Showing papers by "Helsinki Institute for Information Technology published in 2009"

Smartphones: An Emerging Tool for Social Scientists

Abstract: Recent developments in mobile technologies have produced a new kind of device: a programmable mobile phone, the smartphone. In this article, the authors argue that the technological and social char...

Virtual item sales as a revenue model: identifying attributes that drive purchase decisions

Abstract: The global market for virtual items, characters and currencies was estimated to exceed 2.1 Billion USD in 2007. Selling virtual goods for real money is an increasingly common revenue model not only for online games and virtual worlds, but for social networking sites and other mainstream online services as well. What drives consumer spending on virtual items is an increasingly relevant question, but little research has been devoted to the topic so far. Previous literature suggests that demand for virtual items is based on the items' ability to confer gameplay advantages on one hand, and on the items' decorative value on the other hand. In this paper, I adopt a perspective from the sociology of consumption and analyse examples from 14 virtual asset platforms to suggest a more detailed set of item attributes that drive virtual item purchase decisions, consisting of functional, hedonic and social attributes.

Like bees around the hive: a comparative study of a mobile augmented reality map

Abstract: We present findings from field trials of MapLens, a mobile augmented reality (AR) map using a magic lens over a paper map. Twenty-six participants used MapLens to play a location-based game in a city centre. Comparisons to a group of 11 users with a standard 2D mobile map uncover phenomena that arise uniquely when interacting with AR features in the wild. The main finding is that AR features facilitate place-making by creating a constant need for referencing to the physical, and in that it allows for ease of bodily configurations for the group, encourages establishment of common ground, and thereby invites discussion, negotiation and public problem-solving. The main potential of AR maps lies in their use as a collaborative tool.

All My People Right Here, Right Now: management of group co-presence on a social networking site

Abstract: A mundane but theoretically interesting and practically relevant situation presents itself on social networking sites: the co-presence of multiple groups important to an individual. This primarily qualitative study concentrates on the point of view of individual SNS users and their perspectives on multiple group affiliations. After charting the perceived multiplicity of groups on the social networking site Facebook, we investigated the relevance of multiple groups to the users and the effect of group co-presence on psychological identification processes. Users deal with group co-presence by managing the situation to prevent anticipated conflictive and identity-threatening situations. Their behavioral strategies consist of dividing the platform into separate spaces, using suitable channels of communication, and performing self-censorship. Mental strategies include both the creation of more inclusive in-group identities and the reciprocity of trusting other users and being responsible. In addition to giving further evidence of the existence of group co-presence on SNSs, the study sheds light on the management of the phenomenon. Management of group co-presence should be supported, since otherwise users may feel the urge to resort to defensive strategies of social identity protection such as ceasing to use SNSs altogether or, less dramatically, limit their use according to "the least common denominator". Hence, the phenomenon merits the attention of researchers, developers, and designers alike.

MOODS: fast search for position weight matrix matches in DNA sequences

Abstract: Summary: MOODS (MOtif Occurrence Detection Suite) is a software package for matching position weight matrices against DNA sequences. MOODS implements state-of-the-art online matching algorithms, achieving considerably faster scanning speed than with a simple brute-force search. MOODS is written in C++, with bindings for the popular BioPerl and Biopython toolkits. It can easily be adapted for different purposes and integrated into existing workflows. It can also be used as a C++ library. Availability: The package with documentation and examples of usage is available at http://www.cs.helsinki.fi/group/pssmfind. The source code is also available under the terms of a GNU General Public License (GPL). Contact: if.iknisleh@nenohrok.h.ennaj

Learning Natural Image Structure with a Horizontal Product Model

Abstract: We present a novel extension to Independent Component Analysis (ICA), where the data is generated as the product of two submodels, each of which follow an ICA model, and which combine in a horizontal fashion. This is in contrast to previous nonlinear extensions to ICA which were based on a hierarchy of layers. We apply the product model to natural image patches and report the emergence of localized masks in the additional network layer, while the Gabor features that are obtained in the primary layer change their tuning properties and become less localized. As an interpretation we suggest that the model learns to separate the localization of image features from other properties, since identity and position of a feature are plausibly independent. We also show that the horizontal model can be interpreted as an overcomplete model where the features are no longer independent.

Embodied interaction with a 3D versus 2D mobile map

Abstract: In comparison to 2D maps, 3D mobile maps involve volumetric instead of flat representation of space, realistic instead of symbolic representation of objects, more variable views that are directional and bound to a first-person perspective, more degrees of freedom in movement, and dynamically changing object details. We conducted a field experiment to understand the influence of these qualities on a mobile spatial task where buildings shown on the map were to be localized in the real world. The representational differences were reflected in how often users interact with the physical environment and in when they are more likely to physically turn and move the device, instead of using virtual commands. 2D maps direct users into using reliable and ubiquitous environmental cues like street names and crossings, and 2D better affords the use of pre-knowledge and bodily action to reduce cognitive workload. Both acclaimed virtues of 3D mobile maps--rapid identification of objects and ego-centric alignment--worked poorly due reasons we discuss. However, with practice, some 3D users learned to shift to 2D-like strategies and could thereby improve performance. We conclude with a discussion of how representational differences in mobile maps affect strategies of embodied interaction.

