Student Thesis Abstracts G - P

GEOLOGY

Reconstructing Glacial Flow Through the San Juan Islands, WA: Striae as Correlative Temporal and Spatial Flow Indicators

Christopher Miles Brookfield

The results for this study demonstrate that during retreat, the southwestern margin of the Cordilleran ice sheet flowed in several distinct directions through the San Juan Islands, Washington. Previous workers have relied primarily on drumlins and other sedimentological evidence to describe a staggered retreat of two lobes, the Juan de Fuca and the Puget, which formed the termini of the continental ice. I collected and compiled over 250 measurements of striae direction in the vicinity of the San Juan Islands, where only a few had been taken by previous workers. Using a promising new technique of intensive, outcrop scale, striae measurement, I collected over 1,000 additional striae directions. Utilizing the outcrop scale measurements, which preserved the full statistical texture of the striae data, I describe a new method for establishing the relative chronology of divergent striae. A synthesis of both the regional and outcrop scale data suggests that there were three temporally distinct flow directions across San Juan Island: 232° before 13.8 ka, 220° near 13.8 ka, and 203° during latest retreat. My local analysis refines and supports the broad regional model of a staggered retreat for the southwestern Cordilleran ice sheet that has been previously posited for the deglaciation of the Puget Lowland (Thorson, 1980, Booth, 1987).

Hovey Clark

Coastal Geometry and Facies Control in the Late Cretaceous Rocky Shores of Punta Cabras, Baja California, Mexico

Rocky shores comprise roughly 33% of the world's coastlines. They are frequently set on active tectonic margins where volcanism related to subduction results in the production of a resistant substrate on which wave energy can act directly. However, due to the inherent intensity of wave assault, and their proximity to active tectonic margins, rocky shores are rarely preserved in the stratigraphic record. Thus, the discovery of a preserved rocky shore calls for its exploration and documentation.

On the Pacific Coast of northern Baja California, Mexico, modern rocky shores function in the sites of their ancestral counterparts, allowing for the juxtaposition of modern and ancient dynamics. In the Punta Cabras region, modern rocky shores share the same (Alisitos Formation) andesite substrate as their Late Cretaceous analogs. Thus, this study first concentrates on recognizing geometric patterns common to both the modern and ancient coastlines, as they are determined by structural characteristics of the andesite. Of importance in this realm was the discovery and documentation of a heretofore undescribed feature, the keyhole inlet.

After evaluating the substrate, the focus of the study shifts up-section, as it were, to examine Rosario Formation rocky shore facies as they are preserved at Punta Cabras. Previous studies of this area were conducted by Lescinsky et al. (1991) and Johnson and Hayes (1993). Paleoecological and sedimentological methods are used to evaluate the Johnson and Hayes (1993) model, which attempted to explain wind, wave, and current directions, as they affected Cretaceous Punta Cabras.

Finally, the study continues further up-section to examine the sub-tidal facies associated with the Cretaceous rocky shores. Again, more evidence for substantiation of the Johnson and Hayes (1993) model is sought.

Methods for this study included the measurement of keyhole trends and ancillary joints. Also, the dimensions of keyholes were measured. In total, 16 keyholes were measured. These could be characterized as either Type I or Type II on the basis of joint frequency and dominance and keyhole dimension. Also, for the study of preserved intertidal and subtidal deposits, a map of the coastline was derived and 27 stratigraphic column descriptions were made.

Final conclusions are based on these observations, on the measurement of flow indicators, and on general empirical observations made during the course of two trips to the Punta Cabras region. Three fossil islands and three fossil bays were recognized, and the movement of Cretaceous wind and waves through this patterned coastline can be inferred from evidence found in the field. The culmination of conclusions includes a map of the paleogeography of Cretaceous Punta Cabras, as it might have been patterned by the jointing of the andesite substrate.

Michelle L. Coombs

Petrology and Geochemistry of the Southern Shatter Zone, Cadillac Mountain Pluton, Mount Desert Island, Maine

This project is part of a larger study by members of the Keck Geology Consortium that took place on Mount Desert Island, Maine, during 1993-1994. The goal of this study was to look at features of the Late Silurian Cadillac Mountain Intrusive Complex (CMIC) which had previously been only summarily investigated. The main body of the CMG, an a-type, hypersolvus, hornblende granite, is underlain by a unit of layered gabbro-diorite that is believed to be the result of multiple infusions of mafic magma into the partially crystalline granitic magma of the pluton (Wiebe and Chapman, 1993). Mafic enclaves found through all levels of the CMG are evidence that magma mixing occurred following these infusions.

