Showing papers by "Helsinki Institute for Information Technology published in 2008"

It's Mine, Don't Touch!: interactions at a large multi-touch display in a city centre

Abstract: We present data from detailed observations of CityWall, a large multi-touch display installed in a central location in Helsinki, Finland. During eight days of installation, 1199 persons interacted with the system in various social configurations. Videos of these encounters were examined qualitatively as well as quantitatively based on human coding of events. The data convey phenomena that arise uniquely in public use: crowding, massively parallel interaction, teamwork, games, negotiations of transitions and handovers, conflict management, gestures and overt remarks to co-present people, and "marking" the display for others. We analyze how public availability is achieved through social learning and negotiation, why interaction becomes performative and, finally, how the display restructures the public space. The multi-touch feature, gesture-based interaction, and the physical display size contributed differentially to these uses. Our findings on the social organization of the use of public displays can be useful for designing such systems for urban environments.

The Discrete Basis Problem

Abstract: Matrix decomposition methods represent a data matrix as a product of two factor matrices: one containing basis vectors that represent meaningful concepts in the data, and another describing how the observed data can be expressed as combinations of the basis vectors. Decomposition methods have been studied extensively, but many methods return real-valued matrices. Interpreting real-valued factor matrices is hard if the original data is Boolean. In this paper, we describe a matrix decomposition formulation for Boolean data, the Discrete Basis Problem. The problem seeks for a Boolean decomposition of a binary matrix, thus allowing the user to easily interpret the basis vectors. We also describe a variation of the problem, the Discrete Basis Partitioning Problem. We show that both problems are NP-hard. For the Discrete Basis Problem, we give a simple greedy algorithm for solving it; for the Discrete Basis Partitioning Problem we show how it can be solved using existing methods. We present experimental results for the greedy algorithm and compare it against other, well known methods. Our algorithm gives intuitive basis vectors, but its reconstruction error is usually larger than with the real-valued methods. We discuss about the reasons for this behavior.

The psychophysiology of James Bond: phasic emotional responses to violent video game events

Abstract: The authors examined emotional valence- and arousal-related phasic psychophysiological responses to different violent events in the first-person shooter video game "James Bond 007: NightFire" among 36 young adults. Event-related changes in zygomaticus major, corrugator supercilii, and orbicularis oculi electromyographic (EMG) activity and skin conductance level (SCL) were recorded, and the participants rated their emotions and the trait psychoticism based on the Psychoticism dimension of the Eysenck Personality Questionnaire--Revised, Short Form. Wounding and killing the opponent elicited an increase in SCL and a decrease in zygomatic and orbicularis oculi EMG activity. The decrease in zygomatic and orbicularis oculi activity was less pronounced among high Psychoticism scorers compared with low Psychoticism scorers. The wounding and death of the player's own character (James Bond) elicited an increase in SCL and zygomatic and orbicularis oculi EMG activity and a decrease in corrugator activity. Instead of joy resulting from victory and success, wounding and killing the opponent may elicit high-arousal negative affect (anxiety), with high Psychoticism scorers experiencing less anxiety than low Psychoticism scorers. Although counterintuitive, the wounding and death of the player's own character may increase some aspect of positive emotion.

Spatial frequency tuning in human retinotopic visual areas

Abstract: Human medial occipital cortex comprises multiple visual areas, each with a distinct retinotopic representation of visual environment. We measured spatial frequency (SF) tuning curves with functional magnetic resonance imaging (fMRI) and found consistent differences between these areas. Areas V1, V2, VP, V3, V4v, and V3A were all band-pass tuned, with progressively lower SF optima in V1, V2, and V3A. In VP and V3, the SF optima were similar to optima in V2, whereas V4v showed more individual variation and scattered SF representations on the cortical surface. Area V5+ showed low-pass SF tuning. In each area, the SF optimum declined with increasing eccentricity. After accounting for the cortical magnification, the cortical extent of the optimal spatial wavelengths was approximately constant across eccentricity in V1, which suggests an anatomical constraint for the optimal SF, and this extent is actually comparable to the extent of horizontal connections within primate V1. The optimal spatial wavelengths in the visual field are also of similar extent to the spatial summation fields of macaque V1. The progressive decline in the SF tuning from V1 to V2 and V3A is compatible with the view that these areas represent visual information at different spatial scales.

