Types of Measures in Speech-Language Pathology

Instrumentation in Speech-Language Pathology

Types of Measures

• Nominal measures: categories that are not relative to each other, e.g. "male" vs. "female"
• Ordinal scales: attributes or categories ranked relative to each other, e.g. "mild", "moderate", and "severe" ratings
• Interval scales: equal increments, e.g. a value of 50 is greater than 40 to the same degree that 60 is greater than 50
• Ratio scales: have a true zero value, e.g. age, height, and weight

Accuracy of Measurement

• Precision: includes calibration, accuracy, and reliability
• Calibration: process of converting voltage output into a reference standard measurement
• Reliability: consistency of measurement, e.g. 5% error
• Bias: systematic error, e.g. if the measure usually differs from the reference in one direction

Technical Issues

• Signal transducers: devices that change one form of energy into another, e.g. microphones, strain gauges, and pressure sensors
• Active transducers: do not require a power source, e.g. thermocouple
• Passive transducers: require a power source, e.g. photocell

Signals

• Analog signal: continuous signal containing time-varying quantities
• Digital signal: discrete in both time and amplitude
• Signal types: acoustic, aerodynamic, electrical, mechanical, optical

Signal Processing

• Amplification: increasing the strength of the signal
• Filtering: selecting specific frequencies or removing noise
• Digitization: converting analog signals into digital format
• Anti-aliasing filtering: filtering before a signal sampler to restrict bandwidth

Basics of Electricity

• Electricity: movement of charged particles
• Current: flow of charged particles, measured in amperes (amps)
• Personal safety: avoiding electrical shock, e.g. putting one hand in your pocket

Basics of Instrumentation

• Instrumentation: device or system to visualize and quantify phenomena
• Input stage: transducers (e.g. microphones)
• Signal conditioning stage: amplification, filtering, digitization
• Output stage: display devices (e.g. monitors, loudspeakers)

Safety

• Electrical safety: avoiding electrical shock, using valid ground contact
• Infection control: minimizing risk of spreading infection, e.g. handwashing, sterilizing

Analog to Digital Conversion (ADC)

• ADC: producing a binary output proportional to input voltage
• Sampling rate: how fast conversions occur
• Precision: determined by sampling rate and number of bits

Amplification

• Preamplification: enhancing signal changes prior to recording
• Differential amplification: amplifying difference between electrical field changes

Calibration

• Calibration: converting voltage output into a reference standard measurement
• Calibration is determined by transducing a known reference signal

Digitization

• Digitization: digital sampling of an analog voltage signal
• Sampling rate: dependent on type of signal, e.g. slow movement signals, voice, speech

Instrumental Measures in the Voice Lab

• Acoustic recording and analysis

• Aerodynamic measurement

• Laryngeal imaging

• Electroglottography (EGG)

• Laryngeal electromyography (LEMG)### Acoustic Analysis of Voice

• Fundamental Frequency (Fo): measures the period of an acoustic waveform using the peak-picking method.

• Frequency Range (Fo Range): measures the highest and lowest pitch a patient can produce.

Intensity

• Vocal Intensity: the acoustic correlate of vocal loudness, referenced to sound pressure level (SPL) and measured on a logarithmic decibel (dB) scale.
• Intensity Measures: can be derived from various instruments, including Sound Level Meters, Acoustic Analysis Programs, and Aerodynamic Measurement Devices.
• Habitual Intensity and Intensity Range (max and min): useful clinically.

Frequency-Intensity Profiling

• Voice Range Profile: a plot of vowel production at minimum and maximum intensity (dB range) across minimum and maximum frequency (Hz and musical note range).
• Phonetogram: a tool that provides a thorough description of a patient's physiologic limits of frequency and intensity.
• Physiologic Frequency Range of Phonation: a tool that provides a thorough description of a patient's physiologic limits of frequency and intensity.

Perturbation Measures

• Jitter: cycle-to-cycle variability in frequency (a.k.a. frequency perturbation, pitch perturbation), measured from sustained vowel productions or "extracted" vowels from connected speech.
• Shimmer: cycle-to-cycle variability in amplitude (a.k.a. amplitude perturbation), measured from sustained vowel productions or "extracted" vowels from connected speech.
• Calculation: requires a quasi-periodic signal for reliable/valid perturbation analysis (i.e., Type I signal).
• Jitter Purpose: measures frequency stability in sustained vowels.
• Jitter Procedure: can be measured when recording sustained vowel(s) for MPT.
• Jitter Norms: adults have a certain range of jitter values.