The Influence of the Human Stress Response on Navigation Strategy and Efficiency

Navigating between locations in a known environment is a task we undertake in our daily lives, but not everyone uses the same strategy to navigate. Some people navigate by a route-based strategy of following well-known routes supported by the caudate nucleus while others readily take shortcuts using a hippocampal-dependent place-based strategy (Marchette, Bakker, & Shelton, 2011). Stress is also an everyday occurrence, for most. Interestingly, the largest concentration of the stress hormone cortisol in the brain after a stressor is the hippocampus. Thus, cortisol may influence these navigation strategies differentially such that stress may force place-based navigators into using route-based strategies while route-based navigators may be spared. Further, navigation efficiency may be hindered in either type of navigator. However, little research has been attempted in this area.To test this prediction in this dissertation, the Dual Solution Paradigm (DSP; Marchette et al., 2011) is used as the navigation task. In this task, participants learn a route in a virtual maze. After learning, participants are placed along the learned route and are asked to navigate between previously learned locations. Each trial is structured such that taking either the learned route or reversing the route lead to the goal; however, in all cases, taking a shortcut is more efficient. After testing, each trial is categorized by strategy selection (e.g., shortcut, learned route) and a measure is computed to assess relative dependence on each type of strategy. In order to test participants twice, once under stress and once under control conditions, two equivalent mazes were required. The first two experiments in this dissertation were conducted as pilot experiments in order to develop two equivalent mazes for later use. Experiment 1 tested the original DSP maze relative to its mirrored structure and was used to determine the most diagnostic trials. Experiment 1b included more subjects but also reduced the number of trials based on considerations of time. Performance in these mazes was similar, however, the results in Experiment 1b are noticeably weaker than Experiment 1a. These mazes were used for Experiments 2, 3, and 4. For the stress component, three stressors were used: a physiological stressor (Experiment 2), a social stressor (Experiment 3), and a cognitive fatigue stressor (Experiment 4), each presented after the learning phase but before the testing phase. Experiment 2 used the Cold Pressor Task in which participants place their feet in ice water (stress) and room temperature water (control). Despite differences in cortisol between the two conditions and the subjective measures of stress, there were no differences found between control and stress conditions within individuals in terms of objective strategy measures or efficiency of navigation. Post-hoc analyses of high and low stress responders indicated no differences in navigation between these navigators.Experiment 3 used the social-evaluative stressor known as the Trier Social Stressor task in which participants prepare and deliver a speech to peers followed by a mental subtraction task (stress) and a speech about their daily routine and a simple addition task (control). In this experiment, differences were found between conditions for subjective stress and in cortisol between the control and the stress condition. However, no differences were found between control and stress conditions within individuals in navigation strategy or efficiency of navigation. Post-hoc analyses of high and low stress responders indicated no differences in navigation between these navigators.Experiment 4 used a mental fatigue task in which participants schedule workers on various tasks with increasing difficulty per trial (stress) and a simple word search task (control) for a two-hour period. Here, differences were found between conditions for subjective stress relating to the stressor, but no differences were found in cortisol between the control and the stress condition. Further, no differences were found between control and stress conditions within individuals in navigation strategy or efficiency. Post-hoc analyses of high and low stress responders indicated less shortcuts and less efficient navigation in those responding less to the scheduling task stressor. This results suggests a possible facilitation of navigation behavior when under acute stress.This work indicates several important conclusions. First, navigation strategy and efficiency may be robust to the effects of various stressors may have little influence over our navigation strategy systems in virtual environments. Navigation strategy remains stable even in the presence of stressful stimuli. Differences found between the Experiment 1b and the stressor studies indicates a potential stress effect in the controlled lab setting, such that participants took generally fewer shortcuts in Experiment 1b compared to both the Experiment 2 (cold pressor) and Experiment 4 (cognitive fatigue). Results are discussed in the context of the overarching cognitive theory as well as it’s connection to other task domains such as emergency egress

What Geoscience Experts And Novices Look At, And What They See, When Viewing Data Visualizations

