The pastor and his privacy

Pastoral Psychology -     

Shorter articles and notes two more visual theorems

The basis of the widely held opinion that the spectral sensitivities of the mechanisms determining trichromacy must be linearly related to the spectral mixture functions is examined, and a proof from simple assumptions is stated.

It is proved also that, on the van der Velden hypothesis of independent sensitive units, a spatial or temporal summation law of the form AIⁿ = c implies a frequency-of-seeing curve of the form Q = I—e^-KIn (Q = probability of detecting a stimulus of size A and intensity I; n, c and K are constants).     

Studies in olfactory acuity. II.: Relative detectability of n-aliphatic alcohols by the rat

The ability of albino and black rats to detect n-aliphatic alcohols in the vapour phase has been investigated and probit analysis used to evaluate the results. At median threshold (= 50 per cent, success level) detectability tends to increase by logarithmic increments as the number of carbon atoms in the molecule is increased. However, a similar but reverse relationship occurs between carbon chain length and the gradient of the probit regression lines; and detectability at the 85 per cent. success level, as estimated by interpolation, shows a trend towards oscillation. It is suggested that this finding can resolve the apparent conflict in the literature concerning the pattern of odour intensity in homologous series, and that it may reflect the influence of low water solubility in limiting response to high concentrations of longer chain alcohols.

When expressed as pressures, median threshold values for alcohols in the rat vary directly with saturated vapour pressures; when expressed as thermodynamic activities intermediate and longer chain alcohols appear to be equally stimulating, whilst short chain alcohols show decreasing activities as the series is ascended. In several of the relations considered the position of methanol and dodecanol appears anomalous.     

Choice reaction times for skilled responses

Two kinds of choice reaction time experiments are reported, both of which make use of a highly overlearned sensori-motor response. When a response is required for each stimulus presented, no increase in reaction time occurs as a function of the number of alternative stimuli available. It is proposed that the increase in choice reaction times commonly thought to accompany an increase in the number of alternative choices provided reflects the unpractised state of the responder. When a response is required for only one out of n possible stimuli, a slight but consistent increase in reaction time takes place with an increase in the number of alternatives. An analogy is drawn between the second experiment and a vigilance task and an expectancy hypothesis is invoked to explain the results.