Hearing and Deafness 2 Ear as a frequency

Hearing and Deafness 2. Ear as a frequency analyzer Chris Darwin

Demo Class • Tuesday 24 th Oct 2006 at 12: 00 in CHI LT • Demonstration of Excel spreadsheet to illustrate: auditory filtering & excitation patterns. • Spreadsheet available at: http: //www. lifesci. sussex. ac. uk/home/Chris _Darwin/Perception/Lectures/ Amadeus

Frequency: 100 -Hz Sine Wave 1. 0 Spectrum 0 Amplitude against frequency -1. 0 0 Time (s) Waveform 0. 05 1 amp Amplitude against time 100 Hz frequency

Frequency: 500 -Hz Sine Wave 1. 0 Spectrum 0 Amplitude against frequency -1. 0 0 Time (s) 0. 05 1 Waveform amp Amplitude against time frequency 100 500 frequency

Amplitude: 500 -Hz Sine Wave Spectrum Amplitude against frequency 0 1 0 Time (s) 0. 05 amp frequency 100 0 0 Time (s) 0. 05 500 frequency

Phase: 500 -Hz Sine Wave sine The amplitude spectrum does not show phase 1 amp cosine frequency 100 500 frequency

adding sine waves Spectrum of Sum 1 Sine wave Sum 1 amp 0 ﾐ 11 frequency 0 ﾐ 11 1 0 amp ﾐ 1 0 0. 025 Time (s) 0. 05

100 -Hz fundamental Complex Wave 5. 0 Spectrum Amplitude against frequency 0 -1. 7 0 Time (s) Waveform 0. 05 1 amp Amplitude against time frequency 100 500 frequency

frequency -> Staggered sine-waves adding simultaneous staggered time ->

Bandpass filtering (narrow) 5. 0 1 amp 0 -1. 7 0 Time (s) 0. 05 frequency 100 500 frequency 1 amp 0 0 Time (s) 0. 05 frequency 100 500 frequency

Bandpass filtering (wide) 5. 0 1 amp 0 -1. 7 0 Time (s) frequency 100 0. 05 500 frequency 1 amp frequency 100

Beats Repetition rate is the difference in frequency between the two sine-wave components 1/100 th second 500 - 400 = 100 Hz 1 amp frequency 100 400 500 frequency

Excitation patterns (envelope of excitation) Basilar membrane excitation pattern is like a spectrum

Excitation pattern of complex tone on bm

Measurement of auditory bandwidth with band-limited noise 1000 Hz 250 Hz Broadband Noise frequency 2000 Hz Amadeus

A gardening analogy

A gardening analogy

A gardening analogy Tone Noise Auditory bandwidth Noise bandwidth Detection mechanism

Wider auditory filter

Psychophysical tuning curves Bandwidth Masker center frequency

Human auditory bandwidth 1000 SNHL 800 Normal 600 400 200 0 0 2000 4000 At 1 k. Hz the bandwidth is about 130 Hz; at 5 k. Hz the bandwidth is about 650 Hz. 6000 8000 BW = freq / 8 roughly

Normal auditory non-linearities • Normal loudness growth (follows Weber’s Law, which is logarithmic, not linear) • Combination tones • Two-tone suppression • Oto-acoustic emissions

Combinations Tones (Tartini tones) 1 amp frequency 800 1000 1200 frequency

Two-tone suppression

Conductive vs Sensori-neural deafness SNHL usually a combination of OHC and IHC damage BM response becomes linear, so • No combination tones • No two-tone suppression

Symptoms of SNHL • Raised thresholds: helped by amplification • Wider bandwidths: no help possible • Recruitment (restricted dynamic range): partly helped by automatic gain controls in modern digital aids • Other non-linearities also reduced: combination tones, two-tone suppression • Often accompanied by tinnitus

Normal vs Impaired Dynamic Range