Principal component decomposition of acoustic and neural representations of time-varying pitch reveals adaptive efficient coding of speech covariation patterns.

Understanding the effects of statistical regularities on speech processing is a central issue in auditory neuroscience. To investigate the effects of distributional covariance on the neural processing of speech features, we introduce and validate a novel approach: decomposition of time-varying signals into patterns of covariation extracted with Principal Component Analysis. We used this decomposition to assay the sensory representation of pitch covariation patterns in native Chinese listeners and non-native learners of Mandarin Chinese tones. Sensory representations were examined using the frequency-following response, a far-field potential that reflects phase-locked activity from neural ensembles along the auditory pathway. We found a more efficient representation of the covariation patterns that accounted for more redundancy in the form of distributional covariance. Notably, long-term language and short-term training experiences enhanced the sensory representation of these covariation patterns.

Frequency-Following Responses to Speech Sounds Are Highly Conserved across Species and Contain Cortical Contributions.

Time-varying pitch is a vital cue for human speech perception. Neural processing of time-varying pitch has been extensively assayed using scalp-recorded frequency-following responses (FFRs), an electrophysiological signal thought to reflect integrated phase-locked neural ensemble activity from subcortical auditory areas. Emerging evidence increasingly points to a putative contribution of auditory cortical ensembles to the scalp-recorded FFRs. However, the properties of cortical FFRs and precise characterization of laminar sources are still unclear. Here we used direct human intracortical recordings as well as extracranial and intracranial recordings from macaques and guinea pigs to characterize the properties of cortical sources of FFRs to time-varying pitch patterns. We found robust FFRs in the auditory cortex across all species. We leveraged representational similarity analysis as a translational bridge to characterize similarities between the human and animal models. Laminar recordings in animal models showed FFRs emerging primarily from the thalamorecipient layers of the auditory cortex. FFRs arising from these cortical sources significantly contributed to the scalp-recorded FFRs via volume conduction. Our research paves the way for a wide array of studies to investigate the role of cortical FFRs in auditory perception and plasticity.

Infants adapt to speaking rate differences in word segmentation.

Throughout their development, infants are exposed to varying speaking rates. Thus, it is important to determine whether they are able to adapt to speech at varying rates and recognize target words from continuous speech despite speaking rate differences. To address this question, a series of four experiments were conducted to test whether infants can recognize words in continuous speech when rate is variable. In addition, the underlying mechanisms that infants may use to cope with variations induced by different speaking rates were also examined. Specifically, using the Headturn Preference procedure [Jusczyk and Aslin (1995). Cognitive Psychol. 29, 1-23], infants were familiarized with normal-rate passages containing two trisyllabic target words (e.g., elephants and dinosaurs), and tested with familiar (elephants and dinosaurs) and unfamiliar (crocodiles and platypus) words embedded in normal-rate (experiment 1), fast-rate (experiments 2 and 3), or slow-rate passages (experiment 4). The results indicate that 14-month-olds, but not 11-month-olds, recognized target words in passages with a fast speaking rate. In addition, findings suggest that infants used context to normalize speech across different speaking rates.

Auditory enhancement and second language experience in Spanish and English weighting of secondary voicing cues.

The role of secondary cues in voicing categorization was investigated in three listener groups: Monolingual English (n = 20) and Spanish speakers (n = 20), and Spanish speakers with significant English experience (n = 16). Results showed that, in all three groups, participants used onset f0 in making voicing decisions only in the positive voice onset time (VOT) range (short lag and long lag tokens), while there was no effect of onset f0 on voicing categorization within the negative VOT range (voicing lead tokens) for any of the participant groups. These results support an auditory enhancement view of perceptual cue weighting: Onset f0 serves as a secondary cue to voicing only in the positive VOT range where it is not overshadowed by the presence of pre-voicing. Moreover, results showed that Spanish learners of English gave a significantly greater weight to onset f0 in their voicing decisions than did listeners in either of the other two groups. This result supports the view that learners may overweight secondary cues to distinguish between non-native categories that are assimilated to the same native category on the basis of a primary cue.

Differential cue weighting in perception and production of consonant voicing.

This study examines English speakers' relative weighting of two voicing cues in production and perception. Participants repeated words differing in initial consonant voicing ([b] or [p]) and labeled synthesized tokens ranging between [ba] and [pa] orthogonally according to voice onset time (VOT) and onset f0. Discriminant function analysis and logistic regression were used to calculate individuals' relative weighting of each cue. Production results showed a significant negative correlation of VOT and onset f0, while perception results showed a trend toward a positive correlation. No significant correlations were found across perception and production, suggesting a complex relationship between the two domains.

Safety and efficacy of moxifloxacin monotherapy for treatment of orthopedic implant-related staphylococcal infections.

The rifampin-ciprofloxacin combination is recommended for treatment of orthopedic implant-related staphylococcal infections to avoid the emergence of ciprofloxacin resistance; however, the efficacy of this combination is limited by the tolerability problems associated with the use of rifampin. Moxifloxacin is a quinolone up to 10 times more active against staphylococci than ciprofloxacin and the risk of resistance development during monotherapy against staphylococci is theoretically lower for moxifloxacin, but information regarding its use in bone infections is lacking. The aim of the present study was to evaluate the safety and clinical efficacy of moxifloxacin monotherapy in patients with orthopedic implant-related staphylococcal infections. From June 2006 to April 2009, all patients with culture-proven infection by quinolone-sensitive staphylococcal strains associated with orthopedic implants at our institution were included in a management protocol that mostly included specific surgery, 1 to 2 weeks of an intravenous course of cloxacillin-cefazolin or vancomycin, and long-term therapy with moxifloxacin (400 mg/day for 3 months). Cure was defined as (i) a lack of clinical signs and symptoms of infection, (ii) a C-reactive protein level less than 5 mg/liter, and (iii) absence of radiological signs of loosening or infection at the latest follow-up visit. Failure was defined as (i) persisting clinical and/or laboratory signs of infection or (ii) persisting or new isolation of the initial microorganism. A total of 48 patients with a median follow-up of 716 days (range, 102 to 1,613 days) were included in the study. Complete drug compliance was achieved in all but two patients (4.2%), who required drug discontinuation because of side effects (diarrhea and dizziness). No moxifloxacin-induced arrhythmia was reported. Twenty patients had joint prosthesis infections (5 acute-onset infections and 15 chronic infections), and 28 patients had osteosynthesis material infections (4 acute-onset infections and 24 chronic infections). The etiologies were methicillin-sensitive Staphylococcus aureus in 33 patients and a coagulase-negative staphylococcus (CoNS) in 15. Surgical management was performed for the majority of patients (37/48; 77%), and the implant was retained in 21 patients (43.8%). The global cure rate was 38/46 (82.6%), and the cure rate for patients with implant retention was 15/21 (71.4%). The global cure rate for the 32 patients with a minimum follow-up of 2 years was 80%. Of the eight cases of relapse, we obtained microbiological confirmation in six cases, and all bacteria recovered were quinolone susceptible. Monotherapy with moxifloxacin seems to be an effective, safe, and easy alternative for the long-term treatment of orthopedic implant-related staphylococcal infections by quinolone-sensitive strains. Comparative studies with rifampin-containing regimens are warranted.