My particular project dealt specifically with the intrusive breccia, or shatter zone, along the southern margin of the pluton. The granitic material that comprises the igneous matrix of the shatter zone exhibits mineralogy and composition which is distinct from typical CMG. The study involved five shatter zone localities along the southern coastline of the island that were studied for field relations, petrography, and geochemistry. Particular attention was paid to the transition from shatter zone matrix to typical CMG. Granitic matrix found deep within the shatter zone is rich in biotite, and occasionally in plagioclase, and is free of mafic enclaves. Chilled textures are locally developed within the granite matrix and attest to rapid emplacement within the shatter zone. Strain indicators are locally prominent in quartz. Directly above the shatter zone lies a thin, basal zone rich in plagioclase with subhedral clinopyroxene and fayalite. This cumulate-like layer grades into typical CMG. These mineralogical variations may indicate a sudden change in temperature within the pluton at the time of shatter zone emplacement. Also found within the shatter zone are leucocratic fine-grained injections (FGI) which appear to be highly evolved magmatic liquids emplaced before complete crystallization of the granitic matrix. REE patterns indicate that FGI and MGM originated as components of one magma. Comparison of CMG compositions with those of shatter zone matrix indicate that magma mixing had limited affect on the chemical composition of Cadillac Mountain Granite.

Petrographic textures and limited country rock assimilation indicate that the shatter zone was shallowly emplaced. Evidence for rapid crystallization of shatter zone magmas, coupled with an increase in temperature within the pluton during the formation of shatter zone, suggests that the shatter zone formed suddenly, perhaps due to an explosive eruption triggered by an influx of basaltic magma into the CMG chamber. A model of side-wall crystallization is proposed to explain cumulate textures within the shatter zone, as well as the presence of FGI, which are interpreted as derivatives of MGM. As crystallization occurred along the margins of the pluton, FGI were displaced to the interior. During brecciation of wall rocks, FGI were injected outwards back into the MGM from which they originated.

A preliminary investigation of the tectonic setting of the CMG and related rocks was undertaken using chemical compositions of shatter zone rocks in chemical discrimination diagrams. The shatter zone and CMG appear to have been emplaced in an extensional environment, perhaps related to back- arc rifting within Avalon prior to the Acadian orogeny.

Rebecca Edwards

40Ar/39Ar Geochronology of the Main Central Thrust Zone Region: Indications of Pliocene Hydrothermal Activity along the MCT; Marsyandi River Valley, West-Central Nepal

The purpose of this study is to investigate the mechanisms at work in the collisional regime of the Nepal Himalayas using 40Ar/39Ar geochronology on biotites and muscovites. The convergence in the Himalayas since the original collision of the Indian and Eurasian plates has been taken up by a series of thrust faults; one of the most important of these faults is the Main Central Thrust fault (MCT) which is the focal point of this study. Little geochronology has been done in the Nepal Himalayas, and the history of the MCT is not yet well understood.

The samples collected for dating in this study came from within 5 kilometers on either side of the MCT in the Marsyandi River valley and suggest the presence of Pliocene hydrothermal activity along the MCT. They also indicate that late-stage brittle faulting along the MCT as suggested for the Langtang region of Nepal by Macfarlane (1993) may not be a dominant mechanism in the Himalayas. They show a range of biotite and muscovite isochron ages from 2.6 Ma to 9.4 Ma. These ages show no particular trends in their spatial distribution in relation to the MCT. The particularly young late Miocene to Pliocene cooling ages of these samples, the highly localized nature of the ages across the sample region, and the abundance of modern hot springs along the MCT suggest that hot fluids have heated the MCT zone rocks according to the model proposed by Copeland et al. (1991). This model explains hydrothermal activity in the MCT zone to be the result of fluids derived from the footwall of the structurally lower Main Boundary Fault (MBF). These hot fluids travel upsection along planes of weakness in the MCT footwall until they reach the MCT where they migrate quickly to the surface using the fault as a conduit. Thus, the ages also indicate Pliocene thrusting along the MBT.

The ages obtained also show biotite cooling ages to be older than muscovite cooling ages, despite the higher closure temperature of muscovites. This phenomenon seems to be present elsewhere in the Himalayas and may indicate widespread tendencies for biotites to undergo argon loss in the Himalayas.

