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One likely mechanism in learning new skills is change in synchronous connections between distributed neural networks, which can be measured by coherence analysis of electroencephalographic patterns. This study examined coherence changes during the learning of two tasks, a word association task and a figure association task. Although learning curves were similar for both tasks, distinct patterns of coherence change were observed. Coherence tended to increase as learning progressed in the figure association task. In contrast, coherence tended to decrease in the word association task, especially within hemisphere. Word learning was coupled with negative intrahemispheric and positive interhemispheric performance-coherence relations in the gamma frequency. Unique to the figure learning task was an increase in the number of positive coherence-performance relations in both delta and theta frequencies across blocks. Results are discussed in light of ongoing efforts to identify the mechanisms that coordinate distributed brain activities during the process of learning. Further research is needed to define patterns of coherence change for different tasks, goals, and brain regions.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.comnet.2010.06.006 Byline: Ying Zhang (a), Damien Fay (b), Liam Kilmartin (a), Andrew W. Moore (b) Keywords: ARMA; Garch; Playout delay; Time series forecasting; VoIP Abstract: Network delay, packet loss and network delay variability (jitter) are important factors that impact on perceived voice quality in VoIP networks. An adaptive playout buffer is used in a VoIP terminal to overcome jitter. Such a buffer-control must operate a trade-off between the buffer-induced delay and any additional packet loss rate. In this paper, a Garch-based adaptive playout algorithm is proposed which is capable of operating in both inter-talkspurt and intra-talkspurt modes. The proposed new model is based on a Garch model approach; an ARMA model is used to model changes in the mean and the variance. In addition, a parameter estimation procedure is proposed, termed Direct Garch whose cost function is designed to implement a desired packet loss rate whilst minimising the probability of consecutive packet losses occurring. Simulations were carried out to evaluate the performance of the proposed algorithm using recorded VoIP traces. The main result is as follows; given a target Packet Loss Rate (PLR) the Direct Garch algorithm produces parameter estimates which result in a PLR closer than other algorithms. In addition, the proposed Direct Garch algorithm offers the best trade-off between additional buffering delay and Packet Loss Rate (PLR) compared with other traditional algorithms. Author Affiliation: (a) Electrical & Electronic Engineering, College of Engineering and Informatics, National University of Ireland, Galway, Ireland (b) Computer Laboratory, University of Cambridge, UK Article History: Received 10 August 2009; Revised 9 April 2010; Accepted 3 June 2010 Article Note: (miscellaneous) Responsible Editor: N. Agoulmine

Playout delay adaptation algorithms are often used in real time voice communication over packet-switched networks to counteract the effects of network jitter at the receiver. Whilst the conventional algorithms developed for silence-suppressed speech transmission focused on preserving the relative temporal structure of speech frames/packets within a taikspurt (intertalkspurt adaptation), more recently developed algorithms strive to achieve better quality by allowing for playout delay adaptation within a talkspurt (intratalkspurt adaptation). The adaptation algorithms, both intertaikspurt and intratalkspurt based, rely on short term estimations of the characteristics of network delay that would be experienced by up-coming voice packets. The use of novel neural networks and fuzzy systems as estimators of network delay characteristics are presented in this paper. Their performance is analyzed in comparison with a number of traditional techniques for both inter and intratalkspurt adaptation paradigms. The design of a novel fuzzy trend analyzer system (FTAS) for network delay trend analysis and its usage in intratalkspurt playout delay adaptation are presented in greater detail. The performance of the proposed mechanism is analyzed based on measured Internet delays. Index Terms--Fuzzy delay trend analysis, intertalkspurt, intratalkspurt, multilayer perceptrons (MLPs), network delay estimation, playout buffering, playout delay adaptation, time delay neural networks (TDNNs), voice over Internet protocol (VoIP).