Successive luminance difference thresholds and brightness as a function of the interstimulus interval and durations of successive flashes

Monocular,successive luminance difference thresholds (ΔI) and brightness matches (PSE) were obtained by the method of constant stimuli for two flashes successively presented to the same retinal area. Variations in interstimulus interval first-flash duration,and second-flash duration were the independent variables investigated. ΔI decreased as a function of ISI,while PSE remained relatively uninfluenced. An intensity-duration reciprocity was observed with increases in either first- or second-flash duration. Equal increases in duration of both flashes led to a constant value of ΔI. A Broca-Sulzer effect was also noted. In another study, a 10-msec, variable-luminance Standard was followed after 500 msec by either a 10-msec or a 320-msec test flash that was compared to the Standard. The results indicated that the rate of change of brightness with changes in luminance of the Standard was faster for the 10-msec flash than for the 320-msec flash. The rate-of-change hypothesis would predict that the 10-msec flash should have the smaller ΔI. The results for two Ss indicated the opposite: AI was smaller for 320-msec than for 10-msec flashes. A modification of the hypothesis was suggested such that it may be the energy increment (Δlt) required for detection that is related to the rate at which brightness changes with energy.     

The effects of amount of training per reversal on successive reversals of a color discrimination

Three groups of pigeons were trained on a red-green discrimination in which the stimuli were alternately presented in a multiple schedule of reinforcement. The discrimination was reversed 24 times. Groups were given 1, 2, or 4 hr of training on each discrimination. Increasing the length of training had two principal effects on reversal performance: it increased the rate of extinction of responding to one of the stimuli and increased the rate of reacquisition of responding to the other. The latter effect involved both an increase in reacquisition of responding to a positive stimulus within reversals and an increase in recovery of responding to the previous negative stimulus between reversals. Improvements in performance of each group over the series of reversals were qualitatively similar to the two effects of length of training on each discrimination, and were analogous to effects obtained in other studies involving overtraining and successive reversals of simultaneous discriminations.     

Orthogonal rotation algorithms

The quartimax and varimax algorithms for orthogonal rotation attempt to maximize particular simplicity criteria by a sequence of two-factor rotations. Derivations of these algorithms have been fairly complex. A simple general theory for obtaining two factor at a time algorithms for any polynomial simplicity criteria satisfying a natural symmetry condition is presented. It is shown that the degree of any symmetric criterion must be a multiple of four. A basic fourth degree algorithm, which is applicable to all symmetric fourth degree criteria, is derived and applied using a variety of criteria. When used with the quartimax and varimax criteria the algorithm is mathematically identical to the standard algorithms for these criteria. A basic eighth degree algorithm is also obtained and applied using a variety of eighth degree criteria. In general the problem of writing a basic algorithm for all symmetric criteria of any specified degree reduces to the problem of maximizing a trigonometric polynomial of degree one-fourth that of the criteria.This research was supported by the Bell Telephone Laboratories, Murray Hill, New Jersey and NIH Grant FR-3.