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Human ability in identification of location and pulse number for electrocutaneous stimulation applied on the forearm.

Geng B, Jensen W - J Neuroeng Rehabil (2014)

Bottom Line: The study consisted of three experiments.The performance degraded when both parameters had to be identified likely due to increased cognitive load resulting from multiple tasks.Utilizing the proposed coding strategy in practical prosthetic hands remains to be investigated for clinical evaluation of its feasibility.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Health Science and Technology, Aalborg University, Fredrik Bajers vej 7D, Aalborg, Denmark. bogeng@hst.aau.dk.

ABSTRACT

Background: The need of a sensory feedback system that would improve users' acceptance in prostheses is generally recognized. Feedback of hand opening and position are among the most important concerns of prosthetic users. To address the two concerns, this study investigated the human capability to identify pulse number and location when electrical stimulation applied on the forearm skin. The pulse number may potentially be used to encode the opening of prosthetic hands and stimulation location to encode finger position.

Methods: Ten able-bodied subjects participated in the study. Three electrodes were placed transversely across the ventral forearm spatially encoding three fingers (i.e., thumb, index, and middle finger). Five different pulse numbers (1, 4, 8, 12, and 20) encoded five levels of hand opening. The study consisted of three experiments. In the three experiments, each after a training session, the subjects were required to identify among: (a) five stimulation locations, (b) five pulse numbers, or (c) ten paired combinations of location and pulse number, respectively. The subjects' performance in the three identification tasks was evaluated.

Results: The main results included: 1) the overall identification rate for stimulation location was 92.2 ± 6.2%, while the success rate in two-site stimulation was lower than one-site stimulation; 2) the overall identification rate for pulse number was 90.8 ± 6.0%, and the subjects showed different performance in identification of the five pulse numbers; 3) the overall identification rate decreased to 80.2 ± 11.7% when the subjects were identifying paired parameters.

Conclusions: The results indicated that the spatial (location) and temporal (pulse number) identification performance are promising in electrocutaneous stimulation on the forearm. The performance degraded when both parameters had to be identified likely due to increased cognitive load resulting from multiple tasks. Utilizing the proposed coding strategy in practical prosthetic hands remains to be investigated for clinical evaluation of its feasibility.

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Just noticeable difference (JND) for pulse number. The curves of JND for pulse number were drawn based on the measurement at three pulse rates: 10, 20, 40 pps in one subject. A group of five pulse numbers was selected for each pulse rate, ensuring that the ‘spacing’ between two successive pulse numbers equal to or larger than the JND. The three groups of selected pulse numbers were marked on the three curves, respectively.
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Figure 4: Just noticeable difference (JND) for pulse number. The curves of JND for pulse number were drawn based on the measurement at three pulse rates: 10, 20, 40 pps in one subject. A group of five pulse numbers was selected for each pulse rate, ensuring that the ‘spacing’ between two successive pulse numbers equal to or larger than the JND. The three groups of selected pulse numbers were marked on the three curves, respectively.

Mentions: Since the choice of pulse rate and the ‘spacing’ between two successive pulse numbers could highly influence the performance in pulse number identification, the ‘optimal’ pulse rate and pulse numbers were selected in preliminary experiments. The pulse rates of 10, 20, and 40 pulses per second (pps) were tested and compared. Low pulse rates were considered because high pulse rates have previously been reported to be less clear and harder for the subjects to interpret [18].The selection of ‘optimal’ pulse numbers was based on a method using just noticeable difference (JND) of pulse numbers. The JND of a specific pulse number was determined using the following method: (1) A pair of stimuli was presented in sequence with the first as the baseline stimulus and the second having a greater pulse number; (2) After each stimulus pair presented, the participant was asked to report whether he perceived the difference between the two stimuli or not; (3) The second stimulus increased until the participant detected the difference; (4) The difference in pulse number between these two stimuli was then recorded as the JND of the base stimulus. JNDs of a range of pulse numbers were measured for each of the three pulse rates. That is, JNDs of pulse number 1, 2, 3,…, 10 for pulse rate 10 pps (i.e., totally 10 JNDs obtained), JNDs of pulse number 1, 2, 4, 6, …, 20 for pulse rate 20 pps (i.e., totally 11 JNDs obtained), JNDs of pulse number 1, 2, 4, 6, …, 20, 24, 28,…, 40 for pulse rate 40 pps (i.e., totally 16 JNDs obtained). Five pulse numbers were selected for each pulse rate, according to: (a) PN1 was always equal to 1, (b) PN5 equal to the maximum pulses in one second (i.e. the pulse rate), and (c) PN2 ≥ PN1 + JND (PN1), PN3 ≥ PN2 + JND (PN2) and so on. The selection criterion was that the five values distributed within one second and meanwhile their spacing equal to or larger than the JNDs. This JND-based method ensured the selected pulse numbers were theoretically distinguishable. Figure 4 shows the measured JNDs and selected pulse numbers for each of the three pulse rates.


