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C T Scialfa

Publications and source records attributed to C T Scialfa.

13 recordsLinked to original sources
PubMed1992

Age differences in dynamic contrast thresholds.

Contrast thresholds for sinusoidal gratings of 1.5-18 cpd were measured in young (M = 24 years) and older adults (M = 69 years). Thresholds were determined for stationary gratings, and for gratings that traveled along a circular path at 5, 10, and 15 deg/sec. For static gratings, age differences in thresholds were greater for intermediate and higher spatial frequencies. Grating motion increased thresholds for all observers, but older adults exhibited threshold increases at lower target velocities than the young. Age differences in velocity effects were generally greater at intermediate and higher spatial frequencies. Results are discussed in relation to age changes in temporal resolution and smooth pursuit gain.

Adolescent↗
PubMed1991

Age differences in estimating vehicle velocity.

Automobile accidents among older adults may be related to difficulties in judging the speed of other vehicles. To examine this possibility, 3 groups of observers in the young adult, middle-aged, and older adult age ranges were asked to estimate the velocity of an isolated automobile traveling at 15-50 mph (24-80 kph). Across all age groups, perceived and actual velocity were related by a power function with an exponent of 1.36. Age was significantly and positively correlated with intercepts, but negatively correlated with exponents; that is, older observers showed less sensitivity to changes in actual velocity. Results bear on the issues of ontogenetic changes in accident involvement and sensitivity to motion.

Acceleration↗
PubMed1991

Reliability of the Vistech Contrast Test System in a life-span adult sample.

To assess the reliability of the Vistech Contrast Test System (VCTS), contrast sensitivity functions (CSF's) were estimated using all forms of the VCTS in 92 subjects aged 20 to 73 years, who were refracted for the test distance. Over a 3-month period, nine estimates at each spatial frequency and an equivalent number of acuity measures were obtained. The contrast sensitivity of older adults was lower than that of the younger adults, particularly at higher spatial frequencies. Practice effects which varied as a function of spatial frequency were also observed. Reliabilities for single-form estimates of contrast sensitivity (CS) were frequency-dependent, and ranged from 0.41 to 0.65. Three-form average estimates of CS yielded reliabilities ranging from 0.62 to 0.77. Consistent with the assertion that low VCTS reliabilities are due, in part, to measurement error, the reliabilities for acuity were uniformly higher than for the VCTS. Results are discussed in relation to clinical use of the VCTS across the life-span.

Adult↗
PubMed1990

Bandwidth of the contrast sensitivity function as an index of spatial vision with application to refraction.

The contrast sensitivity function (CSF), although containing more information than traditional measures of acuity, has found difficulty gaining clinical acceptance. The hesitancy of clinicians to adopt the CSF stems, in part, from the fact that it is not as readily interpreted as is acuity. In order to facilitate such interpretation, five indices of spatial vision which are derivable from the CSF were examined in a sample of 287 persons aged 5 to 85 years. All indices were found to be both age-sensitive and strongly related to each other, but bandwidth of the CSF was chosen as a practical index for clinical settings. In a second study, acuity and CSF bandwidth were measured under 0 to +/- 1 D optical blur. It was found that the correction providing best acuity also maximized CSF bandwidth, and that bandwidth was more sensitive to optical blur than was acuity. Results support the assertion that CSF bandwidth is a readily interpreted index of spatial vision that can be measured efficiently within the context of clinical refraction.

Adolescent↗
PubMed1989

Age differences in peripheral refractive error.

Refractive error was measured at 0 degrees to 40 degrees temporal to fixation in 10 young adults (M age = 26 years) and 10 older adults (M age = 63 years). Older adults exhibited a greater amount of sphere (i.e., overall) error, but no more so in the periphery than in the fovea. Although age differences were small, younger adults were found to exhibit more peripheral astigmatism than the older adults. Discrepancies between obtained results and those of Millodot (1985) may be attributed to the relationship between peripheral astigmatism and presenting refractive status. Alternatively, a two-mechanism model of age-related change in lens curvature is capable of accounting for across-study outcome differences. Recommendations are made concerning optimal viewing conditions for the study of age differences in visual perceptual processes.

Adult↗
PubMed1988

Effects of noise type and retinal eccentricity on age differences in identification and localization.

