Grounding cognitive-level processes in behavior: the view from dynamic systems theory

Marr's seminal work laid out a program of research by specifying key questions for cognitive science at different levels of analysis. Because dynamic systems theory (DST) focuses on time and interdependence of components, DST research programs come to very different conclusions regarding the nature of cognitive change. We review a specific DST approach to cognitive-level processes: dynamic field theory (DFT). We review research applying DFT to several cognitive-level processes: object permanence, naming hierarchical categories, and inferring intent, that demonstrate the difference in understanding of behavior and cognition that results from a DST perspective. These point to a central challenge for cognitive science research as defined by Marr-emergence. We argue that appreciating emergence raises questions about the utility of computational-level analyses and opens the door to insights concerning the origin of novel forms of behavior and thought (e.g., a new chess strategy). We contend this is one of the most fundamental questions about cognition and behavior

A review of hippocampal activation in post‐traumatic stress disorder

Post‐traumatic stress disorder (PTSD) is often characterized by deficits in memory encoding and retrieval and aberrant fear and extinction learning. The hippocampus plays a critical role in memory and contextual processing and has been implicated in intrinsic functional connectivity networks involved in self‐referential thought and memory‐related processes. This review focuses on hippocampal activation findings during memory and fear and extinction learning tasks, as well as resting state hippocampal connectivity in individuals with PTSD. A preponderance of functional neuroimaging studies to date, using memory, fear learning, and extinction tasks, report decreased or “controls comparable” hippocampal activation in individuals with PTSD, which is usually associated with poorer performance on the task imaged. Existing evidence thus raises the possibility that greater hippocampal recruitment in PTSD participants may be required for similar performance levels. Studies of resting state functional connectivity in PTSD predominantly report reduced within‐network connectivity in the default mode network (DMN), as well as greater coupling between the DMN and salience network (SN) via the hippocampus. Together, these findings suggest that deficient hippocampal activation in PTSD may be associated with poorer performance during memory, extinction recall, and fear renewal tasks. Furthermore, studies of resting state connectivity implicate the hippocampus in decreased within‐network DMN connectivity and greater coupling with SN regions characteristic of PTSD.The hippocampus plays a key role in memory, fear learning and extinction, and default mode network resting state connectivity, all processes which have known deficits in post‐traumatic stress disorder (PTSD). In this review, we examine recent fMRI studies on hippocampal function in PTSD and controls and identify critical areas for future research to explore.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/153031/1/psyp13357.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/153031/2/psyp13357_am.pd

How Robust is Comparative Advantage?

This paper reviews the theoretical development of the concept of comparative advantage, starting with the two-good model of Ricardo and the two-good extension and reinterpretation by Haberler. In both, the presence of comparative advantage provides the scope for countries to gain from trade by specializing, and the pattern of that trade is explained by the pattern of comparative advantage. These strong results of the two-good model can be extended under certain circumstances to multiple goods and countries, but under more general assumptions such strong results no longer are assured. Instead one can derive much weaker results, usually in the form of correlations between comparative advantage and trade, and these weaker results hold in a much wider variety of circumstances. The paper examines those assumptions that permit such generalizations, but then also examines when those assumptions are most likely to fail, and what happens as a result.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73670/1/j.1467-9396.2005.00552.x.pd

Use of Equivalent Relative Utility (ERU) to Evaluate Artificial Intelligence-Enabled Rule-Out Devices

We investigated the use of equivalent relative utility (ERU) to evaluate the effectiveness of artificial intelligence (AI)-enabled rule-out devices that use AI to identify and autonomously remove non-cancer patient images from radiologist review in screening mammography.We reviewed two performance metrics that can be used to compare the diagnostic performance between the radiologist-with-rule-out-device and radiologist-without-device workflows: positive/negative predictive values (PPV/NPV) and equivalent relative utility (ERU). To demonstrate the use of the two evaluation metrics, we applied both methods to a recent US-based study that reported an improved performance of the radiologist-with-device workflow compared to the one without the device by retrospectively applying their AI algorithm to a large mammography dataset. We further applied the ERU method to a European study utilizing their reported recall rates and cancer detection rates at different thresholds of their AI algorithm to compare the potential utility among different thresholds. For the study using US data, neither the PPV/NPV nor the ERU method can conclude a significant improvement in diagnostic performance for any of the algorithm thresholds reported. For the study using European data, ERU values at lower AI thresholds are found to be higher than that at a higher threshold because more false-negative cases would be ruled-out at higher threshold, reducing the overall diagnostic performance. Both PPV/NPV and ERU methods can be used to compare the diagnostic performance between the radiologist-with-device workflow and that without. One limitation of the ERU method is the need to measure the baseline, standard-of-care relative utility (RU) value for mammography screening in the US. Once the baseline value is known, the ERU method can be applied to large US datasets without knowing the true prevalence of the dataset

