Phonetic Discrimination at birth

Smith et al 2003

• foetal auditory system is functional at 20 weeks gestational age

• indicates early auditory sensitivity

• fetuses can detect and respond to sounds in their environment

Mehler et al 1988

• Newborns found to be sensitive to the properties of the language of their parents

• showed a preference for their native language (the language spoken by their parents) over foreign languages.

• Measured by changes in sucking rate: babies sucked more strongly when hearing their native language compared to a foreign one.

• Babies are already familiar with the rhythm and sound patterns of their native language at birth, suggesting language learning begins before birth through exposure in the womb

Draganova et al 2007

MEG study of fetal/newborn auditory discriminative evoked responses

• mismatch negativity (MMN) response elicited to auditory stimuli is an indicator of sound discrimination in adults

• recordings on fetuses started at 29wk of gestation, follow up recording 2 weeks after birth

• two tone bursts presented: standard (500Hz) and deviant tone (750Hz)

• The discriminative brain responses to tone frequency change could be detected as early as 28 weeks.

• The ability of the foetus to detect changes in sounds is a prerequisite to normal development for cognitive function; related to language learning and clinical aspects of auditory disorders.

• auditory discrimination abilities, essential for language learning are already functional before birth

• startle reflex: automatic physical response (like body movement or heart rate change) that a fetus shows when detecting a sudden or different sound

Kisilvesky et al 2009

• Fetal sensitivity to properties of maternal speech and language

• Fetal language abilities examined in 104 fetuses at 33–41 weeks GA using a familiarization/novelty paradigm.

• Fetuses were familiarized with tape recording of either mother or a female stranger reading the same passage and subsequently presented with a novel speaker or language

• Heart rate was recorded continuously

• a novelty response to the mother’s voice and a novel foreign language.

• evidence of foetal attention, memory, and learning of voices and language, indicating that newborn speech/language abilities have their origins before birth

• suggest that neural networks sensitive to properties of the mother’s voice and native-language speech are being formed.

infant phoneme discrimination

high amplitude sucking (HAS) technique Measures pressure produced by sucking.  Pacifier connected to a pressure transducer and a computer. When baby starts sucking, the computer measures infant’s average sucking amplitude (strength of the sucks). sound is presented to the infant every time a strong or “high amplitude” suck occurs. infants quickly learn that their sucking controls the sounds, and they will suck more strongly and more often to hear sounds the like the most Infant's sucking rate increases when they are interested decreases when not. They lose interest in a sound when it is presented repeatedly but they will become interested if a new sound is presented The sucking rate can also be measured to see if an infant notices when new sounds are played.

Eimas et al 1971

• high amplitude sucking technique

• infants as young as 1m old can discriminate and categorise speech sounds similarly to adults

• measured infants sucking rates in response to speech sounds like B and P

• infants could distinguish between phonemes based on voice onset time: interval between release of a stop consonant and the vibration of vocal cords

• infants view phonemes as distinct categories

• highlights the innate ability of infants to process speech sounds

discriminating sound differences

• Kuhl & Millar: chinchillas, primates and birds can discriminate phonetically

• Because our auditory system (whose characteristics  are shared with other species) is not a perfect channel to transmit sound. 

• The sound wave arrives distorted to the brain through the ear and nervous system. This distortion prevents the perception of some differences in the sound wave.

• Categorical perception might be a product of a biologically determined perceptual mechanism but this mechanism does not seem to have been selected to give children the advantage in processing speech sounds.

6 Months Old Citizens of the World

• 6 months old infants are often referred to as "Citizens of the World" because of their ability to distinguish between phonetic contrasts from all languages

• infants possess a universal sensitivity to speech sounds, can tell difference between /ra/ and /la/, which are distinct phonemes in English but not in Japanese

• Head Turn Preference Method: used to study infants' speech discrimination abilities, exposed to two different sounds/stimuli, When new sound is introduced, infants typically turn their heads toward the source of the sound, indicating they perceive the difference.

• American and Japanese infants can both distinguish /ra/ and /la/ at 6 months, Japanese infants begin to lose ability by 10-12 months as they tune their phonetic perception to their native language, which doesn’t use this distinction, American infants retain the ability because it is relevant in English.

• universal sensitivity narrows as infants specialize in the sounds of the language(s) they hear regularly—a process known as perceptual narrowing

The Innately Guided Learning Hypothesis Juscyk & Bertocini 1988

• infants biologically predisposed to pay attention to specific aspects of environment

• prewired with categorical perception abilities, distinguish contrasts across languages, shaped by exposure to specific language

• speech sounds more salient to infants than other acoustic stimuli, speech sounds attract attention and prioritised for processing

• perceptual systems are flexible and can adapt to specific phonetic and linguistic environment

• link between innate predisposition and environmental influences in language acquisition