Michael Seckler

Field Relations, Petrology, and Geochemistry of Layered Gabbro-Diorite Units on the West Coast of Mount Desert Island, Maine

A repeating sequence of layered mafic to intermediate plutonic rocks makes up the western edge of the Silurian Cadillac Mountain Intrusive Complex that dominates Mount Desert Island, Maine. In an attempt to understand the petrogenesis of these rocks, a detailed study was taken of three distinct macrorhythmic units, as defined by Wiebe (1992), along 130 meters of wavy coast at Stewart Head. Each sequence of layers in the gabbro-diorite constitutes a macrorhythmic unit with a chilled gabbroic base that grades upward into more felsic compositions and ends with the chilled base of another unit. The chilled zones record influxes of basaltic magma into a cooler evolving felsic magma chamber. In this paper, field relations, petrography, and geochemical data have been synthesized to provide a rounded analysis of the two magmas' interaction and crystallization history. This study is part of a larger research project, sponsored by the W. M. Keck Foundation, that aims to characterize the Cadillac Mountain Intrusive Complex.

The three macrorhythmic units' hybrid nature is the result of a succession of processes. When the two different magmas came into contact at the bottom of the magma chamber, the base of the hotter basalt chilled against the cooler, more felsic magma. This contact with the cooler magma also induced rapid crystallization and fracturing along the bottom of the injected magma. The underlying more felsic magma, kept partially crystalline by the heat of the basaltic magma, was filter pressed up through the fractures in the overlying basalt. This contact of the basalt and the underlying cumulates produced most of the mingling observed in the field and minor amounts of mixing as well.

Other processes developed at the basalt's contact with the overlying silicic liquid. Here, the literature suggests, a double diffusive interface developed and the silicic melt began convecting. The amount of mixing produced at this interface is ambiguous but seems minor in comparison with other studies of magma mixing. The major processes involved at this interface appear to have been the transfer of heat and volatiles. These interactions altered the fractionation sequences in each macrorhythmic unit.

The nature of these interactions at both the top and bottom of the basalt influx, however, appears to have varied between units. Unit 2 evolved much differently than the other two units. This can be explained by an extended period of calcium-rich cumulate accumulation or an extended period of basalt influx. Complete explanation of these variations is impossible due to the spacing of samples and the lack of vertical exposure for the three units.

Further work must evaluate why pipes form in some layers and not in others; what accounts for the parallel relationship of Ba and Zr; and, most generally, how do the observed trends relate to the variable sizes of replenishments and the nature of the basaltic magma's interaction with the resident magma?

Heather Stoll

Geochemistry and Tectonic Implications of Paleozoic Volcanics and Intrusives from Western New England

New geochemical data on Early Ordovician and Silurian units in the Barnard Volcanic Member, Unnamed Schist-Amphibolite Unit, Moretown Member, and Russell Mountain Formation in eastern Vermont (Hepburn et al., 1984) and on the Early Ordovician Collinsville Formation and Hallockville Pond Gneiss in western Massachusetts indicate that these units include rocks which are characteristic of volcanic arc settings and rocks which are characteristic of continental rift or back-arc rift settings. The volcanic arc tholeiites are characterized by HFSE depletion, slight LREE enrichment, and high La/Ce ratios. Rift-related tholeiites possess MORB-like abundances of HFSE, relatively flat REE patterns which are slightly humped in the MREE, and high Th/Nb ratios. La/Ce vs. Zr/Hf diagrams indicate that these two geochemical groups have distinct sources. Dated Early Ordovician felsic rocks have higher REE abundances and Th/Yb ratios than Silurian felsic rocks. Both volcanic arc and rift- related rocks occur in the Barnard Volcanic Member and Moretown Member of the Missisquoi Formation. Volcanic arc rocks predominate in the Collinsville Formation and Hallockville Pond Gneiss, whereas rift-related rocks predominate in the Unnamed Schist-Amphibolite Unit and Russell Mountain Formation of Hepburn et al. (1984). Nearly all mafic units in the Collinsville Formation are comagmatic with Early Ordovician dated samples in this unit, suggesting that mafic units with volcanic arc affinity are Early Ordovician in age and are part of the Shelburne Falls Arc. Geochemical similarities and the La/Ce vs. Zr/Hf source diagram suggest that the rift-related tholeiites are genetically related to tholeiites of the Silurian Standing Pond Volcanics. The volcanic arc rocks are part of the Early Ordovician Shelburne Falls Arc which formed over an east-dipping subduction zone. This oceanic arc collided with North America in Early to Middle Ordovician time, causing the Taconian Orogeny. Following collision, a west-dipping subduction zone was established beneath the North American continent. The Late Ordovician Bronson Hill Arc formed on this active continental margin. Silurian extension in western New England most likely resulted from back-arc rifting behind the Bronson Hill Arc.

