Development of a mental workload index: A systems approach

The objective of this study is to develop a method for determining the mental workload imposed on train control officers that is objective and quantifiable and can stand up to the tests of validity and reliability. This technical note reports on the methodology used in the development process, as well as the assessment of the criteria considered for the mental workload index (MWLI). The MWLI aims at solving an existing operational shortcoming and could be used as a tool for predicting the mental workload imposed on an operator at a particular train control centre. The method could be applied to manage and improve operational safety in the rail transport environment. A participative approach was followed in the development process. A work group comprising expert users of the system was involved in identifying task factors and assigning weights for task and moderating factors. The newly developed MWLI consists of three task factors and 11 moderating factors, each with a different weight in terms of its contribution to overall mental workload. The work group performed several iterations to reach final consensus and acceptance of the factors and their respective contributions to the MWLI. The criteria and development processes are discussed and the final index with the task and moderating factors is presented.     

Mobile pupillometry in manual assembly: A pilot study exploring the wearability and external validity of a renowned mental workload lab measure

Human operators in the upcoming Industry 4.0 workplace will face accelerating job demands such as elevated cognitive complexity. Unobtrusive objective measures of mental workload (MWL) are therefore in high demand as indicated by both theory and practice. This pilot study explored the wearability and external validity of pupillometry, a MWL measure robustly validated in laboratory settings and now deployable in work settings demanding operator mobility. In an ecologically valid work environment, 21 participants performed two manual assemblies - one of low and one of high complexity - while wearing eye-tracking glasses for pupil size measurement. Results revealed that the device was perceived as fairly wearable in terms of physical and mental comfort. In terms of validity, no significant differences in mean pupil size were found between the assemblies even though subjective mental workload differed significantly. Exploratory analyses on the pupil size when attending to the assembly instructions only, were inconclusive. The present work suggests that current lab-based procedures might not be adequate yet for in-the-field mobile pupillometry. From a broader perspective, these findings also invite a more nuanced view on the current validity of lab-validated physiological MWL-measures when applied in real-life settings. We therefore conclude with some key insights for future development of mobile pupillometry.     

Evaluation of decision-tree rating scales for mental workload estimation

Recent studies suggest that a decision-tree rating scale called the Modified Cooper-Harper (MCH) rating scale is a globally sensitive indicator of change in mental loading (Wierwille and Casali 1983 a). The present study was directed at developing refinements in the scale and at obtaining additional background information. The MCH scale and five design variations of the scale were studied in two independent aircraft-simulator experiments. Aspects studied were the decision-tree structure, the number of categories, the decision sequence and the effects of computer implementation. Results using the rating scales indicate that the MCH scale and its computerized version are generally more consistent than the others. Attendant questionnaire results indicate that pilots base their ratings on the same factors that researchers believe are the important elements of the multidimensional construct of workload.     

三维视频编码技术的发展与挑战

介绍了三维视频编码的核心技术。首先比较了纯视频格式和深度增强格式三维视频编码技术的发展方向及面临的挑战,其中重点分析了深度估计技术和视点合成技术的研究思路;然后概括了国际3DV/FTV标准的制定现状;最后对三维视频编码技术进行了总结和展望。     

完全可伸缩视频编码的实现和改进*

提出了一种完全可伸缩视频编码的改进方法。首先给出了一种采用运动补偿时域滤波、二维离散小波变换和EZW编码的传统可伸缩编码方案,该方案将时间、空间、质量三方面的伸缩性有机地结合在一起,实现了完全可伸缩性能。针对运动补偿时域滤波技术中的GOP（group of pictures）结构和更新操作进行了改进,引入GOP结构自适应选择,降低系统内存需求和运算复杂度;采用基于人眼视觉系统特性的最小可觉差对更新操作中所引进的误差进行内容自适应修正。实验结果表明,编码效率和视频序列的重建质量都得到了显著的提高。     

An examination of two mental workload measurement approaches to understanding multimedia learning

This study reports on an examination of two measures of mental workload: the NASA-TLX and Paas’ Subjective Cognitive Load (SCL) measure. The goal was to assess the relative efficacy of the measures in the design and research of multimedia learning environments. Benchmarks based on the literature as to the goals for mental workload measurement in learning research are established. A multifaceted study was conducted which manipulated various aspects of mental workload in order to study the utility of these two measures in detecting changes in load and their relationship to learning outcomes. The results indicate that the weighted version of the NASA-TLX provided little additional value over the unweighted version of the measure. While both the NASA-TLX and SCL measures were sensitive to changes in both intrinsic and extraneous load, the study revealed differences in the measures based on levels of each of these load factors. The study also concludes that a better understanding of the third factor, germane load, will be needed to both expand the theoretical framework about mental workload in instructional settings and further understand the utility of these two measures.     

