Suffix effects and intrusion errors in young and elderly subjects.

Potential age differences in selective attention and response inhibition in 16 young and 16 elderly college students were explored using the stimulus suffix paradigm. Subjects were presented with auditory and visual lists of seven-letter sequences. Half the lists were appended with a letter suffix that was not to be recalled. Recall was spoken and written and in strict serial order. Despite similar letter spans, serial recall was more difficult for the elderly than for the young. Final-item recall advantage in the control condition was reduced more for the elderly than for the young in the auditory modality, and the elderly were more susceptible to a small degree of visual suffix interference. Older subjects made more suffix and extralist intrusion errors than did young subjects. Oral recall, along with the method of recording written responses, may have allowed these errors to surface. The extralist intrusion errors were phonological or based on alphabetic order, suggesting that the elderly may experience task-competitive, internally generated noise, which enters the response set. The suffix intrusions, along with greater susceptibility to the suffix, suggest an attentional type of deficit related to ineffective response inhibition in the elderly.