Daniel White

Sediment Deposition and Erosion during the Fraser Glaciation (Late Pleistocene), San Juan Islands, Washington

The San Juan Islands provide the most extensive terrestrial exposures of Quaternary sediment in the north central Puget Lowland, Washington, and record latest Pleistocene deposition and erosion by the Puget Lobe of the Cordilleran Ice Sheet. Research consisted of sampling 1400 well logs and numerous surface sea cliff and gravel pit exposures in order to determine the extent, stratigraphy, and implications of sediment deposits in the San Juan Islands.

The Islands have been covered by Cordilleran ice sheets repeatedly during the Pleistocene. The latest glacial event, the Fraser Glaciation, reached a maximum 15,000 years ago as the Vashon ice sheet advanced south through the Lowland, depositing advance outwash as a flat sheet adjacent to the glacier margin. As the ice sheet overrode the Islands with up to 1300 m of ice, basal scouring and meltwater stream erosion shaped the pre-Fraser sediments and previously deposited advance outwash, and a uniform layer of till was deposited. As the ice margin retreated through the Islands, temporary stillstands caused deposition of glaciomarine drift below the 90 m marine limit, much of which was later removed by wave action during isostatic rebound.

Contour maps of sediment thickness confirmed previously observed patterns that most areas of the Islands have less than 6 m of sediment cover, but two large zones on Lopez and Orcas Islands preserve deposits greater than 120 m thick, composed mainly of advance outwash. Till blankets both bedrock and sediment deposits with a layer up to 10 m thick, giving an indication of the subglacial topography during the latter stages of glaciation. Other extensive deposits consist of advance outwash and glaciomarine outwash. The most prominent glaciomarine deposits are two high ridges at Pear Point and Cattle Point on San Juan Island, each over 90 m high.

The glaciomarine deposits on San Juan, Lopez, Orcas, and Waldron Islands and submarine banks around the Islands provide strong evidence that extensive subglacial meltwater channels developed between and around the Islands during ice retreat, particularly San Juan Channel. Sediments carried by the meltwater were deposited at the ice margin in submarine fans during stillstands in retreat of the ice sheet, most likely caused by temporary grounding of the ice margin on bedrock highs in the Islands and a subsequently reduced rate of calving.

The correspondence between bedrock elevation and static water level in the Islands is strong, showing the marked difference in permeabilities of bedrock and sediment aquifers. The coarse-grained sediment aquifers have much larger yields and higher recharge rates than bedrock aquifers, but also are more prone to pollution from a variety of sources. Protection of these important but delicate aquifers should include use of improved pollution-prevention technologies, regulation of potential contaminants, and zoning of non point-source activity. Because ground water is a primary water source, it plays a strongly limiting role in the development of the Islands.

Jennifer Zwiebel

Pleistocene Rocky Shorelines at Punta Cabras, Baja California, Mexico

Ancient rocky shores provide a record of an important coastal ecosystem. Paleoshorelines represent, among other things, the stratigraphic make-up, biology, and tectonism of a coastal environment. They also serve as an important indicator of climatic conditions and changes in sea level. Due to the harshness of this environment, however, rocky shores have been poorly documented in the paleorecord. In June 1993, field research was conducted at Punta Cabras, Baja California, Mexico. Three different Late Pleistocene shore environments were examined, the open rocky coast, the protected outer coast, and terrestrial deposits.

For the outer coast environment, two localities were studied, Keyhole Beach and Paseo Cueva. At Keyhole Beach the modern pocket beach represents a type of neptunian dike which is continually being filled with debris, including andesite pebbles and cobbles and a large amount of Mytilus californianus shells. A Late Pleistocene deposit on the eastern wall of the beach provides a detailed record of five distinct layers, composed of alternating coarse and fine-grained material, primarily that of Mytilus shell fragments. The coarser beds represent periods of berm formation (when sea level was slightly lower), while the finer beds represent the accumulation of sediments in the lower foreshore (when sea level was slightly higher). At the second site, Paseo Cueva, sample quadrates were used to map a late Pleistocene drape which covers an igneous basement rock. This deposit exhibits fossilized Petricola carditoides shells, nestled in bore holes within Cretaceous andesite.

