A rectangular figure moving horizontally at a constant speed shows a decrease in its perceived length parallel to the direction of movement. This study concerns the effect of the luminance relationship between figure and background upon this phenomenon. The perceived length in a stationary state was also measured for different exposure times corresponding to the speeds used, in order to obtain the relative difference between the perceived length of a figure in a stationary state and that of the figure in a dynamic state. Three linear figures of 1.5°, 3°and 6°were used; all of them had a constant height of 0.25°. The stimulus figure was attached to a horizontally moving belt. Speeds of 28°/s, 35°/s and 42°/s were used. The points of subjective equality of the stimulus figures were obtained by the method of limits. Eight students served as subjects. The same reduction tendencies were shown at the different speeds despite the different luminance relationships.
Illumination of a cross-shaped pattern composed of five black to white squares on a white background was varied over 2.6 log units. The task given to 10 Ss was to make achromatic color namings and to make numerical judgments of lightness for each of the five squares in the cross as well as the background. Achromatic color constancy was almost perfect for the region of the highest contrast ratio of surround to focal luminance and less perfect for the regions with lower contrast ratios. Lightness judgments were found to change as a curvilinear function (concave downward) for a log transformation of illumination. Linearly decreasing functions were exceptional. It can be concluded, therefore, that the theoretical claim for the generality of negative functions for lightness-illumination relationships should be reconsidered.
Pigeons were trained on PAN ambiguous-cue problems which involved three stimuli: a positive stimulus, a negative stimulus, and an ambiguous stimulus, to which responding was sometimes reinforced and sometimes nonreinforced depending on the paired stimulus. All subjects attained higher level of performance in terms of correct response on the trials where the ambiguous stimulus was paired with the negative stimulus than on the trials where the ambiguous stimulus was paired with the positive stimulus. This result could be interpreted by the interfering effect ascribed to the positive property of the ambiguous stimulus. It was, however, found that level of performance in terms of latencies of correct responses differed markedly between the types of problems: that is, responses to A stimulus on NA trials had longer latencies than those to P on PA trials. This finding suggests some interfering effect of alternative property of the ambiguous stimulus, the negative property, which can be detected by measuring response latencies.