Clustering in the output of behavior

Pigeons exposed to fixed-interval schedules of 3, 5, 15, 40, and 120 minutes all maintained considerable variability in daily response rates for as many as 104 sessions. However, variations did not occur at random. Instead, rate in a session appeared dependent on those occurring previously. The series displayed a wave-like form arising because a group of high rates was followed by a group of low rates and vice versa. These sequential relations produced a curve having irregular periodicity, sometimes superimposed on a declining or rising linear trend. Whether grouping of response rates stemmed from experimental or extra-experimental sources was not determined. If the phenomenon was either totally or partially produced by the schedule itself, it suggests that response rate is determined by a combination of positive and negative feedback. Control by factors extrinisic to the experiment itself implies that response rate may be influenced by some rhythmic physiological process.     

The Dependency Structure of Coordinate Phrases: A Corpus Approach

Hudson (1990) proposes that each conjunct in a coordinate phrase forms dependency relations with heads or dependents outside the coordinate phrase (the “multi-head” view). This proposal is tested through corpus analysis of Wall Street Journal text. For right-branching constituents (such as direct-object NPs), a short-long preference for conjunct ordering is observed; this is predicted by the multi-head view, under the assumption that structures resulting in shorter dependencies are preferred. A short-long preference is also observed for left-branching constituents (such as subject NPs), which is less obviously accommodated by the multi-head view but not incompatible with it. The repetition of determiners was also examined (the dog and cat versus the dog and the cat), and a stronger preference was found for repetition with singular count nouns as opposed to mass or plural nouns; this accords well with the multi-head view, under the reasoning that single-determiner constructions require crossing dependencies with count nouns but not with plural or mass nouns.     

Exact tests for the rasch model via sequential importance sampling

Rasch proposed an exact conditional inference approach to testing his model but never implemented it because it involves the calculation of a complicated probability. This paper furthers Rasch’s approach by (1) providing an efficient Monte Carlo methodology for accurately approximating the required probability and (2) illustrating the usefulness of Rasch’s approach for several important testing problems through simulation studies. Our Monte Carlo methodology is shown to compare favorably to other Monte Carlo methods proposed for this problem in two respects: it is considerably faster and it provides more reliable estimates of the Monte Carlo standard error.This Research was supported in part by National Science Foundation grant DMS-0203762 and a University of Pennsylvania Research Foundation grant.The authors are grateful to Don Burdick for helpful comments. In addition, the authors wish to thank the editor, the associate editor, and the referees for their helpful suggestions.This revised article was published online in August 2005 with the PDF paginated correctly.     

Sequential Down Syndrome Screening: The Importance of First and Second Trimester Test Correlations when Calculating Risk

Down syndrome screening can be particularly effective when both first and second trimester tests are performed. However, the counseling of women who have received sequential first and second trimester screening can be problematic. We evaluated an approximation where the post-test risk from the first trimester screening is used as the new a priori risk for the second trimester screening. The approximation disregards between-trimester test correlations. The Down syndrome detection rate based on the approximation (90.2%) would be close to that obtained when all correlations were considered (90.8%) but the false positive rate would be 26% higher (3.9% versus 3.1%, respectively). For any particular woman, the use of the approximation could result in highly inaccurate risks. We conclude that the correlations that exist between first and second trimester screening tests preclude the use of second trimester risks derived from the direct product of separate first and second trimester screening. Counseling issues in the delivery of sequential screening are discussed.     

Serial conditioning as a function of stimulus, response, and temporal dependencies

Six experiments were used to examine the effects of explicit response, stimulus, and temporal dependencies on responding in an interfood interval. The first two experiments demonstrated that 10-segment 60-s interfood clocks controlled similar distributions of key pecking in pigeons regardless of whether response–reinforcement contiguity was required, allowed, or precluded. The third and fourth experiments found that in the absence of an explicit response–reinforcement dependency, systematic explicit stimuli in an interfood interval were sufficient to establish and maintain the characteristic distribution of key pecking and that an interval without an explicit clock failed to establish or maintain key pecking. The last two experiments demonstrated that the interfood interval need not be of fixed length, and that a simple correlation of stimuli with increments from either a minimum to a maximum imminency or probability of food presentation controlled behavior in a similar manner. Successively higher rates generally occurred to successively later stimuli in the upper half of the range.     

Chlordiazepoxide effects on ethanol self-administration: dependence on concurrent conditions.

Experiments examined the effects of acute doses of chlordiazepoxide upon ethanol self-administration in the rat. A concurrent-schedule procedure was used that employed choice between ethanol (5%) and a second fluid (either water or a 1% sucrose solution). When ethanol and water were the available fluids, chlordiazepoxide at doses of 15 and 20 mg/kg reduced ethanol-reinforced responding and intake, with a greater reduction occurring at the 20 mg/kg dose. However, when ethanol and sucrose were concurrently available, in many rats only the 20 mg/kg dose of chlordiazepoxide reduced ethanol-reinforced responding. The differences in dose response function occurred in most animals without large changes in the baseline ethanol-reinforced responding across the two concurrent conditions. Thus the dose-effect curve relating chlordiazepoxide and ethanol self-administration can be altered, dependent upon the nature of the concurrently available reinforcers.     

An evaluation of lineup presentation,weapon presence,and a distinctive feature using ROC analysis

We conducted an experiment (N = 2675) including both laboratory and online participants to test hypotheses regarding important system and estimator variables for eyewitness identification. Simultaneous lineups were compared to sequential lineups with the suspect presented early versus late because there is evidence that suspect position could be an important factor determining a simultaneous versus sequential advantage in guilty-innocent suspect discriminability. We also manipulated whether or not the perpetrator held a weapon or had a distinctive feature on his face, to re-evaluate recent evidence that these factors interact. Overall, the simultaneous lineup yielded higher discriminability than the sequential lineup, and there was no effect of sequential position. Discriminability was higher when the perpetrator had no weapon, but only when no distinctive feature was present. We conclude with a discussion of the importance of exploring interactions between system and estimator variables using Receiver Operating Characteristic (ROC) analysis.     

Fuzzy Genes: Epistemic Tensions in Genomics

Genomics contributed to making modern biology a prolific multi-disciplinary field leading to new approaches such as systems biology. Reporting in the media reflects the high stakes involved in these changes, but such reporting often appears inconsistent as contradictory claims are made about new applications contrasting with uncertainties from new insights. Such inconsistent claims might relate to different disciplines involved in the field. New approaches from engineering disciplines such as computer science have changed research practices and approaches towards the object; the meaning of genes having become context-dependent. Since disciplines must cooperate, tensions arise over methods, evidence criteria and the significance of hypotheses. The concept of epistemic cultures, developed to highlight differences between distant fields such as high-energy physics and molecular biology, can render insights into the ‘cultures’ related to practices and approaches within genomics. Qualitative interviews with scientists shed light on how computer science and experimental molecular biology co-operate and which problems arise from epistemic differences as the criteria for relevant findings become subject to the disciplinary context. In addition, genomics-like approaches have entered other fields of biological research, whilst systems biology further challenges hypothesis-driven experimentation. This may lead to a new epistemic culture differing from the one previously described. These findings provide insights into how different accounts arise and shed light on general properties of prolific multi-disciplinary research fields. Inconsistencies in the way such fields appear from outside might be considered normal rather than the exception.