- [Show abstract] [Hide abstract] ABSTRACT: What governs the degree of perceived transparency? Can it be related to physical properties of filters, such as reflectance from the front surface, or transmittance through the absorptive media? Achromatic backgrounds composed of random sized, overlapping ellipses were generated on a CRT. Two neutral density filters were simulated as moving on top of this surface. The standard filter was fixed in reflectance and transmittance, and observers adjusted the test filter so that the two appeared equally transparent (if possible). In one set of conditions, the test filter had a fixed reflectance and observers adjusted transmittance. In the other set, the test filter had a fixed transmittance and observers adjusted reflectance. Trials from both conditions were randomly interleaved and the observer was not informed whether reflectance or transmittance was adjustable. Results showed that: (1) When the fixed parameters of the two filters were set to be equal, observers adjusted the variable parameter to also be equal. (2) When the reflectances of the two filters were fixed at values differing up to 20%, observers were almost always able to adjust transmittance to make a match, and the transmittance of the test filter was set very close to that of the standard. There was a slight trend to reduce the transmittance when the test reflectance was higher than the standard. (3) When transmittance was fixed at different values between filters, observers found it difficult to match transparency. However, when the difference in transmittances was small, the reflectance of the test filter was increased to match filters with lower transmittance and decreased to match filters with higher transmittance. The findings indicate that transmittance may be more important than reflectance in perceived transparency. However, some tradeoff is possible between transmittance and reflectance, and observers may adjust brightness to equate contrast of overlaid regions.
- [Show abstract] [Hide abstract] ABSTRACT: Robilotto, Khang, & Zaidi (2001) showed that for physically different filters on identical backgrounds, perceived transparency is predicted by both perceived contrast of the overlaid region and filter transmittance (proportion of incident light passing through the back surface). We now extend this study to filters on dissimilar backgrounds. Two Achromatic backgrounds differing either in contrast or mean luminance were generated on a CRT as random overlapping ellipses. Two neutral density filters were simulated as moving in circular motions, one on each background. The filters were generated based on two independent physical properties, reflectivity (proportion of light reflected at a change in media), and inner transmittance (proportion of light passing from front to back surface within the filter). The Standard filter had both physical properties fixed. The Matching filter had one property fixed while observers adjusted the other. In Exp. 1, observers adjusted the variable parameter to make the two filters appear equally transparent. In Exp. 2, the overlaid regions were rotated to abolish transparency cues, and observers adjusted the variable parameter to make the two overlaid regions appear equal in contrast. In all background conditions, observers were able to equate the perceived transparency of physically different filters through a linear tradeoff between reflectivity and inner transmittance. Equated transmittance was the physical determinant of equated perceived transparency and equated perceived contrast of the overlaid region was the sensory determinant. In conditions where Standard filters were presented over backgrounds of lower contrast or lower mean luminance, observers made settings so that the transmittance of the Matching filter was lower than for identical backgrounds. When identical filters were placed on dissimilar backgrounds, perceived transparency was lower on backgrounds of lower contrast or luminance, as was perceived contrast.
- [Show abstract] [Hide abstract] ABSTRACT: To compare objectively the rotational stability of two differently designed toric soft contact lenses over a range of natural viewing conditions using a novel infrared, video-based technique. Two contact lenses using different methods of stabilization were assessed: Accelerated Stabilization Design (ACUVUE ADVANCE for ASTIGMATISM) and Lo-Torque Design (B&L SofLens Toric). Four tasks involving saccades were performed: settling time with free viewing, reading, visual search, and execution of large versional tasks. Lens position (degrees of rotation) was continuously recorded with a head mounted, infrared, video-based system and a digital photo slit-lamp in 20 adult subjects. All measurements were obtained from the left eye under binocular viewing conditions with contact lenses on both eyes. The ACUVUE lens was significantly more stable during the settling time and large saccadic versional tasks than the SofLens. For the two other tasks (reading, visual search), performance was similar. The ACUVUE design was superior in stability for two of the four conditions tested. This resulted in a more stable lens immediately after insertion as well as during some visual tasks involving either naturally occurring or programmed large versional eye movements. Both lens designs provided acceptable performance in terms of induced astigmatism produced by off-axis rotation.
