Abstract
We tested 14-month-olds and adults in an event-related potentials (ERPs) study in which pictures of familiar objects generated expectations about upcoming word forms. Expected word forms labelled the picture (word condition), while unexpected word forms mismatched by either a small deviation in word medial vowel height (mispronunciation condition) or a large deviation from the onset of the first speech segment (pseudoword condition).Both infants and adults showed sensitivity to both types of unexpected word form. Adults showed a chain of discrete effects: positivity over the N1 wave, negativity over the P2 wave (PMN effect) and negativity over the N2 wave (N400 effect). Infants showed a similar pattern, including a robust effect similar to the adult P2 effect. These observations were underpinned by a novel visualisation method which shows the dynamics of the ERP within bands of the scalp over time. The results demonstrate shared processing mechanisms across development, as even subtle deviations from expected word forms were indexed in both age groups by a reduction in the amplitude of characteristic waves in the early auditory evoked potential.
Highlights
To understand natural speech, adults require detailed perception of individual speech sounds, well-defined lexical representations of word forms, and the ability to access these representations rapidly as incoming speech is processed
Response to expected word form The waveform in Fig. 2(top), shows a sequence of deflections characteristic of the PNP complex: a small positive deflection peaking at about 50 ms, followed by a large negative deflection peaking at about 100 ms, and a bifidal positive deflection with a large primary peak at about 200 ms and a smaller secondary peak at about 360 ms
The static topographic maps show no hemispheric differences during time windows capturing the N1 wave (80–180 ms) and the P2 wave (180–280 ms) indicating that the coronal orientation of the dynamic scalp bands is representative of the general pattern of effects during the PNP complex
Summary
Adults require detailed perception of individual speech sounds, well-defined lexical representations of word forms, and the ability to access these representations rapidly as incoming speech is processed. Duta et al / Developmental Cognitive Neuroscience 2 (2012) 223–234 infants are able to extract sufficient information from the first 200 ms of a word to reliably shift their gaze away from pictures which do not match the unfolding speech stream (Swingley et al, 1999; Fernald et al, 2001) The speed of this online, incremental processing of speech makes it likely that the neural correlates of segmental integration will be evident in the early auditory evoked potential
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