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Psychophysical tuning curves measured in simultaneous and forward masking

Brian C.J. Moore J. Acoust. Soc. Am. , 1978 23 Feb 2009. Psychophysical tuning curves measured in simultaneous and forward masking. Background. Phenomena of simultaneous and forward masking previously described

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Psychophysical tuning curves measured in simultaneous and forward masking

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  1. Brian C.J. Moore J. Acoust. Soc. Am., 1978 23 Feb 2009 Psychophysical tuning curves measured in simultaneous and forward masking

  2. Background • Phenomena of simultaneous and forward masking previously described • Some ambiguity about how the results of these methods for deriving psychophysical tuning curves differ • Goal: Investigate the frequency tuning curves produced by simultaneous vs. forward masking in a within-subject design • Consider effects of absolute probe threshold • Compare results to neural tuning curves

  3. Method • Masker: • 334ms (rise, fall = 17ms)‏ • varied in frequency and amplitude • Probe: • 34ms (rise, fall = 17ms)‏ • 1000Hz • 5, 10, 20, 30 dB SL. • Masker thresholds • 75% detection • measured in 2AFC • staircase method • 5dB until first reversal, 2dB thereafter • Simultaneous and forward masking conditions 800Hz masker, 40dB; 1kHz probe, 10dB

  4. Effects of probe level in simultaneous masking • Broad tuning • Noisy behavior at ±20Hz of probe due to random phase relationship w/ masker • Low-level linear response • Non-linearity at high frequency maskers for low-level probe

  5. Effects of probe level in forward masking • Sharper tuning at higher probe levels • Non-linear effects of probe level at all frequencies • No more “random” behavior when masker ≈ probe

  6. Comparison of simultaneousand forwardmasking at 1kHz • Greater selectivity in forward masking condition • Smaller bandwidths, larger slopes • Near probe frequency, threshold of forward maskers is lower than that of simultaneous maskers • Simultaneous maskers best at frequencies just above probe • Qualitatively similar results at 6kHz

  7. Tuning curves in forward masking as a function of probe frequency • Similar threshold functions across probe frequency • Selectivity sharpens as ν → 4kHz, broadens again at 8kHz.

  8. Summary • Best simultaneous masking at frequencies just above probe frequency • Action of simultaneous masking may be in lateral suppression • Not analogous to neural tuning, but to “suppression areas” • Cf. two-tone suppression • Forward masking produces steeper slopes, narrower bandwidths (greater selectivity) than simultaneous masking • Similar to, but sharper than, neural tuning curves • Other factors besides sensory selectivity may play a role in psychophysical tuning curves • When probe and forward masker are close in frequency, detection may be based on fine temporal characteristics (absolute duration, AM).

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