DOI: 10.5061/dryad.ps6b1c4
title: Data from: Bringing the nonlinearity of the movement system to gestural theories of language use: multifractal structure of spoken English supports the compensation for coarticulation in human speech perception

description: Coarticulation is the tendency for speech vocalization and articulation
 even at the phonemic level to change with context, and compensation for
 coarticulation (CfC) reflects the striking human ability to perceive
 phonemic stability despite this variability. A current controversy centers
 on whether CfC depends on contrast between formants of a speech-signal
 spectrogram—specifically, contrast between offset formants concluding
 context stimuli and onset formants opening the target sound—or on
 speech-sound variability specific to the coordinative movement of speech
 articulators (e.g., vocal folds, postural muscles, lips, tongues). This
 manuscript aims to encode that coordinative-movement context in terms of
 speech-signal multifractal structure and to determine whether
 speech's multifractal structure might explain the crucial gestural
 support for any proposed spectral contrast. We asked human participants to
 categorize individual target stimuli drawn from an 11-step [ga]-to-[da]
 continuum as either phonemes “GA” or “DA.” Three groups each heard a
 specific-type context stimulus preceding target stimuli: either
 real-speech [al] or [a], sine-wave tones at the third-formant offset
 frequency of either [al] or [aɹ], and either simulated-speech contexts
 [al] or [aɹ]. Here, simulating speech contexts involved randomizing the
 sequence of relatively homogeneous pitch periods within vowel-sound [a] of
 each [al] and [aɹ]. Crucially, simulated-speech contexts had the same
 offset and extremely similar vowel formants as and, to additional naïve
 participants, sounded identical to real-speech contexts. However,
 randomization distorted original speech-context multifractality, and
 effects of spectral contrast following speech only appeared after
 regression modeling of trial-by-trial “GA” judgments controlled for
 context-stimulus multifractality. Furthermore, simulated-speech contexts
 elicited faster responses (like tone contexts do) and weakened known
 biases in CfC, suggesting that spectral contrast depends on the nonlinear
 interactions across multiple scales that articulatory gestures express
 through the speech signal. Traditional mouse-tracking behaviors measured
 as participants moved their computer-mouse cursor to register their
 “GA”-or-“DA” decisions with mouse-clicks suggest that listening to speech
 leads the movement system to resonate with the multifractality of context
 stimuli. We interpret these results as shedding light on a new
 multifractal terrain upon which to found a better understanding in which
 movement systems play an important role in shaping how speech perception
 makes use of acoustic information.
description: tone condition
 stimulinatural speech condition
 stimulisimulated speech
 stimuliga_to_da Target
 continuume-prime
 filesIndividual participant
 files from e-prime including mouse-tracking coordinates: Conditions 1, 2,
 and 3 indicate natural-speech, tone, and simulated-speech,
 respectively.peronperioddataIncludes multifractal estimates of context stimuli as well as geometric and information-theoretic measures of mouse-tracking behaviors.