Statistical methods for absorbing Markov-chain models for learning: Estimation and identification

General algorithms for computing the likelihood of any sequence generated by an absorbing Markov-chain are described. These algorithms enable an investigator to compute maximum likelihood estimates of parameters using unconstrained optimization techniques. The problem of parameter identifiability is reformulated into questions concerning the behavior of the likelihood function in the neighborhood of an extremum. An alternative characterization of the concept of identifiability is proposed. A procedure is developed for deciding whether or not this definition is satisfied.This research was undertaken within the Institute for the Study of Intellectual Behavior, University of Colorado, and is Publication No. 42 of the Institute. The work was supported by NSF Grant GB-34077X. The logic underlying Algorithm I was suggested by Clint Schumacher.     

Determination of CIE chromaticity coordinates of colored lights produced by a projection color mixer

A procedure for measuring the CIE chromaticity coordinates which avoids some of the problems encountered with the method reported by Murch (1972) is described.     

Detection of temporal gaps within and between perceptual tonal groups

Two experiments were conducted to explore the hypothesis that tones widely separated in frequency are processed in separate communication channels. Listeners attempted to detect brief temporal gaps between items in a simple tonal sequence of two high tones followed by two low tones. Temporal resolution within both the high and low groups was near perfect; between-group detection scores were significantly lower. Results are interpreted as evidence for a processing time delay when shifts of focal attention occur between perceptual structures organized within the frequency domain.     

Some acute effects of d-lysergic acid diethylamide on the rat

There is a wealth of literature available on the psychosis-like effects of very small doses of d-lysergic acid diethylamide (LSD-25) in human subjects. It is reported that the drug produces profound changes in emotional behaviour, feelings of depersonalization, visual and auditory hallucinations, catharsis-like episodes and slight changes in autonomic nervous system activity.

The present experiment investigates the possibility of relating the behavioural disturbances induced by LSD-25 to known physiological data. Variation in the latency and running times of trained albino rats is examined. It is demonstrated that latency scores are directly affected by the cerebral concentration of the drug; and that sensory thresholds appear to be raised. It is further shown that when the level of stimulation is raised the rats appear to behave normally.     

The effect of repetition of items on two phases of paired associate learning

An investigation is reported in which the effect of repetition of items on two learning tasks is determined. These tasks are considered to be analogous to the response-learning and associative phases of paired associate learning. The findings tend to support the hypotheses under investigation, that response learning is an all-or-none occurrence and that the associative phase may be explained by the dual factor hypothesis.     

The Brier Rule Is not a Good Measure of Epistemic Utility (and Other Useful Facts about Epistemic Betterness)

Measures of epistemic utility are used by formal epistemologists to make determinations of epistemic betterness among cognitive states. The Brier rule is the most popular choice (by far) among formal epistemologists for such a measure. In this paper, however, we show that the Brier rule is sometimes seriously wrong about whether one cognitive state is epistemically better than another. In particular, there are cases where an agent gets evidence that definitively eliminates a false hypothesis (and the probabilities assigned to the other hypotheses stay in the same ratios), but where the Brier rule says that things have become epistemically worse. Along the way to this ‘elimination experiment’ counter-example to the Brier rule as a measure of epistemic utility, we identify several useful monotonicity principles for epistemic betterness. We also reply to several potential objections to this counter-example.