Human ability in identification of location and pulse number for electrocutaneous stimulation applied on the forearm.

Geng B, Jensen W - J Neuroeng Rehabil (2014)

Just noticeable difference (JND) for pulse number. The curves of JND for pulse number were drawn based on the measurement at three pulse rates: 10, 20, 40 pps in one subject. A group of five pulse numbers was selected for each pulse rate, ensuring that the ‘spacing’ between two successive pulse numbers equal to or larger than the JND. The three groups of selected pulse numbers were marked on the three curves, respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4060858&req=5

Figure 4: Just noticeable difference (JND) for pulse number. The curves of JND for pulse number were drawn based on the measurement at three pulse rates: 10, 20, 40 pps in one subject. A group of five pulse numbers was selected for each pulse rate, ensuring that the ‘spacing’ between two successive pulse numbers equal to or larger than the JND. The three groups of selected pulse numbers were marked on the three curves, respectively.
Mentions: Since the choice of pulse rate and the ‘spacing’ between two successive pulse numbers could highly influence the performance in pulse number identification, the ‘optimal’ pulse rate and pulse numbers were selected in preliminary experiments. The pulse rates of 10, 20, and 40 pulses per second (pps) were tested and compared. Low pulse rates were considered because high pulse rates have previously been reported to be less clear and harder for the subjects to interpret [18].The selection of ‘optimal’ pulse numbers was based on a method using just noticeable difference (JND) of pulse numbers. The JND of a specific pulse number was determined using the following method: (1) A pair of stimuli was presented in sequence with the first as the baseline stimulus and the second having a greater pulse number; (2) After each stimulus pair presented, the participant was asked to report whether he perceived the difference between the two stimuli or not; (3) The second stimulus increased until the participant detected the difference; (4) The difference in pulse number between these two stimuli was then recorded as the JND of the base stimulus. JNDs of a range of pulse numbers were measured for each of the three pulse rates. That is, JNDs of pulse number 1, 2, 3,…, 10 for pulse rate 10 pps (i.e., totally 10 JNDs obtained), JNDs of pulse number 1, 2, 4, 6, …, 20 for pulse rate 20 pps (i.e., totally 11 JNDs obtained), JNDs of pulse number 1, 2, 4, 6, …, 20, 24, 28,…, 40 for pulse rate 40 pps (i.e., totally 16 JNDs obtained). Five pulse numbers were selected for each pulse rate, according to: (a) PN1 was always equal to 1, (b) PN5 equal to the maximum pulses in one second (i.e. the pulse rate), and (c) PN2 ≥ PN1 + JND (PN1), PN3 ≥ PN2 + JND (PN2) and so on. The selection criterion was that the five values distributed within one second and meanwhile their spacing equal to or larger than the JNDs. This JND-based method ensured the selected pulse numbers were theoretically distinguishable. Figure 4 shows the measured JNDs and selected pulse numbers for each of the three pulse rates.

Bottom Line: The study consisted of three experiments.The performance degraded when both parameters had to be identified likely due to increased cognitive load resulting from multiple tasks.Utilizing the proposed coding strategy in practical prosthetic hands remains to be investigated for clinical evaluation of its feasibility.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Health Science and Technology, Aalborg University, Fredrik Bajers vej 7D, Aalborg, Denmark. bogeng@hst.aau.dk.

ABSTRACT

Background: The need of a sensory feedback system that would improve users' acceptance in prostheses is generally recognized. Feedback of hand opening and position are among the most important concerns of prosthetic users. To address the two concerns, this study investigated the human capability to identify pulse number and location when electrical stimulation applied on the forearm skin. The pulse number may potentially be used to encode the opening of prosthetic hands and stimulation location to encode finger position.

Methods: Ten able-bodied subjects participated in the study. Three electrodes were placed transversely across the ventral forearm spatially encoding three fingers (i.e., thumb, index, and middle finger). Five different pulse numbers (1, 4, 8, 12, and 20) encoded five levels of hand opening. The study consisted of three experiments. In the three experiments, each after a training session, the subjects were required to identify among: (a) five stimulation locations, (b) five pulse numbers, or (c) ten paired combinations of location and pulse number, respectively. The subjects' performance in the three identification tasks was evaluated.

Results: The main results included: 1) the overall identification rate for stimulation location was 92.2 ± 6.2%, while the success rate in two-site stimulation was lower than one-site stimulation; 2) the overall identification rate for pulse number was 90.8 ± 6.0%, and the subjects showed different performance in identification of the five pulse numbers; 3) the overall identification rate decreased to 80.2 ± 11.7% when the subjects were identifying paired parameters.

Conclusions: The results indicated that the spatial (location) and temporal (pulse number) identification performance are promising in electrocutaneous stimulation on the forearm. The performance degraded when both parameters had to be identified likely due to increased cognitive load resulting from multiple tasks. Utilizing the proposed coding strategy in practical prosthetic hands remains to be investigated for clinical evaluation of its feasibility.

Show MeSH