Aging and the use of implicit standards in the visual perception of length

摘要

A single experiment compared younger (mean age was 23.7 years) and older (mean age was 74.0 years) observers' ability to visually discriminate line length using both explicit and implicit standard stimuli. In some conditions, the method of constant stimuli (i.e., explicitly presented standard stimulus) was used to determine the observers' difference thresholds, whereas the method of single stimuli (no explicit standard stimulus) was used in other conditions. In the method of single stimuli, younger observers readily form a mental representation of the standard stimulus and can then use that mental standard in order to make judgments about test stimuli (i.e., whether a a??testa?? line on any given trial is longer or shorter than the standard). The current experiment was designed to evaluate whether increases in age affect observers' ability to form effective mental standards from a series of test stimuli. If older observers cannot form effective mental standards, then their discrimination performance should deteriorate in the single stimuli conditions relative to that exhibited by younger observers. In our experiment, the observers' difference thresholds were 5.845 percent of the standard when the method of constant stimuli was used and improved to 4.57 percent of the standard for the method of single stimuli (a decrease in threshold of 22 percent). Both age groups performed similarly: the older adults discrimination performance was equivalent to that of the younger observers. The results of the experiment demonstrate that older observers retain the ability to form effective mental standards from a series of visual stimuli.