A study of word association aids in information retrieval

Issued as Final project reports [nos. 1-2], Project no. G-36-65

The role of idiotypic interactions in the adaptive immune system: a belief-propagation approach

In this work we use belief-propagation techniques to study the equilibrium behaviour of a minimal model for the immune system comprising interacting T and B clones. We investigate the effect of the so-called idiotypic interactions among complementary B clones on the system's activation. Our result shows that B-B interactions increase the system's resilience to noise, making clonal activation more stable, while increasing the cross-talk between different clones. We derive analytically the noise level at which a B clone gets activated, in the absence of cross-talk, and find that this increases with the strength of idiotypic interactions and with the number of T cells signalling the B clone. We also derive, analytically and numerically, via population dynamics, the critical line where clonal cross-talk arises. Our approach allows us to derive the B clone size distribution, which can be experimentally measured and gives important information about the adaptive immune system response to antigens and vaccination.Comment: 37 pages, 18 figure

CHORUS Deliverable 2.2: Second report - identification of multi-disciplinary key issues for gap analysis toward EU multimedia search engines roadmap

After addressing the state-of-the-art during the first year of Chorus and establishing the existing landscape in multimedia search engines, we have identified and analyzed gaps within European research effort during our second year. In this period we focused on three directions, notably technological issues, user-centred issues and use-cases and socio- economic and legal aspects. These were assessed by two central studies: firstly, a concerted vision of functional breakdown of generic multimedia search engine, and secondly, a representative use-cases descriptions with the related discussion on requirement for technological challenges. Both studies have been carried out in cooperation and consultation with the community at large through EC concertation meetings (multimedia search engines cluster), several meetings with our Think-Tank, presentations in international conferences, and surveys addressed to EU projects coordinators as well as National initiatives coordinators. Based on the obtained feedback we identified two types of gaps, namely core technological gaps that involve research challenges, and “enablers”, which are not necessarily technical research challenges, but have impact on innovation progress. New socio-economic trends are presented as well as emerging legal challenges

Putting some order in person memory: memory for (serial) order in impression formation

American Psychological Association (PsycINFO Classification Categories and Codes) 2340 Cognitive Processes; 2343 Learning & Memory; 3000 Social Psychology; 3040 Social Perception and CognitionThe present work examines the representation and retrieval of order information in person memory. The study of memory for serial order has been absent from the research on the underling memory processes of impression formation, which has been focusing exclusively on item information. In this work we argue that our understanding of person memory is incomplete without an account for order and item information representation and retrieval. According to a chaining hypothesis, we predicted that the organizational processes involved in impression formation would hinder the ability to represent order by means of associations between items in successive positions. The first three experiments indicated, contradicting our hypothesis, that when people form impressions they are able to represent, retrieve and use order information for order judgements and (serial) recall. The two following studies, experiment 4 and 5, directly manipulated the associations that were built in memory when people formed impressions, to understand whether order information representation was based on associations between items that appeared in successive serial positions. Results showed that the ability to use order information was unaffected by changes in the structure of non-serial inter-item associations, which suggests that order representation is not derived from mere serial associations. Experiment 6, the last from the set of experiments reported here, suggested that the representation of order information is less dependent on episodic memory, in contrast to item information. The findings from this set of 6 experiments suggested, firstly, that when people form impressions they are able to reconstruct serial order (even when such order has no meaning), and secondly, that order representation in person memory seem not to be derived from the inter-item associations formed at encoding. Finally, an ordinal proposal for the representation and use of order in person memory is discussed.O objectivo central do presente trabalho é o estudo da representação e recuperação da informação de ordem em memória de pessoas. A memória de ordem serial tem permanecido fora da investigação sobre os processos mnésicos subjacentes à formação de impressões, investigação esta que se tem centrado exclusivamente na informação de item. Argumentamos que o conhecimento sobre memória de pessoas não pode ser completo sem que haja uma compreensão dos processos envolvidos na representação e recuperação da informação de ordem. De acordo com a hipótese de chaining, os processos que caracterizam a formação de impressões prejudicam o estabelecimento de associações entre itens em posições sucessivas, interferindo com a representação da informação de ordem. As três primeiras experiências sugerem, contrariamente ao esperado, que quando as pessoas formam impressões estão a representar informação de ordem, que pode ser utilizada em tarefas de julgamento e recordação. Nas experiências 4 e 5 manipulámos directamente as associações que se formam durante a codificação, quando as pessoas formam impressões, tentando perceber se a representação de ordem se basearia em associações entre itens em posições seriais sucessivas. Os resultados indicam que, independentemente da mudança na densidade associativa da rede, a capacidade de os participantes acederem e utilizarem informação de ordem não é afectada. Estes dados sugerem que a representação da informação não acontece pela mera associação de itens em posições sucessivas. A experiência 6 sugere que a representação da informação de ordem, em contraste com a informação de item, depende menos da memória episódica. Este conjunto de resultados sugere (i) que quando as pessoas formam impressões são capazes de reconstruir a ordem e (ii) que a representação da informação de ordem em memória de pessoas não é dependente das associações que se estabelecem entre os itens, durante a codificação. Finalmente, uma proposta ordinal para a representação e recuperação da ordem em memória de pessoas é discutida.The present work was sponsored by a Doctoral Grant (Ref. SFRH/BD/23748/2005) of the Science and Technology Foundation (FCT), Portugal, and the Program POCI2010, which is funded by the Portuguese Ministry of Science, Technology and Higher Education, and the European Social Fund (Community Support Framework III)

A Computational Cognitive Model of Syntactic Priming

The psycholinguistic literature has identified two syntactic adaptation effects in language production: rapidly decaying short-term priming and long-lasting adaptation. To explain both effects, we present an ACT-R model of syntactic priming based on a wide-coverage, lexicalized syntactic theory that explains priming as facilitation of lexical access. In this model, two well-established ACT-R mechanisms, base-level learning and spreading activation, account for long-term adaptation and short-term priming, respectively. Our model simulates incremental language production and in a series of modeling studies we show that it accounts for (a) the inverse frequency interaction; (b) the absence of a decay in long-term priming; and (c) the cumulativity of long-term adaptation. The model also explains the lexical boost effect and the fact that it only applies to short-term priming. We also present corpus data that verifies a prediction of the model, i.e., that the lexical boost affects all lexical material, rather than just heads. Keywords: syntactic priming, adaptation, cognitive architectures, ACT-R, categorial grammar, incrementality

A Dynamic Approach to Recognition Memory

Thesis (Ph.D.) - Indiana University,Psychological and Brain Sciences/Cognitive Science, 2015We argue that taking a dynamic approach to the understanding of memory will lead to advances that are not possible via other routes. To that end, we present a model of recognition memory that specifies how memory retrieval and recognition decisions jointly evolve over time and show that it is able to jointly predict accuracy, response time, and speed-accuracy trade-off functions. The model affords insights into the effects of study time, list length, and instructions. The model leads to a novel qualitative and quantitative test of the source of word frequency effects in recognition, showing that the relatively high distinctiveness of the features of low frequency words provide the best account. We also show how the dynamic model can be extended to account for paradigms like associative recognition and list discrimination, leading to another novel test of the presence of recall-like processes. Associative recognition, list discrimination, recognition of similar foils, and source exclusion are all better explained by the formation of a compound cue rather than recall, although source memory is found to be better modeled by a recall process