Spatial heterogeneity of habitat suitability for Rift Valley fever occurrence in Tanzania: an ecological niche modelling approach

Despite the long history of Rift Valley fever (RVF) in Tanzania, extent of its suitable habitat in the country remains unclear. In this study we investigated potential effects of temperature, precipitation, elevation, soil type, livestock density, rainfall pattern, proximity to wild animals, protected areas and forest on the habitat suitability for RVF occurrence in Tanzania. Presence-only records of 193 RVF outbreak locations from 1930 to 2007 together with potential predictor variables were used to model and map the suitable habitats for RVF occurrence using ecological niche modelling. Ground-truthing of the model outputs was conducted by comparing the levels of RVF virus specific antibodies in cattle, sheep and goats sampled from locations in Tanzania that presented different predicted habitat suitability values. Habitat suitability values for RVF occurrence were higher in the northern and central-eastern regions of Tanzania than the rest of the regions in the country. Soil type and precipitation of the wettest quarter contributed equally to habitat suitability (32.4% each), followed by livestock density (25.9%) and rainfall pattern (9.3%). Ground-truthing of model outputs revealed that the odds of an animal being seropositive for RVFV when sampled from areas predicted to be most suitable for RVF occurrence were twice the odds of an animal sampled from areas least suitable for RVF occurrence (95% CI: 1.43, 2.76, p < 0.001). The regions in the northern and central-eastern Tanzania were more suitable for RVF occurrence than the rest of the regions in the country. The modelled suitable habitat is characterised by impermeable soils, moderate precipitation in the wettest quarter, high livestock density and a bimodal rainfall pattern. The findings of this study should provide guidance for the design of appropriate RVF surveillance, prevention and control strategies which target areas with these characteristics

