Place: 2460 A.V. Williams

Time: 3:00 PM

Host: Dr. Carol Espy-Wilson

Abstract: In the last 20 years our understanding of the cochlea has dramatically improved. In the mid 1980 time frame, and certainly before 1970, little was understood of inner and outer hair cell function. Furthermore the role of the cochlea was poorly understood when it came to the most important problem, speech processing by the auditory system. Today this is all changed. We now know that the outer hair cells play a key role in controlling the dynamic range of hearing, and are the source of wide dynamic range compression in the cochlea. We know that the narrow band tuning of the cochlear filters, arising from dispersive wave propagation within the cochlea, is responsible for the detection of signals, such as tones, music, and the most important signal, speech in high levels of noise. I shall show that the problem of the robustness of human speech recognition may be traced back to the cochlea. The question of the role of the cochlea and speech processing was extensively explored at Bell Labs by Harvey Fletcher, and then by many others, also at Bell Labs. These studies were quantified in terms of a measure called the articulation index (AI). The AI accurately measures the average phone score for maximum entropy (MaxEnt) speech sounds [Fletcher (1921); Fletcher and Galt (1951), French and Steinberg (1947), Allen (1996, 2005)].