Biomedical subjects
Publications and source records attributed to J P Tuck.
While visual acuity was related to performance on several pseudoisochromatic color tests for 73 male college students, no evidence was found that perceptual closure also affected performance. No scores were correlated for the 69 undergraduate women.
The contrast sensitivity functions of a large group of observers (N = 71) were determined for three orientations of test gratings: vertical, oblique, and horizontal. Comparison of group means indicated that, consistent with previous findings for the 'oblique effect', sensitivity was poorer for the oblique orientation-but only for the mid-high spatial frequencies. Correlation analyses indicated that contrast sensitivity for a particular spatial frequency at a given orientation was highly correlated with contrast sensitivity for that same frequency at the other two orientations. Factor analysis of the intercorrelations revealed two strong factors, a low frequency factor, and a mid-high frequency factor. Results are discussed in terms of: (a) the implications for contrast-sensitivity testing across orientations, (b) the basis for the oblique effect, and (c) a different type of evidence for a dichotomy among spatial-frequency channels that may reflect the distinction between X cells and Y cells or between the parvocellular and magnocellular systems.
The present work extends the findings of previous efforts examining the comparability of current colour-screening tests. Several popular tests are shown to differ greatly in the performance exhibited by colour-normal observers as well as in their differential sensitivity to experimental manipulations of viewing duration and viewing distance. Those tests designed to identify yellow-blue dichromacy are especially sensitive to the manipulation of viewing distance, which is interpreted as reflecting 'small-field tritanopia' and the asymmetry in retinal density of the three cone types. These findings are discussed in terms of factors that influence the comparability of current colour-screening devices and the particular need for close adherence to standardized conditions with such instruments.
We examined the effect of variations in viewing distance and viewing duration on the performance of color-normal observers with four standard tests of color vision. Significant effects of the experimental manipulations were obtained: both increasing viewing distance and decreasing viewing duration significantly increased the number of errors made by observers. Moreover, the four tests differed widely in their sensitivity to the variations in viewing conditions. Practical implications of the findings for the administration and selection of plate tests are discussed, and possible mechanisms underlying the results are suggested.
In four studies, the comparability of several measures of contrast sensitivity functions (CSF's) as well as their individual test-retest reliabilities were determined with observers drawn from a college population. The relation between CSF scores obtained by different tests or by different psychophysical procedures with the same test was consistently low and frequently nonexistent. These low intertest reliabilities were found to be due to the lack of reliability of some of the individual tests. In particular, with both stationary and flickering gratings, the von Bekesy tracking procedure produced unacceptable variations in contrast estimates. Fortunately, the reliabilities of other procedures, particularly the simple adjustment method, were much higher (greater than 0.70). CSF scores obtained from the wallchart method exhibited insufficient variability among observers in the college sample to permit similar reliability estimates to be determined. Implications of the test characteristics are discussed for users of the CSF.
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Two experiments are reported that examine the effects of viewing distance, viewing duration, and stimulus clarity on performance with three popular versions of the pseudoisochromatic tests of colour deficiency. With a large sample of colour-normal observers, highly significant effects of these viewing conditions are found. In addition, large differences in sensitivity to these conditions are obtained among the three tests employed (The American Optical Corporation test, the Dvorine test, and the Ishihara test). Results are discussed in terms of practical implications for test administration and in terms of likely processes, in addition to colour discrimination, assessed by these tests.
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Three problems in the Munz and Smouse procedure make it unacceptable as an operationalization of four reactions to test anxiety alluded to by Alpert and Haber. As a demonstration of two of the problems, the procedure was applied to the scores of 176 male and female college students. A new procedure for operationalizing the four reactions, which avoids the problems in the Munz and Smouse procedure, was described. Practical problems likely to be encountered in using the new procedure were discussed.
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The most popular techniques for assessing color vision, the pseudoisochromatic tests, have been found to differ widely in their sensitivity to changes in viewing conditions. A significant number of color-normal subjects will be misdiagnosed as color defective by some of the standard tests with even relatively minor variations from standardized viewing conditions. These results appear to have strong implications for the use of the tests in many applied settings which precise control over viewing conditions is difficult. In particular, as the consequences of a misdiagnosis become very serious, the tests must be used with special caution. If we were to recommend one test for use, our findings point to the Ishihara, which appears impervious to variation in viewing conditions.