9.2 Speech Perception and Production

Speech perception is a complex process that transforms sound waves into meaningful language. It involves auditory processing, phoneme identification, and segmentation of continuous speech. Our brains use context and expectations to fill in missing sounds and navigate the challenges of coarticulation.

Categorical perception helps us efficiently process speech sounds as distinct categories. Voice onset time distinguishes between similar consonants, while perceptual boundaries mark sharp transitions between phoneme categories. Context plays a crucial role, with lexical, syntactic, and semantic information influencing our interpretation of speech.

Speech Perception

Process of speech perception

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• Auditory processing transforms acoustic signals into neural representations
  • Ear detects sound waves converts to electrical impulses
  • Auditory nerve transmits signals to brainstem and auditory cortex for processing
• Phoneme identification distinguishes meaningful sound units in language
  • Categorizes speech sounds into discrete phonemes (/b/ in "bat", /p/ in "pat")
  • Allows differentiation of words with similar sounds (cat vs. hat)
• Segmentation breaks continuous speech stream into individual words
  • Uses acoustic cues, stress patterns, and language-specific rules
  • Enables listeners to identify word boundaries in fluent speech
• Phoneme restoration effect fills in missing or obscured sounds
  • Brain uses context and expectations to "hear" missing phonemes
  • Demonstrates top-down processing in speech perception (s*eech vs. speech)
• Coarticulation involves overlapping of adjacent speech sounds
  • Reflects natural fluidity of speech production
  • Challenges segmentation but provides additional cues for word recognition

Categorical perception in speech

• Perception of speech sounds as distinct categories not continuous variations
  • Enhances efficiency of speech processing
  • Facilitates rapid phoneme identification (ba vs. pa)
• Voice onset time (VOT) distinguishes voiced from voiceless consonants
  • Measures time between stop release and vocal cord vibration
  • Critical for differentiating sounds like /b/ and /p/ (/b/ has shorter VOT)
• Perceptual boundaries mark sharp transitions between phoneme categories
  • Listeners more sensitive to differences across category boundaries
  • Within-category differences often perceived as the same sound
• Cross-linguistic differences reflect language-specific phoneme categories
  • Japanese speakers may struggle to distinguish /r/ and /l/ in English
  • English speakers may not perceive tonal differences in Mandarin

Context in speech perception

• Lexical effects leverage word knowledge to influence phoneme perception
  • Ambiguous sounds interpreted based on lexical context (beef vs. leaf)
  • Demonstrates interaction between bottom-up and top-down processing
• Syntactic context impacts word recognition and interpretation
  • Sentence structure guides expectations for upcoming words
  • Facilitates faster processing of grammatically consistent speech
• Semantic context uses meaning to enhance speech perception
  • Listeners more accurately perceive words in meaningful contexts
  • Improves comprehension in noisy environments
• McGurk effect shows visual information can alter auditory perception
  • Lip movements influence what listeners "hear" (ba + ga visual = da percept)
  • Highlights multimodal nature of speech perception
• Perceptual learning enables adaptation to unfamiliar speech patterns
  • Listeners improve comprehension of accented speech with exposure
  • Demonstrates plasticity in speech perception systems
• Expectations and prior knowledge shape interpretation of ambiguous speech
  • Cultural and personal experiences influence perception
  • Can lead to misinterpretations in cross-cultural communication

Speech Production

Mechanisms of speech production

• Respiratory system provides airflow for speech
  • Lungs generate subglottal pressure
  • Diaphragm and intercostal muscles control breath support
• Larynx houses vocal folds responsible for phonation
  • Vocal fold vibration produces voiced sounds
  • Adjustments in tension and length create pitch variations
• Vocal tract shapes sound produced by larynx
  • Oral cavity, nasal cavity, and pharynx act as resonators
  • Modifications in shape alter acoustic properties of speech sounds
• Articulators form specific speech sounds
  • Tongue, lips, teeth, and palate create constrictions and closures
  • Different configurations produce various consonants and vowels
• Neuromuscular control coordinates muscles for precise articulation
  • Brain sends signals to speech muscles via cranial and spinal nerves
  • Requires fine motor control and timing
• Coarticulation in production involves anticipatory and carryover effects
  • Articulator positions influenced by preceding and following sounds
  • Results in more efficient speech production
• Prosody conveys additional meaning through intonation, stress, and rhythm
  • Pitch variations indicate questions, statements, or emphasis
  • Stress patterns distinguish between words (record vs. record)
• Feedback mechanisms monitor and correct speech output
  • Auditory feedback allows speakers to hear their own voice
  • Proprioceptive feedback provides information about articulator positions