The Role of Inhibition in Age-related Off-Topic Verbosity: Not Access but Deletion and Restraint Functions

Selective attention requires the ability to focus on relevant information and to ignore irrelevant information. The ability to inhibit irrelevant information has been proposed to be the main source of age-related cognitive change (e.g., Hasher & Zacks, 1988). Although age-related distraction by irrelevant information has been extensively demonstrated in the visual modality, studies involving auditory and cross-modal paradigms have revealed a mixed pattern of results. A comparative evaluation of these paradigms according to sensory modality suggests a twofold trend: Age-related distraction is more likely (a) in unimodal than in cross-modal paradigms and (b) when irrelevant information is presented in the visual modality, rather than in the auditory modality. This distinct pattern of age-related changes in selective attention may be linked to the reliance of the visual and auditory modalities on different filtering mechanisms. Distractors presented through the auditory modality can be filtered at both central and peripheral neurocognitive levels. In contrast, distractors presented through the visual modality are primarily suppressed at more central levels of processing, which may be more vulnerable to aging. We propose the hypothesis that age-related distractibility is modality dependent, a notion that might need to be incorporated in current theories of cognitive aging. Ultimately, this might lead to a more accurate account for the mixed pattern of impaired and preserved selective attention found in advancing age.

The hypothesis that off-target verbosity, defined as extended speech that is lacking in focus or coherence, is mediated by an age-related decline in the ability to inhibit task-irrelevant thoughts, was evaluated in a sample of 205 community-dwelling elderly volunteers aged 61-90. Results showed that performance on four tasks that measured the ability to suppress or remove irrelevant information stored in working memory accounted for a significant proportion of the variance in verbosity, whereas performance on other cognitive measures was unrelated to it. Shared effects between the measures of the ability to inhibit task-irrelevant information and age suggested that age declines in this particular ability may underlie previously observed age-related increases in verbosity. In contrast, the contribution of psychosocial factors to explained variance in verbosity scores was relatively independent of that of inhibition-related measures and age. The results were discussed as suggesting a possible frontal lobe involvement in off-target speech.

Changes in language as a function of the normal aging process were studied. Eighty adults between the ages of 20 and 78 described three pictures. Quantifiable measures reflecting speech production, elaboration, and complexity; speech dysfluency; conciseness; and information imparted were abstracted from each description. No relationships between age and these measures were found, except for an increase in the use of prepositional phrases and indefinite words and longer pauses among older persons. Indefinite wording reflects word-finding or naming difficulty, and longer pauses may reflect cognitive slowing. No age-related differences in amount of information imparted were found in either time-limited or time-unlimited speech samples.