Belief revision,epistemic conditionals and the Ramsey test

Epistemic conditionals have often been thought to satisfy the Ramsey test (RT): If A, then B is acceptable in a belief state G if and only if B should be accepted upon revising G with A. But as Peter Gärdenfors has shown, RT conflicts with the intuitively plausible condition of Preservation on belief revision. We investigate what happens if (a) RT is retained while Preservation is weakened, or (b) vice versa. We also generalize Gärdenfors' approach by treating belief revision as a relation rather than as a function.In our semantic approach, the same relation is used to model belief revision and to give truth-conditions for conditionals. The approach validates a weak version of the Ramsey Test (WRR) — essentially, a restriction of RT to maximally consistent belief states.We prove that alternatives (a) and (b) are both consistent, but argue that (b) is philosophically more promising. Gärdenfors' belief-revision axioms are compatible with WRR together with RT from left to right: the only direction of the test that is defensible on intuitive grounds.An earlier version of this paper was presented at the conference on the dynamics of knowledge and belief at Lund University, 24–26 August 1989. We wish to thank Sven Danielsson, Peter Gärdenfors, Sören Halldén, David Makinson, Hugh Mellor, Michael Morreau, Nils-Eric Sahlin and Brian Skyrms for their very helpful suggestions and remarks. We are also grateful for thought-provoking criticism and comments from two anonymous referees.     

A MODERN LOOK AT THE ORIGIN OF THE UNIVERSE

Abstract. In what follows, I review the modern theory of the origin of the universe as astronomers and physicists are coming to understand it during the last decades of the twentieth century. An unexpected discovery of this study is that the story of "cosmogenesis" cannot be completely told unless we understand the fundamental nature of matter, space, and time. In the context of modern cosmology space has become not only the bedrock (so to speak) of our physical existence, it may yield a fuller understanding of the universe itself.     

Interhemispheric transfer of lever pressing as stimulus generalization of the effects of spreading depression

Rats trained to lever-press with spreading depression in one cerebral hemisphere showed weak responding when tested with depression shifted to the trained hemisphere. The rats were then divided into two groups: one group (normal) was permitted a single reinforced response with neither hemisphere depressed, the other group (depressed) was permitted a single reinforced response with the trained hemisphere depressed; both groups were then tested with the trained hemisphere depressed. Responding during this second test increased for both groups, but the magnitude of the increase tended to be greater for the depressed than for the normal group. Since memory transfer could not have occurred with the trained hemisphere depressed, the results were taken to indicate that the single reinforced response strengthened stimulus generalization between train-test conditions.     

A PARADOX IN THE PERCEPTION OF LUMINANCE GRADIENTS. I

Under certain conditions subjects looking at a luminance gradient report a physically darker part of the gradient to be brighter than an adjacent area of higher luminance. This brightness paradox was studied in a series of experiments using a magnitude estimation method. The main results were that both the changing sign of the second derivative of the luminance function (Mach's hypothesis) and the higher or lower luminance of an adjacent area (McDougall's drainage theory) are critical conditions for the appearance of the paradox. In the present study none of these conditions per se resulted in a brightness paradox.     

THE EQUIVALENCE COEFFICIENT AND THE KUDER-RICHARDSON COEFFICIENT 20

H enrysson , S. The equivalence coefficient and the Kuder-Richardson coefficient 20. Scand. J. Psychol ., 1962, 3 , 40–46.—The relation between the equivalence coefficient and the Kuder-Richardson coefficient 20 is discussed. Formulas, tables and graphs of the difference between the two coefficients are given. In most cases the difference between the two coefficients will be rather small.     

Reinforcement and substitution in humans: a multiple-response analysis

Three adult human subjects engaged in activities such as reading, sewing, artwork, and candlemaking while living alone in a laboratory apartment 24 hours per day for several weeks. After a baseline period in which the activities were fully available, access to a particular activity (contingent response) was made dependent on engaging in another less-preferred activity (instrumental response). The contingencies produced substantial increases in instrumental responding, and responding decreased toward baseline levels when the dependency was removed. Under the contingent conditions, time earned for the concurrent activity was always less than the baseline level. To determine the contribution of this reduction to the instrumental increase, access to the contingent activity was restricted in the absence of any dependency. The results indicated that increases among responses that filled the newly available time could be selective, e.g., artwork increased when reading was restricted but candlemaking did not. It was concluded that the reductions in the contingent response that accompany contingencies usually do not exclusively determine instrumental increases, but selective increases can contribute to the increase in time devoted to the instrumental response.     

Regional cerebral blood flow and verbal memory after chronic exposure to organic solvents

Regional cerebral blood flow (rCBF; 133Xe-inhalation method) was investigated in 32 industrial workers (age: 51 +/- 9 years) who had been exposed to organic solvents during an average of 24.5 years. The measurements were made at rest and during learning of associated word pairs. The resting flow level was 17% lower than expected for normal subjects of similar age and the activation-induced changes of rCBF during the test lacked the frontal activation normally seen. Significant correlations between age, length of exposure, and rCBF level were found. In order to control for the age factor, results were also calculated from two subgroups of similar age but with very different levels of exposure (13 and 31 years of average exposure). The two groups differed only slightly in resting rCBF. A marked difference was, however, seen during activation, with significant post-central flow increases recorded in the lower-exposed group only. The results indicate the potential of the rCBF method for elucidating functional cortical changes related to neurotoxic effects of organic solvents.     

Observational goals and schema activation: A theoretical framework for behavior perception

A framework for behavioral observation is described in which the processing of a stream of behavior is influenced by an individual's prior knowledge about behavior, organized into cognitive “schemas.” It is proposed that observational goals determine the selection of goal-relevant schemas which, in turn, influence the observer's processing of an actor's behavior. Subjects watched a series of videotaped sequences featuring a female actor with instructions either to form an impression of her or to remember the details of the tasks she engaged in. They were then asked to answer questions that were either consistent or inconsistent with these instructions. Subjects were also instructed to unitize the actions or events that occurred in the sequence (D. A. Newtson, Journal of Personality and Social Psychology, 1973, 28 28–38). According to the unitizing measure, subjects observing with different goals attended to different behavioral features. Further, impression-forming subjects were apparently more influenced by their implicit theories of personality than were task-learning subjects when asked to give ratings of the actor's personality, and task-learning subjects were relatively more accurate in recalling task-related details. Implications of this framework and these results for research in behavioral unitization and implicit personality theory are discussed.