无线多跳网络视频流的联合源编码优化算法

由于网络媒体的共享性和不可靠性,对无线多跳网络中视频流的支持面临更大的技术挑战.研究了视频流优化问题并提出了一种联合源网络编码机制.该机制将视频流的源分段,并分为不同的世代,以达到视频流质量的最大化.算法首先分析世代规模对网络性能如源速率、编码效率和解码延时的影响,然后为了使源速率较大,在源端产生较多数据分组,并设计一种联合网络编码机制确定各个中间节点发送到网络中分组的最佳数量,使视频流的质量达到最高.仿真实验结果表明,在世代规模合适的情况下,使用所提联合源编码机制可以增强无线多跳网络视频流的性能.     

丢包环境中H.264视频编码的快速模式判决

目的 视频编码中传统的快速模式判决算法通常基于对视频源特性的分析,但如果考虑到信道传输中的差错,编码模式的率失真特性就会随之改变,快速模式判决算法的性能也会随之下降,需要考虑丢包环境对快速模式判决算法进行优化。方法 为了解决这一问题,首先分析了丢包环境下各种编码模式的端到端率失真特性,在此基础上提出了一个分层结构的快速模式判决算法。通过快速估计出丢包环境下skip和intra模式的编码率失真代价,进而将模式判决的路径划分为non-intra和non-skip。结果 将本文算法与基于遍历算法的容错视频编码算法进行对比实验,本文算法平均可以降低50%左右的编码时间,同时几乎不会降低率失真性能。结论 实验结果表明,在对丢包环境下端到端率失真代价进行估计的基础上,所提出的分层结构快速模式判决的算法,可以在保证解码端图像质量的同时,显著节省编码时间,满足实时视频通信中对低复杂度和鲁棒性的要求。     

视频流传输中的网络编码综述

网络视频应用增长迅猛,利用网络编码（NC）来提高网络吞吐量和传输可靠性进而改善视频流传输质量成为研究热点。针对如何优化网络编码进行视频流传输这一问题,必须要结合视频流自身特性作出改进并综合考虑所处的网络环境,才能充分发挥网络编码的优势。首先回顾了网络编码的基本概念和方法;然后对网络编码应用于视频流传输时需要考虑的视频业务特性,包括进行不等差错保护以优先保障重要等级视频数据包、降低数据包传输延迟以满足视频流实时性需求、增强网络差错恢复策略以提升传输可靠性等作了分析和归纳;接着阐述了基于网络编码的视频流传输策略在包括P2P、多源协作及内容中心网络等典型场景中的应用;最后对网络编码应用于视频流传输的研究趋势进行展望。     

低码率下可扩展视频编码中的环路滤波改进

针对低码率的情况下效应比较严重的情况,提出在低码率下对环路滤波的一种改进的方法。对于空间基本层的环路滤波,采取与H.264/AVC兼容的环路滤波算法。但是对于空间增强层,特别是在低码率的情况下,加入一个对图像边界判断的算法,使其在滤波的时候,不会滤掉真实边界。与原来的算法相比,在低码率的情况下,码率有所降低,而且PSNR值也有增加,主观视觉上,也比原来的算法有提高。     

用于虚拟现实的360度视频编码技术新进展*

随着虚拟现实技术不断发展,360度视频编码开始成为研究热点。应用于虚拟现实的360度视频与传统的视频相比分辨率更高,编码数据量更大,在实际应用中面临传输带宽有限的瓶颈,编码效率问题有待解决。归纳分析了国际标准组织联合视频研究组（joint video exploration team, JVET）正在制定的360度视频编码投影变换技术及其编码优化方法,综合对比了各变换技术的编码性能。根据当前最新研究成果,对下一步研究需要解决的问题进行了探讨总结,给出未来的研究方向和思路。     

Component-adaptive up-sampling for inter layer interpolation in scalable video coding

Scalable video coding (SVC) is a newly emerging standard to be finalized as an extension of H.264/AVC. The most attractive characters in SVC are the inter layer prediction techniques, such as Intra_BL mode. But in current SVC scheme, a uniform up-sampling filter (UUSF) is employed to magnify all components of an image, which will be very inefficient and result in a lot of redundant computational complexity. To overcome this, we propose an efficient component-adaptive up-sampling filter (CAUSF) for inter layer interpolation. In CAUSF, one character of human vision system is considered, and different up-sampling filters are assigned to different components. In particular, the six-tap FIR filter used in UUSF is kept and assigned for luminance component. But for chrominance components, a new four-tap FIR filter is used. Experimental results show that CAUSF maintains the performances of coded bit-rate and PSNR-Y without any noticeable loss, and provides significant reduction in computational complexity. Supported by China Postdoctoral Science Foundation (Grant No. 20080430454), the Key Laboratory of Geo-informatics of State Bureau of Surveying and Mapping (Grant No. 200834), the National High-Tech Research and Development Program of China (Grant No. 2007AA12Z151), and the National Basic Research Program of China (Grant No. 2006CB701303)     

