TIME TRAVEL WITHOUT CAUSAL LOOPS

It has sometimes been suggested that backwards time travel always incurs causal loops. I show that this is mistaken, by describing worlds where backwards time travel occurs and yet no causal loops occur. Arguments that backwards time travel can occur without causal loops have been given before in the literature, but I show that those arguments are unconvincing.     

Short-term gains, long-term pains: How cues about state aid learning in dynamic environments

Successful investors seeking returns, animals foraging for food, and pilots controlling aircraft all must take into account how their current decisions will impact their future standing. One challenge facing decision makers is that options that appear attractive in the short-term may not turn out best in the long run. In this paper, we explore human learning in a dynamic decision making task which places short- and long-term rewards in conflict. Our goal in these studies was to evaluate how people’s mental representation of a task affects their ability to discover an optimal decision strategy. We find that perceptual cues that readily align with the underlying state of the task environment help people overcome the impulsive appeal of short-term rewards. Our experimental manipulations, predictions, and analyses are motivated by current work in reinforcement learning which details how learners value delayed outcomes in sequential tasks and the importance that “state” identification plays in effective learning.     

Performance,cardiovascular, and health behavior effects of an inhibitory strength training intervention

Female undergraduates were assigned to one of three groups, two involving regulatory training and one not. Training participants performed for 2 weeks tasks that required strong behavioral restraint (Strong Training) or weak behavioral restraint (Weak Training). Later, they took part in (1) a laboratory session in which they performed tasks with inhibitory components, and (2) a follow-up week in which they provided health behavior reports and used designated dental supplies. No Training participants took part only in the session and follow-up week. As expected, laboratory performance was improved for Strong- relative to No Training participants, with performance for Weak Training participants falling in between. Also as expected, Strong Training participants used more floss in the follow-up week than did the No Training participants, with floss for Weak Training participants falling between. Contrary to expectation, Strong Training participants used less toothpaste and reported having brushed less than the No Training participants. In addition, Strong Training participants evinced exaggerated—rather than diminished—cardiovascular responses during the laboratory tasks. The performance and floss use data support the suggestion that inhibitory system strength can be increased through use. The brushing and cardiovascular findings may be interpretable in inhibitory strength terms.     

Reactions to and Desire for Prognostic Testing in Choroidal Melanoma Patients

To determine if choroidal melanoma patients want cytogenetic prognostic information. Ninety-nine choroidal melanoma patients completed a questionnaire regarding their opinions about receiving prognostic information. The perceived usefulness of prognostic information was evaluated in patients who had undergone cytogenetic testing. Depressive symptoms, quality of life, and interest in supportive counseling during test receipt were assessed. Ninety-seven percent of respondents reported that they would have wanted prognostic information at the time of their treatment and 98% of respondents reported that supportive counseling should be offered when prognostic information is given. Patients who had received a more favorable prognostic result were more likely to endorse the usefulness of cytogenetic testing than were patients who had received a less favorable prognostic result. Psychological status did not vary significantly as a function of cytogenetic test result. Prognostic information was important to patients with choroidal melanoma, even in the absence of prophylactic measures which might improve prognosis.     

Navigating through abstract decision spaces: Evaluating the role of state generalization in a dynamic decision-making task

Research on dynamic decision-making tasks, in which the payoffs associated with each choice vary with participants’ recent choice history, shows that humans have difficulty making long-term optimal choices in the presence of attractive immediate rewards. However, a number of recent studies have shown that simple cues providing information about the underlying state of the task environment may facilitate optimal responding. In this study, we examined the mechanism by which this state knowledge influences choice behavior. We examined the possibility that participants use state information in conjunction with changing payoffs to extrapolate payoffs in future states. We found support for this hypothesis in an experiment in which generalizations based on this state information worked to the benefit or detriment of task performance, depending on the task’s payoff structure.     

The kinematics of belief and desire

Richard Jeffrey regarded the version of Bayesian decision theory he floated in ‘The Logic of Decision’ and the idea of a probability kinematics—a generalisation of Bayesian conditioning to contexts in which the evidence is ‘uncertain’—as his two most important contributions to philosophy. This paper aims to connect them by developing kinematical models for the study of preference change and practical deliberation. Preference change is treated in a manner analogous to Jeffrey’s handling of belief change: not as mechanical outputs of combinations of intrinsic desires plus information, but as a matter of judgement and of making up one’s mind. In the first section Jeffrey’s probability kinematics is motivated and extended to the treatment of changes in conditional belief. In the second, analogous kinematical models are developed for preference change and in particular belief-induced change that depends on an invariance condition for conditional preference. The two are the brought together in the last section in a tentative model of pratical deliberation. This paper is one of a pair dedicated to Richard Jeffrey and prepared for a workshop held in his memory at the 26th International Wittgenstein Symposium. My thanks to the organisers of, and the participants in, this workshop and to two anonymous referees for their comments.