Superiority of global features in classification and matching

Summary Global superiority refers to the phenomenon that stimuli can be discriminated, classified, and matched faster using a global feature than a local feature. Global superiority has been shown by several authors with forms (global feature) composed of smaller forms (local features) as stimuli. In contrast, the local features used in the present study had about the same spatial extent as the global feature and each local feature was structurally relevant to the global feature. Nevertheless, global superiority was consistently observed in several classification and matching tasks. This result, together with the results of other researchers using different stimulus materials shows that global superiority is a pervasive phenomenon. Under brief exposure durations within the threshold range, local features could, however, be better discriminated than global features. This finding invalidates the perceptual explanation of global superiority that global features are faster extracted and, in this way, become available earlier than local features. Considering the magnitude of the observed differences between classification times and threshold durations of global and local features, it is argued that under normal viewing conditions global features can be better selected and utilized for the given task than local features, and that this advantage by far outweighs the faster feature extraction of local features.This research was supported by Grant Wa 419/3 from the Deutsche Forschungsgemeinschaft     

Illumination change at a depth edge can reduce lightness constancy

Lightness constancy requires that a surface retain its lightness not only when the illumination is changed but also when the surface is moved from one background to another. Occlusion of one surface by another frequently results in a retinal juxtaposition of patches under different illuminations. At such edges, retinal luminance ratios can be much higher than in scenes with a single illumination. We demonstrate that such retinal adjacencies can produce failures of lightness constancy. We argue that they are responsible for departures from perfect lightness constancy in two prior experiments that examined the effects of depth relations on lightness constancy.     

Mesopic lightness,brightness, and brightness contrast

At mesopic mean luminances, a fixed luminance contrast produces less brightness contrast than it does at photopic luminances. This suggests that lightnesses of surfaces might also be altered at low luminances. I measured lightness, brightness, and brightness contrast in CRT simulations of achromatic paper patchworks. The illuminance of the standard pattern was fixed, producing 0.12,1.2, or 12 cd/m². The illuminance on the test pattern was varied in a lightness constancy paradigm. Constant brightness contrast required more luminance contrast at lower mean luminances. Failures of lightness constancy occurred at the lowest mean luminances, but they were minor in comparison with the loss of brightness contrast in the same pattern. These results have implications for imaging applications. Often, image content falls in both the photopic and the mesopic ranges. Our results indicate that brightness contrast may decrease substantially in low-luminance regions without large changes of surface lightness.     

Lightness,brightness, and brightness contrast: 2. Reflectance variation

Changes of annulus luminance in traditional disk-and-annulus patterns can be perceived to be either reflectance or illuminance changes. In the present experiments, we examined the effect of varying annulus reflectance. In Experiment 1, we placed test and standard patch-and-surround patterns in identical Mondrian patchworks. Only the luminance of the test surround changed from trial to triaL., appearing as reflectance variation under constant illumination. Lightness matches were identical to brightness matches, as expected. In Experiment 2, we used only the patch and surround (no Mondrian). Instructions said that the illumination would change from trial to trial. Lightness and brightness-contrast data were identical; illumination gradients were indistinguishable from reflectance gradients. In Experiment 3, the patterns were the same, but the instructions said that the shade of gray of the test surround would change from trial to trial. Lightness matches were identical to brightness matches, again confirming the ambiguity of disk-and-annulus patterns.     

Perceived lightness, but not brightness, of achromatic surfaces depends on perceived depth information

Three experiments were conducted in an attempt to replicate and clarify Gilchrist's (1977, 1980) experiments on the effects of depth information on judgments of achromatic surface color. Gilchrist found that coplanarity, and not retinal adjacency, was the dominant factor in determining achromatic color matches. Because such matches can be made on the basis of either brightness or lightness, we obtained judgments of both qualities. Stereopsis was added to enhance the perceived depth effect of Gilchrist's display, which was otherwise simulated closely on a high-resolution CRT. The results for lightness followed the same pattern as those of Gilchrist, but were smaller in magnitude. This discrepancy may reflect reduced extraneous lighting effects in our displays. Our results therefore agree with related studies in suggesting that lightness matches are based on relationships among coplanar surfaces. Brightness matches, however, were not influenced by perceived depth.     

Nonlocal determination of brightness in spatially periodic patterns

Recent data require nonlinear spatial summation processes in models for detection of spatially periodic and aperiodic patterns. Contrast matching experiments with suprathreshold grating and spot patterns suggest that nonlinear models may be required for suprathreshold contrast data, but differences between the psychophysical tasks used with periodic and aperiodic patterns make comparison difficult. A series of experiments are reported in which subjects matched local brightnesses and brightness differences within single cycles of grating patterns. This task closely resembles the matching task in classical contrast experiments with aperiodic stimuli, allowing comparison of the data from the two types of experiments. Brightnesses within a 5-cycle/degree (c/deg) sinusoidal grating were largely unaffected by addition of a large 15-c/deg modulation component in either of two phases, in spite of the resulting large change in local luminances within the pattern. As at threshold, complex models are required in order to account for apparent differences between spatial interactions within periodic and aperiodic patterns.     

Difference information in brightness perception

Contour information generated by moving retinal images has been shown by others to be the principal determinant of perceived color. The data presented here show that, for brightness, this information reflects only differences between adjacent stimulus areas. The entire distribution of difference information from contours in the visual field must be specified in order to predict the brightness at any point.     

Movement structure in young and elderly adults during goal-directed movements of the left and right arm

Elderly adults often exhibit performance deficits during goal-directed movements of the dominant arm compared with young adults. Recent studies involving hemispheric lateralization have provided evidence that the dominant and non-dominant hemisphere-arm systems are specialized for controlling different movement parameters and that hemispheric specialization may be reduced during normal aging. The purpose was to examine age-related differences in the movement structure for the dominant (right) and non-dominant (left) during goal-directed movements. Young and elderly adults performed 72 aiming movements as fast and as accurately as possible to visual targets with both arms. The findings suggest that previous research utilizing the dominant arm can be generalized to the non-dominant arm because performance was similar for the two arms. However, as expected, the elderly adults showed shorter relative primary submovement lengths and longer relative primary submovement durations, reaction times, movement durations, and normalized jerk scores compared to the young adults.     

The Dutch curve: The introduction and reception of intelligence testing in the Netherlands, 1908–1940

In the Netherlands, intelligence testing has been pragmatic and has not generated the heated controversies found in other cultures. Four historical reasons are presented for this paradoxical development. First, the Binet test was used mainly as a diagnostic instrument for professional judgments about admission to special education. Second, the eugenic use of IQ tests was moderated by the marginal position of eugenics in Dutch society. Third, the process of “pillarization” gave considerable power to denominational groups in Dutch society, and they strongly criticized deterministic ideas about the heredity of intelligence. Fourth, the educational scientist, cognitive psychologist, philosopher, and government adviser, Philip Kohnstamm, was very influential in Dutch science and politics. He rejected intelligence testing and its deterministic connotations in favor of the idea of the educability of cognitive capacities. © 1998 John Wiley & Sons, Inc.