EMG experiment

8/7/2019 EMG experiment

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Abstract

In this experiment, certain facial muscles generated a potential difference once a subject

was exposed to several visual stimuli producing an emotional response measured by anelectromyogram (EMG). We analyzed the facial activity of the corrugator supercilii and

zygomatic major muscle regions in seven males and two females, who were exposed to

pictures evoking expressions of sadness and arousal as well as a video showing a joyful

expression. A problem solving activity (arithmetic) and an English reading task provoked

stress stimuli. Our results showed that an increase in activity of the zygomatic major

muscle was caused by joyful and arousal stimuli, whilst a difference in the level of

activity in the corrugator supercilii muscle was caused by sadness and stressful stimuli.

However, accuracy of our results was limited due to non-technologically advanced

equipment as well as an insufficient number of participants used for a population average

hence; new strategies need be derived for an improved sustainable outcome.

Introduction

Physiological psychologists have more recently looked into, the production of facial

expression and in the relationship between facial and autonomic measures of arousal.

There are currently many different studies observing the characteristics of the face in

order to determine how we know how we feel(link 1). The study carried out in this

experiment involved electromyographic analysis of facial expressions.

Electromyography (EMG) is a technique for evaluating and recording physiologic

properties of muscles at rest and while contracting. EMG is performed using an

instrument called an electromyograph, to produce a record called an electromyogram. An

electromyograph detects the electrical potential generated by muscle cells when these

cells contract, and also when the cells are at rest(wiky). EMG can be conducted in two

ways using either invasive or surface electrodes (Figure 1) connected to appropriate

computer hardware and software for analysis.
http://en.wikipedia.org/wiki/Medical_instrumenthttp://en.wikipedia.org/wiki/Electrical_potentialhttp://en.wikipedia.org/wiki/Cell_(biology)http://en.wikipedia.org/wiki/Medical_instrumenthttp://en.wikipedia.org/wiki/Electrical_potentialhttp://en.wikipedia.org/wiki/Cell_(biology)


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(b)

(a)

Figure 1. (Invasive and Non-invasive EMG)

http://www.teleemg.com/new/picthipel.htm

A subject from UTS demonstrating the skin surface electrode placement.

(a) Invasive EMG: uses a needle to measure the electrical activity in a muscle at rest and

during a contraction. The presence, size, and shape of the wave form of the action

potential produced on the oscilloscope, provides information about the ability of the

muscle to respond to nervous stimulation.

(b) Non-invasive EMG: Electrodes attached to skin surface to measure portions of

electrical potentials transmitted to the skin during muscular contraction. The strength of

electrical activity recorded is dependant on muscular proximity to the skin.

Every facial muscle can be involved in one or more emotional expressions, so there is no

distinction between emotional and non-emotional muscles. The facial muscles which the

electrodes were placed on are the Zygomatic major muscle and the Corrugator supercilii

shown in Figure 2.

Left Corrugator Supercilii

Electrode

Right Corrugator Supercilii

Electrode

Left Zygomatic Major ElectrodeRight Zygomatic Major Electrode

Reference Point
http://www.teleemg.com/new/picthipel.htmhttp://www.teleemg.com/new/picthipel.htm


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Some muscles always signal a particular emotion, such as zygomatic major which

produces a smile and is characteristic of happiness. It is never involved in a negative

emotional expression without blending its own message. Other muscles, such as the

corrugator, are involved in expressions which convey many different emotional messages

and nonemotional messages. Some emotions, such as happiness and disgust, can be

signaled by the action of only one muscle, but other emotions, such as sadness, need the

action of more than one muscle to be signaled unambiguously.

Figure 2. (Anterior view (a) and Lateral view (b) of two muscles used)

There are many previous studies showing the correlation between facial muscle activity

and emotion. Fair and Schwartz reported that majority of participants in their experiments

show stronger zygomatic response and weaker corrugator responses during positive

affective imagery. Link 3 Whilst expressions of anger and sadness produced increased

corrugator supercilii muscle activity (S. R. Vrana and D. Gross, 2002). Other experiments

also examined the facial corrugator and zygomatic muscles in response to sexual arousal

and stress. It was observed that there was an increase in corrugator activity when subjects

viewed unpleasant (sexual and non-sexual) videotape narratives and an increase in

zygomatic activity during pleasant videotape narratives. Link5.