This study examines how geoscience experts and novices make meaning from an iconic type of data visualization: shaded relief images of bathymetry and topography.  Participants examined, described, and interpreted a global image, two high-resolution seafloor images, and 2 high-resolution continental images, while having their gaze direction eye-tracked and their utterances and gestures videoed. In addition, experts were asked about how they would coach an undergraduate intern on how to interpret this data.  Not unexpectedly, all experts were more skillful than any of the novices at describing and explaining what they were seeing.  However, the novices showed a wide range of performance.  Along the continuum from weakest novice to strongest expert, proficiency developed in the following order: making qualitative observations of salient features, making simple interpretations, making quantitative observations.  The eye-tracking analysis examined how the experts and novices invested 20 seconds of unguided exploration, after the image came into view but before the researcher began to ask questions.  On the cartographic elements of the images, experts and novices allocated their exploration time differently:  experts invested proportionately more fixations on the latitude and longitude axes, while students paid more attention to the color bar.  In contrast, within the parts of the image showing the actual geomorphological data, experts and novices on average allocated their attention similarly, attending preferentially to the geologically significant landforms.   Combining their spoken responses with their eye-tracking behavior, we conclude that the experts and novices are looking in the same places but “seeing” different things

On the Use of Response Chunking as a Tool to Investigate Strategies

In this perspective we suggest that chunking can be used as an investigative tool to determine the characteristics of other cognitive phenomena. We present an example of the usefulness of chunking multiple responses to aid in understanding object switch costs. Switch costs refer to the shorter response times for manipulation of the same item on two trials in a row compared to a switch between items. It is presently unclear if this result is due to structural or strategic processes. We provide a short review of past literature on switch costs and a proof-of-concept example that chunking may shed new light on this topic. We examined this question with boxes filled with numbers to be arithmetically updated and memorized. A situation in which there were two response items to be manipulated per trial eliminated or reversed the switch cost effect. We suggest that participants use a strategy in which the two output responses were chunked together, making it unfeasible to prepare separately for a repetition of the most recent item as participants do in other circumstances. Our data suggest that even a well-studied phenomenon can benefit theoretically from the use of chunking as a research tool

Simultaneous multi-wavelength observations of the TeV Blazar Mrk 421 during February - March 2003: X-ray and NIR correlated variability

In the present paper, we have reported the result of simultaneous multi-wavelength observations of the TeV blazar Mrk 421 during February $-$ March 2003. In this period, we have observed Mrk 421 using Pachmarhi Array of \v{C}erenkov Telescopes (PACT) of Tata Institute of Fundamental Research at Pachmarhi, India. Other simultaneous data were taken from the published literature and public data archives. We have analyzed the high quality X-ray (2-20 keV) observations from the NASA Rossi X-Ray Timing Explorer (RXTE). We have seen a possible correlated variability between X-ray and J band (1.25 $\mu$) near infrared (NIR) wavelength. This is the first case of X-ray and NIR correlated variability in Mrk 421 or any high energy peaked (HBL) blazar. The correlated variability reported here is indicating a similar origin for NIR and X-ray emission. The emission is not affected much by the environment of the surrounding medium around the central engine of the Mrk 421. The observations are consistent with the shock-in-jet model for the emission of radiations.Comment: 11 pages, 5 figures, Accepted for Publication in ChJA

Feeding versus Feedback in NGC 4151 probed with Gemini NIFS. I. Excitation

We have used the Gemini Near-infrared Integral Field Spectrograph (NIFS) to map the emission-line intensity distributions and ratios in the Narrow-Line Region (NLR) of the Seyfert galaxy NGC 4151 in the Z, J, H and K bands at a resolving power ~ 5000, covering the inner 200 pc x 300 pc of the galaxy at a spatial resolution of 8 pc. We present intensity distributions I(r) in 14 emission lines. (1) For the ionized gas, I(r) is extended to ~ 100 pc from the nucleus along pos. angle PA=60/240 deg-- NE--SW), consistent with an origin in the known biconical outflow; while for the recombination lines I(r) ~ r^-1, for the forbidden lines I(r) is flat (r^0). (2) The H_2 emission lines intensity distributions avoid the region of the bicone, extending to r ~ 60 pc, perpendicular to the bicone axis, supporting an origin for the H_2-emitting gas in the galaxy plane. (3) The coronal lines show a steep intensity profile, described by r^-2. Using the line-ratio maps [Fe II]1.644/1.257 and Pa_b/Br_g we obtain a reddening of E(B-V)~0.5 along the NLR and E(B-V)>1 at the nucleus. Our line-ratio map [Fe II] 1.257/[P II] 1.189 is the first such map of an extragalactic source. Together with the [Fe II]/Pa_b map, these line ratios correlate with the radio intensity distribution, mapping the effects of shocks produced by the radio jet, which probably release the Fe locked in grains and produce the enhancement of the [Fe II] emission observed at ~ 1 arcsec from the nucleus. At these regions, we obtain densities N_e ~4000 cm^-3 and temperatures T_e ~ 15000K for the [Fe II]-emitting gas. For the H_2-emitting gas we obtain T ~ 2100K. The distinct intensity distributions, physical properties and locations of the ionized and molecular gas suggest that the H_2-emitting gas traces the AGN feeding, while the ionized gas traces its feedback.Comment: 22 pages. 14 figures, accepted for publication in MNRA

