Hearing Science

1. Hearing Science HSLS 253 Chapter 10 Auditory Sensitivity

2. psychophysics (pp 275-279) • auditory sensitivity to frequency • auditory sensitivity to level • durations • temporal integration • differential sensitivity • frequency discrimination • intensity discrimination • temporal discrimination Chapter 10 – Auditory Sensitivity

3. Psychophysics Study of the relationship between psychological perception and physical aspects of a stimulus Sensitivity discrimination

4. Psychometric function • Psychometric function can be used to define threshold • Absolute threshold – the lowest level that a subject can just hear • Threshold = the level a subject can just hear 50% of the time Figure D.1

6. Classical psychophysics procedures • Method of limits - most often used - used in audiometry [bracketing (down 10/up 5)] - experimenter presents tones at various levels to find the level of interest • Method of constant stimuli - more rigorous - 5 to 10 levels presented a fixed number of times - construction of psychometric function • Modern psychophysics procedures • Alternative Forced-Choice procedures (e.g., 2-AFC procedure)

7. Frequency sensitivity • 20 to 20,000 Hz • Experiment (demo_freqsensitivity.m) • For 0 dB SPL at 1000 Hz (i.e., 20 Pa), the eardrum is vibrating through a total distance approximately equal to the diameter of a hydrogen atom. • Ultra-sound: > 20 kHz • Infra-sound: < 20 Hz

8. Intensity sensitivity • Threshold vs sensitivity • MAF vs MAP (Fig. 10.2) • ANSI 3.6 – 1996 (Tab. 10.1) • dB HL (decibel hearing level)

9. Psychometric functions for six frequencies. Figure 10.1

10. Supra-aural headphone Insert earphone Circumaural headphone

11. MAF (Minimum Audible Field) threshold • MAP (Minimal Audible Pressure) • Chalk board illustration Fig. 10.2

12. HA-2 coupler mounted with ER-3A earphone

13. For example, Subject A has a 30 dB HL threshold at 1000Hz measured using a supra-aural phone. • The threshold in dB SPL = 30 + 7.5 = 37.5 dB SPL • dB SPL=dB HL + RETSPL

14. Threshold of Pain • Threshold of discomfort • Dynamic range = threshold of discomfort – threshold of audibility • DR= ~125-135 dB at 1000 Hz ~80-90 dB at 100 Hz Fig. 10.2

15. Each line is an equal loudness contour • A phon is the level in dB SPL of an equally loud 1000-Hz tone. • E.g., all tones judged equal in loudness to a 40-dB SPL • 1000-Hz tone have a loudness level of 40 phons

16. Discrimination (i.e., differential sensitivity) Weber fraction ΔS / S ΔS – just noticeable difference S – the smaller of the two values being discriminated Weber’s law ΔS / S = constant For example Easy to distinguish b/w 1 vs. 2 pounds, but difficult to distinguish b/w 1000 vs. 1001 pounds

17. Difference threshold (∆F) for frequency discrimination • ∆F remains constant until > 1000 Hz • Slightly level-dependent Frequency Discrimination SL demo_freqdiscrim.m Fig. 10.5

18. Weber’s law Frequency Discrimination • In mid frequencies, Weber fraction is constant (i.e., follows Weber’s law). • ∆F/F = 0.002 = 0.2% • E.g, at 800 Hz, ∆F/F = 0.002 x 800 = 1.6 Hz Fig. 10.6

19. Near miss to the Weber fraction Intensity Discrimination • ΔI in dB for Intensity discrimination for six tonal frequencies and for noise. Fig. 10.7

20. Intensity Discrimination • For noise: ∆I in dB = ~ 0.5 - 1.0 dB (approximately constant) • If ∆I in dB is constant, ∆I/I is also a constant • For tones, ∆I decreases with increasing Intensity (i.e., near miss to the Weber fraction) Chalkboard illustration…

21. Plot the psychometric functions for the following three frequencies. • Table: Percent correct (%) detection of tones of the given frequency and level. • Frequency (Hz)Level in dB SPL • 10 12 14 16 18 20 22 • 500 50 55 60 65 70 75 80 • 1000 55 60 65 70 75 80 85 • 2000 60 65 70 75 80 85 90 •  2. If 75% correct is used as the definition of threshold, plot the thresholds of detection as a function of the three frequencies shown in problem 1. That is, plot the three-frequency thresholds of audibility curve for the data shown in problem 1. • 3. If 110 dB SPL was the level at which the listener experienced discomfort at 500, 1000, and also at 2000 Hz. What is the dynamic range of hearing at these frequencies given the thresholds of hearing shown in problem 1?

22. A child was tested in a sound-treated room by listening to test tones over loudspeakers. This child had thresholds of 23.9 dB SPL at 1000 Hz, 30.6 dB SPL at 2000 Hz, and 44.4 dB SPL at 4000 Hz. These results suggest that the child has hearing loss. Why? How many decibels is the hearing loss at each of the three frequencies given the Standardized Thresholds of Audibility? (Tab 10.1) • Refer to the Standardized Thresholds of Audibility (Tab 10.1) again, a patient tested with supra-aural headphones (TDH type) was reported to have threshold of 70 dB HL at 4 kHz. What is the level in dB SPL? • Refer to the Standardized Thresholds of Audibility (Tab 10.1) again, an audiometer at 0 dB HL produces 2 dB SPL at 1 kHz, what does that tell you?

23. 9. The data shown in the table below are the frequency difference thresholds for discriminating a change in frequency from the standard test tone. Re-do the table so the entries are in terms of the Weber fraction for Frequency Discrimination. Standard Frequency (Hz) 500 1000 2000 4000 8000 Diff. Thr. (Hz) 2Hz 4Hz 8Hz 16Hz 32Hz Weber fraction From the above problem, what is your best guess as to the difference in frequency that this listener could discriminate if the standard tone were 5000 Hz? Show your calculation.