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Midterm 2

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Psychology 2134A/B
Marc Joanisse

21 Speech Perception 121104 621 PM Recognizing Spoken Wordshumans are very good at recognizing speechwe can understand all speakers of our language even people weve never heard before computers are very bad at itat best can recognize very general speech or the speech of one personeven though computers are pretty good at other taskswhat makes speech so differentThe Nature of Sound Wavessound travels as wavesthese waves have several important propertiesfor example pitch and volumeFrequencymeasured in Hz cycles per secondhigher frequencieshigher pitchAmplitudechanging the amplitude of a sound wave changes its volumeAcoustics of Speechspeech waveforms are much more complexSpectrogramswe can analyze the acoustic properties of signals by looking at a spectrogramshows the amplitude of a waveform at different frequenciesSpeech Spectrogramsspeech is made up of areas of concentrated acoustic energy called formantsAcoustic Cues to Speechformants bands of highamplitude frequencies in speechformant transitions consonantssteadystate formants vowelsSo Whats the Problemwe know a lot about the acoustics of speechbut the task of decoding speech isnt as simple as it seemslack of invariancespeaker variabilitysegmentationAre Phonemes Like Beads on a Stringscientists tried cutting a recording of speech into separate phonemesthen reordered them into new wordsresult wasnt so greatProblem 1 Lack of Invariancethere isnt always a consistent acoustic cue for a given phonemeeffects of context phonemes vary depending on what it precedes for follows coarticulationCoarticulationHockett CF 1955imagine a row of Easter eggs carried along a moving a belt the belt carries the row of eggs between the two rollers of a wringer which quite effectively smash them and rub them more or less into each otherthe mess that emerges from the wringer represents the output of the speech transmitterwe have an inspector whose task it is to examine the passing mess and decide on the basis of broken and unbroken yolks the variously spreadout albumen and the variously colored bits of shell the nature of the flow of eggs which previously arrived at the wringerthe inspector represents the hearerCoarticulationkeep and cope both start with kbut they are acoustically differentarticulated differentlyhowwhy are they perceived as the same phonemeProblem 2 Speaker Variabilitythe acoustic properties of speech vary across speakersdialects accentssex differencesrate of speechand individuals produce the same words differentlyhow do we pick out what is consistent across all this variabilityProblem 3 Segmentationwe produce words as an unbroken stringbut we need to identity these individual segmentsI read a book todayCategorical Perception of Formant Transitionsba vs gavary only the F2 onset frequencySoformant transitions vary in even stepsbut people hear a change as all or nonecategorical perceptionvery robustalmost all speech sounds are perceived categoricallyMcGurk EffectWhats Going Onspeech is being integrated using different types of informationmonitoring both sounds and visual informationconflicting informationleads to misperceptionsThe Motor Theory of Speechmodular theory there is a dedicated speech processor in our headsspeech is specialspeech module not used for other sounds
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