ICaD 2013

6–10 july, 2013, ÌódË, Polandinternational Conference on auditory Display

HOW IS AUDITORY EMG BIOFEEDBACK
EFFECTIVE FOR BLIND PEOPLE?
Masaki Iguchi1, Masaki Matsubara2, Hideki Kadone2,
Hiroko Terasawa2,3, Kenji Suzuki2,3
1

Tsukuba University of Technology
2
University of Tsukuba
3
JST PRESTO
iguchi@k.tsukuba-tech.ac.jp
masaki@slis.tsukuba.ac.jp
kadone@ccr.tsukuba.ac.jp
terasawa@slis.tsukuba.ac.jp
kenji@ieee.org

ABSTRACTIn this study, 11 sighted and 10 blind subjects performed a
motor task requiring 20 muscle contractions at a pre-determinedtarget (20% maximal voluntary contraction, MVC) with orwithout auditory EMG biofeedback (AEB) to examine whether
the AEB-induced changes in motor performance differ between
groups. The AEB reduced the absolute difference from one
previous contraction only in the blind subjects (-34% on
average; p = 0.026), and the error with no biofeedback was
greater for the blind subjects compared to that for the sighted
subjects (5.20% MVC SD (2.05) and 3.30% MVC SD (1.26); p= 0.024). This was consistent with subjective rating data
showing a trend that the blind subjects felt performing the taskwith no biofeedback more difficult than did the sighted subjects(p = 0.06). These data suggest that poor motor performance ofblind people can be improved with AEB.

1. INTRODUCTION
Seeing or hearing information converted from internal
biological signals (biofeedback) can improve motor
performance [1]. The amplitude of electromyography (EMG)
reflects how active the specific muscle is working, and therefore,
it has been reported that EMG biofeedback has a beneficial
effect in motor control in various circumstances [1, 2].
Visual image is most commonly used for EMG biofeedback[3-5]. However, sound generated from EMG signal has beenshown to provide as much information as visual image when
performing a certain motor task [6-8]. Although use of soundhas the advantage for anyone because one can move more freely
without staring at a display, for blind individuals who have todepend on non-visual information, sound would be the first
choice when EMG biofeedback is conducted.
It has been shown that blind individuals can successfully
learn facial expression with use of auditory EMG biofeedback(AEB) of facial muscles [9, 10]. Therefore, it seems obviousthat AEB is applicable to blind individuals. However, how blind
individuals respond to AEB when directly compared to sighted
individuals is not known. Because blind individuals have beenshown to compensate for their visual deprive by sharpening
auditory processes [11], they may behave differently to AEB
when compared to sighted individuals. Moreover, there aresome studies showing that blind individuals do not perform
motor tasks as well as sighted individuals [12-16], and therefore
whether poor motor performance could be compensated by the
sharpened auditory process in the blind is an interesting question.
If so, more active use of AEB is suggested when precise,repetitive motions are required such as in rehabilitation or
sporting activities.
The purpose of this study was to determine whether AEBinduced changes in motor performance differ between blind andsighted people. We hypothesized that AEB would improve
motor performance in both sighted and blind individuals, butblind individuals would benefit more from AEB than sighted
individuals.

2. MATERIALS AND METHODS

2.1. Subjects and general design
A total of 21 (10 blind and 11 sighted) subjects were recruited.
There were two females in each group, and their mean age was
22.9 years with no between-group difference. The blindness
was congenital for 6 subjects, and the rest (4 subjects) acquired
blindness at the age of 12 to 21. All subjects gave written
informed consent to the study, which was approved by theinternal review board at Tsukuba University of Technology.
The subjects were asked to perform a same motor task ofgripping a dynamometer repetitively at 20% of their maximum
voluntary contraction (MVC), under three different biofeedback307

ICAD 2013
HOW IS aUDITORY EMG BIOFEEDBaCK EFFECTIVE FOR BLIND PEOPLE?

