Subject: cognitive science technical reports

the following new technical reports are now available from the institute for research in cognitive science : probabilistic matching of brain images j . c . gee l . lebriquer c . barillot d . r . haynor ircs-95 - 07 $ 2 . 20 image matching has emerged as an important area of investigation in medical image analysis . in particular , much attention has been focused on the atlas problem , in which a template representing the structural anatomy of the human brain is deformed to match anatomic brain images from a given individual . the problem is made difficult because there are important differences in both the gross and local morphology of the brain among normal individuals . we have formulated the image matching problem under a bayesian framework . the bayesian methodology facilitates a principled approach to the development of a matching model . of special interest is its capacity to deal with uncertainty in the estimates , a potentially important but generally ignored aspect of the solution . in the construction of a reference system for the human brain , the bayesian approach is well suited to the task of modeling variation in morphology . statistical information about morphological variability , accumulated over past samples , can be formally introduced into the problem formulation to guide the matching or normalization of future data sets . bayesian approach to the brain image matching problem j . c . gee l . lebriquer c . barillot d . r . haynor r . bajcsy ircs-95 - 08 $ 1 . 80 the application of image matching to the problem of localizing structural anatomy in images of the human brain forms the specific aim of our work . the interpretation of such images is a difficult task for human observers because of the many ways in which the identity of a given structure can be obscured . our approach is based on the assumption that a common topology underlies the anatomy of normal individuals . to the degree that this assumption holds , the localization problem can be solved by determining the mapping from the anatomy of a given individual to some referential atlas of cerebral anatomy . previous such approaches have in many cases relied on a physical interpretation of this mapping . in this paper , we examine a more general bayesian formulation of the image matching problem and demonstrate the approach on two-dimensional magnetic resonance images . xtag system - a wide coverage grammar for english christy doran dania egedi beth ann hockey b . srinivas martin zaidel ircs-95 - 09 $ 1 . 03 this paper presents the xtag system , a grammar development tool based on the tree adjoining grammar ( tag ) formalism that includes a wide-coverage syntactic grammar for english . the various components of the system are discussed and preliminary evaluation results from the parsing of various corpora are given . results from the comparison of xtag against the ibm statistical parser and the alvey natural language tool parser are also given . disambiguation of super parts of speech ( or supertags ) : almost parsing aravind k . joshi b . srinivas ircs-95 - 10 $ 1 . 28 in a lexicalized grammar formalism such as lexicalized tree - adjoining grammar ( ltag ) , each lexical item is associated with at least one elementary structure ( supertag ) that localizes syntactic and semantic dependencies . thus a parser for a lexicalized grammar must search a large set of supertags to choose the right ones to combine for the parse of the sentence . we present techniques for disambiguating supertags using local information such as lexical preference and local lexical dependencies . the similarity between ltag and dependency grammars is exploited in the dependency model of supertag disambiguation . the performance results for various models of supertag disambiguation such as unigram , trigram and dependency-based models are presented . a freely available syntactic lexicon for english dania egedi patrick martin ircs-95 - 11 $ 1 . 18 this paper presents a syntactic lexicon for english that was originally derived from the oxford advanced learner 's dictionary and the oxford dictionary of current idiomatic english , and then modified and augmented by hand . there are more than 37 , 000 syntactic entries from all 8 parts of speech . an x - windows based tool is available for maintaining the lexicon and performing searches . c and lisp hooks are also available so that the lexicon can be easily utilized by parsers and other programs . lexicalization and grammar development b . srinivas dania egedi christy doran tilman becker ircs-95 - 12 $ 1 . 18 in this paper we present a fully lexicalized grammar formalism as a particularly attractive framework for the specification of natural language grammars . we discuss in detail feature - based , lexicalized tree adjoining grammars ( fb-ltag s ) , a representative of the class of lexicalized grammars . we illustrate the advantages of lexicalized grammars in various contexts of natural language processing , ranging from wide-coverage grammar development to parsing and machine translation . we also present a method for compact and efficient representation of lexicalized trees . a processing model for free word order languages owen rambow aravind k . joshi ircs-95 - 13 $ 2 . 00 like many verb-final languages , german displays considerable word-order freedom : there is no syntactic constraint on the ordering of the nominal arguments of a verb , as long as the verb remains in final position . this effect is referred to as ` ` scrambling ' ' , and is interpreted in transformational frameworks as leftward movement of the arguments . furthermore , arguments from an embedded clause may move out of their clause ; this effect is referred to as ` ` long-distance scrambling ' ' . while scrambling has recently received considerable attention in the syntactic literature , the status of long-distance scrambling has only rarely been addressed . the reason for this is the problematic status of the data : not only is long-distance scrambling highly dependent on pragmatic context , it also is strongly subject to degradation due to processing constraints . as in the case of center-embedding , it is not immediately clear whether to assume that observed unacceptability of highly complex sentences is due to grammatical restrictions , or whether we should assume that the competence grammar does not place any restrictions on scrambling ( and that , therefore , all such sentences are in fact grammatical ) , and the unacceptability of some ( or most ) of the grammatically possible word orders is due to processing limitations . in this paper , we will argue for the second view by presenting a processing model for german . * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * how to access reports : the reports are available in bound form for the price listed above , or may be obtained for free , electronically . to obtain a compressed postscript copy of the report , open an anonymous ftp session on ftp . cis . upenn . edu path : pub / ircs / technical-reports the files are named according to their number . for example , report 95-01 is stored as 95-01 . ps . z , 95-02 is stored as 95-02 . ps . z , etc . if you are using ftp , change the setting to binary and download the file . to get a copy of report 95-01 , you would type : binary get 95-01 . ps . z you can also obtain files through electronic mail . send a mail message to ircsserv @ ftp . cis . upenn . edu . the message should read " send technical-reports filename " . you will receive the compressed postscript file in reply . requests for bound copies should be sent to the address listed below , and include a check for the price of the desired report . checks should be made payable to " trustees of the university of pennsylvania . " jodi kerper jbkerper @ central . cis . upenn . edu institute for research in cognitive science 3401 walnut street , suite 400c philadelphia , pa 19104-6228
