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Viewing Conditions (viewing + condition)
Selected AbstractsHuman Perception of Dental Porcelain Translucency Correlated to Spectrophotometric MeasurementsJOURNAL OF PROSTHODONTICS, Issue 3 2010Min-Chieh Liu DDS Abstract Purpose: This study evaluated the relationship between instrumental measurements and subjective visual assessment of differences in dental porcelain translucency. Materials and Methods: Unshaded feldspathic porcelain was used with controlled amounts of tin oxide to create two groups of 12-mm diameter disks with incremental changes in opacity. Contrast ratio (CR = Yb/Yw) was determined with a spectrophotometer, and used as a measure of porcelain translucency (Group A = 0.20 to 0.40; Group B = 0.6,0.8). Within each group, there were 14 specimens with 11 CRs. Three observer groups (first year dental students, residents, faculty with >10 years of shade matching experience) were recruited to assess the translucency between porcelain disks under two lighting conditions (reflected light, transmitted light). Each subject's ability to distinguish between specimens of differing translucency was determined. Descriptive statistics and three-way ANOVA followed by a post-hoc Tukey-Kramer test were used to evaluate the translucency perception threshold (TPT) of subjects (,= 0.05). Results: The overall mean TPT (,C) was 0.07, while 50% of the subjects could perceive a 0.06 CR difference between porcelain specimens. Three-way ANOVA revealed a significant difference in translucency perception among the observer groups (p < 0.0001), whereas the main effects for porcelain opacity (p= 0.3038) and lighting condition (p= 0.0645) were not significant, and no significant interactions were found. Post-hoc Tukey-Kramer test indicated that the mean TPT observed in the faculty group (,C = 0.04) was significantly lower than those observed in student (,C = 0.09) and resident groups (,C = 0.08), while there was no significant difference between students and residents. Conclusions: The overall mean TPT of all subjects was 0.07, and 50% of the study population perceived a 0.06 CR difference in translucency. Increased shade matching experience (,10 years) significantly improved the ability to perceive differences in translucency; however, neither the viewing condition nor porcelain opacity affected the perceived translucency threshold. [source] Idiocentric and allocentric differences in emotional expression, experience, and the coherence between expression and experienceASIAN JOURNAL OF SOCIAL PSYCHOLOGY, Issue 2 2001David Matsumoto This study examined differences in emotional expression, experience, and the coherence between expression and experience in idiocentric and allocentric individuals, who participated in a study similar to Ekman (1972) and Friesen's (1972) original display rule study. Encoders, classified as idiocentric or allocentric based on a measure of psychological culture, were unobtrusively videotaped as they viewed positive and negative films in two contexts , alone, and then a second time either alone or with an experimenter present. Subjective emotional responding was assessed following each of the film viewing sessions and, using the encoders' videotaped data, their emotional expressions were judged by a separate sample of decoders. Emotional expression and coherence differed as a function of encoder culture and viewing condition; experience did not. These findings replicate and extend the only other cross-cultural experiment of spontaneous emotional expressions in adults conducted over thirty years ago (Ekman, 1972; Friesen, 1972), and speak to the influence of culture as a socio-psychological construct, given that all participants were European American females. [source] Infant Perception of Surface Texture and Relative Height as Distance Information: A Preferential-Reaching StudyINFANCY, Issue 1 2010Laura Hemker Two preferential-reaching experiments explored 5- and 7-month-olds' sensitivity to pictorial depth cues. In the first experiment, infants viewed a display in which texture gradients, linear perspective of the surface contours, and relative height in the visual field provided information that two objects were at different distances. Five- and 7-month-old infants reached preferentially for the apparently nearer object under monocular but not binocular viewing conditions, indicating that infants in both age groups respond to pictorial depth cues. In the second experiment, texture gradients and linear perspective of the surface contours were eliminated from the experimental display, making relative height the sole pictorial depth cue. Seven-month-olds again reached more often for the apparently nearer object under monocular, but not binocular viewing conditions. By contrast, the 5-month-olds' reaching behavior did not differ between viewing conditions. These results indicate that 7-month-olds respond to the depth cue of relative height but provide no evidence of responsiveness to relative height in 5-month-olds. Both age groups responded more consistently to pictorial depth in Experiment 1 than in Experiment 2. [source] Influence of background and surround on image color matchingINTERNATIONAL JOURNAL OF IMAGING SYSTEMS AND TECHNOLOGY, Issue 4 2007Lidija Mandic Abstract In this article, the corresponding-color data for complex images reproduced on different media were obtained by simultaneous matching using an adjustment method. In our experiment printed color images and images displayed on a monitor were compared in different viewing conditions. The viewing condition varied in surround relative luminance and background. The experimental data show that surround relative luminance has little influence on color matching between printed and monitor images while changes in background modify color appearance. These results were used to evaluate different chromatic adaptation transforms (CAT). We found that for the same viewing conditions the SHARP transform shows the best agreement between the experimental and predicted data. SHARP transform can not predict accurately corresponding colors for blue and black regions. Therefore, we proposed new CAT that shows better characteristics than other transforms for cyan, green, and black colors and similar characteristics for other colors. © 2007 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 17, 244,251, 2007 [source] Just how useless is an amblyopic eye?OPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 1 2008Eve Panesar Purpose:, The extent to which individuals with amblyopia are visually disadvantaged has generated renewed research interest. Investigation of the contribution of the amblyopic eye to visual performance under habitual conditions is a key component of this issue. This study aims to evaluate the contribution of each eye to a simple light detection task when both eyes are open and in their habitual motor position. Methods:, A custom program on the Humphrey Field Analyzer (Carl Zeiss Meditec Inc., Dublin, CA, USA) was used to measure detection thresholds