Scalability approaches for causal multicast: a survey

The final publication is available at Springer via http://dx.doi.org/10.1007/s00607-015-0479-0Many distributed services need to be scalable: internet search, electronic commerce, e-government... In order to achieve scalability, high availability and fault tolerance, such applications rely on replicated components. Because of the dynamics of growth and volatility of customer markets, applications need to be hosted by adaptive, highly scalable systems. In particular, the scalability of the reliable multicast mechanisms used for supporting the consistency of replicas is of crucial importance. Reliable multicast might propagate updates in a pre-determined order (e.g., FIFO, total or causal). Since total order needs more communication rounds than causal order, the latter appears to be the preferable candidate for achieving multicast scalability, although the consistency guarantees based on causal order are weaker than those of total order. This paper provides a historical survey of different scalability approaches for reliable causal multicast protocols.This work was supported by European Regional Development Fund (FEDER) and Ministerio de Economia y Competitividad (MINECO) under research Grant TIN2012-37719-C03-01.Juan Marín, RD.; Decker, H.; Armendáriz Íñigo, JE.; Bernabeu Aubán, JM.; Muñoz Escoí, FD. (2016). Scalability approaches for causal multicast: a survey. Computing. 98(9):923-947. https://doi.org/10.1007/s00607-015-0479-0S923947989Adly N, Nagi M (1995) Maintaining causal order in large scale distributed systems using a logical hierarchy. In: IASTED Intnl Conf on Appl Inform, pp 214–219Aguilera MK, Chen W, Toueg S (1997) Heartbeat: a timeout-free failure detector for quiescent reliable communication. In: 11th Intnl Wshop on Distrib Alg (WDAG), Saarbrücken, pp 126–140Almeida JB, Almeida PS, Baquero C (2004) Bounded version vectors. In: 18th Intnl Conf Distrib Comput (DISC), Amsterdam, pp 102–116Almeida PS, Baquero C, Fonte V (2008) Interval tree clocks. In: 12th Intnl Conf Distrib Syst (OPODIS), Luxor, pp 259–274Almeida S, Leitão J, Rodrigues LET (2013) ChainReaction: a causal+ consistent datastore based on chain replication. In: 8th EuroSys Conf, Czech Republic, pp 85–98Álvarez A, Arévalo S, Cholvi V, Fernández A, Jiménez E (2008) On the interconnection of message passing systems. Inf Process Lett 105(6):249–254Amir Y, Stanton J (1998) The Spread wide area group communication system. Tech. rep., CDNS-98-4, The Center for Networking and Distributed Systems, The Johns Hopkins UnivAmir Y, Dolev D, Kramer S, Malki D (1992) Transis: a communication subsystem for high availability. In: 22nd Intnl Symp Fault-Tolerant Comp (FTCS), Boston, pp 76–84Anastasi G, Bartoli A, Spadoni F (2001) A reliable multicast protocol for distributed mobile systems: design and evaluation. IEEE Trans Parallel Distrib Syst 12(10):1009–1022Bailis P, Ghodsi A, Hellerstein JM, Stoica I (2013) Bolt-on causal consistency. In: Intnl Conf Mgmnt Data (SIGMOD), New York, pp 761–772Baldoni R, Raynal M, Prakash R, Singhal M (1996) Broadcast with time and causality constraints for multimedia applications. In: 22nd Intnl Euromicro Conf, Prague, pp 617–624Baldoni R, Friedman R, van Renesse R (1997) The hierarchical daisy architecture for causal delivery. In: 17th Intnl Conf Distrib Comput Syst (ICDCS), Maryland, pp 570–577Ban B (2002) JGroups—a toolkit for reliable multicast communication. http://www.jgroups.orgBaquero C, Almeida PS, Shoker A (2014) Making operation-based CRDTs operation-based. In: 14th Intnl Conf Distrib Appl Interop Syst (DAIS), Berlin, pp 126–140Benslimane A, Abouaissa A (2002) Dynamical grouping model for distributed real time causal ordering. Comput Commun 25:288–302Birman KP, Joseph TA (1987) Reliable communication in the presence of failures. ACM Trans Comput Syst 5(1):47–76Birman KP, Schiper A, Stephenson P (1991) Lightweigt causal and atomic group multicast. ACM Trans Comput Syst 9(3):272–314Cachin C, Guerraoui R, Rodrigues LET (2011) Introduction to reliable and secure distributed programming, 2nd edn. Springer, BerlinChandra P, Gambhire P, Kshemkalyani AD (2004) Performance of the optimal causal multicast algorithm: a statistical analysis. IEEE Trans Parall Distr 15(1):40–52Chandra TD, Toueg S (1996) Unreliable failure detectors for reliable distributed systems. J ACM 43(2):225–267de Juan-Marín R, Cholvi V, Jiménez E, Muñoz-Escoí FD (2009) Parallel interconnection of broadcast systems with multiple FIFO channels. In: 11th Intnl Symp on Distrib Obj, Middleware and Appl (DOA), Vilamoura, LNCS, vol 5870, pp 449–466Défago X, Schiper A, Urbán P (2004) Total order broadcast and multicast algorithms: taxonomy and survey. ACM Comput Surv 36(4):372–421Demers AJ, Greene DH, Hauser C, Irish W, Larson J, Shenker S, Sturgis HE, Swinehart DC, Terry DB (1987) Epidemic algorithms for replicated database maintenance. In: 6th ACM Symp on Princ of Distrib Comput (PODC), Canada, pp 1–12Du J, Elnikety S, Roy A, Zwaenepoel W (2013) Orbe: scalable causal consistency using dependency matrices and physical clocks. In: ACM Symp on Cloud Comput (SoCC), Santa Clara, pp 11:1–11:14Fernández A, Jiménez E, Cholvi V (2000) On the interconnection of causal memory systems. In: 19th Annual ACM Symp on Princ of Distrib Comput (PODC), Portland, pp 163–170Fidge CJ (1988) Timestamps in message-passing systems that preserve the partial ordering. In: 11th Australian Comput Conf, pp 56–66Friedman R, Vitenberg R, Chockler G (2003) On the composability of consistency conditions. Inf Process Lett 86(4):169–176Gilbert S, Lynch N (2002) Brewer’s conjecture and the feasibility of consistent, available, partition-tolerant web services. SIGACT News 33(2):51–59Gray J, Helland P, O’Neil PE, Shasha D (1996) The dangers of replication and a solution. In: SIGMOD Conf, pp 173–182Hadzilacos V, Toueg S (1993) Fault-tolerant broadcasts and related problems. In: Mullender S (ed) Distributed systems, chap 5, 2nd edn. ACM Press, pp 97–145Johnson S, Jahanian F, Shah J (1999) The inter-group router approach to scalable group composition. In: 19th Intnl Conf on Distrib Comput Syst (ICDCS), Austin, pp 4–14Kalantar MH, Birman KP (1999) Causally ordered multicast: the conservative approach. In: 19th Intnl Conf on Distrib Comput Syst (ICDCS), Austin, pp 36–44Kawanami S, Enokido T, Takizawa M (2004) A group communication protocol for scalable causal ordering. In: 18th Intnl Conf on Adv Inform Netw Appl (AINA), Fukuoka, pp 296–302Kawanami