Investigations with Electromyography

Electromyography (EMG) has been a primary research tool for understanding how laryngeal muscles coordinate to control fundamental frequency. This technique records electrical activity in muscles during phonation, providing insight into which muscles are active and their relative levels of contraction. However, interpreting EMG data in terms of biomechanical outcomes has proven challenging.

Statistical Correlations in Laryngeal Control

A comprehensive statistical analysis of results from intrinsic and extrinsic laryngeal muscle EMG was conducted using the speech material “Bev loves Bob” with various pitch contours, stress patterns, sentence types, and intensity changes.

Correlation Findings

Legend: F₀ = fundamental frequency, SH = sternohyoid, LCA = lateral cricoarytenoid, TA = thyroarytenoid, CT = cricothyroid, Ps = subglottal pressure, ST = sternothyroid

Key Observations

Cricothyroid Dominance

• Highest correlation with F₀ (r = 0.72)
• Consistently identified across studies as primary F₀ controller
• Positive correlation indicates increased activity raises F₀

Thyroarytenoid Contribution

• Moderate positive correlation with F₀ (r = 0.45)
• Secondary but significant role in F₀ regulation
• Correlation varies with pitch range and register

Lateral Cricoarytenoid Activity

• Positive correlation with F₀ (r = 0.59)
• Strong correlation with CT activity (r = 0.85)
• May function more for laryngeal stability than direct F₀ control

Extrinsic Muscle Effects

• Sternohyoid (SH) shows negative F₀ correlation (r = -0.65)
• Sternothyroid (ST) also negatively correlated (r = -0.49)
• These muscles may lower larynx position, loosening cover tissue

Subglottal Pressure

• Surprising slight negative average correlation (r = -0.19)
• Result of heavily averaged data across different speech conditions
• Specific correlations differ when data are partitioned by context

Survey of EMG Research Findings

Multiple investigations have examined laryngeal muscle activity patterns during F₀ control, with both consistent findings and some contradictions:

Hirano, Ohala, and Vennard (1969)

Primary findings:

• CT identified as primary F₀ controller
• LCA and TA of secondary importance in raising F₀
• Results consistent for both speech and singing

Gay et al. (1972)

Primary findings:

• CT and TA both identified as primary controllers
• PCA (posterior cricoarytenoid) sometimes involved
• IA (interarytenoid) and LCA have moderate to light F₀ effects
• All muscle activities decrease from chest to falsetto register
• All activities increase when F₀ raised within a register
• Control for singing differs from control for speech

Shipp and McGlone (1971)

Primary findings:

• CT and TA act synergistically to regulate F₀
• CT is primary, TA is secondary
• Posterior cricothyroid and interarytenoid have insignificant F₀ effects

Baer, Gay, and Niimi (1976)

Primary findings:

• CT most significant in F₀ control
• Extrinsic muscles (SH, ST) active in both high and low pitch ranges
• Extrinsic activity may provide laryngeal framework stability

Limitations of EMG Analysis

While EMG provides valuable information about muscle activation patterns, several limitations complicate interpretation:

Cause-Effect Ambiguity

Activity in muscles doesn’t necessarily mean those muscles are causing F₀ changes. For example:

• Muscles may provide restraining forces to counteract gross laryngeal movement
• Activity at pitch extremes may ensure stability rather than drive frequency change
• EMG cannot distinguish between muscles causing change versus maintaining position

Missing Configuration Information

Most EMG studies lack accurate specification of:

• Vocal fold length and thickness
• Depth of tissue in vibration
• Surface contours and geometry
• Viscoelastic properties

Research Note: Recent work has begun studying laryngeal configuration changes simultaneously with EMG recordings, representing an important methodological advance.

Context Dependency

Correlations vary with:

• Pitch range (low, middle, high)
• Register (modal, falsetto, etc.)
• Intensity level
• Speech versus singing
• Individual anatomical variations

Consistent Findings Across Studies

Despite methodological variations and some contradictory results, certain patterns emerge consistently:

Primary Findings

1. CT is most positively correlated with F₀ across nearly all studies
2. TA follows closely as a secondary F₀ controller
3. Activity in other intrinsic muscles (LCA, PCA, IA) varies more across studies
4. Extrinsic muscle activity at pitch extremes suggests role in framework stability
5. Register changes involve shifts in relative muscle activities

Interpretation Challenges

The variation in secondary muscle findings likely reflects:

• Different speech or singing tasks
• Individual vocal strategies
• Register transitions during recordings
• Difficulty isolating specific muscle contributions

Implications for F₀ Control Models

EMG research has established that:

• Multiple muscles contribute to F₀ regulation
• CT and TA are the dominant tensor muscles
• Other muscles play supporting roles in stability and configuration
• Accurate prediction of F₀ requires knowing both muscle activity AND laryngeal geometry

This understanding motivates the need for quantitative biomechanical models that can predict F₀ from measured muscle activities and anatomical configurations, which are developed in subsequent sections of this chapter.

Summary

Electromyographic investigations have provided crucial insights into F₀ control, consistently identifying the cricothyroid muscle as the primary controller and thyroarytenoid as secondary. However, EMG alone cannot fully predict F₀ changes because the acoustic outcome depends not just on muscle activity but also on the resulting laryngeal configuration and tissue mechanical properties. The field has moved toward integrated approaches that combine EMG with direct measurement of vocal fold geometry and modeling of tissue biomechanics.

Key Takeaways

• ✅ EMG reveals which muscles are active but cannot alone predict F₀ changes
• ✅ Cricothyroid consistently shows highest correlation with F₀ across studies (r ≈ 0.70)
• ✅ Thyroarytenoid activity is positively correlated with F₀ in most conditions
• ✅ Extrinsic laryngeal muscles (sternohyoid, sternothyroid) show negative F₀ correlations
• ✅ Activity in stabilizing muscles (LCA, PCA, IA) doesn’t necessarily cause F₀ change
• ✅ Correlations vary with pitch range, register, intensity, and individual strategy
• ✅ Modern research combines EMG with direct measurement of laryngeal configuration
• ✅ Quantitative biomechanical models are needed to link muscle activity to acoustic output

Related Topics

• Descriptive Overview of F₀ Control
• The Cover Model of F₀ Control
• Muscle Activation Plot for the Body-Cover Model

Further Reading

1. Atkinson, J. E. (1978). Correlation analysis of the physiological factors controlling fundamental voice frequency. Journal of the Acoustical Society of America, 63(1), 211-222.
2. Hirano, M., Ohala, J., & Vennard, W. (1969). Regulation of register, pitch and intensity of voice. Folia Phoniatrica, 22, 1-20.
3. Titze, I. R., Luschei, E. S., & Hirano, M. (1989). Role of the thyroarytenoid muscle in regulation of fundamental frequency. Journal of Voice, 3, 213-224.