Neural Representations and Mechanisms for the Performance of Simple Speech Sequences

Abstract

Speakers plan the phonological content of their utterances prior to their release as speech motor acts. Using a finite alphabet of learned phonemes and a relatively small number of syllable structures, speakers are able to rapidly plan and produce arbitrary syllable sequences that fall within the rules of their language. The class of computational models of sequence planning and performance termed competitive queuing (CQ) models have followed Lashley (1951) in assuming that inherently parallel neural representations underlie serial action, and this idea is increasingly supported by experimental evidence. In this paper we develop a neural model that extends the existing DIVA model of speech production in two complementary ways. The new model includes paired structure and content subsystems (cf. MacNeilage, 1998) that provide parallel representations of a forthcoming speech plan, as well as mechanisms for interfacing these phonological planning representations with learned sensorimotor programs to enable stepping through multi-syllabic speech plans. On the basis of previous reports, the model's components are hypothesized to be localized to specific cortical and subcortical structures, including the left inferior frontal sulcus, the medial premotor cortex, the basal ganglia and thalamus. The new model, called GODIVA (Gradient Order DIVA), thus fills a void in current speech research by providing formal mechanistic hypotheses about both phonological and phonetic processes that are grounded by neuroanatomy and physiology. This framework also generates predictions that can be tested in future neuroimaging and clinical case studies.

Language Control and Code-switching

“…Competitive queuing (CQ) networks comprising a planning layer and competitive choice layer provide a neuroanatomically plausible way to achieve this goal (Bohland et al 2009;Grossberg 1978;Houghton 1990). The gradient of item activations in the planning layer indicates production order (see Figure 2).…”

Typing is writing: Linguistic properties modulate typing execution

“…Given the current interest in understanding motor planning (e.g., pre-motor, motor, monitoring, etc.) in the context of language production (for speech, see e.g., Bohland, Bullock, & Guenther, 2010;Hickok, 2014), such a separation seems no longer tenable.…”

Kinematic Analysis of Speech Sound Sequencing Errors Induced by Delayed Auditory Feedback

“…Under this view, coordinated neural mechanisms must sequentially select the appropriate phonological units from a planning buffer, while concurrently activating lower-level sensory-motor programs that drive the production of individual syllables (Bohland et al, 2010). At this lower level, which is described computationally by the DIVA model, continuous external auditory feedback is compared against stored sensory expectations specified as formant trajectories over time.…”

“…Such productions represent examples in which the speech planning system appears to have selected and released the produced sounds in the improper order. Such serial ordering errors might resemble many normally occurring slips of the tongue, which can be, in part, explained by various models that include an abstract phonological representation of the forthcoming speech plan (Bohland et al, 2010;e.g., Dell, 1986;Hartley & Houghton, 1996;Vousden, Brown, & Harley, 2000). We hypothesize that these errors may arise due to mechanisms normally used for detection and correction of such discrete errors in speech output, which must enact changes to the speech planning buffer (i.e., a reordering of planned sounds) to interrupt and correct running speech.…”

“…These models tend to lack either the specification of mechanisms for sequencing multiple sounds in a speech plan (Guenther et al, 2006;Hickok, 2012;Hickok et al, 2011;Houde & Nagarajan, 2011), which are essential to explaining the observed discrete serial order errors, or do not explicitly address the use of online auditory feedback (Saltzman & Munhall, 1989;Tilsen, 2013). Although the Gradient Order DIVA model (Directions Into Velocities of Articulators; Bohland, Bullock, & Guenther, 2010) extends the DIVA speech motor control framework (Guenther et al, 2006) to address how the brain may plan and produce sequences of speech sounds, it does not yet account for the effects of DAF due to an incomplete treatment of the auditory-perceptual system.…”