Interaural time coincidence detectors are present at birth: evidence from binaural interaction.
Level 4 - case-series / case-control
Cross-sectional physiological study in neonates without a comparative control group.
PubMed 14698088 · doi:10.1016/s0378-5955(03)00331-9
What was done
Auditory brainstem responses were recorded in 34 human neonates using monaural and binaural click stimuli. Binaural difference (BD) waveforms were computed by subtracting the binaural response from the sum of left and right monaural responses across interaural time differences (ITDs) between 0 and 1000 microseconds. Researchers evaluated the detection rate of the first positive peak (beta) across ITDs to assess whether neural coincidence detector mechanisms are present at birth.
What was found
At an ITD of 0 microseconds, the beta peak was detectable in 56% of neonates. Beta detectability decreased as ITD increased, with 9% of infants displaying a detectable beta peak across all tested ITDs (up to 1000 microseconds). Detection of beta did not correlate with other monaural or binaural auditory brainstem response characteristics. The second peak (delta) correlated strongly with the presence of wave VI in monaural and binaural waveforms.
Why it matters
This indicates that the brainstem pathways responsible for detecting interaural time differences are operational at birth rather than constructed or recalibrated postnatally as head circumference increases.
Limits
The sample size was small (n = 34). Detectability of the physiological signal was low (absent in 44% at zero ITD and absent in 91% across all ITDs), which the authors attribute to incomplete myelination and synchrony. The study lacked an internal adult comparison group tested under identical recording conditions and did not assess behavioral localization.
Cited by
- supports An infant's head is approximately half the width of an adult's head, resulting in a maximum interaural time difference of approximately 0.25 milliseconds.