Change blindness: eradication of gestalt strategies

Arrays of eight, texture-defined rectangles were used as stimuli in a one-shot change blindness (CB) task where there was a 50% chance that one rectangle would change orientation between two successive presentations separated by an interval. CB was eliminated by cueing the target rectangle in the first stimulus, reduced by cueing in the interval and unaffected by cueing in the second presentation. This supports the idea that a representation was formed that persisted through the interval before being 'overwritten' by the second presentation (Landman et al, 2003 Vision Research 43149–164]. Another possibility is that participants used some kind of grouping or Gestalt strategy. To test this we changed the spatial position of the rectangles in the second presentation by shifting them along imaginary spokes (by ±1 degree) emanating from the central fixation point. There was no significant difference seen in performance between this and the standard task [F(1,4)=2.565, p=0.185]. This may suggest two things: (i) Gestalt grouping is not used as a strategy in these tasks, and (ii) it gives further weight to the argument that objects may be stored and retrieved from a pre-attentional store during this task

Change blindness: size matters

It is easy to detect a small change between two sequential presentations of a visual stimulus, but, if they are separated by a blank interval, performance is around chance. This change blindness (CB) can be rectified, or improved, by cueing the spatial location of the change either in the first stimulus or the interval; however, no advantage is conferred when the cue appears during the second presentation of the stimulus. This supports the idea that a representation of the first stimulus is formed and persists through the course of the interval before being 'overwritten' by the second presentation of the stimulus (Landman et al, 2003 Vision Research 43 149 - 164). We were interested in the time course of the cueing effect during the interval. Following Landman et al, our first stimulus was an array of eight rectangles defined by texture and there was a 50% chance that one of the rectangles would change orientation in the second stimulus. Five cues were used, one within the first stimulus, three across the interval, and one in the second stimulus. Only one of these cues appeared in each trial. The cued rectangle was the one that would change between the first and second stimulus when a change occurred. The cue was a yellow line. Eighty-five observers showed the characteristic cueing performance supporting 'overwriting', but performance decreased over the duration of the interval suggesting that the initial representation of the first stimulus fades over time. However, when the size of the rectangles was increased, performance across the interval improved significantly. We consider two possible explanations: one is that simply by increasing rectangle size we raise the storage capacity for the number of rectangles in our representation, the other is that storage is related to task difficulty

'Behind Enemy Lines' Menzies, Evatt and Passports for Peking

This article focuses primarily on Australian government responses to the 1952 Peace Conference for Asia and the Pacific Regions. Because the conference was to be held in Peking, it was the subject of immense controversy: Chinese communists were fighting Australian soldiers in Korea and Australian peace activists, most communist or 'fellow travellers', sought to travel behind the 'bamboo curtain'. In this context, the Menzies government's policies on passports were sharply silhouetted. Although this conference has been overlooked in the literature, we can infer from the trajectory of relevant Cold War historiography that Prime Minister Menzies would adopt restrictive, even draconian, policies. This article argues otherwise. It suggests that it was that consistent champion of civil liberties, former deputy prime minister, attorney-general and secretary of the General Assembly of the United Nations and now, in 1952, Leader of the Opposition, Dr Evatt, who favoured more repressive action towards prospective delegates. In contrast, Menzies and his Cabinet were more lenient and shifted towards a harsher policy belatedly and reluctantly. This episode, therefore, challenges some comfortable assumptions about how the early Cold War was fought in Australia

Change blindness: the longer the better

Arrays of 8, texture-defined rectangles were used as stimuli in a one-shot change blindness (CB)task where there was a 50% chance that one rectangle would change orientation between stimuli. The effects of CB were reduced by cueing the spatial location of the change in either the first stimulus or, importantly, the interval. This supports the idea that a representation of the first stim- ulus is formed and persists through the interval before being `overwritten' by the second presentation of the stimulus (Landman et al, 2003 Vision Research 43 149 ^ 164). Previously we used eighty-five naive observers to investigate task difficulty using large and small rectangles (Wilson et al,2005 Perception 34 146 ^ 147). Here we used two experienced observers to test if the representation remains robust across longer intervals. Observers showed steady performance across the interval suggesting a robust representation up to an interval of 5000 ms.We consider two possible explanations: (i) a pre-attentional representation may last much longer than previously expected; (ii) observers are using a strategy

