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Temporal Masking.docx

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McMaster University
Paul Faure

November 20 , 2013 Psych 3A03: Audition Temporal Masking Frequency Discrimination - Humans are good at discriminating across a broad range of frequencies especially in the range of human speech - Dramatically increase as the frequency increases - Frequency discrimination threshold (JND) changes as a function of frequency - Replot data of frequency discrimination thresholds as Weber Fraction  Weber fraction is .2% and increases to 1-2% for higher frequencies - Weber fraction is nearly constant over frequency range - Weber fraction = .2% in the best frequency range - Can use weber fraction to quickly estimate difference limens for most frequencies - Relatively intensity invariant Intensity Discrimination - Can discriminate across a broad range of SPLs - More sensitive to changes in dB at higher levels - Curve for broadband noise is flat, maximally stimulating different frequencies so there is maximum discrimination detection - I/I is not changing and is following Weber’s law - We are sensitive to small changes in sound intensity, ΔI in dB - If ΔI measured in dB is relatively constant, then the Weber fraction (ΔI/I) in units of pressure, energy or power should also be constant - Can use Weber fraction (ΔI/I) to estimate difference limens at individual frequencies in ΔI dB - ΔI/I = c = Weber Fraction - ΔI/I + 1 = c + 1 (=K) - ΔI/I + I/I = K - ΔI + 1/I = K - 10log(ΔI+I/I) = 10logK - 10log(ΔI + 1) – 10log(I) = ΔI in dB - Intensity discrimination better for broadband noise than tones - Near miss to Weber’s Law for tonal intensity discrimination Temporal Discrimination - Interested in measuring temporal resolution of auditory system - Temporal discrimination, like duration discrimination, is difficult to study as if the tone is too short it will create white noise (wider broadband) so are they detecting temporal or broadband - Providing the tones on a background of noise to minimize the spectral cues - Recall that signal energy and spectral purity change when stimulus duration decreases - Variables unrelated to duration serve as confounding cues for signal detection - Some researchers use acoustic gaps Temporal Discrimination: Gap Detection - Gap detection task: acoustic markers with a time interval - This task measures the ability of Ss to detect temporal gaps that vary in absolute duration - As time separation (T) between acoustic markers increases, gap detection threshold (ΔT) also increases - Gap detection threshold does not follow Weber’s law - ΔT/T ≠ constant Temporal Modulation Discrimination - Interested in measuring temporal resolution of auditory system - Another way: ask subjects to detect amplitude modulations - SAM signal = sinusoidally amplitude modulated signal - SAM tones contain energy at the carrier and sideband frequencies - x(t) = A[1 + msin(2πF t)sin(2πF t)] m c - Fm= frequency of modulation - m = depth of modulation (0≤m≤1) - Fc= carrier frequency of stimulus - Use wideband SAM noise: x(t) = 1 +msin(2πF t)n(t) m - Wideband SAM noise: fine structure of signal changes more quickly than does envelope, thus no additional cues - Listener’s task: detect which noise signal is amplitud
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