As for the second environment, the protected outer coast, two sites were studied. The first, Half Moon Bay, represents the record of a strait of water between the mainland and an andesite island, which was reconnected to the mainland by a tombolo and subsequent dunes in the Late Pleistocene time. The paleorecord shows a variety of coastal environments, including subtidal zones, intertidal zones, and terrestrial deposits. Research at the second site, the Punta Cabras embayment, expands on previous research by Addicott and Emmerson (1959) to explore the paleobiology of organisms living in what was a protected coastal bay.

The third environment studied is that of proto-dunes and massive sand dunes at Half Moon Bay. This was documented in order to complete the history of events which led from the initial infilling of this strait of water, to the building of terrestrial dunes. The dunes also reveal fossilized root casts, which provide evidence for similarities between the stabilization and habitation of the modern versus ancient dunes.

In comparing and contrasting these environments, the Late Pleistocene deposits provide a record of modest marine transgression and regression. Comparison with oxygen isotope records provides a basis for labeling interglaciation and glaciation cycles. The alternating layers, seen specifically at Keyhole Beach and in Half Moon Bay, can be correlated with the events which occurred during the past 150,000 years of the late Pleistocene.

Finally, detailed stratigraphy allowed units to be correlated between Keyhole Beach and Half Moon Bay, reflecting climatic changes which took place during the transition from the last interglacial period to the last glacial period.

MATHEMATICS

John Alberg

Projection Methods for Neural Networks

A neural network is a collection of simple processing elements which allows for highly parallel and distributed computation. Such models are based loosely on the processing capabilities of biological neural systems and have been used to perform a number of intelligent computational tasks. Herein, we investigate techniques that minimize the size of a neural network to improve its generalization ability. We derive a simple constructive algorithm for determining hidden layer weights in a single hidden layer neural network based on an algebraic condition necessary for the existence of the output layer weights. We introduce the 'orthogonal projection' to derive a recursive relationship between the minimum error values of the network as the number of hidden units in the network increases. The algorithm adds hidden units iteratively -- performing a simple optimization with the addition of each unit -- until the algebraic condition is met. Consequently, the difficult problem of specifying the number of hidden units a priori is eliminated. The optimization of each node is only as computationally taxing as the simplest forms of the Hebb learning rule and hence should enable fast training of feed forward neural networks.

Douglas R. Briggs

Hamiltonicity of Grid Graphs Without Holes

The problem in graph theory of finding hamiltonian cycles in unrestricted graphs is known to be computationally intractable. By making restrictions on the class of graphs under consideration for hamiltonicity, however, we can often reduce the problem to a computationally feasible one. We note that for the general class of grid graphs without holes, there are a number of subclasses which guarantee hamiltonicity, and we characterize a number of these as well as some which are guaranteed to be non-hamiltonian.

Margaret Donavan

Modeling Innate Immunity

The nature of the innate immune response is studied using mathematical models of in vitro cell dynamics. Three models are constructed. The first model describes the in vitro dynamics of purified macrophages. Using this model, the cytokine interleukin (IL)-10 is shown to suppress macrophage activation and IL-12 production only relatively late after antigenic stimulation. The second model captures the in vitro behavior of purified natural killer (NK) cells. These two models are integrated to create a third model, which captures the in vitro dynamics of the innate immune system. This model elucidates the mechanisms of action of interferon gamma (IFN-g) and IL-10 on the innate immune system. The model results are explained in reference to in vivo biological experiments.

PHYSICS

Peter M. Bronk

Rebuilding a Hewlett Packard H10A Hydrogen Maser: Process and Potential Experiments

The Williams Maser Lab acquired a Hewlett Packard H10A hydrogen maser in the middle 1980's from the U.S. Naval Observatory. Rebuilding the H10A maser constituted a significant portion of this thesis project. The maser is intended for use in introductory quantum mechanics laboratory experiments at Williams. This thesis will describe the process of rebuilding the maser along with some preliminary performance data. Some potential maser experiments with sample data will also be presented.

Arthur L. Cole

A Frequency Sampling Spectrometer for a Cryogenic Hydrogen Maser

We present details of the operation and design of a modified LabVIEWTM based Frequency Sampling Spectrometer (FSS) and its accompanying interface circuit. The circuit converts difference periods between a reference signal and the new Cryogenic Hydrogen Maser (CHM) into logic pules which feed into digital LabVIEWTM frequency counters. The FSS then records and displays real time frequency measurements. We present an experiment which uses the FSS to characterize frequency drifts in the CHM. Finally we present a second experiment, motivated by the first, to investigate the source of the observed frequency drifts.

