| Temporal resolution |
| The ability to follow rapid changes in a sound over time |
| The bottom line |
| People manage to maintain good temporal resolution without compromising sensitivity by using intelligent processing. |
| Temporal resolution: How good is a listener at following rapid changes in a sound? |
| Auditory nerve fibers do not fire at the instant at which sounds begin or end. | |
| Auditory nerve fibers do not fire on every cycle of sound. | |
| Adaptation occurs to longer duration sounds. | |
| Spontaneous activity occurs when no sound is present |
| Following rapid changes in sound |
| The auditory nerve response does not follow changes with perfect precision |
| Averaging over time is one way the auditory system could Òsmooth outÓ the bumpy response of auditory nerve fibers |
| The time over which you average makes a difference |
| The temporal window |
| The temporal window |
| Hydraulic analogy: How long before the next bucket leaves for the brain? |
| Hydraulic analogy: How long before the next bucket leaves for the brain? |
| People can Òadd upÓ sound energy for |
| 5 ms | |
| 50 ms | |
| 200 ms | |
| 1500 ms |
| Temporal resolution: How short are the ÒsamplesÓ of sound? |
| Hypothesis # 1: We integrate over 200-300 ms. |
| Sensitivity-resolution tradeoff |
| If you extend the integration time to improve sensitivity, you lose resolution. |
| So how well should I be able to discriminate a change in the duration of a sound? |
| How to measure temporal resolution |
| Duration discrimination | |
| Gap detection | |
| Amplitude modulation detection |
| Problem in measuring temporal resolution: ÒSpectral splatterÓ |
| Duration discrimination |
| Duration discrimination |
| WeberÕs Law? NO | |
| Duration discrimination can be very acute - much better than 50-75 ms. |
| Gap detection |
| Gap detection |
| Is it temporal resolution or intensity resolution? |
| Amplitude modulation detection |
| By how much do I have to modulate the amplitude of the sound for the listener to tell that it is amplitude modulated, at different rates of modulation? |
| Slide 23 |
| Modulation depth |
| 2AFC AM Detection |
| Modulation depth, 20 log m |
| AM detection as a function of modulation rate |
| The temporal modulation transfer function (TMTF) |
| What sort of filter has a response that looks like this? |
| low-pass | |
| high-pass | |
| bandpass | |
| band reject |
| The TMTF is like a low-pass filter. That means that we canÕt hear |
| slow amplitude modulations | |
| high frequencies | |
| low frequencies | |
| fast amplitude modulations |
| TMTF at different carrier frequencies |
| Conclusions from TMTF |
| People are very good at AM detection up to 50-60 Hz modulation rate (and intensity resolution effects are controlled) | |
| 50-60 Hz = 17-20 ms/cycle of modulation | |
| 17-20 ms < 40 ms | |
| Somehow the auditory system is getting around the sensitivity-resolution tradeoff |
| The auditory system can follow amplitude modulation well up to about |
| 50-60 Hz | |
| 120 Hz | |
| 4 Hz | |
| 2000 Hz |
| So how can we detect such short changes in a sound and still be able to integrate sound energy over 200-300 ms? |
| Two theories of temporal resolution-temporal integration discrepancy |
| Multiple integrators | |
| Multiple looks |
| Multiple integrators |
| Multiple integrators |
| Multiple integrators |
| AN fibers donÕt have different integration times |
| But of course the integrators could be somewhere else in the brain. |
| Multiple looks |
| Multiple looks theory says |
| we have good temporal resolution because we use memory to integrate sound ÒenergyÓ | |
| we have good temporal resolution because we have some neurons that have good temporal resolution and some neurons that donÕt. |
| Multiple integrators theory says |
| we have good temporal resolution because we use memory to integrate sound ÒenergyÓ | |
| we have good temporal resolution because we have some neurons that have good temporal resolution and some neurons that donÕt. |
| A test of the multiple looks theory: Viemeister & Wakefield (1991) |
| Set up a situation in which the two theories predict different outcomes... |
| Viemeister & Wakefield (1991) |
| Viemeister & Wakefield (1991) |
| Viemeister & Wakefield (1991) |
| Viemeister & Wakefield (1991): Results |
| The results of Viemeister & Wakefield are most consistent with |
| multiple looks theory | |
| multiple integrators theory |
| Conclusions |
| People can detect very short duration changes in sound, such as 2-3 ms long interruptions. | |
| People can integrate sound energy over 200-300 ms to improve sound detection. | |
| The auditory system gets around the sensitivity-resolution tradeoff by using short-term integration and intelligent central processing. |
| Text sources |
| Gelfand, S.A. (1998) Hearing: An introduction to psychological and physiological acoustics. New York: Marcel Dekker. | |
| Moore, B.C.J. (1997) An introduction to the psychology of hearing. (4th Edition) San Diego: Academic Press. | |
| Viemeister, N.F. (1979). Temporal modulation transfer functions based upon modulation thresholds. J. Acoust. Soc. Am., 66, 1564-1380. | |
| Viemeister, N.F. & Wakefield, G. (1991) Temporal integration and multiple looks. J. Acoust. Soc. Am., 90, 858-865. | |
| Yost, W.A. (1994) Fundamentals of hearing: an introduction. San Diego: Academic Press. |
| Text sources |
| Gelfand, S.A. (1998) Hearing: An introduction to psychological and physiological acoustics. New York: Marcel Dekker. | |
| Moore, B.C.J. (1997) An introduction to the psychology of hearing. (4th Edition) San Diego: Academic Press. | |
| Viemeister, N.F. (1979). Temporal modulation transfer functions based upon modulation thresholds. J. Acoust. Soc. Am., 66, 1564-1380. | |
| Viemeister, N.F. & Wakefield, G. (1991) Temporal integration and multiple looks. J. Acoust. Soc. Am., 90, 858-865. | |
| Yost, W.A. (1994) Fundamentals of hearing: an introduction. San Diego: Academic Press. |