S, Nishimura T, Enokido T, Takizawa M (2005) A scalable group communication protocol with global clock. In: 19th Intnl Conf on Adv Inform Netw Appl (AINA), Taipei, pp 625–630Kshemkalyani AD, Singhal M (1998) Necessary and sufficient conditions on information for causal message ordering and their optimal implementation. Distrib Comput 11(2):91–111Kshemkalyani AD, Singhal M (2011) Distributed computing: principles, algorithms, and systems, 2nd edn. Cambridge University Press, New YorkLadin R, Liskov B, Shrira L, Ghemawat S (1992) Providing high availability using lazy replication. ACM Trans Comput Syst 10(4):360–391Lamport L (1978) Time, clocks, and the ordering of events in a distributed system. Commun ACM 21(7):558–565Laumay P, Bruneton E, de Palma N, Krakowiak S (2001) Preserving causality in a scalable message-oriented middleware. In: Intnl Conf on Distrib Syst Platf (Middleware), pp 311–328Liu N, Liu M, Cao J, Chen G, Lou W (2010) When transportation meets communication: V2P over VANETs. In: 30th Intnl Conf Distrib Comput Syst (ICDCS), GenovaLwin CH, Mohanty H, Ghosh RK (2004) Causal ordering in event notification service systems for mobile users. In: Intnl Conf Inform Tech: Coding Comput (ITCC), Las Vegas, pp 735–740Mahajan P, Alvisi L, Dahlin M (2011) Consistency, availability and covergence. Tech. rep., UTCS TR-11-22, The University of Texas at AustinMatos M, Sousa A, Pereira J, Oliveira R, Deliot E, Murray P (2009) CLON: overlay networks and gossip protocols for cloud environments. In: 11th Intnl Symp on Dist Obj, Middleware and Appl (DOA), Vilamoura, LNCS, vol 5870, pp 549–566Mattern F (1989) Virtual time and global states of distributed systems. In: Parallel and distributed algorithms, North-Holland, pp 215–226Mattern F, Fünfrocken S (1994) A non-blocking lightweight implementation of causal order message delivery. Lect Notes Comput Sci 938:197–213Meldal S, Sankar S, Vera J (1991) Exploiting locality in maintaining potential causality. In: 10th ACM Symp on Princ of Distrib Comp (PODC), Montreal, pp 231–239Meling H, Montresor A, Helvik BE, Babaoglu Ö (2008) Jgroup/ARM: a distributed object group platform with autonomous replication management. Softw Pract Exp 38(9):885–923Mosberger D (1993) Memory consistency models. Oper Syst Rev 27(1):18–26Mostéfaoui A, Raynal M (1993) Causal multicast in overlapping groups: towards a low cost approach. In: 4th Intnl Wshop on Future Trends of Distrib Comp Syst (FTDCS), Lisbon, pp 136–142Mostéfaoui A, Raynal M, Travers C, Patterson S, Agrawal D, El Abbadi A (2005) From static distributed systems to dynamic systems. In: 24th Symp on Rel Distrib Syst (SRDS), Orlando, pp 109–118Nishimura T, Hayashibara N, Takizawa M, Enokido T (2005) Causally ordered delivery with global clock in hierarchical group. In: ICPADS (2), Fukuoka, pp 560–564Parker DS Jr, Popek GJ, Rudisin G, Stoughton A, Walker BJ, Walton E, Chow JM, Edwards DA, Kiser S, Kline CS (1983) Detection of mutual inconsistency in distributed systems. IEEE Trans Softw Eng 9(3):240–247Pascual-Miret L (2014) Consistency models in modern distributed systems. An approach to eventual consistency. Master’s thesis, Depto. de Sistemas Informáticos y Computación, Univ. Politècnica de ValènciaPascual-Miret L, González de Mendívil JR, Bernabéu-Aubán JM, Muñoz-Escoí FD (2015) Widening CAP consistency. Tech. rep., IUMTI-SIDI-2015/003, Univ. Politècnica de València, ValenciaPeterson LL, Buchholz NC, Schlichting RD (1989) Preserving and using context information in interprocess communication. ACM Trans Comput Syst 7(3):217–246Pomares Hernández S, Fanchon J, Drira K, Diaz M (2001) Causal broadcast protocol for very large group communication systems. In: 5th Intnl Conf on Princ of Distrib Syst (OPODIS), Manzanillo, pp 175–188Prakash R, Baldoni R (2004) Causality and the spatial-temporal ordering in mobile systems. Mobile Netw Appl 9(5):507–516Prakash R, Raynal M, Singhal M (1997) An adaptive causal ordering algorithm suited to mobile computing environments. J Parallel Distrib Comput 41(2):190–204Raynal M, Schiper A, Toueg S (1991) The causal ordering abstraction and a simple way to implement it. Inf Process Lett 39(6):343–350Rodrigues L, Veríssimo P (1995a) Causal separators and topological timestamping: An approach to support causal multicast in large-scale systems. Tech. Rep. AR-05/95, Instituto de Engenharia de Sistemas e Computadores (INESC), LisbonRodrigues L, Veríssimo P (1995b) Causal separators for large-scale multicast communication. In: 15th Intnl Conf on Distrib Comput Syst (ICDCS), Vancouver, pp 83–91Schiper A, Eggli J, Sandoz A (1989) A new algorithm to implement causal ordering. In: 3rd Intnl Wshop on Distrib Alg (WDAG), Nice, pp 219–232Schiper N, Pedone F (2010) Fast, flexible and highly resilient genuine FIFO and causal multicast algorithms. In: 25th ACM Symp on Applied Comp (SAC), Sierre, pp 418–422Shapiro M, Preguiça NM, Baquero C, Zawirski M (2011) Convergent and commutative replicated data types. Bull EATCS 104:67–88Shen M, Kshemkalyani AD, Hsu TY (2015) Causal consistency for geo-replicated cloud storage under partial replication. In: Intnl Paral Distrib Proces Symp (IPDPS) Wshop, Hyderabad, pp 509–518Singhal M, Kshemkalyani AD (1992) An efficient implementation of vector clocks. Inf Process Lett 43(1):47–52Sotomayor B, Montero RS, Llorente IM, Foster IT (2009) Virtual infrastructure management in private and hybrid clouds. IEEE Internet Comput 13(5):14–22Stephenson P (1991) Fast ordered multicasts. PhD thesis, Dept. of Comp. Sc., Cornell Univ., IthacaStonebraker M (1986) The case for shared nothing. IEEE Database Eng Bull 9(1):4–9Vogels W (2009) Eventually consistent. Commun ACM 52(1):40–44Wischhof L, Ebner A, Rohling H (2005) Information dissemination in self-organizing intervehicle networks. IEEE Trans Intell Transp 6(1):90–101Yavatkar R (1992) MCP: a protocol for coordination and temporal synchronization in multimedia collaborative applications. In: 12th Intnl Conf on Distrib Comput Syst (ICDCS), Yokohama, pp 606–613Yen LH, Huang TL, Hwang SY (1997) A protocol for causally ordered message delivery in mobile computing systems. Mobile Netw Appl 2(4):365–372Zawirski M, Preguiça N, Duarte S, Bieniusa A, Balegas V, Shapiro M (2015) Write fast, read in the past: causal consistency for client-side applications. In: 16th Intnl Middleware Conf, VancouverZhou S, Cai W, Turner SJ, Lee BS, Wei J (2007) Critical causal order of events in distributed virtual environments. ACM Trans Mult Comp Commun Appl 3(3):1