Jason T. Eglit

A Statistical Analysis of The Accessible Information Inherent in a Two-Dimensional Quantum System

The problem of finding the accessible information inherent in an arbitrary ensemble of quantum states is one for which there is yet no known solution. In this paper we attempt such a solution for the two- dimensional case of photon polarizations via the application of a neural network. We first consider the relatively simple case of three-state ensembles with three measurement outcomes and then proceed to the more difficult case of five-state ensembles with four measurement outcomes. Later sections also discuss some statistical properties related to the function of information.

Craig C. Epifanio

Motional Narrowing in the Atomic Hydrogen Maser

We describe an experiment designed to test Hirchfeld's density matrix perturbation theory approach to motional narrowing using the atomic hydrogen maser. Our methodology involves using pulsed magnetic resonance techniques to determine the ground-state level populations of atomic hydrogen resulting from the application of a spatially varying, oscillating electromagnetic field. We compare empirically determined steady-state level population spectra to the predictions of Hirchfeld's theory using two approximate forms of the correlation function. Preliminary results show promising (but not conclusive) agreement between theory and experiment.

James W. Partan

Progress Towards a Magneto-Optic Trap for Rubidium

Progress is reported toward achieving a magneto-optic trap of Rubidium using diode lasers tuned to the 52S 1/2 Æ 52 P3/2 transition at 780.1 nm. We have improved all major subsystems of the project setup; the main laser now locks consistently with a linewidth of 2 MHz; the magnetic fields are zeroed to within 0.3 Gauss with a 10 Gauss/cm magnetic field gradient; the pressure within the six-cell can be controlled with a short time constant. With these parameters for the experimental apparatus, we should be able to create a magneto-optic trap for Rubidium.

Eleanor M. Winston

Design, Construction, and Evaluation of Experimental Apparatus for Research on Soliton Interactions in Dual-Core Optical Fiber

We designed, constructed, and evaluated an optical/electronic apparatus for coupling two laser beams with a fixed phase relationship into a dual-core optical fiber. The apparatus, which consists of a modified Mach-Zehnder interferometer with a control circuit for phase stabilization, will eventually be used in an experiment to test the theory of coupled solitons in dual-core fiber. We succeeded in focusing the beams down to approximately 12 microns in diameter, with a center-to-center separation of 12 microns between beams; these dimensions corresponded to maximum coupling into the dual- core fiber. In addition, we were able to lock the control circuit around a certain phase relationship between the two beams; using a 1.52 micron wavelength laser, we achieved phase stabilization to within approximately 1 degree of an interference fringe, while keeping the dual-core fiber beams properly focused and aligned.

PSYCHOLOGY

Elizabeth B. Burnett

Cognitions and Conflict: Toward an Understanding of Mother-Daughter Relationships

Unrealistic beliefs and perspective-taking ability were studied as potential predictors of mother- daughter conflict for 50 early (ages 13-14) and late (ages 17-18) adolescent pairs. Unrealistic beliefs and perspective-taking ability did not predict perceived conflict for mothers of either age group. However, the model significantly predicted perceived conflict for early adolescent daughters, with unrealistic beliefs contributing significantly to the prediction of conflict. The model marginally predicted perceived conflict for late adolescent daughters. Perspective-taking ability contributed significantly to the prediction of perceived conflict for late adolescents, with a statistical trend toward significance for unrealistic beliefs. Contrary to predictions, daughters performed more successfully on a perspective-taking task than did mothers, and mothers and daughters reported similar levels of conflict. Perspective-taking ability and perceived conflict did not vary significantly with adolescent age. The results supported the contribution of cognitive factors to perceived conflict for daughters, and the importance of continued research in this area.

Jessica Cross

Effects of Stereotype-Consistency and Self-Esteem Threat on Male Homophobia

An experiment was conducted to study effects of stereotype-consistency and self-esteem threat on expressions of male homophobia, using overt and unobtrusive measures. Subjects were 103 male college students. Half of subjects received self-esteem threat; the other half did not. Subjects anticipated interacting with a target, who was: (1) gay and consistent with gay stereotypes, (2) gay and inconsistent with gay stereotypes, (3) straight and consistent with gay stereotypes, or (4) straight and inconsistent with gay stereotypes. Subjects evaluated the target on six dimensions. The distance subjects placed their chair from the target's chair was measured. Subjects evaluated the gay stereotype-consistent target more negatively than the other targets on five of the six dimensions; threat had little impact on evaluations. When the target was inconsistent with gay stereotypes, threatened subjects placed the chair farther from the gay than from the straight target. This effect did not occur without threat. Implications for cognitive and motivational prejudice theories are discussed.

