Dynamics of infant cortical auditory evoked potentials (CAEPs) for tone and speech tokens

Abstract

Objectives Cortical auditory evoked potentials (CAEPs) to tones and speech sounds were obtained in infants to: 1) further knowledge of auditory development above the level of the brainstem during the first year of life; 2) establish CAEP input-output functions for tonal and speech stimuli as a function of stimulus level and to 3) elaborate the data-base that establishes CAEP in infants tested while awake using clinically relevant stimuli, thus providing methodology that would have translation to pediatric audiological assessment. Hypotheses concerning CAEP development were that the latency and amplitude input-output functions would reflect immaturity in encoding stimulus level. In a second experiment, infants were tested with the same stimuli used to evoke the CAEPs. Thresholds for these stimuli were determined using observer-based psychophysical techniques. The hypothesis was that the behavioral thresholds would be correlated with CAEP input-output functions because of shared cortical response areas known to be active in sound detection. Design 36 infants, between the ages of 4-12 months (mean= 8 months, s.d.=1.8 months) and 9 young adults (mean age 21 years) with normal hearing were tested. First, CAEPs amplitude and latency input-output functions were obtained for 4 tone bursts and 7 speech tokens. The tone bursts stimuli were 50 ms tokens of pure tones at 0.5, 1.0, 2.0 and 4.0 kHz. The speech sound tokens, /a/, /i/, /o/, /u/, /m/, /s/, and /∫/, were created from natural speech samples and were also 50 ms in duration. CAEPs were obtained for tone burst and speech token stimuli at 10 dB level decrements in descending order from 70 dB SPL. All CAEP tests were completed while the infants were awake and engaged in quiet play. For the second experiment, observer-based psychophysical methods were used to establish perceptual threshold for the same speech sound and tone tokens. Results Infant CAEP component latencies were prolonged by 100-150 ms in comparison to adults. CAEP latency-intensity input output functions were steeper in infants compared to adults. CAEP amplitude growth functions with respect to stimulus SPL are adult-like at this age, particularly for the earliest component, P1-N1. Infant perceptual thresholds were elevated with respect to those found in adults. Furthermore, perceptual thresholds were higher, on average, than levels at which CAEPs could be obtained. When CAEP amplitudes were plotted with respect to perceptual threshold (dB SL), the infant CAEP amplitude growth slopes were steeper than in adults. Conclusions Although CAEP latencies indicate immaturity in neural transmission at the level of the cortex, amplitude growth with respect to stimulus SPL is adult-like at this age, particularly for the earliest component, P1-N1. The latency and amplitude input-output functions may provide additional information as to how infants perceive stimulus level. The reasons for the discrepancy between electrophysiologic and perceptual threshold may be due to immaturity in perceptual temporal resoluti...

Infant cortical electrophysiology and perception of vowel contrasts

“…Recently published research has revealed an apparent discrepancy between infant tone detection threshold and speech threshold, calling into question whether audibility for one can be used to predict the other (Cone & Whitaker, 2013). It is known that children weight speech-feature cues differently than do adults (Nittrouer 2004; 2007; Nittrouer & Lowenstein, 2007), but exactly how infants process temporal and spectral speech information is not well understood (Berg, 1991; Berg & Boswell, 1995).…”

“…Recently, Cone & Whitaker (2013) investigated the relationship between perceptual detection thresholds for tonebursts and speech-sound tokens and CAEPs in 36 infants between the ages of 4–12 months. First, CAEP amplitude and latency input-output functions were obtained for tonebursts and speech tokens.…”

Audição e linguagem em crianças nascidas a termo e pré-termo

“…However, recent studies have suggested the name of P1 and N1 to the positive peak and the predominant deflection in the tracing of the infant population. It is believed that from cortical maturation, these components originate the cortical endogenous complex in adults (20) . In order to clarify the effects of maturation of CAEP components, some studies (6,21) indicate the relationship between the variable age and the reduction of latencies of P1 and N1.…”

Potenciais corticais auditivos: uso de diferentes estímulos de fala em populações infantis

“…The presence of the P1-N1-P2 complex suggests that the speech was coded at the level of the auditory cortex and the absence of response is consistent with some imprecision in this process (6,13,14,15) . Some authors have carried out studies on the influence of vowel and consonant speech stimuli on long-latency auditory evoked potentials in children and adults with normal hearing, and could observe that there was influence on the measurements of the components P1, N1, N2 and P3, due to the level of complexity of the speech stimulus (16,17) . Therefore, the hypothesis of this study was to understand how such stimuli influence the generation of auditory evoked potentials and their components.…”

“…Therefore, because the maturational process is not complete, variations in the response in relation to the acoustic complexity of the speech stimulus and difficulty in its processing are expected (13,14,15,16) . Authors emphasized that using these potentials is important when elicited by speech stimuli, since they allow the monitoring of auditory development in normal children and in children at risk of developing communication disorders and language impairments (17) .…”