Identification and discrimination of the relative onset time of two component tones: Implications for voicing perception in stops David B. Pisoni ( )

Past Studies Lisker and Abramson (1964, 1970) Liberman et al. Mattingly, Liberman, Sydral, and Halwes Eimas (1971) Kuhl Miller (1975) Lasky Streeter Miller et al

Lisker and Abramson They investigated –Voicing and aspiration differences shown across different languages (last class) –Differences in timing and glottal activity They discovered 3 modes of voicing (1964): –Pre-voiced stops = voicing onset precedes the release burst (negative onset, -VOT) –Short-lag voiced stops = voicing onset is simultaneous or briefly lags behind the release burst (0 VOT) –Long-lag voiceless stops in which the voicing onset lags behind the release burst (positive onset, +VOT)

Liberman In perceptual experiments done with synthetic stimuli* they found (1961)… –Subjects ID and discriminate differences in VOT in a categorical-like manner that reflects the phonological categories* of their language –Consistent labeling with sharp crossover points –Discontinuities in discrimination that are correlated with the abrupt changes in the labeling functions –Better at discriminating 2 synthetic stimuli from 2 different phonological categories vs. from the the same

According to Several Empirical Findings –Non-speech signals are perceived in a continuous mode –No other categorical perception studies had been done with synthetic stimuli –Non-monotonic discrimination functions are the result of labeling processes associated with phonetic categorization Interpretation –Evidence for the operation of a special mode of perception…Speech Mode

Liberman et al. (1961) & Mattingly, Liberman, Syrdal and Halwes (1971) Are discontinuities in speech discrimination functions due to the acoustic or psychophysical* attributers of the signals themselves rather than some speech related labeling process? Found no peaks in the non-speech discrimination functions at phoneme boundaries so… Conclusion = Speech Mode –discrimination of speech stimuli were attributable to phonetic categorization resulting from the stimuli being perceived as speech.

Eimas (1971) 2 and 3 month old infants Found that they can discriminate synthetic speech sounds varying in VOT much like English speaking adults Implication = infants have access to mechanisms of phonetic categorization Innate mechanisms Responding to phonetic coding VS. psychophysical differences Environment plays a secondary role

Kuhl and Miller (1975) Study done with chinchillas Trained to respond differently to the consonants /d/ and /t/ (human voice) Used synthetic stimuli varying in VOT with a sharp crossover point The discrimination functions were similar to English speaking human data…but chinchillas don’t have spoken language Suggests a psychophysical basis VS. phonetic basis for the labeling behavior Results = the boundary for voiced and voiceless labial stops occurs at about +25 msec…threshold

Lasky et al. (1975) Cross-language studies 4 to 6 1/2 month old infants born to Spanish-speaking parents Found evidence for 3-categories in discrimination –Boundary occurred in the region of +20 msec and +60 msec (corresponds to the English voiced/voiceless times) –And at -20 msec and -60 msec Spanish only has one phoneme boundary b/w voiced and voiceless stops and it does not coincide with the boundaries they found Conclusion: –Environment plays minor role –Responding to psychophysical attributes

Streeter (1976) Kikuyu infants (Kenya) Show evidence of 3 categories of voicing for labial stops Kikuyu have no voicing contrasts for labial stops (but they exist at other articulation places) Conclusion: –They had not been exposed to these before –Responding to psychophysical attributes –Similar to the Laskey et al. research

Miller et al. (1976) Non-speech control signals –Using VOT in the form of a noise bust and a buzz Adults Results: discrimination functions that were similar to those found with stop consonants differing in VOT –Discrimination was excellent for stimuli selected from b/w categories and poor for stimuli within a category Perceptual threshold Psychophysical account

Pisoni Independent from Miller et al. but at the same time Used stimuli that varied in temporal order of the onsets of 2 component tones at 2 frequencies (Figure 1): –500 Hz –1500 Hz –-50, 0, +50 msec VOT (ranging in 10 msec increments)

Pisoni Goals: –To learn something about how the timing relations in stop consonants are perceived –To provide a more general account of the diverse findings obtained with adults, infants and chinchillas on VOT stimulus –To provide an account of the results obtained with non-speech stimuli

Pisoni: Experiment I 8 paid volunteers from ad in student paper All were right handed and native English speakers Stimuli (Figure 1): –11 digital two-tone sequences –Lower tone = 500 Hz –Higher tone = 1500 Hz –Variable is VOT

Pisoni: Experiment I Stimuli was presented at 80 dB SPL 2 one-hour sessions done over 2 days Day one: –Identification training sequences –Presented with the endpoint stimuli (-50 & +50) –Told to learn (w/their own strategy) which one of the 2 buttons was associated w/ea sound –Immediate feedback for correct responses

Pisoni: Experiment I Day two: –Tested for identification 11 stimuli presented in random order No feedback –Tested for ABX discrimination* 9 two-step pairs along the continuum Feedback provided for correct responses Told to determine whether the 3rd sound (X) was most like the first (A) or second (B) sound Chance performance

Pisoni: Experiment I Figure 2 (p.1355) –Filled in circles = labeling functions response to 2 end points Sharp and consistent for some Crossover points for the category boundary for 6 of the 8 are not at 0 but are displaced towards the lagging (+50) stimuli –Why?

