Key Formulas & Equations
Normal Intelligibility: Age 2: 50%; Age 3: 75%; Age 4: 100%
Mean Length of Utterance (MLU): MLU = Total morphemes / Total utterances
Formant Frequencies: F1 (vowel height): 200-900 Hz; F2 (vowel backness): 500-2500 Hz
Voice Range Profile: Measures frequency and intensity range
Normal Speech Rate: 120-150 words per minute (adults)
Pauses: Pause duration and frequency analysis
12 months: 1-3 words; 24 months: 50+ words, 2-word phrases
36 months: 250+ words, 3-word sentences; 48 months: 4-word sentences, 1500+ words
FOIS Levels: 1 = Nothing by mouth; 2 = Tube dependent with minimal oral intake; 3 = Tube with consistent oral intake; 4 = Total oral diet of single consistency; 5 = Total oral diet with multiple consistencies; 6 = Total oral diet with special preparation; 7 = Total oral diet with no restrictions
Core Concepts
Articulation Disorders
Difficulty producing speech sounds correctly. Includes substitutions, omissions, distortions, and additions. Treated through articulation therapy.
Language Disorders
Difficulty understanding (receptive) or using (expressive) language. Includes developmental language disorder, aphasia, and specific language impairment.
Fluency Disorders
Disruptions in the flow of speech: stuttering, cluttering, and neurogenic stuttering. Treated through fluency shaping and stuttering modification.
Voice Disorders
Abnormal voice quality, pitch, or loudness. Includes vocal nodules, polyps, paralysis, and muscle tension dysphonia. Treated through voice therapy.
Swallowing Disorders (Dysphagia)
Difficulty swallowing safely. Assessment includes clinical bedside evaluation, videofluoroscopy (VFSS), and fiberoptic endoscopic evaluation (FEES).
Augmentative and Alternative Communication (AAC)
Systems to support communication for individuals with severe speech impairments: picture boards, speech-generating devices, and sign language.
Childhood Speech Sound Disorders
Speech errors in children: phonological processes, articulation errors, and childhood apraxia of speech (CAS). Treated through play-based therapy.
Neurogenic Communication Disorders
Communication impairments from neurological damage: aphasia, dysarthria, and cognitive-communication disorders from stroke, TBI, or dementia.
Worked Examples
Example 1: Speech Intelligibility
Problem: A child produces 40 words, and 30 are correctly identified. Calculate intelligibility.
Solution:
Intelligibility = 30/40 × 100% = 75%
Interpretation: Age 3 level (75% expected at age 3)
Example 2: MLU Calculation
Problem: A child produces 5 utterances with 20 total morphemes. Calculate MLU.
Solution:
MLU = 20/5 = 4.0 morphemes per utterance
Interpretation: Typical for 4-year-old (MLU 4.0-4.5)
Example 3: Speech Rate
Problem: A patient speaks 60 syllables in 30 seconds. Calculate speech rate.
Solution:
Rate = 60/30 = 2 syllables/second = 120 syllables/minute
Practice Problems
Problem 1
Calculate intelligibility if 45 out of 50 words are understood.
Answer: 45/50 × 100% = 90%
Problem 2
Calculate MLU for 8 utterances with 32 morphemes.
Answer: MLU = 32/8 = 4.0
Problem 3
Identify normal F0 range for adult females.
Answer: 165-255 Hz
Problem 4
Calculate speech rate for 90 syllables in 45 seconds.
Answer: Rate = 90/45 = 2 syllables/second
Problem 5
Interpret FOIS score of 5.
Answer: Total oral diet with multiple consistencies, but requiring special preparation
Problem 6
What is the expected vocabulary at 24 months?
Answer: 50+ words and 2-word phrases
Problem 7
Calculate intelligibility for 25/30 words understood.
Answer: 25/30 × 100% = 83.3%