VIRTUAL CONSUMERISM: Case Habbo Hotel

Abstract: Selling virtual items for real money is increasingly being used as a revenue model in games and other online services. To some parents and authorities, this has been a shock: previously innocuous ‘consumption games’ suddenly seem to be enticing players into giving away their money for nothing. In this article, we examine the phenomenon from a sociological perspective, aiming to understand how some media representations come to be perceived as ‘virtual commodities’, what motivations individuals have for spending money on these commodities, and how the resulting ‘virtual consumerism’ relates to consumer culture at large. The discussion is based on a study of everyday practices and culture in Habbo Hotel, a popular massively-multiuser online environment permeated with virtual items. Our results suggest that virtual commodities can act in essentially the same social roles as material goods, leading us to ask whether ecologically sustainable virtual consumption could be a substitute to material consumerism in ...

Can eyes reveal interest? Implicit queries from gaze patterns

Abstract: We study a new research problem, where an implicit information retrieval query is inferred from eye movements measured when the user is reading, and used to retrieve new documents. In the training phase, the user's interest is known, and we learn a mapping from how the user looks at a term to the role of the term in the implicit query. Assuming the mapping is universal, that is, the same for all queries in a given domain, we can use it to construct queries even for new topics for which no learning data is available. We constructed a controlled experimental setting to show that when the system has no prior information as to what the user is searching, the eye movements help significantly in the search. This is the case in a proactive search, for instance, where the system monitors the reading behaviour of the user in a new topic. In contrast, during a search or reading session where the set of inspected documents is biased towards being relevant, a stronger strategy is to search for content-wise similar documents than to use the eye movements.

Identifying Meaningful Places: The Non-parametric Way

Abstract: Gathering and analyzing location data is an important part of many ubiquitous computing applications. The most common way to represent location information is to use numerical coordinates, e.g., latitudes and longitudes. A problem with this approach is that numerical coordinates are usually meaningless to a user and they contrast with the way humans refer to locations in daily communication. Instead of using coordinates, humans tend to use descriptive statements about their location; for example, "I'm home" or "I'm at Starbucks." Locations, to which a user can attach meaningful and descriptive semantics, are often called places. In this paper we focus on the automatic extraction of places from discontinuous GPS measurements. We describe and evaluate a non-parametric Bayesian approach for identifying places from this kind of data. The main novelty of our approach is that the algorithm is fully automated and does not require any parameter tuning. Another novel aspect of our algorithm is that it can accurately identify places without temporal information. We evaluate our approach using data that has been gathered from different users and different geographic areas. The traces that we use exhibit different characteristics and contain data from daily life as well as from traveling abroad. We also compare our algorithm against the popular k-means algorithm. The results indicate that our method can accurately identify meaningful places from a variety of location traces and that the algorithm is robust against noise.

On the role of presence in mixed reality

Abstract: Previous paradigms for presence research were primarily established in the context of virtual reality (VR). The objective of this paper is to introduce a new agenda for research on presence suitable for the domain of mixed reality (MR). While established assumptions and methods of presence research from VR are applicable to MR experiences, we argue that they are not necessarily meaningful or informative. Specifically, a shift of attention is needed away from psycho-physiological studies coming from a laboratory experiment tradition, toward an ecological-cultural approach that is applicable in real world situations and relies on ethnographic rather than fully controlled methods. We give a series of examples taken from the work on the European integrated research project IPCity, and discuss the implications of our findings.

Bodily Explorations in Space: Social Experience of a Multimodal Art Installation

Abstract: We contribute with an extensive field study of a public interactive art installation that applies multimodal interface technologies. The installation is part of a Theater production on Galileo Galilei and includes: projected galaxies that are generated and move according to motion of visitors changing colour depending on their voices; projected stars that configure themselves around shadows of visitors. In the study we employ emotion scales (PANAS), qualitative analysis of questionnaire answers and video-recordings. PANAS rates indicate dominantly positive feelings, further described in the subjective verbalizations as gravitating around interest, ludic pleasure and transport. Through the video analysis, we identified three phases in the interaction with the artwork (circumspection, testing, play) and two pervasive features of these phases (experience sharing and imitation), which were also found in the verbalizations. Both video and verbalisations suggest that visitor's experience and ludic pleasure are rooted in the embodied, performative interaction with the installation, and is negotiated with the other visitors.

