functional neuroimaging of speech perception in infants

Functional Neuroimaging of

Speech Perception in Infants

Dehaene-Lambertz, G. , Dehaene S., and Hertz-Pannier,

L.

By Divya Patel

Why study infants?

• Adult human brain: anatomical and functional specialization for speech processing

• How?– clarify how it emerges through

development

Language and infants?

• Considerable language takes place in the 1st year

• Development in:– Phonology: organization of sounds– Prosody: tone of voice, rhythm– Word segmentation: when a word

starts/ends

Motivation

• Not much known about brain mechanisms• Studies mostly use ERPs

– Great know temporal lobes contain neural circuit for phoneme discrimination

– Not as great do not provide spatial information

• This study uses fMRI

Experimental Design

20s Silence 20s Silence

20s of forward speech

20s of backward speech

20 healthy, non-sedated infants (2-3mo)Speech = highly intonated female voice; in French

Hypothesis

• Forward speech = ↑ activation than backward speech

• Fast temporal auditory transitions and phonetic information will be jointly activated

Activation to Sound

• Similar to adults

Brain Lateralization

• Similar to adults

Forward Speech vs. Backward Speech

• In adults, the area is left superior temporal sulcus

Awake vs. Asleep

Was the hypothesis supported?

• Forward speech = ↑ activation than backward speech in left angular gyrus and left mesial parietal lobe

• Fast temporal auditory transitions and phonetic information will be jointly activated in left temporal lobe– From superior temporal gyrus to

surrounding areas of superior temporal sulcus

Yes

Other underlying mechanisms?

• In adults:– Precuneus and dorsolateral PFC (dlPFC)

activated during retrieval • In infants:

– Precuneus and dlPFC activated • May indicate early engagement of

active memory retrieval mechanism

Yes, there seems to be

Strengths

• Approaches were different than prior studies– Used fMRI– Used non-sedated

babies• Very straight forward• Images corresponding

to brain parts

Limitations• Not enough

background – Assumed all

readers would know basic infant brain development

Future Directions• It would be interesting to do a longitudinal

study, to understand when exactly the changes take place

• To create a study where retrieval can be tested, perhaps through habituation

• To find specific evidence for either – nativist view (language mechanisms are

innate) – interactionist view (language

mechanisms are developed through interaction)

QUESTIONS?

Dehaene-Lambertz G, Dehaene S, Hertz-Pannier L.

(2002) Functional neuroimaging of speech perception

in infants. Science 298(5600):2013-5.