Abstract
The premise of this study is that current models of speech perception, which are driven by acoustic features alone, are incomplete, and that the role of decoding time during memory access must be incorporated to account for the patterns of observed recognition phenomena. It is postulated that decoding time is governed by a cascade of neuronal oscillators, which guide template-matching operations at a hierarchy of temporal scales. Cascaded cortical oscillations in the theta, beta, and gamma frequency bands are argued to be crucial for speech intelligibility. Intelligibility is high so long as these oscillations remain phase locked to the auditory input rhythm. A model (Tempo) is presented which is capable of emulating recent psychophysical data on the intelligibility of speech sentences as a function of “packaging” rate (Ghitza and Greenberg, 2009). The data show that intelligibility of speech that is time-compressed by a factor of 3 (i.e., a high syllabic rate) is poor (above 50% word error rate), but is substantially restored when the information stream is re-packaged by the insertion of silent gaps in between successive compressed-signal intervals – a counterintuitive finding, difficult to explain using classical models of speech perception, but emerging naturally from the Tempo architecture.
Highlights
Neuronal oscillations are believed to play a role in various perceptual and cognitive tasks, including attention (Lakatos et al, 2008), navigation (Buzsáki, 2005), memory (Gruber et al, 2008; Palva et al, 2010), motor planning (Donoghue et al, 1998), and in the context of the present work, spoken-language comprehension (Haarman et al, 2002; Bastiaansen and Hagoort, 2006)
Summary The critical thesis at the basis of the approach presented here is that current models of speech perception that only consider properties of the signal derived from the acoustics are incomplete, and that the role of decoding time during memory access should be incorporated
It is hypothesized that decoding time is dictated by neuronal oscillations
Summary
Neuronal oscillations are believed to play a role in various perceptual and cognitive tasks, including attention (Lakatos et al, 2008), navigation (Buzsáki, 2005), memory (Gruber et al, 2008; Palva et al, 2010), motor planning (Donoghue et al, 1998), and in the context of the present work, spoken-language comprehension (Haarman et al, 2002; Bastiaansen and Hagoort, 2006). An oscillatory hierarchy may serve as a central pacemaker, similar to the synchronization facilitator proposed by Singer and others for cortical processing (cf., review by Singer, 1999; Buzsáki, 2006). Such a hierarchy may control excitability in neuronal ensembles (Kopell and LeMasson, 1994; Hopfield, 2004; Lakatos et al, 2005; Palva et al, 2005; Schroeder and Lakatos, 2009). In the context of the present work, both possible functions may play an important role in decoding spoken language (Morillon et al, 2010)
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