A local 2-approximation algorithm for the vertex cover problem

Abstract: We present a distributed 2-approximation algorithm for the minimum vertex cover problem. The algorithm is deterministic, and it runs in (Δ + 1)2 synchronous communication rounds, where Δ is the maximum degree of the graph. For Δ = 3, we give a 2-approximation algorithm also for the weighted version of the problem.

Causal search in structural vector autoregressive models

Abstract: This paper reviews a class of methods to perform causal inference in the framework of a structural vector autoregressive model. We consider three different settings. In the first setting the underlying system is linear with normal disturbances and the structural model is identified by exploiting the information incorporated in the partial correlations of the estimated residuals. Zero partial correlations are used as input of a search algorithm formalized via graphical causal models. In the second, semi-parametric, setting the underlying system is linear with non-Gaussian disturbances. In this case the structural vector autoregressive model is identified through a search procedure based on independent component analysis. Finally, we explore the possibility of causal search in a nonparametric setting by studying the performance of conditional independence tests based on kernel density estimations.

BeTelGeuse: A Platform for Gathering and Processing Situational Data

Abstract: BeTelGeuse is an extensible data collection platform for mobile devices, which also automatically infers higher level context from sensor data. In this article, the authors introduce BeTelGeuse's architecture and current features, and evaluate its impact on mobile phone performance.

Using individual, social and economic persuasion techniques to reduce CO2 emissions in a family setting

Abstract: This paper presents EcoIsland, which is a system persuading individuals and families to change their lifestyle patterns to reduce CO2 emissions. EcoIsland visualizes the user's current eco-friendly behavior as an island shared by his/her family members. Several persuasive techniques developed in behaviorism, social psychology, and economy are used to offer incentives to him/her to encourage eco-friendly behavior. We examine and compare the implementation and effectiveness of different types of persuasive techniques in several user studies.

Probabilistic retrieval and visualization of biologically relevant microarray experiments

Abstract: Motivation: As ArrayExpress and other repositories of genome-wide experiments are reaching a mature size, it is becoming more meaningful to search for related experiments, given a particular study. We introduce methods that allow for the search to be based upon measurement data, instead of the more customary annotation data. The goal is to retrieve experiments in which the same biological processes are activated. This can be due either to experiments targeting the same biological question, or to as yet unknown relationships. Results: We use a combination of existing and new probabilistic machine learning techniques to extract information about the biological processes differentially activated in each experiment, to retrieve earlier experiments where the same processes are activated and to visualize and interpret the retrieval results. Case studies on a subset of ArrayExpress show that, with a sufficient amount of data, our method indeed finds experiments relevant to particular biological questions. Results can be interpreted in terms of biological processes using the visualization techniques. Availability: The code is available from http://www.cis.hut.fi/projects/mi/software/ismb09. Contact: jose.caldas@tkk.fi

Local Algorithms: Self-stabilization on Speed

Abstract: Fault tolerance is one of the main concepts in distributed computing. It has been tackled from different angles, e.g. by building replicated systems that can survive crash failures of individual components, or even systems that can tolerate a minority of arbitrarily malicious ("Byzantine") participants. Self-stabilization, a fault tolerance concept coined by the late Edsger W. Dijkstra in 1973 [1,2], is of a different stamp. A self-stabilizing system must survive arbitrary failures, beyond Byzantine failures, including for instance a total wipe out of volatile memory at all nodes. In other words, the system must self-heal and converge to a correct state even if starting in an arbitrary state, provided that no further faults happen.

Not being (super)thin or solid is hard: A study of grid Hamiltonicity

Abstract: We give a systematic study of Hamiltonicity of grids - the graphs induced by finite subsets of vertices of the tilings of the plane with congruent regular convex polygons (triangles, squares, or hexagons). Summarizing and extending existing classification of the usual, ''square'', grids, we give a comprehensive taxonomy of the grid graphs. For many classes of grid graphs we resolve the computational complexity of the Hamiltonian cycle problem. For graphs for which there exists a polynomial-time algorithm we give efficient algorithms to find a Hamiltonian cycle. We also establish, for any g>=6, a one-to-one correspondence between Hamiltonian cycles in planar bipartite maximum-degree-3 graphs and Hamiltonian cycles in the class C"g of girth-g planar maximum-degree-3 graphs. As applications of the correspondence, we show that for graphs in C"g the Hamiltonian cycle problem is NP-complete and that for any N>=5 there exist graphs in C"g that have exactly N Hamiltonian cycles. We also prove that for the graphs in C"g, a Chinese Postman tour gives a (1+8g)-approximation to TSP, improving thereby the Christofides ratio when g>16. We show further that, in any graph, the tour obtained by Christofides' algorithm is not longer than a Chinese Postman tour.