Quantifying the effects of temperature on mosquito and parasite traits that determine the transmission potential of human malaria

Malaria transmission is known to be strongly impacted by temperature. The current understanding of how temperature affects mosquito and parasite life history traits derives from a limited number of empirical studies. These studies, some dating back to the early part of last century, are often poorly controlled, have limited replication, explore a narrow range of temperatures, and use a mixture of parasite and mosquito species. Here, we use a single pairing of the Asian mosquito vector, An. stephensi and the human malaria parasite, P. falciparum to conduct a comprehensive evaluation of the thermal performance curves of a range of mosquito and parasite traits relevant to transmission. We show that biting rate, adult mortality rate, parasite development rate, and vector competence are temperature sensitive. Importantly, we find qualitative and quantitative differences to the assumed temperature-dependent relationships. To explore the overall implications of temperature for transmission, we first use a standard model of relative vectorial capacity. This approach suggests a temperature optimum for transmission of 29°C, with minimum and maximum temperatures of 12°C and 38°C, respectively. However, the robustness of the vectorial capacity approach is challenged by the fact that the empirical data violate several of the model's simplifying assumptions. Accordingly, we present an alternative model of relative force of infection that better captures the observed biology of the vector-parasite interaction. This model suggests a temperature optimum for transmission of 26°C, with a minimum and maximum of 17°C and 35°C, respectively. The differences between the models lead to potentially divergent predictions for the potential impacts of current and future climate change on malaria transmission. The study provides a framework for more detailed, system-specific studies that are essential to develop an improved understanding on the effects of temperature on malaria transmission

Collaborative denoising autoencoder for high glycated haemoglobin prediction.