Higher origination and extinction rates in larger mammals

Abstract: Do large mammals evolve faster than small mammals or vice versa? Because the answer to this question contributes to our understanding of how life-history affects long-term and large-scale evolutionary patterns, and how microevolutionary rates scale-up to macroevolutionary rates, it has received much attention. A satisfactory or consistent answer to this question is lacking, however. Here, we take a fresh look at this problem using a large fossil dataset of mammals from the Neogene of the Old World (NOW). Controlling for sampling biases, calculating per capita origination and extinction rates of boundary-crossers and estimating survival probabilities using capture-mark-recapture (CMR) methods, we found the recurring pattern that large mammal genera and species have higher origination and extinction rates, and therefore shorter durations. This pattern is surprising in the light of molecular studies, which show that smaller animals, with their shorter generation times and higher metabolic rates, have greater absolute rates of evolution. However, higher molecular rates do not necessarily translate to higher taxon rates because both the biotic and physical environments interact with phenotypic variation, in part fueled by mutations, to affect origination and extinction rates. To explain the observed pattern, we propose that the ability to evolve and maintain behavior such as hibernation, torpor and burrowing, collectively termed "sleep-or-hide" (SLOH) behavior, serves as a means of environmental buffering during expected and unexpected environmental change. SLOH behavior is more common in some small mammals, and, as a result, SLOH small mammals contribute to higher average survivorship and lower origination probabilities among small mammals.

Finding reliable subgraphs from large probabilistic graphs

Abstract: Reliable subgraphs can be used, for example, to find and rank nontrivial links between given vertices, to concisely visualize large graphs, or to reduce the size of input for computationally demanding graph algorithms. We propose two new heuristics for solving the most reliable subgraph extraction problem on large, undirected probabilistic graphs. Such a problem is specified by a probabilistic graph G subject to random edge failures, a set of terminal vertices, and an integer K. The objective is to remove K edges from G such that the probability of connecting the terminals in the remaining subgraph is maximized. We provide some technical details and a rough analysis of the proposed algorithms. The practical performance of the methods is evaluated on real probabilistic graphs from the biological domain. The results indicate that the methods scale much better to large input graphs, both computationally and in terms of the quality of the result.

Target acquisition with camera phones when used as magic lenses

Abstract: When camera phones are used as magic lenses in handheld augmented reality applications involving wall maps or posters, pointing can be divided into two phases: (1) an initial coarse physical pointing phase, in which the target can be directly observed on the background surface, and (2) a fine-control virtual pointing phase, in which the target can only be observed through the device display. In two studies, we show that performance cannot be adequately modeled with standard Fitts' law, but can be adequately modeled with a two-component modification. We chart the performance space and analyze users' target acquisition strategies in varying conditions. Moreover, we show that the standard Fitts' law model does hold for dynamic peephole pointing where there is no guiding background surface and hence the physical pointing component of the extended model is not needed. Finally, implications for the design of magic lens interfaces are considered.

Prototyping Social Interaction

Abstract: Introduction Recent changes in information technology have made social interaction an increasingly important topic for interaction design and technology development. Mobile phones, PDAs, games, and laptops have eased interpersonal communication and brought it into new contexts such as bus stops, trains, cars, and city streets—in fact everywhere people find themselves and move about. In these situations, the old paradigms of one person interacting with technology, or a group at work in an office or collaborating over a shared system, are inadequate for guiding the design of such systems. For interaction design, these technologies represent new kinds of challenges. Interaction design has inherited its methodic baggage mainly from three sources, none of which specifically focuses on how ordinary people use social technologies. Usability research and human-computer interaction (HCI) seldom quote sociological theory in their premises.1 While research in computer-supported collaborative work (CSCW) increasingly has focused on questions outside of the workplace, the basis of this field of study still stems from studies of the workplace, in which social organization is devised to support work rather than ordinary activities.2 New articulations of methods and frameworks are required for designing interactive technologies for social interaction in ordinary activities. This paper describes a series of studies conducted in Helsinki that focused on prototyping how people interact with each other using mobile multimedia. The central claim is that a prototype is not only a representation of a product or technology—such as a paper prototype, a software prototype, or a physical mock-up—but that it consists of both the representation and the social interaction the participants create together. For convenience, we talk about “prototyping social interaction.” The argument of this paper applies in particular to small communication devices meant for everyday life, but it also can be used with other products and services. Social processes inevitably affect the way in which technology is perceived, accepted, and used. If these processes are neglected, designs face risks. In our opinion, there ought to be ways to anticipate at least some of them. 1 Jenny Preece, Human-Computer Interaction (Harlow, England: AddisonWesley, 1994). 2 See Andy Crabtree, Designing Collaborative Systems: A Practical Guide to Ethnography (London: Springer, 2003). Acknowledgement We would like to thank the Ministry of Trade and Industry for funding Mobile Image, Radiolinja for continuous cooperation and support, and Nokia Mobile Phones for funding Mobile Album.

