No abstract

Speech perception and production are intimately linked. There is evidence that speech motor learning results in changes to auditory processing of speech. Whether speech motor control benefits from perceptual learning in speech, however, remains unclear. This event-related potential study investigated whether speech-sound learning can modulate the processing of feedback errors during vocal pitch regulation. Mandarin speakers were trained to perceive five Thai lexical tones while learning to associate pictures with spoken words over 5 days. Before and after training, participants produced sustained vowel sounds while they heard their vocal pitch feedback unexpectedly perturbed. As compared to the pre-training session, the magnitude of vocal compensation significantly decreased for the control group, but remained consistent for the trained group at the post-training session. However, the trained group had smaller and faster N1 responses to pitch perturbations and exhibited enhanced P2 responses that correlated significantly with their learning performance. These findings indicate that the cortical processing of vocal pitch regulation can be shaped by learning new speech-sound associations, suggesting that perceptual learning in speech can produce transfer effects to facilitating the neural mechanisms underlying the online monitoring of auditory feedback regarding vocal production.

Oscillation behaviors of planar opposed jets with acoustic excitation were experimentally investigated. The flow regimes of planar opposed jets at various exit air velocities, nozzle separations, excitation frequencies, and excitation amplitudes have been identified by a flow visualization technique combining with a high-speed camera. Results show that planar opposed jets exhibit horizontal instability at L/H ≤ 4 (where L is the nozzle separation and H is the slit height of the planar nozzle) and deflecting oscillation at L/H ≥ 6. The deflecting oscillation is originally started by the antisymmetric structures in the planar jets and is self-sustained by the periodic changes of the velocity field and the pressure field. At L/H ≤ 4, the acoustic excitation results in the horizontal periodic oscillation, whose frequency is equal to the excitation frequency. The acoustic excitation of oscillation amplitude less than 10% has negligible influence on the deflecting oscillation; for synchronous or asynchronous excitation with higher amplitude, the transition from the deflecting oscillation to a steady state or horizontal oscillation occurs.

Oscillation behaviors of axisymmetric opposed jets with modulated airflow were experimentally studied. The oscillation frequency, the oscillation amplitude, and the movement velocity of the impingement plane at various nozzle separations, excitation frequencies, and exit turbulence intensities have been investigated by a hot-wire anemometer and flow visualization technique combined with a high-speed camera. Results show that the oscillation frequency of the impingement plane is nearly equal to the excitation frequency, whereas the oscillation amplitude decreases with the increase of the excitation frequency. The full-scale amplitude oscillation occurs at low excitation frequencies and 2 L/D 8 (where L is the nozzle separation and D is the diameter of the nozzle exit). With the increase of the exit turbulence intensity caused by a turbulence generating plate, the oscillation amplitude decreases remarkably. Flow regimes of axisymmetric opposed jets with excitations are analyzed and discussed based on the experimental results.

Flow regimes in a cross-shaped reactor with square cross sections of two inlets and two outlets were investigated at 20 ≤ Re ≤ 500, where Re is the Reynolds number. Visualization images on cross sections were obtained by planar laser induced fluorescence, and several flow regimes were identified. Results show that, with increasing Re, a symmetric segregated flow, a steady engulfment flow, an unsteady engulfment flow, and an unsteady symmetric flow emerge in turns. First, the symmetric segregated flow is formed at Re < 48. At 48 ≤ Re < 300, the flow becomes asymmetric and a spiral vortex is formed in the center of the outlet chamber, which is called steady engulfment flow. At 300 ≤ Re ≤ 400, the unsteady engulfment flow occurs and a periodic oscillation is established. With a further increase in Re, the flow regains symmetry to a large extent and is characterized by axial oscillation of the impingement plane in the outlet chamber. For steady engulfment flow, an interesting three-dimensional vortical structure was observed, which rotates around the center axis of the outlet chamber along both outlet channels. For unsteady engulfment flow, the periodic oscillation is characterized by vortex merging and breakup. The flow mechanisms of both steady and unsteady engulfment flows were discussed.