Channelized multi-frequency measurement system based on asymmetric double sideband detection.

A channelized multi-frequency measurement system based on asymmetric double sideband detection is proposed. In this scheme, the sub-modulators of the dual-parallel Mach-Zehnder modulator are utilized for optical frequency comb (OFC) generation and under-test signal modulation. Subsequently, a sawtooth wave voltage is applied to the main modulator to introduce frequency shift to the modulated signals, breaking the symmetry between the RF signals and the OFC. The coupled signal is then divided into upper and lower sidebands for frequency down-conversion. By calibrating the measurement results of the two sidebands with each other, the frequency of the signal can be accurately measured. Simulation is preformed to realize multi-frequency measurement of microwave signals with measurement error less than 2 MHz in the range of 2.2-20 GHz. It is also found that the proposal can solve the problem of frequency ambiguity.

A perceptual learning deficit in Chinese developmental dyslexia as revealed by visual texture discrimination training.

Learning to read involves discriminating between different written forms and establishing connections with phonology and semantics. This process may be partially built upon visual perceptual learning, during which the ability to process the attributes of visual stimuli progressively improves with practice. The present study investigated to what extent Chinese children with developmental dyslexia have deficits in perceptual learning by using a texture discrimination task, in which participants were asked to discriminate the orientation of target bars. Experiment l demonstrated that, when all of the participants started with the same initial stimulus-to-mask onset asynchrony (SOA) at 300 ms, the threshold SOA, adjusted according to response accuracy for reaching 80% accuracy, did not show a decrement over 5 days of training for children with dyslexia, whereas this threshold SOA steadily decreased over the training for the control group. Experiment 2 used an adaptive procedure to determine the threshold SOA for each participant during training. Results showed that both the group of dyslexia and the control group attained perceptual learning over the sessions in 5 days, although the threshold SOAs were significantly higher for the group of dyslexia than for the control group; moreover, over individual participants, the threshold SOA negatively correlated with their performance in Chinese character recognition. These findings suggest that deficits in visual perceptual processing and learning might, in part, underpin difficulty in reading Chinese.

Reading performance is enhanced by visual texture discrimination training in Chinese-speaking children with developmental dyslexia.

BACKGROUND: High order cognitive processing and learning, such as reading, interact with lower-level sensory processing and learning. Previous studies have reported that visual perceptual training enlarges visual span and, consequently, improves reading speed in young and old people with amblyopia. Recently, a visual perceptual training study in Chinese-speaking children with dyslexia found that the visual texture discrimination thresholds of these children in visual perceptual training significantly correlated with their performance in Chinese character recognition, suggesting that deficits in visual perceptual processing/learning might partly underpin the difficulty in reading Chinese. METHODOLOGY/PRINCIPAL FINDINGS: To further clarify whether visual perceptual training improves the measures of reading performance, eighteen children with dyslexia and eighteen typically developed readers that were age- and IQ-matched completed a series of reading measures before and after visual texture discrimination task (TDT) training. Prior to the TDT training, each group of children was split into two equivalent training and non-training groups in terms of all reading measures, IQ, and TDT. The results revealed that the discrimination threshold SOAs of TDT were significantly higher for the children with dyslexia than for the control children before training. Interestingly, training significantly decreased the discrimination threshold SOAs of TDT for both the typically developed readers and the children with dyslexia. More importantly, the training group with dyslexia exhibited significant enhancement in reading fluency, while the non-training group with dyslexia did not show this improvement. Additional follow-up tests showed that the improvement in reading fluency is a long-lasting effect and could be maintained for up to two months in the training group with dyslexia. CONCLUSION/SIGNIFICANCE: These results suggest that basic visual perceptual processing/learning and reading ability in Chinese might at least partially rely on overlapping mechanisms.

Overview of Ultrasound Biomicroscopy.

Ultrasound biomicroscopy (UBM) is a high-resolution ultrasound technique that allows noninvasive in vivo imaging of structural details of the anterior ocular segment at near light microscopic resolution and provides detailed assessment of anterior segment structures, including those obscured by normal anatomic and pathologic relations. This review gives an overview regarding the instrument, technique and its applications.