Response Time Analysis of Hierarchical Scheduling: the Synchronized Deferrable Servers Approach

Hierarchical scheduling allows reservation of processor bandwidth and the use of different schedulers for different applications on a single platform. We propose a hierarchical scheduling interface called synchronized deferrable servers that can reserve different processor bandwidth on each core, and can combine global and partitioned scheduling on a multicore platform. Significant challenges will arise in the response time analysis of a task set if the tasks are globally scheduled on a multiprocessor platform and the processor bandwidth reserved for the tasks on each processor is different; as a result, existing works on response time analysis for dedicated scheduling on identical multiprocessor platforms are no longer applicable. A new response time analysis that overcomes these challenges is presented and evaluated by simulations. Based on this new analysis, we show that evenly allocating bandwidth across cores is “better” than other allocation schemes in terms of schedulability, and that the threshold between lightweight and heavyweight tasks under hierarchical scheduling may be different from the threshold under dedicated scheduling

Bias in perception of ambiguous movement in discrete stimulus presentations

Successive presentations of two different stimulus configurations were used to generate a compelling but ambiguous apparent-motion sequence, such that the likelihood of the perceived motion being resolved as clockwise or anticlockwise was equal. In the first stimulus configuration, four small squares were arranged in a square formation (5 deg × 5 deg) about a central fixation mark; in the second, they were arranged in a diamond formation. Twelve naïve observers reported perceived direction of motion in discrete presentations (< 1 s), comprising three stimulus configurations (square - diamond - square; stimulus configuration duration 100 ms; ISI 200 ms). We were surprised to find that ten of the observers exhibited a strong bias for motion in one or other direction. This bias to report a particular direction persisted even when observers were informed of the inherent ambiguity of the stimulus. Next, in extended presentations (2 min) five observers indicated each occurrence of a perceived switch in direction. Despite individual variation, all observers reported switches in direction; an analysis of the interswitch durations conformed to a gamma distribution. These observations support the notion that uninterrupted presentations are required for perceptual switching to occur in ambiguous displays (Leopold et al, 2002 Nature Neuroscience 5 605 - 609)

Comparison of perceptual reversals with rotating and static versions of the Necker cube

Apparent changes in direction-of-rotation of a Necker cube (NC) signify perceptual reversals (PRs) equivalent to perspective reversals experienced when viewing a static NC. Rotations of 20 turns min-1 generate the same number of PRs as the static NC (Gorea and Agonie, 1997 Vision Research 37 2195 - 2206). We wanted to know if the pattern of reversals during an observation interval would also be the same. For the static form the rate of PRs increases during a fast phase and then becomes constant after 2 - 3 min during a slow phase (Borsellino et al, 1972 Kybernetik 10 139 - 144)

Stochastic Performance Trade-offs in the Design of Real-Time Wireless Sensor Networks

Future sensing applications call for a thorough evaluation of network performance trade-offs so that desired guarantees can be provided for the realization of real-time wireless sensor networks (WSNs). Recent studies provide insight into the performance metrics in terms of first-order statistics, e.g., the expected delay. However, WSNs are characterized by the stochastic nature of the wireless channel and the queuing processes, which result in non-deterministic delay, throughput, and network lifetime. For the design of WSNs with predictable performance, probabilistic analysis of these performance metrics and their intrinsic trade-offs is essential. Moreover, providing stochastic guarantees is crucial since each deployment may result in a different realization. In this paper, the trade-offs between delay, throughput, and lifetime are quantified through a stochastic network design approach. To this end, two novel probabilistic network design measures, quantile and quantile interval, are defined to capture the dependability and predictability of the performance metrics, respectively. Extensive evaluations are conducted to explore the performance trade-offs in real-time WSNs