Corrugator supercilii

Zygomatic major

Corrugator supercilii

Zygomatic major


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Aim

The aim of this experiment is to investigate the effects of different visual stimuli positive

and negative, such as happiness, sadness, stress and arousal on emotion and their effectson the zygomatic major and corrugator supercilii facial muscles.

Hypothesis

Altering emotions work on different facial muscles used to produce an expression. The

corrugator supercilii is involved with frowning whilst the zygomaticus major concerns

smiling. Therefore a stimulus that generates a negative expression like fear, sadness and

stress will protract greater activity of the corrugator muscles whilst positive emotions

such as joy, laughter and arousal will produce greater activity of the zygomatic muscles.

In a general sense, considering females are more emotional than males it can be expected

that they will respond towards a negative stimulus.


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Method

Apparatus:

Alcohol skin swab (Figure 3a)

Five pre-gelled 3M red dot electrodes (Figure 3b) Bipolar recording unit (Figure 3c)

Procedure

The skin is cleansed with alcohol wipes to remove dirt, oil and dead skin that may

alter signals picked up by the electrodes.

Place two electrodes on the zygomatic major muscle (one under the right

cheekbone and the other under the left).

Place the other two electrodes on the Corrugator supercilii (located on the medialend of the eyebrows), one for the left hand side and one for the right hand side.

The last electrode reference lead is attached on the neck on the right hand side.

A baseline of one minute duration is recorded prior to each of the four stimuli for

each subject.

The four stimuli presented were;

i. Funniest home videos show video clip

ii. Photos expressing victims as well as casualties in war

iii. Nerve-racking math questions and English slides

iv. Subtle pornographic clip

Prior to as well as afterward each stimulus, each subject would go through

a relaxing time period answering how they felt at the current time.

(Figure 3c)

(Figure 3a) (Figure 3b)


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Results* The following graphs (Figures 4-7) correspond to the figures tabulated in the appendix.

Figure 4*

EMG recording during a funny stimulus

0

10

20

30

40

50

60

70

80

90

1 2 3 4 5 6 7 8 9

Suject number

EMG(V)

Corrugator Baseline channel 1

Corrugator Activity channel 1

Zygomaticus Baseline channel 2

Zygomaticus Activity channel 2

Figure 4. shows that the potential difference of the Zygomaticus major muscle and the

Corrugator supercilii muscle during a funny stimulus. The Zygomaticus major had a

higher voltage henceforth a greater action potential in activity then that compared to the

Corrugator supercilii for the majority of subjects.

Figure 5*

EMG recording during an Arousal stimulus

0

10

20

30

40

50

1 2 3 4 5 6 7 8 9

Suject number

EMG(V)

Corrugator Baseline channel 1

Corrugator Activity channel 1

Zygomaticus Baseline channel 2

Zygomaticus Activity channel 2

Figure 5. shows that the potential difference of the Zygomaticus major muscle and the

Corrugator supercilii muscle during an arousal stimulus. The Zygomaticus major had a

higher voltage henceforth a greater action potential in activity then that compared to the

Corrugator supercilii for the majority of subjects.


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Discussion

The purpose of conducting this study is to analyze using EMG, whether

different facial muscles respond to changes generated by emotional

stimulus. The two muscles analyzed were the Zygomaticus major and

the Corrugator supercilii. In reflecting on earlier studies our results

coincided, indicating that positive stimuli such as happiness and

arousal generate greater activity in the zygomatic muscle whilst

negative stimuli such as stress and sadness generate greater activity

in the Corrugator supercilii muscles. These findings were consistent

with the hypothesis that emotions work on different facial muscles used to produce

an expression.

In looking at Figure.4 there was an inconsistency in the level of activity throughout the

nine subjects. There are a number of reasons for this; one being that not all subjects found

the stimulus funny and so could not produce a positive expression. Secondly, noise in the

background during the experiment as well as other distractions could have lead to the

subjects flawed level of concentration with the experiment hence, causing an

incompetent result. Also, Figure.6 illustrates similar inconsistencies as in the stimulus of

sadness; the results obtained a lower level of activity in the corrugator supercilii muscle

on certain subjects. However, had the stimulus caused an emotional influence on the

subject, the outcome would have been more favorable but it was a limitation that the

stimulus was not affective.

