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 supercil

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