Effects of Advancing Age on the Processing of Semantic Anomalies in Adults: Evidence from Event-Related Brain Potentials

Abstract

Age-related changes in the processing of sentence-embedded semantic anomalies were examined using auditory event-related potentials (ERPs). Semantically incongruous words elicited an N400 effect in middle-aged (50s: 55.6 years) and elderly (60s: 64.1 years) subjects, whereas in older elderly adults (70s: 74.9 years) this effect approached significance. N400 peak latencies were not delayed with advancing age; however, there was a reliable linear decrease in mean and peak amplitude, with slopes being similar to those previously reported for the visual N400 effect. A P600 effect was obtained in response to semantic anomalies and it was neither delayed in latency nor reduced in amplitude with advancing age. However, it was found to be larger over anterior sites in elderly and older elderly subjects.

The authors would like to thank Aaron Newman for assistance with stimuli design, Catharine Pettigrew for help with stimuli production, and Robert Simon for technical support.

Notes

*Average hearing threshold;

**raw score maximum = 144. Standard deviations are presented in parentheses.

¹N400 refers to the negativity, peaking around 400 ms post stimulus onset, observed in raw ERP waveforms, whereas the term “N400 effect” refers to the difference between semantically correct and semantically anomalous/incongruent conditions. Accordingly, P600 refers to the late positivity observed in raw ERP waveforms, whereas the term “P600 effect” refers to the difference between semantically correct and semantically anomalous/incongruent conditions.

Note. Correct = correct sentence condition; SemMM = semantic mismatch condition. Standard deviations are presented in parentheses.

*Not including frontopolar recording sites.

²Potential age-related differences in the onset of the N400 effect were further explored by calculating separate ANOVAs on the mean amplitude of the N400 in 50-ms intervals between 250 and 500 ms (e.g., Gunter et al., 1992) at electrode CPZ. A significant Group × Congruity interaction was observed for the 250- to 300-ms interval (F(2, 36) = 4.95, p = .013) due to the N400 effect being slightly smaller in the 60s compared to the 50s group (Group × Congruity: F(1, 25) = 14.13, p = .001; congruity: 50s: F(1, 12) = 41.39, p = .000; 60s: F(1, 13) = 6.78, p = .022; 70s: F(1, 11) = 9.66, p = .010). Analyses of all other 50-ms intervals did not reveal significant Group × Congruity interactions (300 to 350ms: F(2, 36) = .94, p > .05; 350 to 400 ms: F(2, 36) = 1.77, p > .05; 400 to 450 ms: F(2, 36) = .64, p > .05; 450 to 500 ms: F(2, 36) = 1.53, p > .05). However, the considerably reduced size of the N400 to semantic anomalies in the 70s group may make it difficult to detect reliable age-related alterations in the onset of the N400 effect.

³Similar results were obtained in a different study comparing ERP effects observed in a larger cohort of young (18 to 30 years old) and older adults (60 to 69 years old), using the same materials and procedures. No differences in the magnitude and latency of the late positive component were observed, though the latter was found to be slightly larger over frontal recording sites in older adults (Faustmann et al., submitted).