Hedging in Field Theory Models of the Term Structure

We use path integrals to calculate hedge parameters and efficacy of hedging in a quantum field theory generalization of the Heath, Jarrow and Morton (HJM) term structure model which parsimoniously describes the evolution of imperfectly correlated forward rates. We also calculate, within the model specification, the effectiveness of hedging over finite periods of time. We use empirical estimates for the parameters of the model to show that a low dimensional hedge portfolio is quite effective.Comment: 18 figures, Invited Talk, International Econophysics Conference, Bali, 28-31 August 200

All-or-none subprocesses in the learning of complex sequences

This paper reports a study designed to investigate whether the all-or-none conception of the learning process can be extended to a learning task more complex than conditioning or simple verbal association. The experimental task is to learn numerical sequences by anticipating each new member of the sequences. Although the obtained sequence learning appears very complex, it proves to be analyzable into constituent all-or-none subprocesses.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/33219/1/0000609.pd

Positive forgetting: The noninterference of Items intentionally forgotten

Efficient remembering is clearly related to efficient forgetting: information no longer needed must be prevented from interfering proactively with the handling of new information. This paper reports three paired-associate probe experiments designed to assess whether Ss could take advantage of a signal to forget some or all of the pairs presented prior to the signal. As it turns out, the effects of a forget signal are considerable: to-be-forgotten pairs do not inferfere at all with the recall of to-be-remembered pairs. A theory of intentional forgetting is proposed that assumes Ss (a) organize the remember items into a grouping that functionally separates them from the forget items and (b) devote all rehearsal activities following the forget instruction to the remember items.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/32745/1/0000114.pd

Recency-sensitive retrieval processes in long-term free recall

In several experiments, each presentation of a to-be-remembered item in a free-recall list was both preceded and followed by a distracting activity and recall was delayed by an additional period of distracting activity. Pronounced long-term effects of recency were obtained, the standard short-term memory interpretation of recency effects in free recall notwithstanding. The results are interpreted as reflecting retrieval processes that are obscured by procedural characteristics of typical free-recall experiments.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/22374/1/0000823.pd

Nitrogen restricts future sub-Arctic treeline advance in an individual-based dynamic vegetation model

Arctic environmental change induces shifts in high-latitude plant community composition and stature with implications for Arctic carbon cycling and energy exchange. Two major components of change in high-latitude ecosystems are the advancement of trees into tundra and the increased abundance and size of shrubs. How future changes in key climatic and environmental drivers will affect distributions of major ecosystem types is an active area of research. Dynamic vegetation models (DVMs) offer a way to investigate multiple and interacting drivers of vegetation distribution and ecosystem function. We employed the LPJ-GUESS tree-individual-based DVM over the Torneträsk area, a sub-Arctic landscape in northern Sweden. Using a highly resolved climate dataset to downscale CMIP5 climate data from three global climate models and two 21st-century future scenarios (RCP2.6 and RCP8.5), we investigated future impacts of climate change on these ecosystems. We also performed model experiments where we factorially varied drivers (climate, nitrogen deposition and [CO2]) to disentangle the effects of each on ecosystem properties and functions. Our model predicted that treelines could advance by between 45 and 195 elevational metres by 2100, depending on the scenario. Temperature was a strong driver of vegetation change, with nitrogen availability identified as an important modulator of treeline advance. While increased CO2 fertilisation drove productivity increases, it did not result in range shifts of trees. Treeline advance was realistically simulated without any temperature dependence on growth, but biomass was overestimated. Our finding that nitrogen cycling could modulate treeline advance underlines the importance of representing plant-soil interactions in models to project future Arctic vegetation change

The spacing effect: Consolidation or differential encoding?

Theoretical explanations of the spacing effect fall into two classes: those that attribute the advantage of two spaced presentations over two massed presentations to better consolidation of the first presentation, and those that attribute the advantage to better encoding of the second presentation. This paper reports an experimental test of the two classes of theory. Rather than manipulate spacing, the experiment varied the information processing difficulty of the activity interpolated between two presentations of an item. Consolidation-type theories imply decreasing consolidation with increasing difficulty of the interpolated activity. In fact, recall performance following two presentations separated by a difficult task was found to be slightly but consistently better than performance following two presentations separated by an easy task. The outcome thus favors encoding-type theories.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/32691/1/0000058.pd

The interaction of encoding and rehearsal processes in the recall of repeated and nonrepeated items

Experiments were designed to clarify the influence of level of processing on the recall of once-presented items and to determine whether spacing effects for repeated items result from differential processing of the second presentation. In a modified Brown-Peterson paradigm, the lengths of distractor-filled spacing and retention intervals were varied, and subjects were cued to rehearse each presentation of five-word pentads in either a primary (rote) or secondary (elaborative) fashion. Type of rehearsal had large and systematic effects, but the pattern of spacing effects was inconsistent with that predicted by a processing interpretation. An alternative theory, in which type of processing is assumed to interact with encoding variability, seems consistent with the results.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/22126/1/0000553.pd

Recall and recognition as a function of primary rehearsal

Three free-recall experiments were motivated by the common-sense notion that an item should be better remembered and less easily forgotten the greater the rehearsal devoted to the item. In each experiment, four lists of words were presented and a cue to remember or to forget was presented after each word in a list in turn. Before each cue was presented, however, there was a variable blank period during which subjects were required to hold the current word in memory. Immediate and final recall of to-be-remembered and to-be-forgotten words were essentially independent of amount of rehearsal, whereas final recognition increased systematically with rehearsal. The results suggest the need for a distinction between rehearsal as a maintenance activity and rehearsal as a constructive activity.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/33768/1/0000020.pd

Feedback at Test Can Reverse the Retrieval-Effort Effect

The testing effect refers to the finding that retrieving previously encoded material typically improves subsequent recall performance more on a later test than does restudying that material. Storm et al. (2014) demonstrated, however, that when feedback is provided on such a later test the testing advantage then turns to a restudying advantage on subsequent tests. The goal of the present research was to examine whether there is a similar consequence of feedback when the difficulty of initial retrieval practice is modulated. Replicating prior research, we found that on an initial delayed test, recall of to-be-learned items was better following difficult than easy practice. Critically, however, providing immediate feedback on an initial delayed test reversed this pattern. Our findings are consistent with a distribution-based interpretation of how feedback at test modifies recall performance