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Syllable stress modulates articulatory planning: evidence from a stop-signal experiment Sam Tilsen University of Southern California [email protected] Ladefoged, Silverstein, & Papçun (1973): "there are some moments in the stream of speech when a speaker would find it more difficult to interrupt himself than at other moments. Thus it might be thought likely that a speaker might find it more difficult to interrupt himself in the middle of a syllable than at the end; and perhaps that interruptions might be much easier at the end of a word or phrase rather than in the middle.” “difficult” : reaction time (RT) to stop-signal • contrary to hypothesis: no particular part of the sentence where speakers found it more difficult to interrupt themselves. • RTs were slower prior to utterance initiation Syllable stress ?? Articulatory gestures Unstressed Shorter duration Lesser magnitude Less resistant to coarticulation More prone to reduction Stressed Longer duration Greater magnitude More resistant to coarticulation Less prone to reduction ? Easier to stop ? Harder to stop (cf. Beckman & Edwards, 1994; Cho, 2002; Cho & McQueen, 2005; Cole et al., 2007; Crystal & House, 1988; de Jong, 1995) Simplified schematic model of gestural planning and inhibitory control: gestural activation σ-activation Ed had ed- it- ed inhibitory process Id cessation of speech Ed had ed- it- ed Id gestural activation The planning activation hypothesis: Hyp. 1a: Speakers will halt phonation more slowly when signaled just prior to a stressed syllable than to an unstressed syllable. The perceptual attention hypothesis: Hyp. 1b: Speakers will halt phonation more quickly when signaled during a stressed syllable than during an unstressed syllable. Evidence from phoneme-monitoring tasks that perceptual attention is heightened during stressed syllables: Shields, McHugh, & Martin (1974), phoneme monitoring: • faster RTs when the target occurred in a stressed syllable as opposed to an unstressed one. but this could be due to differences in acoustic cues. Pitt & Samuel (1990), phoneme monitoring (w/stress-neutral stimuli) • 24 ms faster RTs in stressed syllables but could be due to violation of acoustic expectancy by the "stress-neutral“ stimuli Quene & Port (2005), Arantes & Barbosa (2006), phoneme monitoring: • stress facilitates acoustic perception. BUT the phoneme-monitoring task differs from the stop-signal paradigm in two important respects: 1. Effects of stimuli on attention are unimodal, i.e. effect of stress (an auditory percept) on RT to auditory stimulus. Possible that perception of a visual stimulus will be unaffected. 2. Context stimulus is externally generated, whereas in the stop-signal paradigm, the context stimulus (the utterance) is speaker-generated. Because it is pre-planned (and hence expected), it may have negligible effect on the perception of a response stimulus. METHOD Sentence design sw Target duration: Sally saw the men in Roma naming nine alarms Sal- ly saw the men in Ro- ma na- ming nine a- larms s s w s s w s w s w s w w 2.3 s sww Sally has seen that the women in Roma were naming eleven alarms Sal- ly has seen that the wo- men in Ro- ma were na- ming e- le- ven a- larms s w s w s w s w w w s w w s w w w s w 2.9 s mixed Sally saw that nine men in Roma were naming new mazes Sal- ly saw that nine men in Ro- ma were na- ming new ma- zes s s w s s w w w s s w w s w s Metrical regularity: the degree to which the pattern of stressed and unstressed syllables in an utterance is consistent. Can be quantified by assuming a sequence of syllables is a firstorder Markov process and calculating the entropy rate H according to the formula: sw: sww: mixed: 0.00 0.67 0.78 Hyp. 2. The metrical regularity of an utterance will affect stop-signal RT. 2.5 s METHOD Sally saw the men in Roma naming nine alarms Sally saw the men in Roma naming nine alarms • 75% stop-signal trials, 25% catch trials • feedback on catch trials and stop-signal trials • stop-task instruction: cut off speech sharply Participants: 12 native speakers of English (7 women, 5 men) 2 sessions x 2-3 blocks (per sentence) x 24 trials (18 stop-signal) ≈ 90 stop-signal trials / sentence / speaker METHOD Dependent variable: Independent variable: Perceptual attention: Planning activation: stop-signal RT last pulse of modal voicing location of the stop-signal relative to utterance… stress of the syllable in which the stop-signal occurred stress of the upcoming syllable proximity of stop-signal to onset of nearest stressed syllable RESULTS pre-σstr post-σstr • • RTs are slower when signaled prior to the onset of the nearest σstr supports planning activation hyp. (effect sizes are 15-25 ms) RTs are faster in the sw sentence. partly supports hyp. 2: metrical regularity speeds RT Test of perceptual attention hypothesis ANOVA on RT z-score: SSσstress stress of the syllable that contains the stop-signal SSσnext stress of the upcoming syllable (F = 0.53, p < 0.47) (F = 8.89, p < 0.003) sw sww mixed Syllable-specific correlations between RT and stop-signal location ρ men (in) Ro(ma) na(ming) sw φstress -0.37 ** -0.19 ** -0.13 -0.37 ** -0.21 ** -0.15 * δstress sww φstress δstress mixed φstress δstress Ro(ma were) -0.28 ** -0.30 ** men (in) -0.38 ** -0.37 ** ** p < 0.001, * p < 0.05 na(ming) e-0.32 ** -0.32 ** Ro(ma) were -0.34 ** -0.35 ** le(ven) a-0.02 -0.04 na(ming) -0.06 -0.06 RESULTS sw sww RESULTS mixed MODEL An extension of the task dynamic model of articulatory phonology (Browman & Goldstein, 1988, 1990, 2000; Saltzman & Munhall, 1989; Nam & Saltzman, 2003; Saltzman & Byrd, 2003; Saltzman, Nam, Krivokapic, & Goldstein, 2008). In addition to phase coupled gestural planning oscillators, the extended model (Tilsen, 2009a, 2008) incorporates: 1. syllable- and stress-planning oscillators 2. amplitude coupling between planning systems MODEL MODEL Conclusion and future directions speakers halt phonation more slowly when signaled just prior to a stressed syllable than an unstressed syllable. 1. the planning of syllables modulates articulatory planning and influences the timecourse of inhibitory processes 2. current models of how stress interacts with articulation do not predict stop-signal effects, but these effects can be predicted with amplitude-coupling between syllables and gestural systems. also relates to: • boundary phenomena & articulatory consequences of stress: increased duration, gestural magnitude, resistance to coarticulation • unified account of weight-based stress assignment, extraprosodicity, and extrametricality 3. revived the stop-signal paradigm as a viable approach to investigating cognitive processes related to speech. additional factors in stop-signal RT: • metrical regularity (familiarity, frequency)? • speech-rate • prosodic prominence (e.g. emphatic, contrastive focus) • morphological and syntactic phrase structure • spontaneous vs. prepared speech • articulatory features • supralaryngeal articulatory kinematics of stopping