conditions: Auditory EMG biofeedback (AEB), Visual EMG
biofeedback (VEB), and No Biofeedback.
2.2. Experimental set-up and instrumentationIn this study, sitting subjects placed their fully supinatedforearm on a table in front of them, and were asked to grip a
dynamometer (T.K.K. 5401, Takei) with their dominant hand.
Each task consisted of 20 contractions, and each contraction washeld for 5 seconds at 20% MVC with 10-second rest between(Figure 1).
Prior to performing each motor task described above, thesubjects practiced enough, so that they were able to contract themuscle at the target 20% MVC easily. During the practice,verbal cues were about the level of contraction, such as “more”
or “less”, but once the task started, the verbal cues wereregarding timing only such as “3, 2, 1, go” and “relax”. The
subjects performed the practice and motor task under the same
feedback condition (e.g., practice with no biofeedback and thenperform the task with no biofeedback).
Surface EMG was collected by placing two electrodes on the
flexor digitorum superficialis and a ground electrode on thedorsum of the tested hand. The signal was amplified (x500,
EMG-025, Harada Electronic Industry Ltd) and digitized (1kHz,
USB-6216, National Instruments).
AEB and VEB were achieved with MATLAB (R2012a,
Mathworks). For AEB, two speakers (6010A, Genelec Oy) wereplaced on the table in front of each ear of the sitting subject. We
assigned parameter mapping sonification [17] for synthesizing
sounds. A sinusoid (frequency = 460Hz) was generated, and its
amplitude reflected the EMG amplitude continuously. The study
was done in a quiet research laboratory (48dB), and the loudnessof the sound was adjusted to be 58dB, 65dB, and 72dB when the
EMG amplitude was at 20%, 50% and 100% MVC, respectively.
For VEB, a bar appeared on a display placed in front of thesighted subject, and its height reflected the EMG amplitude. No
sound was used during VEB.
Subjective ratings were obtained by asking how easy it wasto perform the task. The ratings ranged from 1 (“very difficult”)
to 5 (“very easy”) with 3 being “ordinary”.

2.3. Experimental procedureUpon arrival to the laboratory, electrodes were placed and MVC
was measured for EMG normalization purpose. Then subjects
practiced and performed the task described above. The
subjective ratings were collected after the 2 sessions (AEB andno biofeedback sessions), and the VEB session was conducted
for the sighted subjects. After the 20th contraction in each task,
MVC was taken in order to make sure no fatigue was inducedby the task. A 10-minute rest was given between sessions inorder to prevent fatigue.

308

Figure 1: An Experimental set-up and instrumentation. Sitting
subjects placed their fully supinated forearm on a table in frontof them, and were asked to grip a dynamometer.

2.4. Data reduction and analysis
EMG amplitude was calculated from the last 2 seconds of 5-sec
contractions, and normalized to MVC.
In order to examine the motor performance, error was
calculated as the absolute difference from one previous
contraction. This error index represents the effect of thebiofeedback on a shorter term motor and auditory memory,compared, for example, to the absolute error against the task
target (20%MVC) which requires the memory of the reference
given at the beginning. Memory capacity may differ among theindividuals and may make evaluation more complex.
Two-way (  group  x  biofeedback  ) analysis ofvariance (ANOVA) was used with the alpha level of 0.05.

3.

RESULTS3.1. Effect of practice and fatigability
The 1st of the 20 contractions in the task was close to the target
20% MV C, and there were no interaction or main effects of“group” or “biofeedback” (the means ranging from 20.9%MVC
for the sighted with the AEB to 23.2%MVC for the blind withno biofeedback).
Pre-task grip force was similar between groups (21.5kg SD(6.4) and 26.3kg SD (5.7) for the blind and sighted subjects,
respectively; p = 0.10). The post-task MVC grip force did notshow any change from pre-task, and similar results were found
for the post-task MVC EMG amplitude. These results indicatethat no fatigue was induced with the low target contraction(20%MVC) and the long between-contraction rest (10 sec off
and 5 sec on).

