有研究發現過度的媒界多任務處理者(HMMs)在多種認知任務上較輕度的媒界多任務處理者(LMMs)表現得遜色。這表示HMMs的多種認知功能，包括工作記憶的更新及維持、選擇性的注意力及作業轉換的能力，皆次於LMMs。有研究採用有線索的作業轉換典範時，為每一個作業設置了兩個線索，從而將總的作業轉換成本拆分為與作業轉換過程中兩個連續而不同的階段相關的部份。第一部份的成本由線索的改變導致，代表使用線索把作業心向從長期記憶抽出放於工作記憶這一階段所需要的成本。第二部份的成本由作業的改變導致，代表將作業規則應用於刺激這一階段所需的成本。第二階段的成本被大多數研究者視為真正的作業轉換成本。本研究想探討的問題是過度的媒界多任務處理所影響的是哪一階段的作業轉換能力。我們採用一份網上的媒界使用問卷選出二十名HMMs及二十名LMMs來參加實驗。實驗中，被試必須完成一個雙線索對單作業的作業轉換典範，當中的兩個作業分別為一個打字作業及一個性別判斷作業。反應時上的總作業轉換成本被拆成兩個部份: (甲)作業不變而線索改變所引起的線索轉換成本，及(乙)線索轉換成本所不能解釋的剩下的作業轉換成本。我們發現HMMs的線索轉換成本顯著地高於LMMs的線索轉換成本。然而，兩組人之間的作業轉換成本並沒有顯著差異。結果表明，HMMs只在使用線索把作業心向從長期記憶拿出來放在工作記憶這一階段遜色於LMMs。 / Heavy media multitaskers (HMMs) are found to be inferior to light media multitaskers (LMMs) in cognitive functions such as updating and maintenance of working memory representations, selectively attention, and surprisingly, the ability to switch between tasks. Research on task-switching paradigm using a 2:1 mapping between cues and tasks separates the total switch cost into costs related to two distinct, serial processing stages. The first type of cost, relating to the stage of cue-driven retrieval of task-set from long-term memory into working memory, is caused by a change in the task-indicating cue. The second type of cost, relating to the stage of application of task-rules onto the stimuli, is caused by a change of the task-set and has been regarded by some as the actual task-switch cost. In the current study, we examine which stage(s) are affected by media multitasking experience. Twenty HMMs and twenty LMMs identified using an online media-use questionnaire participated in a cued task-switching experiment involving a word typing task and a face gender classification task. The overall switch cost in response time was decomposed into two components: (a) the cue-switch cost as a result of a change of the cue with the task unchanged; and (b) the task-switch cost, which represent the switch cost not accountable by the cue-switch cost. HMMs showed a significantly larger cue-switch cost than LMMs, while the task-switch cost was similar for the two groups. Results suggest that HMMs may only be inferior in the cue-driven retrieval process of task set but not in the task-rule application stage. / Detailed summary in vernacular field only. / Lui, Fai Hong. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2013. / Includes bibliographical references (leaves 25-28). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts also in Chinese. / Chapter Chapter 1: --- Introduction --- p.1 / Media multitasking and its chronic effects --- p.1 / Effects of media multitasking on task switching ability --- p.4 / The typical task-switching paradigm --- p.5 / Task-switching paradigm using a 2:1 mapping between cues and tasks --- p.7 / Design of the current study --- p.10 / Hypotheses of the current study --- p.11 / Chapter Chapter 2: --- 2: Experiment 1: Method --- p.15 / Participants --- p.15 / Apparatus --- p.15 / Stimuli and procedure --- p.16 / Chapter Chapter 3: --- Experiment 1: Results --- p.19 / Chapter Chapter 4: --- Experiment 2 --- p.22 / Chapter Chapter 5: --- Experiment 2: Method --- p.24 / Participants --- p.24 / Apparatus --- p.24 / Stimuli and procedure --- p.24 / Chapter Chapter 6: --- Experiment 2: Results --- p.26 / Chapter Chapter 7: --- Discussions --- p.28

