategy revealed by skilled users in everyday tasks [8], and mirrors findings from novices in other domains (e.g. tool use [9] and laparoscopic surgery [10, 11]). The overall aim of this paper was to assess novel measures of this cognitive burden and to test the efficacy of a novel training technique that might reduce this burden

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