Practical Arguments for Theoretical Theses

Pascals wager is expounded as a paradigm case of a practical,decision-theoretical argument for acting as if a proposition is true when wehave no theoretical reasons to accept or reject it (1.1.–1.2.). Thoughthe paradigm is fallacious in various respects there are valid and adequatearguments for acting as if certain propositions are true: that theoreticalentities exist, that there are material perceptual objects, that the worldis uniform across time (1.3). After this analysis of examples the authorsgeneral approach for developing criteria for the validity and adequacy oftypes of argument (2.1.) is applied: Having discussed some problems(2.2.–2.3.), a general epistemic principle for such pascal argumentsis developed, which characterizes their premisses and, if introduced as anadditional premiss, can make them deductively valid (2.4).     

WHAT IT FEELS LIKE TO BE IN A SUPERPOSITION. AND WHY

This paper attempts an interpretation of Everett's relative state formulation of quantum mechanics that avoids the commitment to new metaphysical entities like worlds or minds. Starting from Everett's quantum mechanical model of an observer, it is argued that an observer's belief to be in an eigenstate of the measurement (corresponding to the observation of a well-defined measurement outcome) is consistent with the fact that she objectively is in a superposition of such states. Subjective states corresponding to such beliefs are constructed. From an analysis of these subjective states and their dynamics it is argued that Everett's pure wave mechanics is subjectively consistent with von Neumann's classical formulation of quantum mechanics. It follows from the argument that the objective state of a system is in principle unobservable. Nevertheless, an adequate concept of empirical reality can be constructed.     

Disparity-processing in Wilde's dot-row phenomenon

Summary In this investigation on Wilde's phenomenon vertical lines were used instead of dots. In three experiments it was found that for the occurrence of Wilde's phenomenon, it is a necessary condition that the distances between all lines including the monocular end-lines are equal. When this is not the case the Panum effect is observed. When the distance between the end-line and its adjacent line deviates slightly from the distance between the central lines, one observes apparent rotation and a Panum effect. The observed depth of the end-line is in accordance with its disparity. The observed rotation is less than can be expected from the position in depth of the end-line. The disparity of the end-line is fully processed. Part of its disparity is used for apparent rotation of the pattern, and part of it is used for a displacement of the whole pattern.     

The array size function in simple visual search tasks: A comparison between “go-no go” and “yes-no” tasks under conditions of high and low target-noise similarity

Summary In research on visual search within a single eye-fixation a number of different tasks are used and referred to interchangeably. Research with other types of tasks suggests that there are possibly important differences between these tasks. In the present study, two types of search tasks were compared under conditions as equal as possible: the go-no go task and the yes-no task. Conditions of low and high target-noise similarity were used. The results obtained showed: a) a steeper slope of the array size function in yes-no tasks than in go-no go tasks on the first day of practice but not on the second: b) a higher intercept value of the same function for yes-no tasks than for go-no go tasks; and c) a greater proportion of errors with yes-no tasks than with comparable go-no go tasks. A tentative model, describing the main features of the results obtained, is briefly sketched.     

Reading ability and disfluency in stuttering and nonstuttering elementary school children

This study was aimed at comparing the reading abilities of elementary school children who stutter with their nonstuttering peers. Forty-four stuttering children from four grade levels were matched with a group of normally fluent controls on the basis of age, sex, and grade level. Reading ability was assessed by means of three Dutch standardized tests yielding a total of six scores. Disfluency scores during oral reading were also obtained for each subject. Results indicated significant differences between the two groups on reading rate and reading errors, but not on reading comprehension. Analysis of reading errors did not show qualitative differences among subjects: stuttering and nonstuttering children made the same kinds of reading errors. Similarly, the two groups did not differ with respect to performances at different grade levels. Among both groups of subjects performances became better with increasing grade on four of the six measures. Correlational analyses indicated that the measures of reading ability used in this study were significantly associated with frequency of disfluency for the nonstuttering children. In contrast, no significant relationship was found between reading ability and disfluency in the stuttering group, except for reading rate. Results are discussed with respect to the possible interaction between verbal performance and linguistic competence in reading ability measures, particularly for the stuttering child.     

Sources of position-perception error for small isolated targets

It has often been reported that, in the presence of static reference stimuli, briefly presented visual targets are perceived as being closer to the fixation point than they actually are. The first purpose of the present study was to investigate whether the same phenomenon can be demonstrated in a situation without static reference stimuli. Experiment 1, with position naming as the task, showed that such a central shift is also observed under these conditions. This finding is of importance because it completes an explanation for central near-location errors in the partial-report bar-probe task. The second purpose of the present study was to provide an explanation for these central shifts. For this explanation information about the exact size of the central shift is required. In Exps. 2, 3, and 4, with cursor setting as the task, it was attempted to assess more precisely the size of the central shifts. These experiments revealed that two different factors determine the results in cursor setting tasks; a factor “target position” and a factor “cursor position.” Experiment 5 showed that it is the point of fixation, not the fixation point, that serves, at least in part, as the reference point in this type of task. All the findings together allow us to conclude that the target positions are underestimated by about 10%. From vision research it is known that saccadic eye movements, performed for bringing a target in the fovea, also show an undershoot of about 10%. It is therefore concluded that the system in charge of saccadic eye movements also provides the metric in visual space within a single eye fixation. Received: 11 February 1998 / Accepted: 25 June 1998