Transitions + Perception March 25, 2010

Tidbits Mystery spectrogram #3 is now up and ready for review! Final project ideas.

Glides Each glide corresponds to a different high vowel. VowelGlidePlace [i][j]palatal(front, unrounded) [u][w]labio-velar(back, rounded) [y]labial-palatal(front, rounded) velar (back, unrounded) Glides are vowel-like sonorants which are produced… with slightly more constriction than a vowel at the same place of articulation. Each glide’s acoustics will be similar to those of the vowel they correspond to.

Glide Acoustics Glides look like high vowels, but… are shorter than vowels They also tend to lack “steady states” and exhibit rapid transitions into (or from) vowels hence: “glides” Also: lower in intensity especially in the higher formants

[j] vs. [i]

[w] vs. [u]

Vowel-Glide-Vowel [iji][uwu]

More Glides [wi:][ju:]

Transitions When stops are released, they go through a transition phase in between the stop and the vowel. From stop to vowel: 1.Stop closure 2.Release burst 3.(glide-like) transition 4.“steady-state” vowel Vowel-to-stop works the same way, in reverse, except: Release burst (if any) comes after the stop closure.

Stop Components From Armenian:[bag] closure voicing vowel formant transitions another closure stop release burst

Confusions When the spectrogram was first invented… phoneticians figured out quite quickly how to identify vowels from their spectral characteristics… but they had a much harder time learning how to identify stops by their place of articulation. Eventually they realized: the formant transitions between vowels and stops provided a reliable cue to place of articulation. Why?

Formant Transitions A: the resonant frequencies of the vocal tract change as stop gestures enter or exit the closure phase. Simplest case: formant frequencies usually decrease near bilabial stops

Stops vs. Glides Note: formant transitions are more rapid for stops than they are for glides. “baby” “wave”

Formant Transitions: alveolars For other places of articulation, the formant transition that appears is more complex. From front vowels into alveolars, F2 tends to slope downward. From back vowels into alveolars, F2 tends to slope upwards. In Perturbation Theory terms: alveolars constrict somewhat closer to an F2 node (the palate) than to an F2 anti-node (the lips)

[hid] [hæd]

Formant Locus Whether in a front vowel or back vowel context... The formant transitions for alveolars tend to point to the same frequency value. (  Hz) This (apparent) frequency value is known as the locus of the formant transition. In the ‘50s, researchers theorized: the locus frequency can be used by listeners to reliably identify place of articulation. However, velars posed a problem…

Velar Transitions Velar formant transitions do not always have a reliable locus frequency for F2. Velars exhibit a lot of coarticulation with neighboring vowels. Fronter (more palatal) next to front vowels Locus is high:  Hz Backer (more velar) next to back vowels Locus is lower: < 1500 Hz F2 and F3 often come together in velar transitions “Velar Pinch”

The Velar Pinch [bag][bak]

“Velar” Co-articulations

The earliest experiments on place perception were conducted in the 1950s, using a speech synthesizer known as the pattern playback. Testing the Theory

Pattern Playback Picture

Haskins Formant Transitions Testing the perception of two-formant stimuli, with varying F2 transitions, led to a phenomenon known as categorical perception.

Categorical Perception Categorical perception = continuous physical distinctions are perceived in discrete categories. In the in-class experiment from last time: There were 11 different syllable stimuli They only differed in the locus of their F2 transition F2 Locus range = Hz Source:

Stimulus #1Stimulus #6 Stimulus #11 Example stimuli from the in-class experiment.

Identification In Categorical Perception: All stimuli within a category boundary should be labeled the same.

Discrimination Original task: ABX discrimination Stimuli across category boundaries should be 100% discriminable. Stimuli within category boundaries should not be discriminable at all. In practice, categorical perception means: the discrimination function can be determined from the identification function.

Identification  Discrimination Let’s consider a case where the two sounds in a discrimination pair are the same. Example: the pair is stimulus 3 followed by stimulus 3 Identification data--Stimulus 3 is identified as: [b] 95% of the time [d] 5% of the time The discrimination pair will be perceived as: [b] - [b]-.95 *.95 =.9025 [d] - [d]-.05 *.05 =.0025 Probability of same response is predicted to be: ( ) =.905 = 90.5%

Identification  Discrimination Let’s consider a case where the two sounds in a discrimination pair are different. Example: the pair is stimulus 9 followed by stimulus 11 Identification data: Stimulus 9: [d] 80% of the time, [g] 20% of the time Stimulus 11: [d] 5% of the time, [g] 95% of the time The discrimination pair will be perceived as: [d] - [d]-.80 *.05 =.04 [g] - [g]-.20 *.95 =.19 Probability of same response is predicted to be: ( ) = 23%

Discrimination In this discrimination graph-- Solid line is the observed data Dashed line is the predicted data (on the basis of the identification scores) Note: the actual listeners did a little bit better than the predictions.

Categorical, Continued Categorical Perception was also found for VOT distinctions. And for stop/glide/vowel distinctions: 10 ms transitions: [b] percept 60 ms transitions: [w] percept 200 ms transitions: [u] percept

Interpretation Main idea: in categorical perception, the mind translates an acoustic stimulus into a phonemic label. (category) The acoustic details of the stimulus are discarded in favor of an abstract representation. A continuous acoustic signal: Is thus transformed into a series of linguistic units:

The Next Level Interestingly, categorical perception is not found for non-speech stimuli. Miyawaki et al: tested perception of an F3 continuum between /r/ and /l/.

The Next Level They also tested perception of the F3 transitions in isolation. Listeners did not perceive these transitions categorically.

The Implications Interpretation: we do not perceive speech in the same way we perceive other sounds. “Speech is special”… and the perception of speech is modular. A module is a special processor in our minds/brains devoted to interpreting a particular kind of environmental stimuli.

Module Characteristics You can think of a module as a “mental reflex”. A module of the mind is defined as having the following characteristics: 1.Domain-specific 2.Automatic 3.Fast 4.Hard-wired in brain 5.Limited top-down access (you can’t “unperceive”) Example: the sense of vision operates modularly.

A Modular Mind Model central processes judgment, imagination, memory, attention modules visionhearingtouchspeech transducers eyesearsskinetc. external, physical reality

Remember this stuff? Speech is a “special” kind of sound because it exhibits spectral change over time.  it’s processed by the speech module, not by the auditory module.

SWS Findings The uninitiated either hear sinewave speech as speech or as “whistles”, “chirps”, etc. Claim: once you hear it as speech, you can’t go back. The speech module takes precedence (Limited top-down access) Analogy: it’s impossible to not perceive real speech as speech. We can’t hear the individual formants as whistles, chirps, etc. Motor theory says: we don’t perceive the “sounds”, we perceive the gestures which shape the spectrum.

More Evidence for Modularity It has also been observed that speech is perceived multi-modally. i.e.: we can perceive it through vision, as well as hearing (or some combination of the two).  We’re perceiving “gestures” …and the gestures are abstract. Interesting evidence: McGurk Effect