for a blue light on a yellow background along the horizontal meridian at two degree intervals to an eccentricity of 25 degrees either side of fixation. Three viewing conditions were used: (1) both eyes open, (2) a yellow filter in front of the amblyopic eye and (3) a yellow filter in front of the fellow eye. The purpose of the yellow filter was to produce minimal dissociation as it only prevented the eye behind the filter from seeing the blue stimulus; the fixation mark and the background remained visible to both eyes. Participants included 10 visual normals and 16 volunteers with amblyopia. Results:, Within the sample of amblyopes there were three basic patterns of results, and each applied to around one third of the group: (1) habitual sensitivity governed by the sensitivity of the fellow eye at each stimulus location, (2) habitual sensitivity exceeding the sensitivities of either eye at each stimulus location and (3) a pattern of contribution that varied across the range of eccentricities. Surprisingly, in one amblyope the habitual sensitivity appeared to be governed by the sensitivity of the amblyopic eye. The pattern of contribution of each eye to the habitual sensitivity did not vary in a manner that was predictable by the visual acuity deficit or the presumed aetiology of the amblyopia. The control sample showed either pattern 2 (70%) or pattern 3 (30%). Conclusions:, The amblyopic eye did not contribute to the habitual performance in approximately one-third of cases in this simple detection task. Thus, in many cases the amblyopic eye may be a useful contributor to visual performance in the binocular field. This challenges the traditional view that an amblyopic eye is useful only for peripheral vision. [source] The prevalence of suppression in amblyopic individualsOPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 1 2008Brendan Barrett Purpose:, A popular view of visual functioning in individuals with amblyopia is that the weaker eye is suppressed in key regions of the binocular visual field. Indeed, some have argued that chronic interocular suppression may represent the cause of amblyopia. Here we evaluate the prevalence of amblyopic-eye suppression in a simple light detection task when the eyes are open, minimally dissociated and in their habitual motor position. Methods:, A custom program on the Humphrey Field Analyzer (Carl Zeiss Meditec Inc., Dublin, CA, USA) was used to measure detection thresholds for a blue light on a yellow background along the horizontal meridian at two-degree intervals to an eccentricity of 25 degrees on either side of the fixation mark. The fellow eye was prevented from seeing the target using three different methods: (1) full-occlusion (i.e. no light entered the fellow eye), (2) a translucent occluder (3) a yellow filter in front of the fellow eye. In (3), the yellow filter only prevented the fellow eye from seeing the blue stimulus; the fixation mark and the background remained visible (minimal-dissociation condition). Fourteen amblyopes participated in the study, of whom 11 had strabismus. Results:, Three basic patterns of results were observed. (1) Only three of the fourteen participants (,21%) showed evidence of suppression, where amblyopic-eye sensitivity was lower with the fellow eye open. In these cases, the retinal locations that showed greatest suppression corresponded to the direction and angle of the strabismus. (2) Three participants (,21%) showed the opposite effect to the result in (1); i.e. amblyopic-eye sensitivity was greatest when the fellow was open with minimal dissociation between the eyes. One possible explanation is that the dominance of the fellow eye caused this reduction. (3) Seven participants (50%) exhibited patterns of amblyopic sensitivity that did not depend upon the occlusion status of the fellow eye. The results for one participant did not fit into any of the above patterns. Conclusions:, Suppression appears not to be a universal feature of central amblyopic vision. Our results for this simple detection task suggest that suppression may exist in as few as 20% of amblyopes. These results present a challenge to the view that suppression represents a root cause of amblyopia but they are consistent with the view that the amblyopic eye makes a useful contribution under habitual viewing conditions. [source] The Mallett Fixation Disparity Test: influence of test instructions and relationship with symptomsOPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 5 2006Rajula Karania Abstract Fixation disparity is a minute ocular misalignment under conditions of binocular single vision and is typically detected in primary eye care practices in the UK using the Mallett Unit Fixation Disparity Test. This instrument creates natural viewing conditions, when the patient's binocular system is fused using both central and peripheral fusion locks. This allows the examiner to determine the minimum prism power that eliminates the fixation disparity: the associated phoria or aligning prism. The spherical power that eliminates the fixation disparity, the aligning sphere, can also be determined. The near Mallett Unit Fixation Disparity Test has been shown to have good sensitivity and specificity for detecting symptomatic heterophoria. Cases of decompensated heterophoria tend to have a fixation disparity and the aligning prism or aligning sphere is a good indicator of the correction that will render the heterophoria compensated. The purpose of this study was, for the first time, to investigate the effect of test instructions on the results of the Mallett Unit Fixation Disparity Test. In study 1, we surveyed and observed practitioners to determine the instructions that are typically used. In study 2, we compared results obtained with this ,standard' method of questioning with a more ,specific' form of questioning that has been suggested in the literature. The participants for study 2 were 105 patients aged 7,70 years who were randomly selected from those attending a community optometric practice. Significantly different results were obtained with the two sets of instructions. The specific form of questioning revealed more cases of fixation disparity and the results with this method showed a better correlation with symptoms. This only held for near vision: for distance vision, symptoms were not significantly correlated with the presence of fixation disparity. This agrees with previous work with the Mallett unit, which showed a significant relationship with symptoms only at near. We also found that patients with more severe symptoms had greater degrees of aligning prism. Our study supports previous work indicating that the Mallett unit is a useful tool for detecting symptomatic heterophoria at near. However, we found that the testing method is important: patients need to be asked not just whether the nonius strips are aligned but also whether one or both of the strips ever moves. More research is needed to investigate the significance of precise test instructions in other optometric and orthoptic tests. [source] | ||||||||||