Some effects of aging on event-related potentials during a linguistic monitoring task

Design and evaluation of the effectiveness of a corpus of congruent and incongruent English sentences for the study of event related potentials

OBJECTIVE

To design and evaluate the effectiveness of a stimulus material in eliciting the N400 event related potential (ERP).

DESIGN

A set of 700 semantically congruent and incongruent sentences was developed in accordance with current linguistic norms, and validated with an electroencephalography (EEG) study, in which the influence of age and gender on the N400 ERP magnitude was analysed.

STUDY SAMPLE

Forty-five normal-hearing subjects (19-57 years, 21 females) participated in the EEG study.

RESULTS

The stimulus material used in the EEG study elicited a robust N400 ERP, with a morphology consistent with the literature. Results also showed no statistically significant effect of age or gender on the N400 magnitude.

CONCLUSIONS

The material presented in this paper constitutes the largest complete stimulus set suitable for both auditory and text-based N400 experiments. This material may help facilitate the efficient implementation of future N400 ERP studies, as well as promote standardisation and consistency across studies.

Looking at the Sunny Side of Life

Studies of the negativity bias have demonstrated that negative information has a stronger influence than positive information in a wide range of cognitive domains. At odds with this literature is extensive work now documenting emotional and motivational shifts that result in a positivity effect in older adults. It remains unclear, however, whether this age-related positivity effect results from increases in processing of positive information or from decreases in processing of negative information. Also unknown is the specific time course of development from a negative bias to an apparently positive one. The present study was designed to investigate the negativity bias across the life span using an event-related potential measure of responding to emotionally valenced images. The results suggest that neural reactivity to negative images declines linearly with age, but responding to positive images is surprisingly age invariant across most of the adult life span.

The effect of aging on event-related potentials and behavioral responses: Comparison of tonal, phonologic and semantic targets

OBJECTIVE

To investigate age-related changes in speech perception by measuring event-related potentials (ERPs) elicited by auditory stimuli varying in their linguistic characteristics from pure tones to words.

METHODS

ERPs were recorded from 64 subjects in three age groups (young, middle age and elderly) to auditory target stimuli, using an oddball paradigm. Three different tasks and stimuli were used: tonal, phonological and semantic.

RESULTS

N100 latency to tonal targets was significantly shorter than to both types of speech targets. P300 latency to tonal targets was significantly shorter than to phonological targets, which in turn was shorter than to semantic targets. P300 amplitude recorded to the speech targets was significantly larger over the left hemisphere than over the right hemisphere in the young subjects. However, the reverse pattern of asymmetry, favoring the right hemisphere was found in the elderly subjects. The pattern of the hemispheric distribution for the middle aged was somewhere in between the young and elderly.

CONCLUSIONS

The data indicate possible progressive changes in left-right asymmetry in language processing with aging.

SIGNIFICANCE

Findings may indicate an increased use of compensatory mechanisms for speech processing, or alternatively, an increased use of different generators as individuals age.