Twenty young (M = 24 yrs), and 20 older adults (M = 62 yrs) identified and localized two target letters presented nonfoveally in each of three noise conditions. Targets were presented in isolation, embedded in featurally similar distractors, or embedded in distractors that were featurally similar to the alternate response. Older adults were generally slower to identify targets, particularly in multi-element arrays. Age differences favoring the elderly were found in target-similar identification accuracy, but the young identified targets more accurately in alternate-similar noise. Localization errors were greater among the elderly, who exhibited a bias to localize targets to central array positions. Age differences in noise effects are explained as resulting from ontogenic change in the duration of temporal integration required to encode arrays to the level of a primary detection response (Estes, 1982). The model's predictions were given small-scale validation when visibility was decreased in young adults who then produced performance profiles similar to the elderly.

Adult↗
PubMed1988

Age differences in Vistech near contrast sensitivity.

Contrast sensitivity was measured at near using the Vistech 6000 Contrast Test System (VCTS) in 287 persons aged 4 to 87 years. Obtained data compared well with those previously reported for the Vistech charts. Results indicate an age-related loss in sensitivity to intermediate and higher spatial frequencies. This is consistent with the age trends observed using other methods for measuring contrast sensitivity functions (CSFs). However, the Vistech charts yield contrast sensitivity values which are lower than those obtained previously with the Nicolet system. These between-method differences are greatest at lower spatial frequencies, and are attributed to the small number of grating cycles in the Vistech charts. The data are used to develop provisional age norms for the Vistech charts which allow the assessment of an individual's performance relative to their age cohort. Recommendations for use and future development of the Vistech charts are also given.

Adolescent↗
PubMed1987

Age differences in target identification as a function of retinal location and noise level: examination of the useful field of view.

Foveal and peripheral target detection were compared in young adults (M age = 22 years) and older adults (M age = 66 years) who were optically corrected for the viewing distance. In a two-alternative, forced-choice task, target letters were presented at 0 degree to 10.5 degrees from fixation. Targets were presented alone, flanked on each side by one noise element (i.e., nontarget letter), or embedded in a horizontal row of 19 noise elements. An Age X Noise Level X Location interaction was obtained, wherein age differences were largest for peripheral targets presented in noise. Slope analyses of latency data showed that the performance of young adults in the high-noise condition was most similar to that of older adults in the low-noise condition. At the functional level, results indicated that aging is associated with a restricted useful field of view. In addition, the data suggest that age differences in search can be described by a model in which older adults take smaller perceptual samples from the visual scene and scan these samples more slowly than do the young adults.

Adult↗
PubMed1987

Problems with step-wise regression in research on aging and recommended alternatives.

The use of step-wise regression techniques in aging research brings with it certain interpretative difficulties. Both geometric and algebraic approaches are used to demonstrate that although step-wise procedures pose little difficulty if predictors are orthogonal, these same procedures, when used with correlated predictors, can lead to poor tests of the predictor regression weights. Techniques that are useful in the detection of multicollinearity are discussed. Principal components regression, ridge regression, and hierarchical regression are evaluated as potential techniques for assessing the relative importance of predictors when these variables are correlated, as is common in aging research. Hierarchical regression is the most recommended technique in that it is theory-driven rather than dependent on empirical relations that may be sample-specific and unstable.

Aging↗
PubMed1986

Age differences in the commonality of free associations.

Commonality of associative response provides an index of the organization of semantic memory. The present study investigated age differences in semantic organization by comparing commonality of associative response. Thirty young (M = 20 yrs) and 30 old (M = 72 yrs) adults gave free associations to single stimulus words of high or low linguistic frequency. Controlling statistically for education and verbal skills, it was determined that there were no age differences in the commonality or variability of associates. Results are discussed in reference to developmental trends in the organization of semantic memory.

Adolescent↗
PubMedDate not supplied

Age differences in the temporal continuity of gratings as a function of their spatial frequency.

This study compared young and elderly observers on the continuity of sinusoidal grating-pairs as a function of interstimulus interval (ISI) and spatial frequency (.5, 1.0, 2.0, 4.0, 8.0, and 12.0 c/deg). Consistent with prior research, the maximum ISI over which pattern continuity was maintained increased with spatial frequency. In addition, among older observers, grating continuity occurred at significantly longer ISI's at the two lowest spatial frequencies; no age difference was observed at the higher spatial frequencies. These results could not be attributed to an age difference in retinal illumination associated with pupillary miosis. However, they do indicate an age-related decline in detecting visual offset and are consistent with the hypothesis of a decline in the effectiveness of the transient visual channels.

Adolescent↗