The Bayesian sampler : generic Bayesian inference causes incoherence in human probability

Human probability judgments are systematically biased, in apparent tension with Bayesian models of cognition. But perhaps the brain does not represent probabilities explicitly, but approximates probabilistic calculations through a process of sampling, as used in computational probabilistic models in statistics. Naïve probability estimates can be obtained by calculating the relative frequency of an event within a sample, but these estimates tend to be extreme when the sample size is small. We propose instead that people use a generic prior to improve the accuracy of their probability estimates based on samples, and we call this model the Bayesian sampler. The Bayesian sampler trades off the coherence of probabilistic judgments for improved accuracy, and provides a single framework for explaining phenomena associated with diverse biases and heuristics such as conservatism and the conjunction fallacy. The approach turns out to provide a rational reinterpretation of “noise” in an important recent model of probability judgment, the probability theory plus noise model (Costello & Watts, 2014, 2016a, 2017; Costello & Watts, 2019; Costello, Watts, & Fisher, 2018), making equivalent average predictions for simple events, conjunctions, and disjunctions. The Bayesian sampler does, however, make distinct predictions for conditional probabilities and distributions of probability estimates. We show in 2 new experiments that this model better captures these mean judgments both qualitatively and quantitatively; which model best fits individual distributions of responses depends on the assumed size of the cognitive sample

Plant dispersal across the tropical Atlantic by wind and sea currents

This review brings together evidence on the monophyly and ages of angiosperm lineages ranging across the tropical Atlantic with data on the direction, strength, and speed of sea currents and wind jets across that ocean. Mainly for pragmatic reasons (data availability), the focus is on genera, which introduces a rank-based constraint into the analysis. However, trans-Atlantic disjunctions at the genus level seemed more likely to be attributable to long-distance dispersal than those involving families or species; family-level disjunctions often may date back to the breakup of Africa and South America, and species-level disjunctions often may be anthropogenic. At least 110 genera (listed in this article) contain species on both sides of the tropical Atlantic. Molecular phylogenies and age estimates from molecular clocks are available for 11 disjunct genera, tribes, and species. Inferred directions and modes of dispersal can be related parsimoniously to water currents between Africa and South America and to exceptional westerly winds blowing from northeastern Brazil to northwest Africa. Based on diaspore morphology and inferred dispersal biology in the 110 genera, trans-Atlantic dispersal by water (in both directions) appears more common than dispersal by wind or on birds. Wind dispersal appears to have occurred in the direction from South America to West Africa but rarely in the opposite direction

(From) A to B (and back)

‘(From) A to B (and back)’ is an article published in Printed Project (issue 13, July 2010). The issue theme was ‘Virtual Fictional’ and O’Riley’s contribution is a reflection on narrative, reading, uncertainty and de-familiarization, and how these ideas have been explored in some of his art works. This article focuses on the notion of a 'distributed' work, a work that can be made up from a number of elements where the viewer is free to draw associations or connections. It explores writings by Sterne, Shklovsky, Flusser and Todorov and considers syntactical terms such as hypotaxis and parataxis as ways of generating, thinking about or looking at artworks. Hypotaxis is often used to establish a narrative sequence or the progression of an argument. Its forms can lead to determined meanings. In paratactical forms, on the contrary, connections are left open. These terms were seen as useful ways to reflect on the lateral, open-endedness of forms of art practice. The article features text and images of O’Riley’s work as well as images from Sterne’s novel, The Life and Opinions of Tristram Shandy, Gentleman (1762), and from the NASA/Hubble Ultra Deep Field astronomical observation (2004). The latter shows a long-exposure view of the cosmos teeming with galaxies in what was previously considered a vacant or empty portion of space. The article’s significance can be seen in the way it brings together seemingly disparate images and ideas to reflect on the sense in which narrative and the construction of interpretation are active elements within one’s response to a work, and to lay bare some of the thinking behind a work’s making. These ideas were also explored in an artist's book published the following year. Conceived as a kind of calendar, the book - A Farmer’s Almanac - is structured around ancient/antique names for the full moon, often derived from Native American appellations. Each page has associated names for each month’s moon. The names have appeared in various North American farmers’ almanacs although there is some correspondence with British usage. The bookwork also features a constructed image of the full moon generated by Dr Tony Cook of Aberystwyth University from the database sent back from the moon by the Clementine spacecraft in 1994. (http://www.ponsonbypress.net; London: Ponsonby Press, October 2011; pp32; ISBN 9780956228697