Sonifying data uncertainty with sound dimensions

The communication of data uncertainty is a crucial problem in data science, information visualization, and geographic information science (GIScience). Effective ways to communicate the uncertainty of data enables data consumers to interpret the data as intended by the producer, reducing the possibilities of misinterpretation. In this article, we report on an empirical investigation of how sound can be used to convey information about data uncertainty in an intuitive way. To answer the research question How intuitive are sound dimensions to communicate uncertainty?, we carry out a cognitive experiment, where participants were asked to interpret the certainty/uncertainty level in two sounds A and B (N=33). We produce sound stimuli by varying sound dimensions, including loudness, duration, location, pitch, register, attack, decay, rate of change, noise, timbre, clarity, order, and harmony. In the stimuli, both synthetic and natural sounds are used to allow comparison. The experiment results identify three sound dimensions (loudness, order, and clarity) as significantly more intuitive to communicate uncertainty, providing guidelines for sonification and information visualization practitioners

EROs found behind lensing clusters. II. Stellar populations and dust properties of optical dropout EROs and comparison with related objects

We determine the nature, redshift, stellar populations and dust properties of optically faint or non-detected extremely red objects (ERO) found from our survey of the lensing clusters A1835 and AC114. We perform SED fitting and use deep optical, HST, VLT, Spitzer data, and for some objects and sub-mm data. For most of the lensed EROs we find photometric redshifts showing a strong degeneracy between "low-z" (z~1-3) and high-z (z~6-7). Although formally best fits are often found at high-z, their resulting bright absolute magnitudes, the number density of these objects, and in some cases Spitzer photometry or longer wavelength observations, suggest strongly that all of these objects are at "low-z". The majority of these objects are best fitted with young (<~ 0.5-0.7 Gyr) and dusty starbursts. Indications for strong extinction, with A_V~2.4-4, are found in some objects. For dusty objects star formation rates (SFR) have been estimated from the bolometric luminosity determined after fitting of semi-empirical starburst, ERO, and ULIRG templates. Typically we find SFR~(1-18) Msun/yr. Again, SMMJ14009+0252 stands out as a LIRG with SFR 1000 Msun/yr. Concerning the comparison objects, we argue that the massive post-starburst z~6.5 galaxy candidate HUDF-J2 showing observed properties very similar to our EROs, is more likely a dusty starburst at z~2.3-2.6. This interpretation also naturally explains the observed 24 micron emission. Both empirically and from our SED fits we find that the IRAC selectec EROs from Yan et al (2004) show very similar properties to our lensed EROs. Reasonable fits are found for most of them with relatively young and dusty stellar populations.Comment: 18 pages, 17 figures, accepted for publication in Astronomy and Astrophysic

Institutional investors and corporate governance

We provide a comprehensive overview of the role of institutional investors in corporate governance with three main components. First, we establish new stylized facts documenting the evolution and importance of institutional ownership. Second, we provide a detailed characterization of key aspects of the legal and regulatory setting within which institutional investors govern portfolio firms. Third, we synthesize the evolving response of the recent theoretical and empirical academic literature in finance to the emergence of institutional investors in corporate governance. We highlight how the defining aspect of institutional investors – the fact that they are financial intermediaries – differentiates them in their governance role from standard principal blockholders. Further, not all institutional investors are identical, and we pay close attention to heterogeneity amongst institutional investors as blockholders