Conclusions
To conclude, this study documents a neural correlate of rapid word
learning, a crucial human skill that plays a defining role in our social
communication abilities. The learning effect is temporally early, emerging
already at ~50 ms after the spoken input can be identified, and demonstrates
a highly automatised process resilient to attention modulation.
Importantly, the strength of the brain response increase predicts the
subsequent recall and recognition of the newly learnt words. However,
this fast automatic neural memory trace build-up is restricted to words
with familiar native-language phonology, benefiting from pre-existing
perception-articulation links in the brain. This, in turn, implies different
neural strategies for learning new words in the native and non-native
languages. The behavioural results together with the lack of attention effect
in the early learning-related response phase suggest that attention
affects word processing only somewhat later on, after the initial automatic
stages of neurolexical activation are complete. The primary cortical
circuits underlying rapid novel word learning comprise structures of the
left posterior middle temporal and inferior frontal cortices, which allow
harnessing both the phonological and lexico-semantic networks critical
for mapping novel speech input onto neural memory representations.
The current findings shed new light on the fascinating facility of the
human brain to rapidly build new memory traces for linguistic elements,
enabling successful human communication. The automatic neural
mechanism described here is what likely underpins the ease in learning
new words of the native tongue even in adulthood. On the other hand,
the specificity of this rapid learning to native phonology can explain
the difficulties experienced by adults when acquiring new languages.
The adult neural language system seems to be highly fine-tuned and receptive
to native language phonology; future research can explore the
development of this mechanism in infancy and childhood.