Surprisingly Rational: Probability theory plus noise explains biases in judgment

The systematic biases seen in people's probability judgments are typically taken as evidence that people do not reason about probability using the rules of probability theory, but instead use heuristics which sometimes yield reasonable judgments and sometimes systematic biases. This view has had a major impact in economics, law, medicine, and other fields; indeed, the idea that people cannot reason with probabilities has become a widespread truism. We present a simple alternative to this view, where people reason about probability according to probability theory but are subject to random variation or noise in the reasoning process. In this account the effect of noise is cancelled for some probabilistic expressions: analysing data from two experiments we find that, for these expressions, people's probability judgments are strikingly close to those required by probability theory. For other expressions this account produces systematic deviations in probability estimates. These deviations explain four reliable biases in human probabilistic reasoning (conservatism, subadditivity, conjunction and disjunction fallacies). These results suggest that people's probability judgments embody the rules of probability theory, and that biases in those judgments are due to the effects of random noise.Comment: 64 pages. Final preprint version. In press, Psychological Revie

Region-based memory management for Mercury programs

Region-based memory management (RBMM) is a form of compile time memory management, well-known from the functional programming world. In this paper we describe our work on implementing RBMM for the logic programming language Mercury. One interesting point about Mercury is that it is designed with strong type, mode, and determinism systems. These systems not only provide Mercury programmers with several direct software engineering benefits, such as self-documenting code and clear program logic, but also give language implementors a large amount of information that is useful for program analyses. In this work, we make use of this information to develop program analyses that determine the distribution of data into regions and transform Mercury programs by inserting into them the necessary region operations. We prove the correctness of our program analyses and transformation. To execute the annotated programs, we have implemented runtime support that tackles the two main challenges posed by backtracking. First, backtracking can require regions removed during forward execution to be "resurrected"; and second, any memory allocated during a computation that has been backtracked over must be recovered promptly and without waiting for the regions involved to come to the end of their life. We describe in detail our solution of both these problems. We study in detail how our RBMM system performs on a selection of benchmark programs, including some well-known difficult cases for RBMM. Even with these difficult cases, our RBMM-enabled Mercury system obtains clearly faster runtimes for 15 out of 18 benchmarks compared to the base Mercury system with its Boehm runtime garbage collector, with an average runtime speedup of 24%, and an average reduction in memory requirements of 95%. In fact, our system achieves optimal memory consumption in some programs.Comment: 74 pages, 23 figures, 11 tables. A shorter version of this paper, without proofs, is to appear in the journal Theory and Practice of Logic Programming (TPLP

Floristics of the South American Páramo moss flora

The South American paramos appeared in Pliocene times and persist to the present day. The moss flora of this habitat consists of an estimated 400 species that comprise 8 floristic groups. In Venezuela these groups and their percent representation are as follows: neotropical 37%, Andean 26%, cosmopolitan 18%, Andean-African 8%, neotropical-Asiatic 3%, neotropical-Australasian 2%, temperate Southern Hemisphere 2% and northern boreal-temperate 2%. Acrocarpous taxa outnumber pleurocarps by nearly 3:1. The neotropical and Andean floristic stocks likely were present prior to late Pliocene orogenies that elevated the cordillera above climatic timberlines. These species may have existed in open, marshy areas (paramillos) or may have evolved from cloud forest ancestors. Taxa of northern boreal- temperate affinities, including those with Asiatic distributions, probably arrived in the paramos during the Pleistocene, a period which may also have seen the establishment in the Northern Andes of some cosmopolitan elements. Species with temperate Southern Hemisphere and Australasian affinities likely spread first to austral South America thence migrated northward during a cool, moist interval sometime over the past 2.5-3 million years or may have become established in the paramos as a result of long- distance dispersal