🫶🏽Psychology of Language Unit 6 – Speech Production & Perception

Key Concepts

• Speech production involves the coordination of various anatomical structures, including the lungs, larynx, vocal cords, tongue, and lips
• Phonetics focuses on the physical properties of speech sounds, such as their acoustic characteristics and articulation
• Phonology studies the sound systems of languages, including the rules governing the combination and distribution of speech sounds
• Speech perception theories attempt to explain how listeners interpret and understand spoken language from the acoustic signal
• The brain plays a crucial role in speech production and perception, with specific areas responsible for language processing (Broca's area, Wernicke's area)
• Language development in children follows a predictable sequence, starting with babbling and progressing to more complex utterances
  • Infants begin to discriminate speech sounds as early as 1 month old
  • Around 6-8 months, infants start babbling, producing repetitive syllables like "bababa" or "dadada"
• Speech disorders can arise from various causes, such as developmental issues, brain damage, or physical abnormalities of the speech organs
• Researchers employ various methods to study speech production and perception, including acoustic analysis, brain imaging techniques, and perceptual experiments

Anatomy of Speech Production

• The respiratory system, consisting of the lungs and diaphragm, provides the air pressure necessary for speech production
• The larynx, commonly known as the voice box, contains the vocal cords, which vibrate to produce voiced sounds
• The vocal cords are two bands of muscle tissue that can be adjusted to change the pitch and volume of the voice
• The articulators, including the tongue, lips, teeth, and palate, shape the airflow to create different speech sounds
  • The tongue is the most flexible articulator, capable of producing a wide range of sounds
  • The lips are used to create sounds like /p/, /b/, and /m/
• The nasal cavity can be coupled with the oral cavity to produce nasal sounds like /m/, /n/, and /ŋ/ (as in "sing")
• The pharynx, a muscular tube connecting the larynx to the oral and nasal cavities, acts as a resonating chamber for speech sounds

Phonetics and Phonology

• Phonetics is divided into three main branches: articulatory phonetics, acoustic phonetics, and auditory phonetics
  • Articulatory phonetics studies the production of speech sounds by the vocal tract
  • Acoustic phonetics examines the physical properties of speech sounds, such as frequency, amplitude, and duration
  • Auditory phonetics focuses on how speech sounds are perceived by the human auditory system
• The International Phonetic Alphabet (IPA) is a standardized set of symbols used to represent speech sounds across languages
• Phonemes are the smallest units of sound that distinguish meaning in a language (e.g., /p/ and /b/ in "pat" vs. "bat")
• Allophones are variations of a phoneme that do not change the meaning of a word (e.g., the aspirated and unaspirated versions of /p/ in "pin" and "spin")
• Phonological rules govern the distribution and combination of phonemes in a language, such as assimilation and deletion rules

Speech Perception Theories

• The Motor Theory of Speech Perception proposes that listeners perceive speech by internally simulating the articulatory gestures required to produce the sounds
• The Acoustic Theory of Speech Perception suggests that listeners rely on the acoustic properties of speech sounds to identify and categorize them
• The Categorical Perception Theory posits that listeners perceive speech sounds as distinct categories rather than as a continuum
  • Listeners are more sensitive to acoustic differences between categories than within categories
  • Categorical perception has been demonstrated for various speech sound contrasts, such as voice onset time (VOT) for stop consonants
• The Perceptual Magnet Effect refers to the phenomenon where certain speech sounds within a category are perceived as better exemplars and attract nearby sounds
• The Fuzzy Logical Model of Perception (FLMP) proposes that listeners integrate multiple sources of information (e.g., acoustic cues, context) to make probabilistic decisions about speech sounds

Neurological Basis of Speech

• Broca's area, located in the left frontal lobe, is involved in speech production and syntax processing
  • Damage to Broca's area can lead to Broca's aphasia, characterized by effortful, non-fluent speech with impaired grammar
• Wernicke's area, situated in the left temporal lobe, is associated with speech comprehension and semantic processing
  • Damage to Wernicke's area can result in Wernicke's aphasia, characterized by fluent but meaningless speech and poor comprehension
• The arcuate fasciculus is a bundle of nerve fibers connecting Broca's and Wernicke's areas, enabling communication between these language centers
• The superior temporal gyrus (STG) is involved in the processing of speech sounds and is important for speech perception
• The inferior frontal gyrus (IFG) is activated during speech production tasks and is thought to play a role in articulatory planning
• Neuroimaging techniques, such as functional magnetic resonance imaging (fMRI) and electroencephalography (EEG), have provided insights into the brain regions involved in speech processing

Language Development

• Infants show a preference for speech sounds over non-speech sounds from an early age, demonstrating an innate sensitivity to human speech
• Around 12 months, infants typically produce their first words and engage in joint attention with caregivers
• Between 18-24 months, children undergo a vocabulary spurt, rapidly acquiring new words and combining them into short phrases
• By age 3, children can produce multi-word utterances and begin to use grammatical markers like plurals and past tense
• Phonological development involves the gradual acquisition of the sound system of the native language
  • Children may initially simplify complex sound patterns through processes like consonant cluster reduction and final consonant deletion
• Syntactic development progresses from simple two-word combinations to more complex sentence structures, including questions and negation
• Pragmatic skills, such as turn-taking and adjusting language to the listener's needs, develop throughout childhood and adolescence

Speech Disorders

• Articulation disorders involve difficulties producing specific speech sounds correctly (e.g., substituting /w/ for /r/)
• Phonological disorders are characterized by patterns of sound errors that affect multiple speech sounds (e.g., fronting all back consonants)
• Stuttering is a fluency disorder marked by repetitions, prolongations, and blocks in speech production
  • Stuttering typically emerges between ages 2-5 and can be influenced by genetic and environmental factors
• Apraxia of speech is a motor speech disorder resulting from impaired planning and coordination of speech movements
• Dysarthria is a group of speech disorders caused by weakness, paralysis, or incoordination of the speech muscles due to neurological damage
• Voice disorders can affect the pitch, loudness, or quality of the voice and may result from vocal cord nodules, polyps, or paralysis
• Speech-language pathologists (SLPs) assess, diagnose, and treat various speech and language disorders using evidence-based interventions

Research Methods and Applications

• Acoustic analysis involves measuring and visualizing the physical properties of speech sounds using specialized software (Praat, WaveSurfer)
  • Acoustic measures such as formant frequencies, fundamental frequency, and duration can provide insights into speech production and perception
• Perceptual experiments investigate how listeners perceive and categorize speech sounds by manipulating acoustic cues and collecting behavioral responses
  • Identification tasks require listeners to label speech sounds or words from a fixed set of options
  • Discrimination tasks assess listeners' ability to detect differences between speech sounds or stimuli
• Brain imaging techniques, such as fMRI, EEG, and magnetoencephalography (MEG), allow researchers to study the neural correlates of speech processing in real-time
• Eye-tracking methods can be used to examine the time course of speech perception and word recognition by measuring listeners' eye movements to visual referents
• Computational models of speech production and perception aim to simulate and predict human speech behavior using mathematical algorithms and machine learning techniques
• Research findings from speech production and perception studies have applications in fields such as speech recognition technology, second language learning, and clinical assessment and intervention for speech disorders