Peggy C. Drucker

The Behavioral Effects of the Neuroactive Steroid Allopregnanolone on Neonatal Rats Prenatally Exposed to Alcohol

This thesis studied the effects of prenatal alcohol exposure on the behavioral response to the neuroactive steroid allopregnanolone (AP) in neonatal rats. Experiment 1 employed an odor associative training task in which an infusion of milk was paired with a novel odor (CS). Subjects from one of the three prenatal conditions (lab chow, alcohol, or pair-fed) received either no injection, a vehicle injection, or one of three doses (1.25 µg AP, 2.5 µg AP or 5.0 µg) of AP either 20 minutes prior to or immediately after training. Retention was assessed one hour later in a two-choice odor preference chamber. The percent time spent over CS odor-scented bedding compared to neutral bedding was used as the retention score. An additional group of subjects who received exposure to the CS alone without the milk infusion was used to determine if conditioning had occurred. Results showed that post-training injections of AP caused a dose-dependent impairment in retention in the odor task, but there was no differential sensitivity to AP in the alcohol-exposed offspring. In addition, all pre-training injections resulted in impairments in retention on the task, indicating that stress may be a key factor in the ability of rats to learn in this paradigm.

In Experiment 2, ultrasonic vocalizations were recorded from pups in the same three prenatal conditions listed above as well as the same drug doses. An additional group of 10.0 µg AP for the alcohol-exposed pups was added. Results from this experiment indicate that alcohol-exposed offspring displayed a dose dependent shift to the right in their response to AP. This decreased sensitivity may possibly indicate that prenatal alcohol exposure causes a decrease in the density of the GABA receptors involved in stress response, resulting in a reduction in the sensitivity to AP.

Leigh Frost

The Effects of Expectations on Perceptions of Presidential Debate Performance

Two studies were conducted to examine the impact of expectations on perceptions of Presidential debate performances. Subjects viewed an excerpt from a 1976 debate between Gerald Ford and Jimmy Carter and evaluated the candidates on several dimensions. Subjects had little knowledge about this debate or about these two former Presidents. Before viewing the excerpt, subjects were given negative information about either the personal characteristics and abilities or the debate-relevant skills of one or the other candidate, in order to lower their expectations for the performance of this candidate. In Study 1, this information was said to be from neutral political analysts. In Study 2, the source of the negative information was said to be either from the candidate's own campaign team, from the opposing candidate's team, or from neutral sources. Results indicated that the negative expectation information made subjects perceive the candidate and his performance more negatively, particularly when the expectancy focused on his debate-relevant skills specifically, and particularly when the information came from the candidate's own campaign team.

Aliina Hirschoff

Towards the Development of a Brief Cognitive Screening Battery Sensitive to Alzheimer's Disease

Accurate diagnosis of probable Alzheimer's Disease (PRAD) requires extensive evaluation by neurologists and neuropsychologists. Because most elderly people are not in regular contact with such specialists, primary care physicians need the tools to make accurate referrals. However, no screening battery compatible with the time and staff constraints of primary care physicians is currently available. The goal of the present study was to begin the process of developing a brief (7-10 minute) cognitive screening battery sensitive to AD. Seven standard neuropsychological tests were administered to 21 normal elderly subjects and 22 subjects with PRAD (as defined by NIH criteria). Discriminant analysis was performed on 2 combinations of tests. Each combination was estimated to take 8 minutes to administer. The first, Enhanced Cued Recall, Boston Naming, Clock Drawing, and Benton Orientation, generated a discriminant function with a sensitivity of 100% and a specificity of 100%. The second, Enhanced Cued Recall, Category Fluency, Clock Drawing, and Benton Orientation, generated a discriminant function with a sensitivity of 95% and a specificity of 100%. Although these combinations have a high degree of sensitivity and specificity in discriminating PRAD patients from normal healthy elderly, there are several important steps necessary before these test combinations will be appropriate for general clinical use. Because the current sample did not include patients with primary degenerative dementias (PDDs) other than PRAD, it is not clear whether it will also be sensitive and specific in discriminating other PDDs from normal aging. We also cannot currently determine if PRAD will present a different pattern on these tests than other PDDs. Additionally, it is not clear if these test combinations will discriminate functional causes of cognitive impairment (e.g., depression), from PDDs, including PRAD. Finally, we will eventually need to determine if this battery is effective in the clinical practice of primary care physicians. The present study took place in the more specialized setting of a memory disorders clinic, and experimenters were not always blind to the subject's conditions. Nevertheless, the present data suggest that a brief screening battery that, at the very least, can discriminate between PRAD sufferers and normal elderly is feasible.

