The infant as a prelinguistic model for language learning impairments: predicting from event-related potentials to behavior

Abstract

Associations between efficient processing of brief, rapidly presented, successive stimuli and language learning impairments (LLI) in older children and adults have been well documented. In this paper we examine the role that impaired rapid auditory processing (RAP) might play during early language acquisition. Using behavioral measures we have demonstrated that RAP abilities in infancy are critically linked to later language abilities for both non-speech and speech stimuli. Variance in infant RAP thresholds reliably predict language outcome at 3 years-of-age for infants at risk for LLI and control infants. We present data here describing patterns of electrocortical (EEG/ERP) activation at 6 month-of-age to the same non-verbal stimuli used in our behavioral studies. Well-defined differences were seen between infants from families with a history of LLI (FH+) and FH- controls in the amplitude of the mismatch response (MMR) as well as the latency of the N250 component in the 70 ms ISI condition only. Smaller mismatch responses and delayed onsets of the N250 component were seen in the FH+ group. The latency differences in the N250 component, but not the MMR amplitude variation, were significantly related to 24-month language outcome. Such converging tasks provide the opportunity to examine early precursors of LLI and allow the opportunity for earlier identification and intervention.

Fig. 1

Photograph of a 6-month-old child seated on his mother’s lap during an ERP testing session using a dense array Geodesic Sensor Net system (Electric Geodesic, Inc., Eugene, Oregon, USA).

Fig. 2

The acoustic stimuli were presented in a passive oddball paradigm using a blocked design. Complex tone pairs had either a 300 or 70 ms within-pair interstimulus interval (ISI). Tones had a fundamental frequency of 100 or 300 Hz with 15 harmonics (6 dB roll-off per octave). In both blocks the 100–100 Hz (low–low) tone pair comprised 85% of the stimuli and the 100–300 Hz (low–high) tone pair comprised the remaining 15%. The 70 ms ISI stimuli were presented first followed by a second block of 300 ms ISI stimuli. The onset-to-onset inter-trial interval (ITI) was 915 and 1140 ms, and the offset-to-onset ITI was 705 and 700 ms for the 70 and 300 ISI ms conditions, respectively.

Fig. 3

Grand averaged ERP waveforms for FH− and FH+ infants to 300 ms ISI (top) and 70 ms ISI (bottom) conditions. Standard (blue line) deviant (red) and difference (green) waveforms are presented for Fc_z (electrode 4). The onsets of the tones are shown by the black vertical lines on the baseline (tones 1–2 represent a single tone pair). Negativities are plotted up, positivities down. The P₁₅₀–N₂₅₀ components are visible in the standard and deviant waveforms in both 300 and 70 ms ISI conditions for both groups. The absence of the N1* waveform in the 70 ms ISI condition from the standard and the deviant waves suggests a merged response for these more rapidly presented stimuli.

Fig. 4

Bar graphs representing the averaged latency of the N₂₅₀ ERP waveforms for the left (blue) and right (red) hemispheres for FH+ and FH− infants to the 70 ms ISI stimuli are presented here. A significant latency by group effect was observed. Overall FH+ infants had longer N₂₅₀ latencies and in this group the latency for the right hemisphere was significantly longer than that of the left side. No such laterality difference was observed in the FH− group.

Fig. 5

Grand averaged ERP waveforms for FH+ (top) and FH− (bottom) infants to the 70 ms ISI stimuli are presented here. The standard (blue line), deviant (red) and difference (green) waveforms for F3 (electrode13; left) and F4 (electrode 62; right) frontal channels are shown. The onsets of the stimuli are shown by the black vertical lines on the baseline (tone 1-tone 2 represent a single tone pair separated by 70 ms ISI). Negativities are plotted up, positivities down. A significant amplitude difference in the MMR was observed both between and within groups: FH+ infants had a smaller MMR overall as compared to FH−infants, and in the frontal areas only a significant laterality effect for FH+ infants was evident (left < right). No such laterality difference was observed in the FH− group.

Fig. 6

Topographic maps representing amplitude of the mismatch response (MMR) over the entire surface of the head for 300 ms ISI (top) and 70 ms ISI (bottom) are shown at peak MMR latency (659 and 414 ms, respectively) for FH+ and FH− infants. Anterior to posterior represented top to bottom (nose at top). There are no significant group differences in the 300 ms ISI, but for the 70 ms ISI condition the FH+ infants show reduced positivity (MMR) at frontal, frontocentral and central channels as compared to the FH− infants. Additionally, FH+ infants demonstrated a significantly smaller MMR (reduced positivity) in the left hemisphere as compared to FH− infants. There was no significant group by hemisphere interaction for the right hemisphere.