The number of Latin squares of order 11

Abstract: Constructive and nonconstructive techniques are employed to enumerate Latin squares and related objects. It is established that there are (i) 2036029552582883134196099 main classes of Latin squares of order 11; (ii) 6108088657705958932053657 isomorphism classes of one-factorizations of $K_{11,11}$; (iii) 12216177315369229261482540 isotopy classes of Latin squares of order 11; (iv) 1478157455158044452849321016 isomorphism classes of loops of order 11; and (v) 19464657391668924966791023043937578299025 isomorphism classes of quasigroups of order 11. The enumeration is constructive for the 1151666641 main classes with an autoparatopy group of order at least 3.

Privacy-preserving 802.11 access-point discovery

Abstract: It is usual for 802.11 WLAN clients to probe actively for access points in order to hasten AP discovery and to find "hidden" APs. These probes reveal the client's list of preferred networks, thus, present a privacy risk: an eavesdropper can infer attributes of the client based on its associations with networks. We propose an access-point discovery protocol that supports fast discovery and hidden networks while also preserving privacy. Our solution is incrementally deployable, efficient, requires only small modifications to current client and AP implementations, interoperates with current networks, and does not change the user experience. We note that our solution is faster than the standard hidden-network discovery protocol based on measurements on a prototype implementation.

Probabilistic retrieval and visualization of biologically relevant microarray experiments

Abstract: Motivation: As ArrayExpress and other repositories of genome-wide experiments are reaching a mature size, it is becoming more meaningful to search for related experiments, given a particular study. We introduce methods that allow for the search to be based upon measurement data, instead of the more customary annotation data. The goal is to retrieve experiments in which the same biological processes are activated. This can be due either to experiments targeting the same biological question, or to as yet unknown relationships. Results: We use a combination of existing and new probabilistic machine learning techniques to extract information about the biological processes differentially activated in each experiment, to retrieve earlier experiments where the same processes are activated and to visualize and interpret the retrieval results. Case studies on a subset of ArrayExpress show that, with a sufficient amount of data, our method indeed finds experiments relevant to particular biological questions. Results can be interpreted in terms of biological processes using the visualization techniques. Availability: The code is available from http://www.cis.hut.fi/projects/mi/software/ismb09. Contact: jose.caldas@tkk.fi

MDL Denoising Revisited

Abstract: We refine and extend an earlier minimum description length (MDL) denoising criterion for wavelet-based denoising. We start by showing that the denoising problem can be reformulated as a clustering problem, where the goal is to obtain separate clusters for informative and noninformative wavelet coefficients, respectively. This suggests two refinements, adding a code-length for the model index, and extending the model in order to account for subband-dependent coefficient distributions. A third refinement is the derivation of soft thresholding inspired by predictive universal coding with weighted mixtures. We propose a practical method incorporating all three refinements, which is shown to achieve good performance and robustness in denoising both artificial and natural signals.

LANES: an inter-domain data-oriented routing architecture

Abstract: Data-oriented networking has attracted research recently, but the efficiency of the state-of-the-art solutions can still be improved. Our work towards this goal is set in a clean-slate architecture consisting of modular rendezvous, routing, and forwarding functions. In this paper we present the interdomain routing layer and its interplay with the other components of the system. The proposed system is built around two types of nodes: forwarding nodes and branching nodes. The forwarding nodes are optimized for throughput with no per-subscription state and no need to change passing packets, while branching nodes contain a large memory for caching and can make complex routing decisions. The amount of storage space and bandwidth can be independently scaled to suit the needs of each network. In the background, topology nodes perform load-balancing and configure routes in each domain using a two-dimensional addressing mechanism. The paths taken by packets adapt to the number of active subscribers to keep the amount of in-network state and latency low. A new data-oriented congestion control scheme is introduced, which takes into account the use of storage resources on-path and is fair to multicast flows.

Virtual Consumerism: Case Habbo Hotel

Abstract: Selling virtual items for real money is increasingly being used as a revenue model in games and other online services. To some parents and authorities, this has been a shock: previously innocuous ‘consumption games’ suddenly seem to be enticing players into giving away their money for nothing. In this article, we examine the phenomenon from a sociological perspective, aiming to understand how some media representations come to be perceived as ‘virtual commodities’, what motivations individuals have for spending money on these commodities, and how the resulting ‘virtual consumerism’ relates to consumer culture at large. The discussion is based on a study of everyday practices and culture in Habbo Hotel, a popular massively-multiuser online environment permeated with virtual items. Our results suggest that virtual commodities can act in essentially the same social roles as material goods, leading us to ask whether ecologically sustainable virtual consumption could be a substitute to material consumerism in the future.