Titan's Tropopause Temperatures from CIRS: Implications for Stratospheric Methane Cloud Formation

Analysis of Cassini Composite Infrared Spectrometer (CIRS) far-IR spectra enable the construction of Titan's temperature profile in the altitude region containing the tropopause. Whereas the methane V4 band at 1306/cm (7.7 microns) is the primary opacity source for deducing thermal structure between 100 km and 500 km, N2-N2 collision-induced absorption between 70 and 140/cm (143 microns and 71 microns) is utilized to determine temperatures at Titan's tropopause. Additional opacity due to aerosol and nitrile ices must also be taken into account in this part of the far-IR spectral region. The spectral characteristics of these particulate opacities have been deduced from CIRS limb data at 58degS, 15degS, 15degN, and 85degN. Empirically, the spectral shapes of these opacities appear to be independent of both latitude and altitude below 300 km (Anderson and Samuelson, 2011, Icarus 212, 762-778), justifying the extension of these spectral properties to all latitudes. We find that Titan's tropopause temperature is cooler than the HAS! value of 70.5K by approx. 6K. This leads to the possibility that subsidence at high northern latitudes can cause methane condensation in the winter polar stratosphere. A search for methane clouds in this region is in progress

Analyzing capacitance-voltage measurements of vertical wrapped-gated nanowires

The capacitance of arrays of vertical wrapped-gate InAs nanowires are analyzed. With the help of a Poisson-Schr"odinger solver, information about the doping density can be obtained directly. Further features in the measured capacitance-voltage characteristics can be attributed to the presence of surface states as well as the coexistence of electrons and holes in the wire. For both scenarios, quantitative estimates are provided. It is furthermore shown that the difference between the actual capacitance and the geometrical limit is quite large, and depends strongly on the nanowire material.Comment: 15 pages, 6 Figures included, to appear in Nanotechnolog

The obscured gamma-ray and UHECR universe

Auger results on clustering of > 60 EeV ultra-high energy cosmic ray (UHECR) ions and the interpretation of the gamma-ray spectra of TeV blazars are connected by effects from the extragalactic background light (EBL). The EBL acts as an obscuring medium for gamma rays and a reprocessing medium for UHECR ions and protons, causing the GZK cutoff. The study of the physics underlying the coincidence between the GZK energy and the clustering energy of UHECR ions favors a composition of > 60 EeV UHECRs in CNO group nucleons. This has interesting implications for the sources of UHECRs. We also comment on the Auger analysis.Comment: 11 pages, 10 figures, in the International Conference on Topics in Astroparticle and Underground Physics (TAUP) 2007, Sendai, Japan, September 11-15, 200

Electronic structure of strained InP/GaInP quantum dots

We calculate the electronic structure of nm scale InP islands embedded in $Ga_{0.51}In_{0.49}P$. The calculations are done in the envelope approximation and include the effects of strain, piezoelectric polarization, and mixing among 6 valence bands. The electrons are confined within the entire island, while the holes are confined to strain induced pockets. One pocket forms a ring at the bottom of the island near the substrate interface, while the other is above the island in the GaInP. The two sets of hole states are decoupled. Polarization dependent dipole matrix elements are calculated for both types of hole states.Comment: Typographical error corrected in strain Hamiltonia

Behavioral implications of shortlisting procedures

We consider two-stage “shortlisting procedures” in which the menu of alternatives is first pruned by some process or criterion and then a binary relation is maximized. Given a particular first-stage process, our main result supplies a necessary and sufficient condition for choice data to be consistent with a procedure in the designated class. This result applies to any class of procedures with a certain lattice structure, including the cases of “consideration filters,” “satisficing with salience effects,” and “rational shortlist methods.” The theory avoids background assumptions made for mathematical convenience; in this and other respects following Richter’s classical analysis of preference-maximizing choice in the absence of shortlisting