Gender-dependent progression of systemic metabolic states in early childhood.

Abstract: Little is known about the human intra-individual metabolic profile changes over an extended period of time. Here, we introduce a novel concept suggesting that children even at a very young age can be categorized in terms of metabolic state as they advance in development. The hidden Markov models were used as a method for discovering the underlying progression in the metabolic state. We applied the methodology to study metabolic trajectories in children between birth and 4 years of age, based on a series of samples selected from a large birth cohort study. We found multiple previously unknown age- and gender-related metabolome changes of potential medical significance. Specifically, we found that the major developmental state differences between girls and boys are attributed to sphingolipids. In addition, we demonstrated the feasibility of state-based alignment of personal metabolic trajectories. We show that children have different development rates at the level of metabolome and thus the state-based approach may be advantageous when applying metabolome profiling in search of markers for subtle (patho)physiological changes.

Designing for privacy and self-presentation in social awareness

Abstract: Social awareness applications are based on the idea of a group sharing real-time context information via personal and ubiquitous terminals. Studies of such applications have shown that users are not only concerned with the preservation privacy through non-disclosure. Instead, disclosure is manipulated for the constant presentation of self to the group in everyday social situations. Basing on 3 years of research with the mobile social awareness system ContextContacts, established findings in social psychology and ubiquitous computing, we propose a number of design principles to support users in this management of privacy and presentation. These principles are to apply even if disclosure is automated, and include support for lightweight permissions, assuming reciprocity, appearing differently to different audiences, providing for feedback on presentation and allowing lying. These principles are applied in interaction design and protocol engineering for the next version of a mobile awareness system called ContextContacts.

Incentive-compatible caching and peering in data-oriented networks

Abstract: Several new, data-oriented internetworking architectures have been proposed recently. However, the practical deployability of such designs is an open question. In this paper, we consider data-oriented network designs in the light of the policy and incentive structures of the present internetworking economy. A main observation of our work is that none of the present proposals is both policy-compliant and incentive-compatible with the current internetworking market, which makes their deployment very challenging if not impossible. This difficulty stems from the unfounded implicit assumption that data-oriented routing policies directly reflect the underlying packet-level inter-domain policies. We find that to enable the more effective network utilization promised by data-oriented networking, essential caching incentives need to exist, and that data-oriented peering needs be considered separately from peering for packet forwarding.

The Travelling Salesman Problem in Bounded Degree Graphs

Abstract: We show that the travelling salesman problem in bounded-degreegraphs can be solved in time $O\bigl((2-\epsilon)^n\bigr)$, wheree> 0 depends only on the degree bound but noton the number of cities, n. The algorithm is a variant ofthe classical dynamic programming solution due to Bellman, and,independently, Held and Karp. In the case of bounded integerweights on the edges, we also present a polynomial-space algorithmwith running time $O\bigl((2-\epsilon)^n\bigr)$ on bounded-degreegraphs.

Improved Approximation Algorithms for Relay Placement

Abstract: In the relay placement problemthe input is a set of sensors and a number ri¾? 1, the communication range of a relay. The objective is to place a minimum number of relays so that between every pair of sensors there is a path through sensors and/or relays such that the consecutive vertices of the path are within distance rif both vertices are relays and within distance 1 otherwise. We present a 3.11-approximation algorithm, and show that the problem admits no PTAS, assuming P${} e{}$NP.

