Chapter 11 - PSYB51

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Mathias Niemier

Chapter 11 – Music and Speech Perception  Sounds from musical instruments and human vocal tracts obey same laws of physical acoustics as all other sounds Music  Pythagoras from Pythagorean theorem in high school geometry – convinced that musical intervals they found most pleasing should provide greatest insights to universe as whole  When listeners hear pleasant sounding chords preceding a word, faster to respond with word like “charm” is positive and slower to respond that world like “evil” is negative  Have deep physiological effects  High levels of neurotransmitter serotonin are responsible for negative aspects of emotion and mood Musical Notes  Pitch: psychological aspect of sound related mainly to fundamental frequency Tone Height and Chroma  Octave: interval between 2 sound frequencies having ration of 2:1  When 1 of 2 periodic sounds is double frequency of other, 2 sounds are one octave apart  In typical Western music, frequencies of notes are adjusted slightly from simple ratios so that combos of notes will sound equally good when played in higher or lower frequency ranges (keys) o Set of notes (scale) used commonly in Western music is “equal temperament”  Tone height: sound quality corresponding to level of pitch. Tone height is monotonically related to frequency  Tone chroma: sound quality shared by tones same octave interval  Visualize musical pitch as helix – frequency and tone height increase with increasing height on helix o Circular laps around helix correspond to changes in tone chroma  Neurons in auditory nerve signal frequency both by their location in cochlea (place) and by timing of their firing (temporal)  Frequencies greater than 5 kHz, temporal coding doesn’t contribute to perception of pitch, and pitch discrimination becomes appreciably worse because only place coding can be used  Most instruments produce notes below 4 kHz Chords  Chords: combo of 3 or more musical notes with different pitches played simultaneously  Major distinction between chords is whether they are consonant or dissonant o Consonant chords: perceived to be more pleasing; combination of notes in which ratios between note th th frequencies are simple. Other major consonant intervals are perfect 5 (3:2) and perfect 4 (4:3) o Dissonant intervals: less elegant ratios; minor 2 (16:15) and augmented 4 (45:32) do not sound pleasing  Because chords defined by ratios of note frequencies combined to produce them, named same no matter what octave they are played in Cultural Differences  Any discussion of musical notes and chords would be incomplete if didn’t note that vast majority of research on music perception has focused on Western tradition  Potent relationships between notes like octaves are universal, different musical traditions used different numbers of notes and spaces between notes within octave  Lynch and Eilers tested degree to which 6 MO infants noticed inappropriate notes within both traditional Western scale and Javanese pelog scale o Infants appeared to be equally good at detecting “mistakes” within both Western and Javanese scales Making Music  Melody: arrangement of notes or chords in succession  When singing with other people possessing higher or lower voices, sing same melody at different pitches – even with single octave, same melody will be heard from different notes if steps between notes stay same  Tempo: perceived speed of presentation of sounds Rhythm  Bolton conducted experiments in which he played sequence of identical sounds perfectly spaced in time; had no rhythm o Listeners readily reported sounds occurred in groups of 2, 3 and 4 and reported hearing first sound of group as “accented” or “stressed” while remaining sounds were unaccented, or unstressed o Listeners are predisposed to group sounds into rhythmic patterns – sounds that are longer, louder and higher in pitch all are more likely to be heard as leading group o Timing relationship between 1 sound and others in sequence also help determine accent  When 2 different rhythms are overlapped, rhythms can collide in interesting ways  Rhythm is psychological and can produce sequences of sounds that are rhythmic Melody Development  Studies of 8 MO listeners reveal that learning of melodies begins quite early in life o Infants sat on parents’ lap while hearing 3 minutes of continuous random repetitions of melodies and then heard both original melodies and series of new 3 tone sequences o New sequences contained same notes as originals, but part of sequence was taken from one melody and another part from another – responded differently and deduce that they learned something about original melodies Speech  Initial observation is that humans are capable of producing incredible range of distinct speech sounds (5000 languages across world use over 850 different speech sounds)  Vocal tract: airway above larynx used for production of speech – includes oral tract and nasal tract  Notorious disadvantage of such low larynx is that humans more susceptible to choking o Another is that beyond infancy, we can’t swallow and breathe at same time Speech Production  Production of speech has 3 basic components – respiration (lungs), phonation (vocal cords), and articulation (vocal tract)  Respiration and Phonation o To initiate speech sound, diaphragm pushes air out of lungs, through trachea and up larynx o At larynx, air passes through 2 vocal folds, which are made up of muscle tissue that can be adjusted to vary hw freely air passes through opening between them o Rate at which vocal folds vibrate depends on stiffness and mass o Kids who have relatively small vocal folds have high pitched voices and adult men generally have lower pitched voices because testosterone increases mass of vocal cords o Measure sound right after larynx, see that vibration of vocal folds creates harmonic spectrum o First harmonic corresponds to actual rate of physical vibration of vocal folds, fundamental frequency  Articulation o Area above larynx – oral tract and nasal tract combined – vocal tract o Articulation: act of manner of producing speech sound using vocal tract o Formants: resonance of vocal tract. Formants are specified by center frequency and denoted by integers that increase with relative frequency  Labeled by F1, F2, F3, etc. o For shorter vocal tracts, formants are at higher frequencies than for longer vocal tracts and because absolute frequencies change depending on who’s talking, listeners must use relationships between formant peaks to perceive speech sounds o Most distinctive characteristics of speech sounds is spectra change over time o Spectrogram: pattern for sound analysis that provides 3d display plotting time on x-axis, frequency on y-axis and intensity on color or gray scale, and amplitude indicated by colour of any point on graph  Formants show up clearly in spectrograms as bands of acoustic energy that undulate up and down, depending on speech sounds being produced  Classifying Speech Sounds o Most often described in terms of articulation o Vowel sounds are all made with relatively open vocal tract, and vary mostly in how high or low and how far forward or back tongue is placed in oral tract, along with whether lips are rounded o Produce consonants by obstructing vocal tract in some way, and each sound can be classified according to 3 articulatory dimensions  1. Place of articulation. Airflow obstructed  At lips (bilabial speech sounds – b, p and m)  At alveolar ridge behind teeth (alveolar speech – d, t, n)  At soft palate (velar speech sounds – g, k, ng)  2. Manner of articulation. Airflow can be  Totally obstructed (stops – b, d, g, p ,t, k)  Partiall obstructed (fricatives – s, z, f, v, th, sh)  First blocked, then allowed to sneak through (-affricates – ch, j)  Blocked at first from going through mouth, but allowed to go through nasal passage (nasals – n, m, ng)  3. Voicing. Whether vocal cords  Are vibrating (voiced consonants – b, m, z, l, r)  Are not vibrating (voiceless consonants – p, s, ch) o To be effective, speech sound repertoires of languages have developed over generations of individuals
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