Biomedical subjects

Ulrike Hahn

Publications and source records attributed to Ulrike Hahn.

5 recordsLinked to original sources

PubMed2005

What makes words sound similar?

Although similarity plays an important role in accounts of language processing, there are surprisingly few direct empirical studies of the phonological similarity between words, and it is therefore not clear whether similarity comparisons between words involve processes similar to those involved in other cognitive domains. In five experiments, participants chose which of two monosyllabic pseudo-words sounded more similar to a target pseudo-word. Our results are generally consistent with the structural alignment theory of comparisons between complex mental representations, suggesting that phonological word similarity parallels similarity involving other kinds of information including visual objects and scenes, events, and word meanings. We use our results to test new metrics of word similarity, and identify predictions for future similarity research both in the domain of word sounds and in other cognitive domains.

Adult↗

PubMed2005

Effects of category diversity on learning, memory, and generalization.

In this study, we examined the effect of within-category diversity on people's ability to learn perceptual categories, their inclination to generalize categories to novel items, and their ability to distinguish new items from old. After learning to distinguish a control category from an experimental category that was either clustered or diverse, participants performed a test of category generalization or old-new recognition. Diversity made learning more difficult, increased generalization to novel items outside the range of training items, and made it difficult to distinguish such novel items from familiar ones. Regression analyses using the generalized context model suggested that the results could be explained in terms of similarities between old and new items combined with a rescaling of the similarity space that varied according to the diversity of the training items. Participants who learned the diverse category were less sensitive to psychological distance than were the participants who learned a more clustered category.

Adolescent↗

PubMed2004

A Bayesian approach to the argument from ignorance.

In this paper, we re-examine a classic informal reasoning fallacy, the so-called argumentam ad ignorantiam. We argue that the structure of some versions of this argument parallels examples of inductive reasoning that are widely viewed as unproblematic. Viewed probabilistically, these versions of the argument from ignorance constitute a legitimate form of reasoning; the textbook examples are inductive arguments that are not unsound but simply weak, due to the nature of the premises and conclusions involved. In an experiment, we demonstrated some of the variables affecting the strength of the argument, and conclude with some general considerations towards an empirical theory of argument strength.

Bayes Theorem↗

PubMed2003

Similarity as transformation.

We propose that similarity is determined by the transformation distance between representations: entities which are perceived to be similar have representations which are readily transformed into one another, whereas transforming between dissimilar entities requires many transformations. We present three experiments that indicate that similarity is strongly influenced by transformation distance. These data present a challenge for featural or spatial accounts of similarity. Finally, we introduce a family of transformation-based accounts of similarity, called 'Representational Distortion', as a specific example of a transformational approach to similarity.

Adolescent↗

PubMed2003

Salmonella enterica serovar typhimurium expressing a chromosomally integrated copy of the Bacillus anthracis protective antigen gene protects mice against an anthrax spore challenge.

Protective immunity against infection with Bacillus anthracis is almost entirely based on a response to the protective antigen (PA), the binding moiety for the two other toxin components. We cloned the PA gene into an auxotrophic mutant of Salmonella enterica serovar Typhimurium as a fusion with the signal sequence of the hemolysin (Hly) A gene of Escherichia coli to allow the export of PA via the Hly export system. To stabilize the export cassette, it was also integrated into the chromosome of the live Salmonella carrier. When S. enterica serovar Typhimurium with the chromosomally integrated PA gene was given intravenously to A/J mice, they developed high levels of antibody to PA. These mice were protected against intraperitoneal challenge with 100 or 1,000 50% lethal doses of B. anthracis strain STI. This work contributes to the development of a Salmonella-based orally delivered anthrax vaccine.

Animals↗