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) 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)
Prenatal cardiac responses to sound 36 28
Prenatal motor responses to sound
Weir (1979): Pure-tone thresholds of newborns Pure tones Hz, various intensities Delivered with insert phones Recorded respiration, heart rate and motor responses; scored as response or not offline Sensitivity expressed as d’
Pure tone thresholds of newborns
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
Pure-tone thresholds of 2-5-week- olds
Trehub et al. (1991): Thresholds for octave-band noises, 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: Adults and children Amplitude Which one is more intense, 1 or 2? Time Amplitude When did the increment occur, 1 or 2?
Intensity discrimination: Infants Amplitude Respond when the intensity changes Time Amplitude Respond when the intensity changes “gated” “continuous” “increment detection”
Intensity discrimination: infants and children
Detection in noise parallels intensity discrimination
Detection in noise in standard psychophysical procedure
Evidence for immature resolution v. other sorts of efficiency? Threshold Stimulus “standard” listener Poor resolution Don’t know
Increment detection: Infants
Increment detection: Children
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.
Reaction time as a measure of loudness Intensity Reaction time (ms)
Loudness: Children Intensity Line length
Loudness discomfort levels: Children
Loudness discomfort levels
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.