A mathematical model which compares the process of stimulus discrimination to a signal measuring system is proposed and partially evaluated in four experiments. Within this system, response variability is partitioned into two parts, a stimulus component and a component due to variation in the psychological scale. The stimulus component depends on the particular stimulus but not on other stimuli in the set. The other component is shown to be directly proportional to the physical range over which criteria vary. When this subjective or criterial range is small, the measurement error contributed by this component is expected to be small. But when the criterial range is large, when the psychological scale must be magnified to fit a larger range which is to say the same thing, there is a corresponding magnification of the measurement error. This system, which predicts the findings of channel capacity, can be viewed as a physical measuring instrument with the scale to which the instrument is set as the primary determinant of resolution. The studies reported show that this range which affects resolution is not the physical range over which stimuli can vary but is related to the subjective range over which decisions must vary.

Although the 'oblique effect' (poorer performance on oblique orientations as compared to performance on vertical and horizontal orientations) is generally understood as a strictly visual phenomenon, a haptic oblique effect occurs for blindfolded subjects required to set a stimulus rod by hand. Because oblique effects are often attributed to the observer's experience with a predominantly horizontal and vertical environment, we assessed the effect of visual and haptic experience by providing subjects with modality-specific inspection periods to familiarize them with the more poorly judged obliques. Oblique error was significantly reduced in magnitude for judgments made by the modality of experience, and for judgments made across modalities. Rate of improvement, consistency of transfer, and the subjective reports of subjects indicate that this haptic oblique effect is more strongly influenced by visual experience and imagery than by haptic experience. It need not be interpreted as an effect based on factors intrinsic to the haptic modality.

This study examined the relationship between degree of visual loss and depression in male veterans over age 60, while controlling for the influences of general health and age. No relationship was established between visual loss and depression. However, self-reports of poor health were found to be a significant predictor of depression in this population.