ICAD 2013
Wednesday, july 10•

Poster Papers and Extended abstracts

with no biofeedback was harder than did the sighted (3 out of
10 blind subjects rated 1 (very difficult), whereas none of the
11 sighted subjects did; p = 0.06).

4. DISCUSSION
The main findings of this study were that blind people felt it
was harder to repetitively contract muscles at a pre-determined
level than did the sighted people when there was nobiofeedback available, and the motor performance in this kindof task was actually poorer than that of the sighted people.
However, auditory EMG biofeedback significantly reduced theerror of the blind people, which was not the case for the sighted
people. The original hypothesis was that the AEB would reduce
the error in both blind and sighted people, but the AEB-induced
reduction in the error would be greater for the blind people
because it has been reported that blind people compensate for
their visual impairment by sharpening auditory process [11].
Our hypothesis has been partially supported (Figure 2). It has
been shown that AEB could provide as much information as
visual image [8], but in this study, the AEB did not change theerror in the sighted people. This is probably due to the task
being too simple (holding 20%MVC for 5 sec), and therefore afloor effect may have played a significant role in the sighted
people.
When no biofeedback was provided, both blind and sighted
subjects were in the same condition where they had to rely on
their somatosensory system. It has been shown that visual
cortical area can be activated by somatosensory input in blind
subjects, but not those with sight [18-20]. One may predict thatblind people would benefit more from somatosensory systemthan sighted people, but this was not the case in this study. Thismay be due to the fact that the task was unusual, novel one(griping a dynamometer with forearm supinated and elbow
flexed).

3.3. Subjective ratings

Modifying the sonification design could increase theeffectiveness of biofeedback. The sonification method employedin the present study varied the loudness corresponding to themuscle activity. Loudness is quite easy to manipulate and isfamiliar to users. However, there were several drawbacks tousing loudness for continuous data sets in sonification; lack ofresolution, and memorability. Neuhoff stated that absolute data
values are particularly difficult to perceive by listening toloudness change alone [21]. In this rehabilitation task, one
possible solution is that sensitivity to rhythm can be exploited toindicate processes. For example, Wallis' study showed changing
in rhythm and tempo is fruitful for stroke rehabilitation [22].

When the subjects were asked to rate how easy it was toperform the task (to reach and maintain the target contraction)for each condition, the overall averages were 2.05 (2 beinghard) and 3.95 (4 being easy) for no biofeedback and the AEB,
respectively (Figure 3). There was no between-group difference,but the blind subjects tended to feel that performing the task

Feedback and practice are considered to be among the mostimportant variables in the process of motor learning [23]. Ourdata suggest that AEB is a powerful biofeedback tool that can beused in rehabilitation and sporting activities for blind people.
Further studies are necessary in order to investigate what kind of
motor task / AEB would lead to the best motor performance inblind, as well as in sighted people.

3.2. Motor performanceThe error was reduced only in the blind subjects (3.45%MVC
SD (0.88) and 5.20%MVC SD (2.05); p = 0.026; Figure 2).
Moreover, the error with no biofeedback was greater for theblind subjects than that for the sighted subjects (p = 0.024).

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HOW IS aUDITORY EMG BIOFEEDBaCK EFFECTIVE FOR BLIND PEOPLE?

5.

CONCLUSION

In this paper, we have examined whether the auditory EMG
biofeedback induced changes in motor performance differ
between sighted and blind groups. The experimental results
showed that the AEB reduced the absolute difference only in theblind subjects. In addition, subjective rating data revealed thatthe blind subjects felt performing a motor task with nobiofeedback was more difficult than did sighted subjects. Our
experimental data indicate that the AEB is as effective as, orprobably even more effective for blind people than for sighted
people, and therefore the more active use of AEB should beconsidered in various activities for blind people.

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