Fast motion and disparity estimation for multiview video coding

Multiview video involves a huge amount of data, and as such, efficiently encoding each view is a critical issue for its wider application. In this paper, a fast motion and disparity estimation algorithm is proposed, utilizing the close correlation between temporal and inter-view reference frames. First, a reliable predictor is found according to the correlation of motion and disparity vectors. Second, an iterative search process is carried out to find the optimal motion and disparity vectors. The proposed algorithm makes use of the prediction vector obtained in the previous motion estimation for the next disparity estimation and achieves both optimal motion and disparity vectors jointly. Experimental results demonstrate that the proposed algorithm can successfully save an average of 86% of computational time with a negligible quality drop when compared to the joint multiview video model (JMVM) full search algorithm. Furthermore, in comparison with the conventional simulcast coding, the proposed algorithm enhances the video quality and also greatly increases coding speed.     

On a system of understanding assembly illustrations in an assembly manual

This paper presents an assembly illustration understanding system. The system is eventually expected to be applied to a robot which specializes in automated mechanical assembly. Assembly illustrations in an assembly manual usually have two features: 1) In addition to the figures corresponding to mechanical parts, several special line-drawings referred to as auxiliary lines in this paper are often employed for the visualization of the assembly relations among mechanical parts; 2) The assembly illustrations in an assembly manual are disposed sequentially so that the subgoal of an assembly illustration will definitely appear in its succeeding illustrations as an assemblage. Both features are important clues to the analysis and understanding of assembly illustrations. By extracting the auxiliary lines, the system recognizes assembly relations among mechanical parts, and the 3D shape of the mechanical parts as well. Moreover, based on the assembly relations, it conjectures the structural details of mechanical parts such as insertion holes which are usually invisible. After that, it characterizes the appearance of the completed assemblage described by the current illustration. The system finally verifies the result by matching with the figures in a succeeding illustration in which the completed assemblage is given as a subpart.     

Assessment of pilot performance and mental workload in rotary wing aircraft

This research examined the processing demands imposed upon experienced pilots by two different communication formats, digital and verbal, in a high fidelity simulation of an advanced multi-function helicopter. The mental workload imposed by die type and magnitude of communications was assessed by a battery of subjective, performance, secondary, and physiological measures. The performance data indicated that the pilots had difficulty adhering to the Nap of the Earth altitude criterion with high communication demands, particularly with the digital communication system. This was presumably due to the requirement to spend more time scanning the multi-function displays with the digital than with the verbal communication system. On the other hand, the pilots were less prone to task shedding when they used the digital communication system possibly due to the provision of a permanent list of queries that was unavailable with the verbal system. Measures of heart rate variability and blink rate were larger with the verbal than with the digital system, presumably reflecting increased respiratory demands in the verbal condition as well as increased visual processing demands with the digital format. Finally, the probe evoked P300 component decreased in amplitude as a function of increases in die magnitude of communications. The results are discussed in terms of the structural and capacity demands of the communications systems that were proposed for the advanced multi-function helicopter.     

A study on the student pilot's mental workload due to personality types of both instructor and student

The main purpose of this paper is to provide the ideal flight crew combination for instructor and student pilots in order to enhance the flight training effects based on Myers Briggs Type Indicator (MBTI) theory. In addition to personality, various levels of flight difficulty are considered in order to investigate their potential interaction effect in terms of student pilots' mental workload measured in heart rate, altitude deviation, NASA-TLX (Task Load Index) and subjective degree of personality harmony. Based on an experiment performed in a real flight situation, we found significant effects of personality combinations in terms of all four outcome measures. Both group C types of instructors and students who are concrete, realistic and have mechanical skills turn out to be the ideal flight crew combination. A structural equation model, fitted to analyse causality among the four response variables, implied that as the heart rate increased, the altitude deviation increased. In addition, as the altitude deviation and personality harmony increased, NASA-TLX increased. The results of this study are expected to provide a theoretical basis for manning the flight crew combinations and thereby enhancing the efficiency of flight training.     