Nino Nikola Marakovic

A Choice-Analytic Approach to Impulsiveness

Impulsiveness can be explained by the fact that people discount value over time. Experiment 1 asked 22 subjects to indicate the minimum amount they would accept immediately in exchange for a larger, later reward. Results showed that hyperbolic discount functions are superior to exponential discount functions in accounting for choices in the discounting paradigm of impulsiveness.

Experiment 2 asked 672 subjects to choose between a smaller, immediate amount and a larger, later reward in 21 choice pairs. The results indicated that gender differences found in psychological impulsiveness literature are also present in the choice-analytic paradigm. The results also showed that the discounting rate is inversely related to the size of the amount. Experiment 3, which subject filled out three different impulsiveness questionnaires, indicated that although both are probably related to a higher order construct, ego-control, the two constructs are different.

Allison L. McCloskey

The Effect of Suspicion and Attribution Theory upon Pretrial Publicity and Juror Verdicts in a Mock Criminal Trial

Two studies examined whether the prejudicial effects of pretrial publicity information could be reduced by making subjects suspicious of the motives underlying the release of the information in the press. Subjects in both studies read newspaper articles about a murder trial, followed by the transcript of that trial. In both studies, subjects' suspicions were correlated negatively with the impact that the publicity had on their judgments. In Study 1, subjects who had read publicity including an inflammatory opinion column, but no specific mention of plausible reasons why the columnist may have been biased, were more likely to avoid the effects of publicity than were subjects who had read other publicity or publicity that did make reference to specific reasons why the columnist may have been biased. Study 2 clarified these results by illustrating that information that was designed to arouse general suspicion about one subset of information, caused subjects to be particularly likely to dismiss the publicity information when making their verdicts. Implications and proposals for future research are discussed.

Lisa Uebelacker

Women, Men, and Self-Presentation of Academic Achievement

This experiment examined sex-related patterns of modesty in the context of a conversation with a peer. First year undergraduate men and women were asked to discuss, with a same or opposite sex peer, a series of questions which required progressively more self-disclosure about academic ability and achievement. The final question asked participants to predict their grade point average (GPA). The conversation was videotaped, following which, participants completed a tape-assisted recall of their subjective experience of the conversation. It was hypothesized that, relative to men, women would be more modest during the conversation, women's GPA predictions would be lower, and women would report being more concerned about their partner's feelings and more concerned about whether or not their partner liked them. Of these hypotheses, one was supported: coding of the videotape showed that women were more modest than were men in the way they spoke about their college performance. That is, there was a sex difference in modesty only when subjects were not aware of how they were presenting their academic achievement. When they were very aware of their self-presentation, i.e., when predicting their GPAs, women and men did not differ in their presentation of their achievement. The results also suggested that, during the conversation, men may have been just as concerned about their partners' feelings as were women.

Akiko Yokoyama

U.S. favoritism and Japan bashing: The moderating roles of self- and group-level threats

Two experiments were conducted to examine the effects of exposure to negative, potentially threatening information directed toward the subjects' selves or their country (the U.S.) on their inter- group perceptions and attitudes. It was hypothesized that exposure to such information may cause or exacerbate ingroup (i.e., U.S.) favoritism and/or outgroup derogation (i.e., Japan-bashing) in order to help subjects reaffirm their threatened self- or group-esteem. In addition, the potentially moderating effects of subjects' trait security/insecurity, and of self- and group-affirmation procedures, were assessed. The results of Study 1 revealed that exposure to the U.S.-threat information tended to cause biased perceptions in favor of the United States compared to the control and self-threat conditions. The results of Study 2 illustrated that exposure to U.S.-threat information caused subjects to endorse more negative, stereotypic perceptions of Japan, and that giving subjects a chance to reaffirm their sense of U.S.-esteem in some other way eliminated this effect.