146 research outputs found
Author's personal copy Decision processes in temporal discrimination
No full textThis article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. The processing dynamics underlying temporal decisions and the response times they generate have received little attention in the study of interval timing. In contrast, models of other simple forms of decision making have been extensively investigated using response times, leading to a substantial disconnect between temporal and non-temporal decision theories. An overarching decision-theoretic framework that encompasses existing, non-temporal decision models may, however, account both for interval timing itself and for time-based decision-making. We sought evidence for this framework in the temporal discrimination performance of humans tested on the temporal bisection task. In this task, participants retrospectively categorized experienced stimulus durations as short or long based on their perceived similarity to two, remembered reference durations and were rewarded only for correct categorization of these references. Our analysis of choice proportions and response times suggests that a two-stage, sequential diffusion process, parameterized to maximize earned rewards, can account for salient patterns of bisection performance. The first diffusion stage times intervals by accumulating an endogenously noisy clock signal; the second stage makes decisions about the first-stage temporal representation by accumulating first-stage evidence corrupted by endogenous noise. Reward-maximization requires that the second-stage accumulation rate and starting point be based on the state of the first-stage timer at the end of the stimulus duration, and that estimates of non-decision-related delays should decrease as a function of stimulus duration. Results are in accord with these predictions and thus support an extension of the drift-diffusion model of static decision making to the domain of interval timing and temporal decisions
Attractive electron-electron interactions within robust local fitting approximations
No full textAn analysis of Dunlap's robust fitting approach reveals that the resulting two-electron integral matrix is not manifestly positive semidefinite when local fitting domains or non-Coulomb fitting metrics are used. We present a highly local approximate method for evaluating four-center two-electron integrals based on the resolution-of-the-identity (RI) approximation and apply it to the construction of the Coulomb and exchange contributions to the Fock matrix. In this pair-atomic resolution-of-the-identity (PARI) approach, atomic-orbital (AO) products are expanded in auxiliary functions centered on the two atoms associated with each product. Numerical tests indicate that in 1% or less of all HartreeFock and KohnSham calculations, the indefinite integral matrix causes nonconvergence in the self-consistent-field iterations. In these cases, the two-electron contribution to the total energy becomes negative, meaning that the electronic interaction is effectively attractive, and the total energy is dramatically lower than that obtained with exact integrals. In the vast majority of our test cases, however, the indefiniteness does not interfere with convergence. The total energy accuracy is comparable to that of the standard Coulomb-metric RI method. The speed-up compared with conventional algorithms is similar to the RI method for Coulomb contributions; exchange contributions are accelerated by a factor of up to eight with a triple-zeta quality basis set. A positive semidefinite integral matrix is recovered within PARI by introducing local auxiliary basis functions spanning the full AO product space, as may be achieved by using Cholesky-decomposition techniques. Local completion, however, slows down the algorithm to a level comparable with or below conventional calculations.
Replication Data for: Hunting method affects cortisol levels in harvested mountain hares (Lepus timidus)
No full textThis dataset contains information on cortisol levels in Norwegian mountain hares (Lepus timidus) after hunting. The dataset includes cortisol level measurements from 20 hares that were hunted using dogs and 32 hares that were hunted without the use of dogs. For addittional information on georeferencing, age, concentration of other blood hormones etc contact senior author. Abstract (of article):
Direct effect of hunting on hunted individuals and populations have been well-known for a long time. However, there has recently been an increased focus also on the indirect, non-lethal effects of hunting. When approached by a possible threat such as a predator, prey releases various stress hormones into the bloodstream. Cortisol is one of these hormones and the blood concentration is an indicator of stress levels in mammals. Here we report on a study on effects of using hunting dogs versus walk-up shooting on mountain hare blood cortisol levels. We sampled 20 hares hunted using dogs and 32 control hares hunted without using dogs. On average cortisol levels in hares hunted using dogs was 44.6 ng/ml, while hares harvested without being chased by dogs was 6.8 ng/ml. Based on the blood hormone levels of this study we cannot conclude if the elevated cortisol levels we see in the hares hunted using dogs was harmful to the hares had they not been shot. However, given what is known about effects of chronic stress, we would caution against repeated chases of individual hares. The cumulative effect of stressors including hunting is likely crucial for any effects on reproduction and survival. Thus, there is a need to evaluate the long-term effects of hunting chases and other human activities on mountain hare stress hormone levels, and to investigate the long-term effect on hare behavior, space use, survival, reproduction and recruitment
Preventing combinatorial explosion in a localist neural network architecture using temporal synchrony
No full textEvidence accumulator or decision threshold - which cortical mechanism are we observing?
