Complexity of Two-Dimensional Patterns

In dynamical systems such as cellular automata and iterated maps, it is often useful to look at a language or set of symbol sequences produced by the system. There are well-established classification schemes, such as the Chomsky hierarchy, with which we can measure the complexity of these sets of sequences, and thus the complexity of the systems which produce them. In this paper, we look at the first few levels of a hierarchy of complexity for two-or-more-dimensional patterns. We show that several definitions of ``regular language'' or ``local rule'' that are equivalent in d=1 lead to distinct classes in d >= 2. We explore the closure properties and computational complexity of these classes, including undecidability and L-, NL- and NP-completeness results. We apply these classes to cellular automata, in particular to their sets of fixed and periodic points, finite-time images, and limit sets. We show that it is undecidable whether a CA in d >= 2 has a periodic point of a given period, and that certain ``local lattice languages'' are not finite-time images or limit sets of any CA. We also show that the entropy of a d-dimensional CA's finite-time image cannot decrease faster than t^{-d} unless it maps every initial condition to a single homogeneous state.Comment: To appear in J. Stat. Phy

Self-induced Footsteps Sounds in Virtual Reality: Latency, Recognition, Quality and Presence

In this paper we describe the results of experiments whose goal is to investigate the effect of enhancing a virtual reality experience with the sound of synthetic footsteps. Results show that the sense of presence is enhanced when the sound of one’s own motion is added. Furthermore, the experiments show that the threshold for detection of latency between motion and sound is raised when visual stimuli is introduced. 1

Increasing the motion of users in photo-realistic virtual environments by utilising auditory rendering of the environment and ego-motion

An occurring problem of the image-based-rendering technology for Virtual Environments has been that subjects in general showed very little movement of head and body. Our hypothesis is that the movement rate could be enhanced by introducing the auditory modality. In the study described in this paper, 126 subjects participated in a between-subjects experiment involving six different experimental conditions, including both uni-and bi-modal stimuli (auditory and visual). The aim of the study was to investigate the influence of auditory rendering in stimulating and enhancing subjects ’ motion in virtual reality. The auditory stimuli consisted of several combinations of auditory feedback, including static sound sources as well as self-induced sounds. Results show that motion in virtual reality is significantly enhanced when moving sound sources and sound of ego-motion are rendered in the environment. 1

Autism and Research Using Magnetic Resonance Imaging

This qualitative study explored the experience of participating in a research study using magnetic resonance imaging (MRI) for children with autism spectrum disorder (ASD), typically developing (TYP) children, and their parent. It also assessed the feasibility, efficacy, and acceptability of the Going to MRI for a Research Study© iPad application (app), developed by the primary author, available for use for MRI preparation. The app provides a description of the steps of the MRI procedure, from the child’s perspective, outlining expected behaviors and responses. Ten English-speaking parent/child dyads (n = 20) participated in an audiotaped question guide-facilitated telephone interview about their experience in the MRI study. Participants confirmed the iPad app\u27s feasibility, efficacy, and acceptability. ASD child/parent themes differed from TYP child/parent themes. More children with ASD who used the app completed the MRI than without it. The iPad app may help children with ASD complete MRIs in future studies