Psychophysical principles of discrete event-driven vibrotactile feedback for prostheses

Abstract

Purpose/aim of the study: We aimed to establish psychophysical principles for non-invasive vibrotactile feedback signalling discrete transition events (e.g., extension to flexion) during use of prostheses, especially for the upper limbs.

Materials and methods: Two vibrotactile actuators were used on both upper arms of 10 able-bodied human participants. Absolute thresholds, psychometric functions, and magnitude estimates were measured to equalize the sensation magnitudes for the tested vibrotactile frequencies and skin sites. Then, same-different and pattern recognition tasks were run to evaluate, respectfully, the discrimination and closed-set identification of stimuli with varying parameters (2 frequencies, 2 magnitudes, 2 sites). Finally, parameters of the left/right stimuli were mapped to hypothetical prosthesis events representing object/force and movement type. The stimuli were applied sequentially in accordance with the discrete event-driven feedback paradigm.

Results: Reliable psychophysical models could be established for individual participants as verified by repetitive threshold measurements and relative adjustment of stimulus levels based on sensation magnitudes. Discrimination accuracy was higher for magnitude versus frequency comparisons; and magnitude discrimination accuracy was correlated with magnitude estimate differences. Pattern recognition recall/precision rates decreased from ∼0.7 to ∼0.5 for sequential delivery of two stimulus patterns to one arm versus to two arms. Using the patterns as two and three consecutive prosthesis events yielded statistically similar performance rates not correlated with magnitude estimate differences.

Conclusions: By careful calibration of stimuli based on psychophysical principles, discrete event-driven vibrotactile feedback can be used to signal manipulated object and movement information with moderate identification rates as shown by confusion matrices.

Keywords:

• Touch
• somatosensory feedback
• vibrotactile stimulus
• discrete event
• prosthesis
• magnitude estimation
• pattern recognition
• confusion matrix

Acknowledgments

The authors thank Assoc. Prof. Erkan Kaplanoğlu, Ahmet Atasoy, Hasan Şahin for the design of the robotic hand which we used for specifying the discrete events. The authors also thank Yavuzer Karakuş for his help in obtaining the actuators and setting up the instrumentation, and Deniz Kılınç Bülbül for her help during Haptuator calibration. The authors are grateful for the patience of all the participants who attended this long study.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Author contributions

B.G. conceived and designed research. İ.K. performed the experiments, analysed data, and prepared the figures. Both of the authors interpreted results of experiments, drafted manuscript, edited and revised the manuscript, and approved final version of the manuscript.

Additional information

Funding

This work was supported by TÜBİTAK BİDEB-2211 and Council of Higher Education ÖYP programme to İ.K., and by TÜBİTAK Grant 117F481 within European Union’s FLAG-ERA JTC 2017 project GRAFIN to B.G.