Articulation vs. Phonological Disorder
It is sometimes difficult to distinguish between an Articulation disorder and a Phonological disorder. They are both sound disorders, however understanding each disorder and their derivation is important.

Articulation Disorder
An articulation disorder involves difficulties producing sounds in isolation, syllables, sentences, paragraphs, and/or in conversational speech. An articulation problem may be defined as difficulty in producing a single or few sounds with no pattern. Articulation errors can be described as a:

• Substitution – replacing one sound with another.
  • Example: “thun” for “sun,” “wock” for “rock” or “dut” for “duck”
    
• Omission (deletion) – omit a sound or a word. This error affects intelligibility (ability to understand the speaker) the most, making speech more difficult for the listener(s) to understand.
  • Example: “g_een _nake” for “green snake” or “p_ay the piano” for “play the piano”
    
• Distortion – produce a sound in an unfamiliar manner.
  
• Addition – insertion of an extra sound within a word.
  • Example: “doguh” for “dog” or “buhlack” for “black”

An easy way to remember these is to use the acronym SODA. Not all sound substitutions and omissions are speech errors. It’s important to take dialect and accent into consideration. Errors such as these can make communication difficult.

Phonological Disorder
A phonological process disorder involves patterns of sound errors. It is a simplification of the sound system that also affects intelligibility. Individuals with phonological process problems demonstrate difficulty organizing and outputting the patterns of sounds in the brain. This is not necessarily in the motor production of the sounds like Articulation errors. There are many types of phonological processes which include:

Syllable Structure Processes: Changes that cause sounds or syllables to be deleted, repeated, or reduced in number.

• Final Consonant Deletion – the deletion of the final consonant or consonant cluster in a syllable or word.
  • Example: “soap” is pronounced “sew” or “pig” is pronounced “pi”
• Cluster Reduction – the deletion of one or more consonants from a two or three consonant cluster.
  • Example: “spot” is pronounced “pot” or “split” is pronounced “sit”
• Syllable Reduction – the deletion of a syllable from a word containing two or more syllables. The deletion usually occurs in the unstressed syllable.
  • Example: “computer” is pronounced “puter”

Substitution Processes: Sound changes in which one sound class replaces another class of sounds.

• Gliding – occurs when /r/ becomes /w/ or /l/ becomes /w/ or ‘y’
  • Example: “rail” is pronounced “whale” or “leap” is pronounced “yeep”
• Vocalization – occurs when /l/ or “er” is replaced by a more neutral vowel.
  • Example: “seal” is pronounced “sio” or “computer” is pronounced “computa”
• Fronting – the substitution of sounds in the front of the mouth
  • Example: “key” is pronounced “tea” or “gate” is pronounced “date”
• Deaffrication – the deletion of a stop component from a word
  • Example: “cheese” is pronounced “sheese” or “jar” is pronounced “zhar”
• Stopping – the substitution of a fricative (sound with a constant air flow such as “ssssss” or ‘ffffff” for example) for a stop consonant or an affricate (speech sound with a stop followed by a fricative).
  • Example: “sail” is pronounced “tail”

Assimilation Processes: Sound changes in which one sound or syllable influences another sound or syllable.

• Prevocalic Voicing – the voicing (vibration of the vocal cords) of an initial voiceless (no vibration of the vocal cords) consonant in a word.
  • Example: “peach” is pronounced “beach”
• Postvocalic Devoicing – the devoicing of a final voiced consonant of a word.
  • Example: “bag” is pronounced “back”