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The monkey lateral intraparietal area (LIP) is involved in visual attention and eye movements. It has traditionally been studied using extracellular recording, where often a single neuron is recorded at a time. Thus we have a wealth of correlational knowledge of what LIP neurons do, but not how or why, i.e. we do not know the circuit mechanisms and functions of the observed LIP activity. In this thesis, we have aimed to uncover the circuit mechanisms underlying LIP activity by building tightly constrained computational models. In Part 1, we found that during two versions of a delayed-saccade task, beneath similar population average firing patterns across time lie radically different network dynamics. When neurons are not influenced by stimuli outside their receptive fields (RFs), dynamics of the high-dimensional LIP network lie predominantly in one multi-neuronal dimension, as predicted by an earlier model. However, when activity is suppressed by stimuli outside the RF, LIP dynamics markedly deviate from a single dimension. The conflicting results can be reconciled if two LIP local networks, each dominated by a single multi-neuronal activity pattern, are suppressively coupled to each other. These results demonstrate the low dimensionality of LIP local dynamics and suggest active involvement of LIP recurrent circuitry in surround suppression and, more generally, in processing attentional and movement priority and in related cognitive functions. In Part 2, we examine the mechanisms of learning in LIP. When monkeys learn to group visual stimuli into arbitrary categories, LIP neurons become category-selective. Surprisingly, the representations of learned categories are overwhelmingly biased: while different categories are behaviorally equivalent, nearly all LIP neurons in a given animal prefer the same category. We propose that Hebbian plasticity, at the synapses to LIP from prefrontal cortex and from lower sensory areas, could lead to the development of biased representations. In our model, LIP category selectivity arises due to competition between inputs encoding different categories, and bias develops due to excitatory lateral interactions among LIP neurons. This model reproduces the different levels of category selectivity and bias observed in multiple experiments. Our results suggest that the connectivity of LIP allows it to learn the behavioral importance of stimuli in order to guide attention.

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Exposure to natural altitude using the "live high-train low" method improves athletic endurance performance at sea level by 1-2%. This method can also be employed with hypoxic devices that simulate altitude, but there is limited and conflicting research on their efficacy. Consequently, three studies were undertaken to investigate changes in sea level performance of endurance runners following exposure to altitude simulated with hypoxic tents. The device was chosen because of its potential for incorporation into the athlete's routine. In Study 1, 10 runners received altitude simulated with hypoxic tents (~9 h overnight at 2500-3500 m) and trained at sea level, while 10 runners in the control group performed usual training. Athletes in both groups performed a lactate-threshold test, but only the altitude group performed a run to exhaustion. The effect on 4-mM lactate speed was unclear, owing to poor reliability of this measure. There was a 16% increase in time to exhaustion in the hypoxic conditioning group, equivalent to a 1.9% (90% likely limits, ±1.4%) increase in speed in a time trial. Effects on performance were not apparent four and eight weeks after use of the tents. To improve precision of the effect of the tents and to determine the effects on performance of different durations, a further controlled trial was performed. A reliability study (Study 2) was first conducted to investigate the potential for runs to exhaustion to provide reliable measures of performance. Eight runners performed a test consisting of three runs to exhaustion lasting ~2, ~4 and ~8 min on six occasions over 14 wk. The critical power and log-log models were used to provide factors for converting variability in time to exhaustion into variability in equivalent time-trial time. Variabilities in time to exhaustion expressed as coefficients of variation for predicted 800-3000 m timetrial times were ~1-3%. A crossover study (Study 3) was then conducted in which 11 athletes performed usual (control) training and usual training with altitude exposure by using tents for 25 ± 3 days (mean ± SD) for 8.1 ± 0.6 h.d-1, progressing from a simulated altitude of 2500 m to 3500 m above sea level. Washout period between control and altitude treatments was four weeks. Performance was assessed with treadmill runs to exhaustion as in Study 2. Improvements in mean predicted times (altitude-control) for standard competition distances of 800, 1500 and 3000 m derived from the runs to exhaustion were 1.0% (±1.3%), 1.4% (±1.2%) and 1.9% (±1.5%) respectively. There was some evidence that hypoxic exposure favoured those athletes carrying the I allele for angiotensin converting enzyme. In summary, the main finding from the series of studies is that hypoxic tents are likely to enhance sea level endurance running performance by ~1-2%.

Scientific knowledge of vocal function and vocal health has increased greatly in recent decades, with new technology capable of displaying the larynx in operation, measuring muscular effort, and acoustically analysing vocal sound. This research addresses five key questions: 1/. What is the current body of voice science knowledge relevant to singing? 2/. What do singing teaching practitioners currently know about the voice? 3/. How do practitioners' understandings of voice influence their teaching of vocal techniques? 4/. How does singing teaching in Australia relate to bel canto precepts? 5/. How does singing teaching in Australia relate to voice science? Data was collected from surveys conducted to answer these questions. Analysis of survey data indicates that practitioners see themselves less as teachers than as singers who teach, and that this role perception carries values that moderate voice knowledge and approaches to teaching. The implications of this conclusion for the professional training of singing teachers in Australia are discussed and suggestions made for further research. In particular, voice scientists and singing teachers need to collaborate more actively in research. Scientific research into singing would have broader application if a model appropriate to both male and female voices were utilised and if larger and better chosen selections of experimental subjects were used. Further research is needed into how the physical skills of singing are best imparted to students / Doctor of Philosophy (PhD)