A pioneering study is presented demonstrating that the presence of high glycated haemoglobin (HbA1c) levels in a patient’s blood can be reliably predicted from routinely collected clinical data. This paves the way for performing early detection of Type-2 Diabetes Mellitus (T2DM). This will save healthcare providers a major cost associated with the administration and assessment of clinical tests for HbA1c. A novel collaborative denoising autoencoder framework is used to address this challenge. The framework builds an independent denoising autoencoder model for the high and low HbA1c level, which extracts feature representations in the latent space. A baseline model using just three features: patient age together with triglycerides and glucose level achieves 76% F1-score with an SVM classifier. The collaborative denoising autoencoder uses 78 features and can predict HbA1c level with 81% F1-score

Chronic non-specific low back pain - sub-groups or a single mechanism?

Copyright 2008 Wand and O'Connell; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.Background: Low back pain is a substantial health problem and has subsequently attracted a considerable amount of research. Clinical trials evaluating the efficacy of a variety of interventions for chronic non-specific low back pain indicate limited effectiveness for most commonly applied interventions and approaches. Discussion: Many clinicians challenge the results of clinical trials as they feel that this lack of effectiveness is at odds with their clinical experience of managing patients with back pain. A common explanation for this discrepancy is the perceived heterogeneity of patients with chronic non-specific low back pain. It is felt that the effects of treatment may be diluted by the application of a single intervention to a complex, heterogeneous group with diverse treatment needs. This argument presupposes that current treatment is effective when applied to the correct patient. An alternative perspective is that the clinical trials are correct and current treatments have limited efficacy. Preoccupation with sub-grouping may stifle engagement with this view and it is important that the sub-grouping paradigm is closely examined. This paper argues that there are numerous problems with the sub-grouping approach and that it may not be an important reason for the disappointing results of clinical trials. We propose instead that current treatment may be ineffective because it has been misdirected. Recent evidence that demonstrates changes within the brain in chronic low back pain sufferers raises the possibility that persistent back pain may be a problem of cortical reorganisation and degeneration. This perspective offers interesting insights into the chronic low back pain experience and suggests alternative models of intervention. Summary: The disappointing results of clinical research are commonly explained by the failure of researchers to adequately attend to sub-grouping of the chronic non-specific low back pain population. Alternatively, current approaches may be ineffective and clinicians and researchers may need to radically rethink the nature of the problem and how it should best be managed

Assessing the congruence of thermal niche estimations derived from distribution and physiological data. A test using diving beetles.

A basic aim of ecology is to understand the determinants of organismal distribution, the niche concept and species distribution models providing key frameworks to approach the problem. As temperature is one of the most important factors affecting species distribution, the estimation of thermal limits is crucially important for inferring range constraints. It is expectable that thermal physiology data derived from laboratory experiments and species' occurrences may express different aspects of the species' niche. However, there is no study systematically testing this prediction in a given taxonomic group while controlling by potential phylogenetic inertia. We estimate the thermal niches of twelve Palaearctic diving beetles species using physiological data derived from experimental analyses in order to examine the extent to which these coincided with those estimated from distribution models based on observed occurrences. We found that thermal niche estimates derived from both approaches lack general congruence, and these results were similar before and after controlling by phylogeny. The congruence between potential distributions obtained from the two different procedures was also explored, and we found again that the percentage of agreement were not very high (~60%). We confirm that both thermal niche estimates derived from geographical and physiological data are likely to misrepresent the true range of climatic variation that these diving beetles are able to tolerate, and so these procedures could be considered as incomplete but complementary estimations of an inaccessible reality

Changes in treatment and mortality of acute myocardial infarction in Estonian tertiary and secondary care hospitals in 2001 and 2007