分布式视频编码中关键帧丢失错误保护

目的 分布式视频编码较其传统视频编码具有编码简单、误码鲁棒性高等特点,可以很好地满足如无人机航拍、无线监控等新型视频业务的需求。在分布式视频编码中,视频图像被交替分为关键帧和Wyner-Ziv帧,由于受到信道衰落和干扰等因素的影响,采用传统帧内编码方式的关键帧的误码鲁棒性远不如基于信道编码的Wyner-Ziv帧。关键帧能否正确传输和解码对于Wyner-Ziv帧能否正确解码起着决定性的作用,进而影响着整个系统的压缩效率和率失真性能。为此针对关键帧在异构网络中的鲁棒性传输问题,提出一种基于小波域的关键帧质量可分级保护传输方案。方法 在编码端对关键帧同时进行传统的帧内视频编码和基于小波域的Wyner-Ziv编码,解码端将经过错误隐藏后的误码关键帧作为基本层,Wyner-Ziv编码产生的校验信息码流作为增强层。为了提高系统的分层特性以便使系统的码率适应不同的网络条件,进一步将小波分解后图像的各个不同层的低频带和高频带组合成不同的增强层,根据不同信道环境,传输不同层的Wyner-Ziv校验数据。同时对误码情况下关键帧的虚拟噪声模型进行了改进,利用第1个增强层已解码重建的频带与其对应边信息来获得第2个和第3个增强层对应频带的更加符合实际的虚拟信道模型的估计。结果 针对不同的视频序列在关键帧误码率为1%20%时,相比较于传统的帧内错误隐藏算法,所提方案可以提高视频重建图像的主观质量和整体系统的率失真性能。例如在关键帧误码率为5%时,通过传输第1个增强层,不同的视频序列峰值信噪比（PSNR）提升可达25 dB左右;如果继续传输第2个增强层的校验信息,视频图像的PSNR也可以提升0.51.6 dB左右;如果3个增强层的校验信息都传输的话,基本上可以达到无误码情况下关键帧的PSNR。结论 本文所提方案可以很好地解决分布式视频编码系统中的关键帧在实际信道传输过程中可能出现的误码问题,同时采用的分层传输方案可以适应不同网络的信道情况。     

无线MMX技术在MPEG-4中的应用

无线MMX(Wireless MMX Technology)是用来提高移动多媒体计算性能的技术。针对无线视频通信的应用，研究了采用无线MMX来实现MPEG-4视频编解码的技术；通过对无线MMX体系结构和指令特点的分析，从指令优化和算法优化两方面给出了MPEG-4编解码器优化的关键策略。经过优化的编解码器可很好地满足无线视频通信要求。     

Evaluation and prediction mental workload in user interface of maritime operations using eye response

Eye response measurement is one of the objective measure methods and useful for assessing of operators' mental workload (MWL). The main objectives of this paper are to consider the relationship between operators' MWL and eye responses in the task of operating marine engine interface. Also, an artificial neural network (ANN) model was developed to predict the operators' MWL based on integrating eye response data. Eye response indices (pupil dilation, blink rate, fixation rate, and saccadic rate) were recorded, and two subjective rating methods (The National Aeronautics and Space Administration's Task Load Index [NASA-TLX] and subjective workload assessment technique [SWAT]) were used for 27 participants. The results again confirm that the eye response is sensitive to MWL in workload levels of the task when using the interface control. The ANN model developed by measuring these indices can predict the operators' MWL with the determination coefficient (R²) of 0.971, 0.912 and 0.918 for training, validation, and testing, respectively. These results indicated that the ANN approach is quite accurate for the prediction of operators' MWL based on eye response indices.Relevance to industryThe developed model is expected to provide the operator with a reference value of their MWL by evaluating their physiological indices. This result might be applied for developing an intelligent prediction model in the actual work environment to inform or support the operator in a variety of ways. From this, the manager can organize the human resources for each task to sustain the appropriate MWL as well as to improve the work performance.     

An extended packetization-aware mapping algorithm for scalable video coding in finite-length fountain codes

We propose an extended packetization-aware mapping algorithm based on fountain codes to enhance video stream performance which is vulnerable to packet losses.By properly utilizing the proposed algorithm in finite-length cases,the edges connecting to a source symbol are scattered over multiple encoding packets so that the decoding probabilities are increased.Furthermore,an improved degree distribution is designed to obtain better decoding probabilities.Numerical results,it is confirmed that the proposed algorithm in finite-length cases can augment decoding probabilities and the improved degree distribution can increase peak signal-to-noise ratio(PSNR) of scalable video coding(SVC) in a hostile communication environment.