QuestPlus: A MATLAB Implementation of the QUEST+ adaptive Psychometric Method

QuestPlus is a MATLAB implementation of the QUEST+ adaptive psychometric method. It provides a rapid and flexible method of estimating the parameters of a psychophysical model, and is also capable of advising the user on the most appropriate stimuli to present, and on when to terminate testing. Of particular note is the algorithm’s ability to use prior information, its ability to determine the maximally informative stimulus on each trial, its ability to fit arbitrarily complex models, and its ability to vary multiple stimulus properties simultaneously

A tutorial on cue combination and Signal Detection Theory: Using changes in sensitivity to evaluate how observers integrate sensory information

Many sensory inputs contain multiple sources of information (‘cues’), such as two sounds of different frequencies, or a voice heard in unison with moving lips. Often, each cue provides a separate estimate of the same physical attribute, such as the size or location of an object. An ideal observer can exploit such redundant sensory information to improve the accuracy of their perceptual judgments. For example, if each cue is modeled as an independent, Gaussian, random variable, then combining Ncues should provide up to a √N improvement in detection/discrimination sensitivity. Alternatively, a less efficient observer may base their decision on only a subset of the available information, and so gain little or no benefit from having access to multiple sources of information. Here we use Signal Detection Theory to formulate and compare various models of cue-combination, many of which are commonly used to explain empirical data. We alert the reader to the key assumptions inherent in each model, and provide formulas for deriving quantitative predictions. Code is also provided for simulating each model, allowing expected levels of measurement error to be quantified. Based on these results, it is shown that predicted sensitivity often differs surprisingly little between qualitatively distinct models of combination. This means that sensitivity alone is not sufficient for understanding decision efficiency, and the implications of this are discussed

End-point of the rp process and periodic gravitational wave emission

The general end-point of the rp process in rapidly accreting neutron stars is believed to be a surface distribution of matter whose nuclear composition may depend on position. Its evolution during compression beyond the neutron-drip threshold density is determined by the presence of nuclear formation enthalpy minima at the proton closed shells. At threshold, a sequence of weak interactions with capture or emission of neutron pairs rapidly transform nuclei to the most accessible proton closed shell. Therefore, angular asymmetries in nuclear composition present in accreted matter at neutron drip are preserved during further compression to higher densities provided transition rates between closed shells are negligible. Although it has been confirmed that this condition is satisfied for predicted internal temperatures and for the formation enthalpy distribution used in this work, it would not be so if the true enthalpy differences between maxima and minima in the distribution were a factor of two smaller. For this reason, it does not appear possible to assert with any confidence that position-dependent surface composition can lead to significant angle-dependence of the equation of state and to potentially observable gravitational radiation. The effect of non-radial internal temperature gradients on angle-dependency of the equation of state is also not quantifiable.Comment: This version corrects a major error in estimating the effect of composition asymmetry on the equation of state. Its conclusions are less definite than those of the previous version. 9 pages RevTex; 1 figure. To be published in Phys. Rev.

Sigurd Lewerentz: Church of St Peter, Klippan, 1963–66

This modest building questions basic assumptions about processes and finishes, about the nature of brickwork and the detailing of window frames – and provides a powerful space for worship