Key facts about speech perception 1 Auditory basis of speech perception 2 Categorical Perception 3 Perceptual parsing 4 Top down effects Auditory basis of speech perception External ear air ear canal is a tube Middle ear bones muscles to damp sound Inner ear fluid cochlea hair cells Auditory point 1 the ear is a filter enhancing some frequencies One part of the filtering is acoustic because the ear canal is a tube closed at one end and open at the other The ear canal is about 2 3 cm long 35000 2 3 x 4 3804 3 Hz Equal loudness curves note the dip at 4000 Hz Auditory point 2 we can hear pitch changes better at low frequencies The inner ear cochlea is a spectrum analyzer Nerve cells near the tip respond to low frequencies the membrane is thicker here Nerve cells near the base respond to high frequencies the membrane is thinner here Auditory frequency scale Bark scale is nonlinear We notice frequency changes at low frequencies where the formants are better than at high frequencies where some fricatives are 1 5 Bark 7 Bark 2000 Hz 2000 Hz 2 Categorical Perception Speech perception is non linear shaped by phonetic categories Study this using a continuum of equal acoustic steps Categorical perception Differences among items that fall into different categories are exaggerated and differences among items that fall into the same category are minimized A classic demonstration of categorical perception Liberman et al 1957 3 Perceptual parsing Phonetic material is parsed into different sources Coarticulatory effects of adjacent segments taken into account Talker differences modulate listener expectations the boundary between s and depends on the following vowel As if listeners are unpacking phonetic effects expecting to be lower in frequency in round vowel environment Men and women have different fricative noises slightly and listeners have different boundaries for men and women Any potential cue is an actual cue 4 top down influences on perception Linguistic expectations influence speech perception This is probably not just post perceptual bias top down effect 1 an effect of lexicality on speech perception Ganong 1980 People tend to hear words dash tash dask task Top down effect 2 Frequency of a sound in the listener s language influences where their boundary is Kataoka Johnson 2007 Boundaries English Japanese t is more common in English American listeners hear more t sounds k is more common in Japanese Japanese listeners hear more k sounds Key facts about speech perception 1 Auditory basis of speech perception 2 Categorical Perception 3 Perceptual parsing 4 Top down effects
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