- [Show abstract] [Hide abstract] ABSTRACT: Conventional studies of lightness constancy have almost exclusively used flat plain stimuli and have shown that lightness matches across illuminants cannot be explained by physical matches of reflectance or luminance. The perceptual qualities that underlie lightness judgments still remain largely unknown. Real objects are often 3-D and patterned, giving additional cues for identification. We examine the perceptual strategies that underlie material identification of real objects. Stimuli were randomly crumpled papers printed with achromatic patterns with precisely calibrated mean reflectance and reflectance contrast, placed in backgrounds under varying levels of illumination. Observers were asked to identify objects based on physical reflectance differences. Reflectance identification functions were simulated by simple models that perform object identification based on dissimilarities in perceived brightness (luminance dissimilarity modified by light adaptation) or perceived contrast (contrast dissimilarity modified by mean luminance). The reflectance identification results were also recreated in two control experiments, using identical stimuli conditions, where choices were based explicitly on dissimilarities in perceived brightness or contrast. Rather than a reverse optics model of lightness perception where observers first estimate illuminant intensity and then extract relative lightness by discounting the illuminant, this study supports the use of simple percepts such as brightness and contrast.
- [Show abstract] [Hide abstract] ABSTRACT: We examined whether observers veridically perceive the reflectances of real objects under natural viewing conditions. A new forced-choice paradigm was used to measure observers' abilities to identify (not match) the reflectance of randomly crumpled gray papers across two levels of illumination, and also to simultaneously measure brightness discrimination thresholds for the same objects. Accuracy of lightness identification differed qualitatively among observers. By explicitly manipulating observer strategies, we show that when observers use brightness dissimilarity, their performance is similar to lightness identification. A brightness adaptation model simulates how instead of extracting lightness, observers can rely on perceived relative brightness to achieve the measured degrees of lightness identification.
- [Show abstract] [Hide abstract] ABSTRACT: We examine how the luminance distributions of overlaid surfaces affect the perception of transparency of neutral density filters. Pairs of neutral density filters were generated overlying variegated backgrounds of varying luminance distributions, and observers adjusted a single parameter of one filter until the pair appeared equally transparent. Physically identical filters appeared equally transparent on similar backgrounds, but did not appear equally transparent when backgrounds differed in luminance or contrast. Reducing luminance or contrast of the background decreased perceived transparency of the overlaying filter by a multiplicative factor. Observers matched perceived transparency of physically dissimilar filters by applying a linear trade-off between reflectivity and inner transmittance. In a second experiment, filters had their spatial structure altered in order to abolish the perception of transparency and appeared as patterned opaque disks, and observers equated perceived contrast of the two overlaid areas. Match settings gave results similar to the previous experiment, indicating that, in general, perceived transparency corresponds closely to the perceived contrast of the overlaid region.
- [Show abstract] [Hide abstract] ABSTRACT: What are the physical and sensory determinants of perceived transparency? To explore this question, we simulated pairs of physically different neutral density filters on a CRT and asked observers to match their perceived transparency. Matching was accomplished by adjusting one of two physically independent filter properties, reflectivity and inner transmittance. Results show that observers can make reliable matches through a linear trade-off of these two properties. In a separate experiment, observers matched the perceived contrast of the overlaid regions. The reflectivity and inner transmittance values for contrast matches are similar to those of perceived transparency matches, suggesting that perceived image contrast is the sensory determinant of perceived transparency. In variegated displays, neither Michelson contrast nor other standard contrast metrics predicts contrast appearance. When perceived transparency is plotted in terms of filter reflectance and filter transmittance, perceived transparency corresponds closely to filter transmittance.