<p>Abstract</p> <p>Background</p> <p>High quality care for acute myocardial infarction (AMI) improves patient outcomes. Still, AMI patients are treated in hospitals with unequal access to percutaneous coronary intervention. The study compares changes in treatment and 30-day and 3-year mortality of AMI patients hospitalized into tertiary and secondary care hospitals in Estonia in 2001 and 2007.</p> <p>Results</p> <p>Final analysis included 423 cases in 2001 (210 from tertiary and 213 from secondary care hospitals) and 687 cases in 2007 (327 from tertiary and 360 from secondary care hospitals). The study sample in 2007 was older and had twice more often diabetes mellitus. The patients in the tertiary care hospitals underwent reperfusion for ST-elevation myocardial infarction, cardiac catheterization and revascularisation up to twice as often in 2007 as in 2001. In the secondary care, patient transfer for further invasive treatment into tertiary care hospitals increased (<it>P </it>< 0.001). Prescription rates of evidence-based medications for in-hospital and for outpatient use were higher in 2007 in both types of hospitals. However, better treatment did not improve significantly the short- and long-term mortality within a hospital type in crude and baseline-adjusted analysis. Still, in 2007 a mortality gap between the two hospital types was observed (<it>P </it>< 0.010).</p> <p>Conclusions</p> <p>AMI treatment improved in both types of hospitals, while the improvement was more pronounced in tertiary care. Still, better treatment did not result in a significantly lower mortality. Higher age and cardiovascular risk are posing a challenge for AMI treatment.</p

Anatomy of the AGN in NGC 5548: II. The spatial, temporal, and physical nature of the outflow from HST/COS Observations

Context. AGN outflows are thought to influence the evolution of their host galaxies and of super massive black holes. Our deep multiwavelength campaign on NGC 5548 has revealed a new, unusually strong X-ray obscuration, accompanied by broad UV absorption troughs observed for the first time in this object. The X-ray obscuration caused a dramatic decrease in the incident ionizing flux on the outflow that produces the long-studied narrow UV absorption lines in this AGN. The resulting data allowed us to construct a comprehensive physical, spatial, and temporal picture for this enduring AGN wind. / Aims. We aim to determine the distance of the narrow UV outflow components from the central source, their total column-density, and the mechanism responsible for their observed absorption variability. Methods. We study the UV spectra acquired during the campaign, as well as from four previous epochs (1998−2011). Our main analysis tools are ionic column-density extraction techniques, photoionization models based on the code CLOUDY, and collisional excitation simulations. / Results. A simple model based on a fixed total column-density absorber, reacting to changes in ionizing illumination, matches the very different ionization states seen in five spectroscopic epochs spanning 16 years. The main component of the enduring outflow is situated at 3.5 ± 1.1 pc from the central source, and its distance and number density are similar to those of the narrow-emitting-line region in this object. Three other components are situated between 5−70 pc and two are farther than 100 pc. The wealth of observational constraints and the anti-correlation between the observed X-ray and UV flux in the 2002 and 2013 epochs make our physical model a leading contender for interpreting trough variability data of quasar outflows. / Conclusions. This campaign, in combination with prior UV and X-ray data, yields the first simple model that can explain the physical characteristics and the substantial variability observed in an AGN outflow

Cue Integration in Categorical Tasks: Insights from Audio-Visual Speech Perception

Previous cue integration studies have examined continuous perceptual dimensions (e.g., size) and have shown that human cue integration is well described by a normative model in which cues are weighted in proportion to their sensory reliability, as estimated from single-cue performance. However, this normative model may not be applicable to categorical perceptual dimensions (e.g., phonemes). In tasks defined over categorical perceptual dimensions, optimal cue weights should depend not only on the sensory variance affecting the perception of each cue but also on the environmental variance inherent in each task-relevant category. Here, we present a computational and experimental investigation of cue integration in a categorical audio-visual (articulatory) speech perception task. Our results show that human performance during audio-visual phonemic labeling is qualitatively consistent with the behavior of a Bayes-optimal observer. Specifically, we show that the participants in our task are sensitive, on a trial-by-trial basis, to the sensory uncertainty associated with the auditory and visual cues, during phonemic categorization. In addition, we show that while sensory uncertainty is a significant factor in determining cue weights, it is not the only one and participants' performance is consistent with an optimal model in which environmental, within category variability also plays a role in determining cue weights. Furthermore, we show that in our task, the sensory variability affecting the visual modality during cue-combination is not well estimated from single-cue performance, but can be estimated from multi-cue performance. The findings and computational principles described here represent a principled first step towards characterizing the mechanisms underlying human cue integration in categorical tasks