Topics in intensity processing Absolute sensitivity Intensity discrimination Loudness
Prenatal absolute sensitivity: measurement problems What is the stimulus that reaches the fetal ear? What is the stimulus that reached the fetal inner ear? What is the message in the fetal auditory nerve? Is the response to the sound or to the maternal response?
Lecanuet et al. (1988) 37-40 wk gestational age fetuses 500, 2000, 5000 Hz octave bands of noise Speaker 20 cm above maternal abdomen (mother listens to music) 100, 110, 115 dB SPL 1 cm above maternal abdomen 5 second duration 5-15 min interstimulus interval High (“awake”) and low (“asleep”) HR variability Cardiac and motor responses (ultrasound)
Weir (1979): Pure-tone thresholds of newborns Pure tones 125-4000 Hz, various intensities Delivered with insert phones Recorded respiration, heart rate and motor responses; scored as response or not offline Sensitivity expressed as d’
Werner & Gillenwater (1990): Pure-tone thresholds at 2-5weeks Observer-based method, but without reinforcement of infant response Tones presented with insert earphones Frequencies 500, 1000, and 4000 Hz, various intensities
Trehub et al. (1991): Thresholds for octave-band noises, 1.5-3.5 mo Observer-based method, with no reinforcement 4-kHz noise band alternated from left to right speakers Observer responded “signal” or “no signal”
Intensity discrimination: Summary Intensity jnd improves from about 5-7 dB at 6 months to 1-2 dB in adulthood. Intensity jnd is mature by about 5-6 years of age. Detection in noise follows the same time course as intensity discrimination. There is some evidence that intensity resolution is poorer during development for low-frequency sounds.
Intensity representation: Summary Absolute sensitivity at high frequencies is adult like in the preschool period, but at low frequencies continues to mature into the school years. Intensity discrimination is mature by 5-6 years, and there is a little evidence indicating immature intensity resolution in infants and toddlers. Loudness may grow faster with increasing intensity in infants than adults, but loudness growth is mature by 4 years.