Dichoptic backward masking of letters, words, and trigrams in old and young subjects.

Age differences in central visual processing were studied in 30 older adults (mean age 67.9 years) and in 30 young adults (mean age 19.8 years) using a dichoptic backward masking paradigm. Single letters, three-letter words, and consonant trigrams were used as target stimuli with a patterned masking stimulus. A significant age difference (p less than .001) was found in the interstimulus intervals necessary to escape the masking effect (ISIc) with older subjects requiring approximately 75 msec longer than the younger ones at each of three target durations. The effect of letters, words, and trigrams on ISIc for both young and old also yielded a significant difference (p = .01) with words most readily identified, letters intermediate, and trigrams requiring the longest processing time. Implications of these data with respect to previous studies and theoretical models are considered.