Causal discovery of linear acyclic models with arbitrary distributions

Abstract: An important task in data analysis is the discovery of causal relationships between observed variables. For continuous-valued data, linear acyclic causal models are commonly used to model the data-generating process, and the inference of such models is a well-studied problem. However, existing methods have significant limitations. Methods based on conditional independencies (Spirtes et al. 1993; Pearl 2000) cannot distinguish between independence-equivalent models, whereas approaches purely based on Independent Component Analysis (Shimizu et al. 2006) are inapplicable to data which is partially Gaussian. In this paper, we generalize and combine the two approaches, to yield a method able to learn the model structure in many cases for which the previous methods provide answers that are either incorrect or are not as informative as possible. We give exact graphical conditions for when two distinct models represent the same family of distributions, and empirically demonstrate the power of our method through thorough simulations.

Circumspect descent prevails in solving random constraint satisfaction problems

Abstract: We study the performance of stochastic local search algorithms for random instances of the K-satisfiability (K-SAT) problem. We present a stochastic local search algorithm, ChainSAT, which moves in the energy landscape of a problem instance by never going upwards in energy. ChainSAT is a focused algorithm in the sense that it focuses on variables occurring in unsatisfied clauses. We show by extensive numerical investigations that ChainSAT and other focused algorithms solve large K-SAT instances almost surely in linear time, up to high clause-to-variable ratios α; for example, for K = 4 we observe linear-time performance well beyond the recently postulated clustering and condensation transitions in the solution space. The performance of ChainSAT is a surprise given that by design the algorithm gets trapped into the first local energy minimum it encounters, yet no such minima are encountered. We also study the geometry of the solution space as accessed by stochastic local search algorithms.

Designing interactions for navigation in 3D mobile maps

Abstract: Due to their intuitiveness, 3D mobile maps have recently emerged as an alternative to 2D mobile maps. However, designing interactions for navigation in a 3D environment using a mobile device is non-trivial. Challenges are posed by the severe limitations of the mobile user interface and of the capacities of the mobile user. This chapter analyses the problem of degrees of freedom: how to make navigation quicker and more intuitive by the means of restricting and guiding movement, yet enabling unrestricted access to all reasonable points-of-interests. Insights from empirical studies of mobile map interaction are presented, in the form of a model of interactive search, to draw requirements for interaction design. Then, the design of controls, landmarks, cameras, interest fields, routes, paths etc. are analysed and several higher-level navigation metaphors are discussed. We propose ways to support spatial updating, rapid alignment of physical and virtual spaces, and overcoming the keyhole problem. A working prototype system is used to illustrate different solutions alongside with alternative designs, weighing their pros and cons.

Mobile 3D City Maps

Abstract: In this paper, the author discusses a living mobile 3D city. It was created by lightweight modeling and 3D optimizations, and implemented an efficient, scalable dynamic entity management solution. A mobile 3D navigation interface was designed and verified the system by field experiments. Based on the results, implications for future research are also discussed.

Inventing new uses for tools: A cognitive foundation for studies on appropriation

Abstract: Appropriation refers to the processes that take place when new uses are invented for tools and when these uses develop into practices and start spreading within a user community. Most research in human–computer interaction and computersupported cooperative work to date has studied this phenomenon from a social sciences approach, thus focusing on the practice side of the phenomenon. This paper addresses appropriation from the other direction, drawing from ecological psychology and focusing on cognitive processes in context. Appropriation from this perspective is understood as an interpretation process in which the user perceives in a tool a new opportunity for action, thus acquiring a new mental usage schema that complements the existing uses. This approach highlights the need to study how schemata are put into use and how they evolve through new interpretations. Ensuing research questions are presented together with three strategies of applying the new approach in system design.

The Boolean column and column-row matrix decompositions

Abstract: Matrix decompositions are used for many data mining purposes One of these purposes is to find a concise but interpretable representation of a given data matrix Different decomposition formulations have been proposed for this task, many of which assume a certain property of the input data (eg, nonnegativity) and aim at preserving that property in the decomposition In this paper we propose new decomposition formulations for binary matrices, namely the Boolean CX and CUR decompositions They are natural combinations of two previously presented decomposition formulations We consider also two subproblems of these decompositions and present a rigorous theoretical study of the subproblems We give algorithms for the decompositions and for the subproblems, and study their performance via extensive experimental evaluation We show that even simple algorithms can give accurate and intuitive decompositions of real data, thus demonstrating the power and usefulness of the proposed decompositions

Subgraph queries by context-free grammars.

