Quantitative analysis of accuracy of an inertial/acoustic 6DOF tracking system in motion

An increasing number of neuroscience experiments are using virtual reality to provide a more immersive and less artificial experimental environment. This is particularly useful to navigation and three-dimensional scene perception experiments. Such experiments require accurate real-time tracking of the observer's head in order to render the virtual scene. Here, we present data on the accuracy of a commonly used six degrees of freedom tracker (Intersense IS900) when it is moved in ways typical of virtual reality applications. We compared the reported location of the tracker with its location computed by an optical tracking method. When the tracker was stationary, the root mean square error in spatial accuracy was 0.64 mm. However, we found that errors increased over ten-fold (up to 17 mm) when the tracker moved at speeds common in virtual reality applications. We demonstrate that the errors we report here are predominantly due to inaccuracies of the IS900 system rather than the optical tracking against which it was compared. (c) 2006 Elsevier B.V. All rights reserved.

The role of the harmonic vector average in motion integration

The local speeds of object contours vary systematically with the cosine of the angle between the normal component of the local velocity and the global object motion direction. An array of Gabor elements whose speed changes with local spatial orientation in accordance with this pattern can appear to move as a single surface. The apparent direction of motion of plaids and Gabor arrays has variously been proposed to result from feature tracking, vector addition and vector averaging in addition to the geometrically correct global velocity as indicated by the intersection of constraints (IOC) solution. Here a new combination rule, the harmonic vector average (HVA), is introduced, as well as a new algorithm for computing the IOC solution. The vector sum can be discounted as an integration strategy as it increases with the number of elements. The vector average over local vectors that vary in direction always provides an underestimate of the true global speed. The HVA, however, provides the correct global speed and direction for an unbiased sample of local velocities with respect to the global motion direction, as is the case for a simple closed contour. The HVA over biased samples provides an aggregate velocity estimate that can still be combined through an IOC computation to give an accurate estimate of the global velocity, which is not true of the vector average. Psychophysical results for type II Gabor arrays show perceived direction and speed falls close to the IOC direction for Gabor arrays having a wide range of orientations but the IOC prediction fails as the mean orientation shifts away from the global motion direction and the orientation range narrows. In this case perceived velocity generally defaults to the HVA.

Numbers in motion

We explore the debates surrounding the constructive and discursive capabilities of accounting information focusing in particular on the reception volatility of numbers once they are produced and ‘exposed’ to various communities of minds. Drawing on Goffman’s (1974) frame analysis and Vollmer’s (2007) work on the three-dimensional character of numerical signs, we explore how numbers can go through gradual or instantaneous transformations, get caught up in public debates and become ‘agents’ or ‘captives’ in creating social order and in some cases social drama. In our analysis we also relate to the work of Durkheim (1993, 2002) on the sociology of morality to illustrate how numbers can become indicators of moral transgression. The study explores both historical and contemporary examples of controversies and recent accounting scandals to demonstrate how preparers (of financial information) can lose control over numbers which then acquire new meanings through social context and collective (re)framing. The main contribution of the study is to illustrate how the narratives attached to numbers are malleable and fluid across both time and space.

Playful learning : Melville's artful art in Moby-Dick

It remains one of the great ironies of American literary history that Melville's Moby-Dick struggled so long for critical and popular recognition. It is a peculiar text (but, then, so are Hawthorne's novels), a romance of the whale fishery that involves such explorations of language itself, of words, metaphor, symbol, allegory and the processes (and significance) of narrative construction. This article analyses its 'peculiarities' as fundamental indicators of Melville's 'playful art' to argue the usefulness of a concept of 'play' to its appreciation. That Moby-Dick is allusive and multi-layered is well known. But for what apparent purpose and to what effect? Here, a claim is made that Melville simultaneously constructs and deconstructs meaning by demonstrating that things ('in complex subjects') never come simply or singly. The later Barthes and Derrida become part of this ship's crew and Moby-Dick is a postmodernist novel avant la lettre.

Celebrating the use of African music : change in motion

I undertook a research project regarding the use of African music at both primary and secondary school level with Victorian teachers in Melbourne in 2004. This study grew out of my first project, which examined the effectiveness of using African music with non-specialist primary teacher education students at Deakin University, Melbourne (see Joseph, 2002, 2003). In this paper the concept of 'change' in relation to teaching and learning is explored regarding practising teachers’ teaching and learning of African music in Australian schools. According to Campbell (2004), a guiding principle for shaping educational experiences designed to promote students’ musical and cultural understanding is for teachers to make music both meaningful and useful in their lives. She further contends that such an experience can 'come alive' for students if teachers promote active involvement for them as music listeners as well as makers of music. This paper discusses some of the findings in relation to why and how teachers are engaging with African music and what their students are learning from it. It may be argued that both students (Deakin University student project) and teachers (Victorian music project) perceived African music to be an effective way to transmit and engage with a 'new music and culture'.

You know how I know you're gay? : masculinity and homophobia in mainstream comedy

You Know How I Know You're Gay?: Masculinity and Homophobia in Contemporary Mainstream Comedy is a three-part senior scholars project that consists of a critical analysis of homophobic humor in contemporary mainstream comedy, an original feature-length comedy script entitled Don 't Be that Freshman, and a DVD of selected scenes from Don't Be that Freshman. The critical analysis first establishes the existence of homophobic humor in mainstream comedy and then links this homophobia to masculine anxiety, applying the ideas set forth in Michael Kimmel's essay, "Masculinity as Homophobia," to contemporary, mainstream, homosocial comedies. The paper goes on to examine audience reactions to this homophobic humor, focusing on audience members who enjoy these movies, yet consider themselves to be accepting of homosexuality and against homophobia. I discuss ways of resistance and the importance of opposing homophobic humor, and finally, I look at comedy as a potentially transgressive medium that could be used to fight homophobia and social inequality. The critical analysis, therefore, leads into Don't Be that Freshman, a film that uses progressive humor to oppose homophobia and expose the potential dangers and pitfalls of conforming to social constructions of gender. Don't Be that Freshman is a film about three pairs of college roommates in their first semester at college who become each other's first friends on campus. It is a character-driven comedy that attempts to normalize non-heterosexual sexual orientation and gender non-conformity, to advocate a type of living that does not conform to problematic social constructions and cultural ideologies, and at the same time to appeal to a mainstream audience. The film version is twenty-five minutes long and consists of ten scenes from the script.

Reducing position error of cantilevered loads in motion systems

The positioning error of a large cantilevered mass that is actuated at its supported end is minimized as this mass travels at challenging high speeds and accelerations. An integrated approach is adopted to realize the task. After selecting the appropriate actuator that would provide higher rigidity, the system is viewed as a multi-degree of freedom system, and hence the concept of system-generated disturbance is introduced. This allows the use of appropriate mechanical design considerations and a proper generation of the kinematics commands to minimize such disturbance. A disturbance observer is then designed to detect and compensate the remaining disturbance, hence minimizing the positioning error.
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