The following stimulus used for arousal had a controversial outcome. Figure.5 illustrates

that seven out of the nine subjects (seven male and two females) were positively aroused

which lead to the speculation that certain stimuli has a gender based affect. The stimuli

used was a pornographic scene by which not all subjects found it appropriate to observe

and so did not accept to participate. Unfortunately this had a negative result on the

experiment as not all subjects were exposed to the stimulus.


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The last stimulus was used to create a stressful situation. The results shown in Figure.7

display varied responses to the stress situations, however the majority of subjects

responded as predicted in the hypothesis by the use of the Corrugator supercilii muscle.

The other subjects that had not responded to that degree may have found the task at hand

not as difficult, therefore did not express there emotion the same way, that is why the

results showed a slight increase in the Zygomaticus major muscle activity alternatively.

Apart from the limitations mentioned above, there are also other factors that may have

caused discrepancies in the EMG result. One of the most common being problems with

the electrodes, such that there is a high level of resistance in the leads; the leads may be

worn out or broken; or the electrode was not properly attached to the subjects face. Also

failure to check the leads regularly leads to a variety of artifacts that can be interpreted as

activity(Gordon,1980)

This experiment has added potential for further improvement, so being new strategies

need be applied in order to do so. The major drawback imposed on the results was related

to the technology used being insensitive and unsophisticated enough to produce an

accurate output. Experimental error could have been reduced by allowing instruction for

the subject in order to set forth an expectation of the stimulus making them over express

themselves, however this would of defiled to purpose of the experiment being unnatural

although the limitations opposing us were known pre-experiment.

Conclusion


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Appendix

Table 1: EMG readings during Funny stimulus for zygomatic major and corrugatorsupercilii.

Subject

Funny

Channel 1

(Corrugator)

Channel 2

(Zygomatic)

Baseline Activity Baseline Activity

1 2.36 7.02 3.61 83.52

2 9.06 10.47 10.27

3 2.94 4.3 5.42

4 4.62 6.06 4.99 17.34

5 9.54 8.28 24.41 33.87

6 39.81 22.22 20.36 68.58

7 29.31 37.55 11.19 20.11

8 20.61 25.7 29.42 75.74

9 3.91 5.3 5.33 34.09

Table 2: EMG readings during an Arousal stimulus for zygomatic major and corrugator

supercilii.

Subject

Aroused

Channel 1

(Corrugator)

Cahnnel 2

(Zygomatic)


1 3.2 3.89 4.97 18.9

2 10.54 11.79 8.74 45.76

3 2.5 2.96 2.57 8.47

4 4.53 6.99 4.53 20.45 15.47 18.01 9.92

6 19.19 16.5 6.34 42.13

7

8 26.99 37.1 15.85

9 5.66 7.31 3.53 9.23


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Table 3: EMG readings during a sad stimulus for zygomatic major, and corrugator

supercilii.

Subject

Sad

Channel 1(Corrugator)

Cahnnel 2(Zygomatic)


1 3.36 4.69 3.27 3.89

2 8.74 11.17 10.16 10.44

3 2.73 3.32 2.9 4.84

4 4.87 5.59 4.23 4.51

5 12.68 12.97 8.64 10.47

6 17.58 21.26 9.38 11.96

7 9.57 16.92 12.51 14.07

8 18.76 20.52 6.99 7.79

9 4.16 4.73 10.15 5.34

Table 4: EMG readings during a Stress stimulus for zygomatic major and corrugator

supercilii.

Subject

Stressed

Channel 1

(Corrugator)

Cahnnel 2

(Zygomatic)


1 2.41 3.32 2.85 6.39

2 10.44 11.6 9.66 6.63

3 3.32 5.26 2.31 4.05

4 4.12 5.76 3.58 8.18

5 12.64 19.63 10.23

6 10.25 17.68 7.74 14.257 11.88 15.48 13.78 14.74

8 25.02 26.84 7.06 9.54

9 5.04 5.66 4.53 4.09


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EMG experiment