Abstract: We describe a method for querying vertex- and edge-labeled graphs using context-free grammars to specify the class of interesting paths. We introduce a novel problem, finding the connection subgraph induced by the set of matching paths between given two vertices or two sets of vertices. Such a subgraph provides a concise summary of the relationship between the vertices. We also present novel algorithms for parsing subgraphs directly without enumerating all the individual paths. We evaluate experimentally the presented parsing algorithms on a set of real graphs derived from publicly available biomedical databases and on randomly generated graphs. The results indicate that parsing the connection subgraph directly is much more effective than parsing individual paths separately. Furthermore, we show that using a bidirectional parsing algorithm, in most cases, allows for searching twice as long paths as using a unidirectional search strategy.

Optimal approximation of signal priors

Abstract: In signal restoration by Bayesian inference, one typically uses a parametric model of the prior distribution of the signal. Here, we consider how the parameters of a prior model should be estimated from observations of uncorrupted signals. A lot of recent work has implicitly assumed that maximum likelihood estimation is the optimal estimation method. Our results imply that this is not the case. We first obtain an objective function that approximates the error occurred in signal restoration due to an imperfect prior model. Next, we show that in an important special case (small gaussian noise), the error is the same as the score-matching objective function, which was previously proposed as an alternative for likelihood based on purely computational considerations. Our analysis thus shows that score matching combines computational simplicity with statistical optimality in signal restoration, providing a viable alternative to maximum likelihood methods. We also show how the method leads to a new intuitive and geometric interpretation of structure inherent in probability distributions.

FEATURE When users "do" the Ubicomp

Abstract: ing with credit is permitted. To copy otherwise, to republish, to post on servers, or to redistribute to lists, requires prior specific permission and/or fee. Request permission to publish from: Publications Dept., ACM, Inc., Fax +1-212-869-0481 or email permissions@acm.org For other copying of articles that carry a code at the bottom of the first or last page or screen display, copying is permitted provided that the per-copy fee indicated in the code is paid through the Copyright Clearance Center, 222 Rosewood Drive, Danvers, MA 01923, +1-978-750-8400, +1-978-750-4470 (fax). A BIMONTHLy PUBLICATION OF ACM in te ra c ti o n s M a rc h + A p ri l 2 0 0 8

Set Covering with our Eyes Closed

Abstract: Given a universe U of n elements and a weighted collection l of m subsets of U, the universal set cover problem is to a-priori map each element u epsi U to a set S(u) epsi l containing u, so that X sube U is covered by S(X)=UuepsiXS(u). The aim is finding a mapping such that the cost of S(X) is as close as possible to the optimal set-cover cost for X. (Such problems are also called oblivious or a-priori optimization problems.) Unfortunately, for every universal mapping, the cost of S(X) can be Omega(radicn) times larger than optimal if the set X is adversarially chosen. In this paper we study the performance on average, when X is a set of randomly chosen elements from the universe: we show how to efficiently find a universal map whose expected cost is O(log mn) times the expected optimal cost. In fact, we give a slightly improved analysis and show that this is the best possible. We generalize these ideas to weighted set cover and show similar guarantees to (non-metric) facility location, where we have to balance the facility opening cost with the cost of connecting clients to the facilities. We show applications of our results to universal multi-cut and disc-covering problems, and show how all these universal mappings give us stochastic online algorithms with the same competitive factors.

There are exactly five biplanes with k = 11

Abstract: A biplane is a 2-(k(k − 1)/2 + 1,k,2) symmetric design. Only sixteen nontrivial biplanes are known: there are exactly nine biplanes with k < 11, at least five biplanes with k = 11, and at least two biplanes with k = 13. It is here shown by exhaustive computer search that the list of five known biplanes with k = 11 is complete. This result further implies that there exists no 3-(57, 12, 2) design, no 11211 symmetric configuration, and no (324, 57, 0, 12) strongly regular graph. The five biplanes have 16 residual designs, which by the Hall–Connor theorem constitute a complete classification of the 2-(45, 9, 2) designs. © 2007 Wiley Periodicals, Inc. J Combin Designs 16: 117–127, 2008