Effects of word frequency and contextual predictability on sentence reading in aphasia: An eye movement analysis

Background: Mild reading difficulties are a pervasive symptom of aphasia. While much research in aphasia has been devoted to the study of single word reading, little is known about the process of (silent) sentence reading. Reading research in the non-brain-damaged population has benefited from the use of eye-tracking methodology, allowing inferences on cognitive processing without participants making an articulatory response. This body of research identified two factors, which strongly influence reading at the sentence level: word frequency and contextual predictability (influence of context). Aims: The main aim of this study was to investigate whether word frequency and contextual predictability influence sentence reading by people with aphasia (PWA), in parallel to that of neurologically healthy individuals (NHI). A second aim was to examine whether readers with aphasia show individual differences in the effects, and whether these are related to their underlying language profile. Methods & Procedures: Seventeen PWA and associated mild reading difficulties and 20 NHI took part in this study. Individuals with aphasia completed a range of language assessments. For the eye-tracking experiment, participants silently read sentences that included target words varying in word frequency and predictability while their eye movements were recorded. Comprehension accuracy, fixation durations, and the probability of first-pass fixations and first-pass regressions were measured. Outcomes & Results: Eye movements by both groups were significantly influenced by word frequency and predictability, but the predictability effect was stronger for the PWA than the neurologically healthy participants. Additionally, effects of word frequency and predictability were independent for the NHI, but the individuals with aphasia showed a more interactive pattern. Correlational analyses revealed (i) a significant relationship between lexical-semantic impairments and the word frequency effect score and (ii) a marginally significant association between the sentence comprehension skills and the predictability effect score. Conclusions: Consistent with compensatory processing theories, these findings indicate that decreased reading efficiency may trigger a more interactive reading strategy that aims to compensate for poorer reading by putting more emphasis on a sentence context, particularly for low-frequency words. For those individuals who have difficulties applying the strategy automatically, using a sentence context could be a beneficial strategy to focus on in reading intervention

ZiSense: Towards interference resilient duty cycling in wireless sensor networks

To save energy, wireless sensor networks often run in a low duty cycle mode, where the radios of sensor nodes are scheduled between ON and OFF states. For nodes to communicate with each other, Low Power Listening (LPL) and Low Power Probing (LPP) are two types of rendezvous mechanisms. Nodes with LPL or LPP rely on signal strength or probe packets to detect potential transmissions, and then keep the radio-on for communications. Unfortunately, in many cases, signal strength and probe packets are susceptible to interference, resulting in undesirable radio on time when the signal strength of interference is above a threshold or a probe packet is interfered. To address the issue, we propose ZiSense, an energy efficient rendezvous mechanism which is resilient to interference. Instead of checking the signal strength or decoding the probe packets, ZiSense detects the existence of ZigBee transmissions and wakes up nodes accordingly. On sensor nodes with limited information and resource, we carefully study and extract short-term features purely from the time-domain RSSI sequence, and design a rule-based approach to efficiently identify the existence of ZigBee. We theoretically analyze the benefit of ZiSense in different environments and implement a prototype in TinyOS with TelosB motes. We examine ZiSense performance under controlled interference and office environments. The evaluation results show that, compared with state-of-the-art rendezvous mechanisms, ZiSense significantly reduces the energy consumption. Copyright 2014 ACM

MAC Layer Support for Delay Tolerant Video Transport in Disruptive MANETs

Part 3: DTN and Sensor NetworksInternational audienceThe overall goal of this work is to improve video delivery in emergency and rescue scenarios using sparse MANETs that might be prone to frequent link breaks and network partitions. The core idea of our approach is to reduce the number of MAC layer retransmissions that are likely to fail. We do not drop packets that could not be sent after the final retransmission. Instead we handle them in an overlay for store-carry-forwarding. The design of the overlay protocol takes the instability of the network into account, in such a way that each overlay entity works autonomously and keeps a minimum amount of state. Our experimental results show that we reduce packet loss seen on broken links, while at the same time significantly reducing overhead in terms of the total amount of packets transmitted at the physical layer