Pisoni: Experiment I Possibly due to limitation on the processing of temporal information or… Due to Masking of the high frequency (1500 Hz) by the low (500 Hz) –So, they accounted for that by running a pilot study Pilot study (p ) –Results: they found no shift in boundary location so…the Limitation on the Processing of Temporal Information is the more like cause of asymmetry

Pisoni: Experiment I ABX-discrimination results –Open circles Fig. 2 –Categorical-like discrimination –Peaks and troughs –S2 ideal

Pisoni: Experiment I Results from ID and ABX: –Categorical perception with non-speech signals –This form of perception is not unique to speech signals –Removes one positive line of evidence for the Speech Mode theory Questions: –Are the findings due to labeling process brought about by the training process? –Or is it do to a simpler psychophysical explanation?

Pisoni: Experiment II Goal (in order to answer the previously asked questions): –To obtain ABX-discrimination functions before any training experience (label training) –If peaks in discrimination exist there will be reason to suspect a psychophysical basis for the observed discrimination functions from E1

Pisoni: Experiment II 12 volunteers Same 11 stimuli used in E1 2 one-hour sessions held on separate days (no label training) 360 ABX trials done ea. day with feedback 9 two-step stimuli comparisons were responded to 80x by ea subject

Pisoni: Experiment II Results: –Figure 3 (p. 1357) –2 patterns shown (except S1 = chance) Single approximately +20 msec Double approximately +20 and -20 –Natural categories are present at places along the stimulus continuum marked by narrow regions of high sensitivity (thresholds) –3 categories corresponding with the temporal events Lower tone leading by 20 msec or more (-) More or less simultaneously within the -20 to +20 msec region Lower tone lags by 20 msec or more (+)

Pisoni: Experiment II These results contrast: –Liberman et al. (1961) –Mattingly et al. (1971) The above both found: –Marked differences in discrimination between speech and non-speech signals –Why?

Pisoni: Experiment II The lack of familiarity with the stimuli used (Liberman = synthetic spectograms of /do/ and /to/; Mattingly = 2nd formant transitions were isolated from the rest of the stimulus pattern) The absence of any feedback during the discrimination task With complex multidimensional signals it may be difficult for subjects to attend to the relevant attributes that distinguish these stimuli

Pisoni: Experiment II Patterns of categorical perception are seen when using speech and non- speech stimuli

Pisoni: Experiment III Goal: –To demonstrate that subjects can classify these same stimuli into three distinct categories whose boundaries occur at precisely these regions on the continuum

Pisoni: Experiment III Same training procedure –Except…3 responses instead of 2 8 additional subjects were recruited Same set of 11 tonal stimuli Took place on 2 separate days

Pisoni: Experiment III Day 1 –Shaping and identification training with the 3 stimuli (-50, 0, +50 msec) –Subjects were free to adopt their own coding strategies –Immediate feedback was provided Day 2 –Labeling tests were conducted

Pisoni: Experiment III Figure 4 (p. 1358) –All subjects partitioned the stimulus continuum into three well-defined categories –Boundaries found at approximately -20 and +20 msec –Perceptual threshold –Ability to discriminate temporal differences

Pisoni: Experiment IV Goal: –Simultaneous vs. non-simultaneous…. –Having the subjects determine whether there are one or two distinct events at stimulus onset

Pisoni: Experiment IV 8 additional volunteers None had participated previously Same 11 tonal stimuli A single 1-hour session 11 stimuli presented randomly Told to listen to ea sound carefully and then determine whether they could hear one or two events at stimulus onset No feedback was given

Pisoni: Experiment IV Figure 5 (p. 1359) –All subjects showed similar U-shaped functions with sharp crossover points between categories Results: –The presence of 3 natural categories that may be distinguished by the relative discriminability of the temporal order of the component events

Pisoni Findings A perceptual effect for processing temporal order information which may also underlie the perception of voicing distinctions in stop consonants in initial position There is a perceptual threshold (consistent with studies done by Hirsh, Hirsh and Sherrick, and Stevens and Klatt) of about 20 msec

Pisoni Findings We know…that VOT (in terms of onset of voicing) must be judged in relation to the temporal attributes of other events (release from closure) So, these events are ordered in TIME, therefore highly distinctive and discriminable changes will be produced at various regions along the temporal continuum Phonological systems apparently have exploited the principle of discriminating discrete attributes (natural categories) during the evolution of language In other words, we’ve positioned our phonemes on either side of the natural auditory boundary provided by the threshold