Age differences in memory-span errors: speed or inhibitory mechanisms?

This study investigated age differences in errors on the digit-span task. Protocols of 119 men and women, aged 18-99 years, were scored for the occurrence of three types of errors derived from the speed-of-processing and inhibition-deficit frameworks: omission errors, intrusion errors, and transposition errors. The types of errors made on the digit-span task varied with span size. At larger span sizes, participants were more likely to omit digits or introduce nonstimulus digits than to transpose those in storage. No age differences in intrusion errors were found, however, old-old women (75+ years) were significantly more likely than young (18-25 years) and old (60-70 years) adults of either sex to exhibit transposition errors. Consequently, old-old women were significantly less likely to exhibit omission errors. The results indicate that the digit-span task may involve two parallel processes: digit storage/recall and serial/position storage-recall. Age differences in the serial-processing component, rather than in the digit storage/recall component, may be age sensitive. These results are discussed within an inhibition-deficit framework of cognitive aging.