Browsing by Author "Hunt, Christopher"
Now showing 1 - 3 of 3
Results Per Page
Sort Options
Item Heightened Sensitivity to Improbable Catastrophes As a Pathogenic Marker of Obsessive-Compulsive Disorder: Theory and Experimental Evidence(2021-09) Hunt, ChristopherAlthough the obsessions implicated in obsessive compulsive disorder (OCD) could theoretically involve any distressing topic, they typically gravitate toward a handful of specific themes (e.g., contamination, religion, sex, etc.). The universality of these themes across OCD patients from different time periods, cultures, and age-groups suggests they are manifestations of a common, underlying process, but little effort has been made to elucidate the identity of this process. One intriguing feature shared across most common obsessions is a heightened concern with consequences that are objectively terrible but highly unlikely (e.g., catching HIV from a door knob, being sent to hell for a fleeting immoral thought). The ubiquity of this particular consequence suggests that OCD may be characterized by an underlying sensitivity to improbable catastrophes (SIC), but this possibility has yet to be explored. The present dissertation sought to address this gap by examining whether OCD symptoms predicted higher anxious reactivity toward unlikely, highly aversive threats across three experimental studies. In the first study, college students with higher OCD symptoms exhibited greater avoidance of improbable, highly aversive threats, as well as greater expectancy and physiological reactivity for improbable threats in general. An extension of this investigation with different types of experimental threats (study two) showed that OCD symptoms predicted heightened expectancy of improbable threats involving both harmful and disgust-related consequences, while relations between OCD symptoms and avoidance of improbable, highly aversive consequences were specific to harmful threats. Finally, study three showed that differences in expectancy, anxiety, and avoidance for improbable threats prospectively predicted changes in OCD symptoms over the first year of college, with indices of anxious reactivity to improbable threat (anxiety, startle, avoidance) emerging as especially predictive among participants who rated the threat as highly aversive. Together, these studies implicate SIC as a novel pathogenic marker of OCD, and suggest its role in the illness may derive from a more general tendency to overestimate the likelihood of improbable outcomes bearing high subjective costs.Item Rock-magnetic proxies of climate change in the loess-palaeosol sequences of the western Loess Plateau of China(Geophysical Journal International (Oxford University Press), 1995) Hunt, Christopher; Banerjee, Subir; Han, J.=M.; Solheid, Peter; Oches, E.A.; Sun, Wei-wei; Liu, T.-S.Results of the first detailed study of the climate proxy record in the loess-palaeosol sequence at Xining—one of the few palaeoclimate sites in the currently arid western Loess Plateau of China—illustrate the importance of making many types of rock-magnetic measurements other than susceptibility. A multiparameter approach yielded confirmation that here, as elsewhere in the Loess Plateau, the susceptibility enhancement in palaeosols was caused primarily by ultrafine magnetite and maghaemite. Nevertheless, magnetic enhancement was caused not exclusively by changes in relative grain size, but also by variations in concentration and mineralogy of the magnetic fraction. The effects of concentration variations were removed through normalization of susceptibility and anhysteretic remanence with saturation magnetization and saturation remanence, respectively. The resulting signal was ascribed more confidently to variation in magnetic grain size, which in turn was interpreted as a better proxy of pedogenesis than simple susceptibility. Variations in magnetic mineralogy were also determined to constrain interpretations further. The data were then used to discuss climate history at Xining. Finally, results from Xining were compared with other western sites and contrasted with eastern sites. In summary: (1) data is presented from a new Loess Plateau site which also appears to yield a global climate signal; (2) a demonstration is made of a more rock-magnetically robust way to separate concentration, composition and grain-size controls on susceptibility and other magnetic parameters; and (3) models are provided for inter-regional comparisons of palaeoclimate proxy records.Item Separation of local signals from the regional paleomonsoon record of the Chinese Loess Plateau: A rock-magnetic approach(Geophysical Research Letters (American Geophysical Union), 1993) Banerjee, Subir; Hunt, Christopher; Liu, Xiu-MingWe propose a method based on thermal unblocking of low-temperature saturation remanent magnetization for a quantitative estimation of the superparamagnetic [Cullity, 1972] fraction (size, d < 30 nm) of magnetite produced by pedogenesis in the Chinese loess plateau [Liu, 1988]. We applied this method to the proxy climatic records of the last 130 ka from two sites 250 km apart, but separated by the mountain range Liupan-shan. Xifeng to the east (35.7°N, 107.6°E) and Baicaoyuan to the west (36.2°N, 105.0°E) currently have humid and arid microclimates, respectively. As expected, the superparamagnetic fraction increases during known warm temperature intervals at each site. Furthermore, the more humid site clearly has higher overall superparamagnetic fractions during most of the last 130 ka. However, during the period 5 to 10 ka ago, the relative humidity at both sites was the same within experimental errors. Bulk grain size evidence confirms the magnetic data, and we suggest that the present easterly summer monsoon in China came from a more southerly direction during this time to flow parallel to Liupan-shan, resulting in very similar summer humidity at Xifeng and Baicaoyuan.