Design for very large-scale conversations

Thesis (Ph.D.)--Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts and Sciences, 2000.Includes bibliographical references (leaves 184-200).On the Internet there are now very large-scale conversations (VLSCs) in which hundreds, even thousands, of people exchange messages across international borders in daily, many-to-many communications. It is my thesis that VLSC is an emergent communication medium that engenders new social and linguistic connections between people. VLSC poses fundamental challenges to the analytic tools and descriptive methodologies of linguistics and sociology previously developed to understand conversations of a much smaller scale. Consequently, the challenge for software design is this: How can the tools of social science be appropriated and improved upon to create better interfaces for participants and interested observers to understand and critically reflect upon conversation? This dissertation accomplishes two pieces of work. Firstly, the design, implementation, and demonstration of a proof-of-concept, VLSC interface is presented. The Conversation Map system provides a means to explore and question the social and linguistic structure of very large-scale conversations (e.g., Usenet newsgroups). Secondly, the thinking that went into the design of the Conversation Map system is generalized and articulated as an aesthetics, ethics, and epistemology of design for VLSC. The goal of the second, theoretical portion of the thesis is to provide a means to describe the emergent phenomenon of VLSC and a vocabulary for critiquing software designed for VLSC and computer-mediated conversation in general.Warren Sack.Ph.D

Pattern matching : a sheaf-theoretic approach

A general theory of pattern matching is presented by adopting an extensional, geometric view of patterns. The extension of the matching relation consists of the occurrences of all possible patterns in a particular target. The geometry of the pattern describes the structure of the pattern and the spatial relationships among parts of the pattern. The extension and the geometry, when combined, produce a structure called a sheaf. Sheaf theory is a well developed branch of mathematics which studies the global consequences of locally defined properties. For pattern matching, an occurrence of a pattern, a global property of the pattern, is obtained by gluing together occurrences of parts of the pattern, which are locally defined properties.A sheaf-theoretic view of pattern rnatching provides a uniforrn treatrnent of pattern matching on any kind of data structure-strings, trees, graphs, hypergraphs, and so on. Such a parametric description is achieved by using the language of category theory, a highly abstract description of commonly occurring structures and relationships in mathematics.A generalized version of the Knuth-Morris-Pratt pattern matching algorithm is derived by gradually converting the extensional description of pattern rnatching as a sheaf into an intensional description. The algorithm results from a synergy of four very general program synthesis/transformation techniques: (1) Divide and conquer: exploit the sheaf condition; assemble a full match by gluing together partial matches; (2) Finite differencing: collect and update partial matches incrementally while traversing the target; (3) Backtracking: instead of saving all partial matches, save just one; when this partial match cannot be extended, fail back to another; (4) Partial evaluation: precompute pattern-based (and therefore constant) computations.The derivation is carried out in a general frarnework using Grothendieck topologies. By appropriately instantiating the underlying data structures and topologies, the sarne scheme results in matching algorithms for patterns with variables and with multiple patterns. Slight variations of the derivation result in Earley's algorithm for context-free parsing, and Waltz filtering, a relaxation algorithm for providing 3-D interpretations to 2-D irnages.Other applications of a geometric view of patterns are briefly considered: rewrites, parallel algorithms, induction and computability

Computations and Computers in the Sciences of Mind and Brain

Computationalism says that brains are computing mechanisms, that is, mechanisms that perform computations. At present, there is no consensus on how to formulate computationalism precisely or adjudicate the dispute between computationalism and its foes, or between different versions of computationalism. An important reason for the current impasse is the lack of a satisfactory philosophical account of computing mechanisms. The main goal of this dissertation is to offer such an account. I also believe that the history of computationalism sheds light on the current debate. By tracing different versions of computationalism to their common historical origin, we can see how the current divisions originated and understand their motivation. Reconstructing debates over computationalism in the context of their own intellectual history can contribute to philosophical progress on the relation between brains and computing mechanisms and help determine how brains and computing mechanisms are alike, and how they differ. Accordingly, my dissertation is divided into a historical part, which traces the early history of computationalism up to 1946, and a philosophical part, which offers an account of computing mechanisms. The two main ideas developed in this dissertation are that (1) computational states are to be identified functionally not semantically, and (2) computing mechanisms are to be studied by functional analysis. The resulting account of computing mechanism, which I call the functional account of computing mechanisms, can be used to identify computing mechanisms and the functions they compute. I use the functional account of computing mechanisms to taxonomize computing mechanisms based on their different computing power, and I use this taxonomy of computing mechanisms to taxonomize different versions of computationalism based on the functional properties that they ascribe to brains. By doing so, I begin to tease out empirically testable statements about the functional organization of the brain that different versions of computationalism are committed to. I submit that when computationalism is reformulated in the more explicit and precise way I propose, the disputes about computationalism can be adjudicated on the grounds of empirical evidence from neuroscience

An argument against the conjunction of direct realism and the standard causal picture

Recent work in defence of direct realism has concentrated on the representationalist and disjunctivist responses to the arguments from illusion and hallucination, whilst relatively little attention has been given to the argument from causation which has been dismissed lightly as irrelevant or confused. However such charges arise from an ambiguity in the thesis which is being defended and the failure to distinguish between metaphysical and epistemological issues and between factual and conceptual claims. The argument from causation, as an argument against the conjunction of metaphysical direct realism and an explanation of the perceptual process in terms of a naturalistically understood causal chain of events, has not been answered in the philosophical literature. Moreover when the process of perception is fleshed out in terms of contemporary cognitive science, the difficulties are compounded. Neither representation-friendly mainstream cognitive science, nor representation-averse radical embodied cognitive science, is compatible with a theory of perception which is at the same time both direct and robustly realist