No full textMost psychological models of perceptual decision making are of the accumulation-to-threshold variety. The neural basis of accumulation in parietal and prefrontal cortex is therefore a topic of great interest in neuroscience. In contrast, threshold mechanisms have received less attention, and their neural basis has usually been sought in subcortical structures. Here I analyze a model of a decision threshold that can be implemented in the same cortical areas as evidence accumulators, and whose behavior bears on two open questions in decision neuroscience: 1) When ramping activity is observed in a brain region during decision making, does it reflect evidence accumulation? 2) Are changes in speed-accuracy tradeoffs and response biases more likely to be achieved by changes in thresholds, or in accumulation rates and starting points? The analysis suggests that task-modulated ramping activity, by itself, is weak evidence that a brain area mediates evidence accumulation as opposed to threshold readout; and that signs of modulated accumulation are as likely to indicate threshold adaptation as adaptation of starting points and accumulation rates. These conclusions imply that how thresholds are modeled can dramatically impact accumulator-based interpretations of this data
Målinger i troposfæren med ALOMAR RMR lidar: Temperaturmålinger med bruk av rotasjons Raman spektrum og bestemmelse av dens optiske overlap.
No full textAlomar troposfæriske lidar var ikke operativ grunnet en feil med laseren og trengte en erstatter. Den fikk en ny laser under skrivingen av denne oppgaven.
I denne oppgaven ble det prøvd en midlertidig løsning hvor RMR-lidaren på ALOMAR ble brukt for troposfæremålinger. RMR-lidaren er ustyrt med rotasjons-Raman kanaler som er brukt til å måle temperaturer i troposfæren. RMR-lidaren er konstruert for målinger i den øvre atmosfære og har derfor en ukomplett optisk overlap i tropsfæren. Den optiske overlapsfunksjonen for RMR teleskopene vil bli funnet på forskjellige metoder slik at RMR-lidaren kan bli brukt for andre målinger i troposfæringen. Overlapsfunksjonen er og blitt brukt til å sammenligne data fra RMR og den troposfæriske lidaren.The ALOMAR tropospheric lidar was not operative as the laser was damaged and needed a replacement. It got the new laser during the writing of this thesis.
In this thesis I will try to give a backup solution using the RMR-lidar for tropospheric measurements, which is also located at ALOMAR. The RMR-lidar is equipped with rotational Raman channels which will be used to calculate temperature in the troposphere.
As the RMR-lidar is built for upper atmospheric measurements the telescopes have an incomplete optical overlap in the troposphere. The optical overlap function for the RMR telescopes will be determined using different methods, such that the RMR-lidar can be used for other measurements in the troposphere. The overlap function will then briefly be used to compare data from tropospheric lidar
Målinger i troposfæren med ALOMAR RMR lidar: Temperaturmålinger med bruk av rotasjons Raman spektrum og bestemmelse av dens optiske overlap.
No full textAlomar troposfæriske lidar var ikke operativ grunnet en feil med laseren og trengte en erstatter. Den fikk en ny laser under skrivingen av denne oppgaven.
I denne oppgaven ble det prøvd en midlertidig løsning hvor RMR-lidaren på ALOMAR ble brukt for troposfæremålinger. RMR-lidaren er ustyrt med rotasjons-Raman kanaler som er brukt til å måle temperaturer i troposfæren. RMR-lidaren er konstruert for målinger i den øvre atmosfære og har derfor en ukomplett optisk overlap i tropsfæren. Den optiske overlapsfunksjonen for RMR teleskopene vil bli funnet på forskjellige metoder slik at RMR-lidaren kan bli brukt for andre målinger i troposfæringen. Overlapsfunksjonen er og blitt brukt til å sammenligne data fra RMR og den troposfæriske lidaren
NEURAL MECHANISMS FOR CONTROL IN COMPLEX COGNITION
No full textin school and out. ii ACKNOWLEDGEMENTS Special thanks go to my adivsor, Dr. Thad Polk, for making it possible to do re-search in this area and for introducing me to the great question of how the prefrontal cortex makes us uniquely human. Thanks also to Dr. Eric Freedman and Dr. Rick Lewis for great critiques and stimulating conversations. Fellow Electrical Engineering and Computer Science students Dr. Chris Brooks, Dr. Rick Groff and Dr. Eric Klavins provided invaluable education, advice, critiques and philosophies, and hardly ever told me to stop talking. The Psychology Department at UM has been exceptionally welcoming. I am grateful for the opportunity to assist in teaching Psychology 340, Cognitive Psychol-ogy, and for the fantastic forums in Cognition and Perception and in Biopsychology
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