Speech Production, Errors, Prediction, and Aphasias

Phonological Encoding & Phonemes

  • Basic speech units = phonemes (≈ 44 in English)
  • Speech production pipeline: intention → lexical selection → grammatical encoding → phonological encoding → articulation
  • Infants (≤ 6 mo) discriminate many phonemic contrasts; ability narrows without exposure
  • Bilingual upbringing preserves broader phoneme discrimination into adulthood

Speech Errors (Exchange Errors)

  • Definition: unintended deviation from planned utterance
  • Types by linguistic unit exchanged
    • Word exchange: “Pass the salt—​I mean pepper”
    • Morpheme exchange: “slicedly thin” vs. “thinly sliced”
    • Phoneme exchange: “heft hemisphere” vs. “left hemisphere”
  • Word-level error categories (L = intended, R = produced)
    • Semantic (related meaning): cat → dog
    • Phonological (sound overlap): cat → hat
    • Mixed (both): cat → rat
    • Unrelated: cat → bread (rare)
    • Non-word: cat → lat (rare)
  • Exchange errors respect hierarchy; units swap only within same level (no cross-level mixes)

Prediction by Production

  • Listeners internally simulate speaker’s upcoming words using their own production system
  • Facilitates real-time comprehension; eye-tracking shows slowdown when prediction fails (e.g., “The defendant examined by the lawyer …”)
  • Aided by:
    • Linguistic structure
    • Physical / situational context
    • Shared background knowledge
  • Requires cognitive resources → less common in children, older adults, L2 speakers

Process Memory & Temporal Receptive Windows (TRW)

  • Process memory: maintains recent info to integrate incoming input
  • TRW size grows with linguistic level
    • Phoneme: milliseconds
    • Word: hundreds of ms
    • Sentence: seconds
    • Paragraph: minutes
    • Narrative: days/months
  • Progression mirrors cortical hierarchy: sensory → lexical/semantic → discourse-level integration

Aphasias

  • Aphasia = language disorder from brain damage
  • Broca’s (non-fluent) aphasia
    • Lesion: Broca’s area (left inferior frontal gyrus)
    • Speech effortful, fragmented; comprehension largely intact; patient aware of errors
  • Wernicke’s (fluent/receptive) aphasia
    • Lesion: Wernicke’s area (posterior left superior temporal gyrus)
    • Speech fluent but nonsensical; severe comprehension deficit; patient unaware of errors

Quick Recall Points

  • \approx 44 English phonemes stitched into words via articulation
  • Speech errors demonstrate modular hierarchy (word, morpheme, phoneme levels)
  • Comprehension benefits from predictive simulation but at cognitive cost
  • TRW length scales with linguistic complexity
  • Broca = broken output; Wernicke = worthless meaning