Neurophysiological mechanisms of reading processes: Aging and context effects

• Author / Creator

  Sahadevan, Shrida S.

• Background. Context use in sentence comprehension is fairly resistant to age-related cognitive decline; however, event-related potentials (ERPs) studies have shown age effects in neural activity associated with sentence comprehension, specifically when contextual information is manipulated. One well-documented ERP component, N400, may reflect the use of context to predict upcoming words. Older adults have smaller and later N400 responses than younger adults for unexpected sentence-endings (Federmeier et al., 2002), suggesting age-related differences in how adults use context. As well, there is the post-N400 positivity (PNP) – both at the frontal and parietal regions - that may index attempted re-analysis of incongruent sentences, or reflect predictive processing, which is also influenced by age (Van Petten & Luka, 2012). The purpose of the present study is to determine whether there are age-related differences in reading comprehension of sentences with varying semantic anomalies, using electroencephalography methods. Methods. Experiment 1 was designed as a pilot study, to investigate whether a passive reading paradigm would elicit the anticipated ERP responses. In Experiment 1, neurologically healthy young adults (n = 34; age range 18 – 30 years, M = 23.8, SD = 3.05) passively read pairs of sentences while wearing an electroencephalography cap. In Experiment 2, EEG was recorded while young (n = 22; age range 18 – 27 years, M = 21.1, SD = 2.62) and older (n = 21; age range 50 to 84 years, M = 62.0, SD = 8.98) adults read the same pairs of sentences as in Experiment 1, followed by a recognition memory task where they had to identify the presented sentence-ending word in order to elicit active processing of the stimuli. In both experiments, the reading task consisted of the presentation of two sentences. The first sentence established the context. The second sentence ended with a target word that was either 1) expected, 2) unexpected but semantically related, or 3) unexpected and unrelated to the context. The amplitude and latency of the N400 and PNP were measured using electroencephalography for the final target word, in each experiment. Reading time and recognition memory accuracy (Experiment 2) was also measured. Results. In Experiment 1, there was no significant N400 effect for the three sentence ending conditions. However, we detected a parietal PNP response in terms of mean amplitude. In Experiment 2, there were no significant differences in the behavioural measures between young and older adults (reading time and memory performance), as anticipated. Younger and older adults demonstrated maximal N400 responses for unexpected-unrelated words and minimal N400 responses for expected words. The latency of the N400 response was different between the groups, in which older adults had delayed processing in the earlier time window. Both groups of adults also demonstrated parietal post-N400 positivity (PNP) responses, contrary to previous literature. Discussion. Younger and older adults performed similarly on behavioural measures and the N400 results indicated that older adults are able to use their semantic memory to assess the stimuli features similar to young adults. However, there was evidence for age-related differences in the N400 latency. The parietal PNP responses also showed differences in the processing of the stimuli between young and older adults. Overall, our findings are important for understanding the neural correlates underlying age effects on context use in sentence comprehension. As reading plays a vital role in our society, understanding how aging affects this ability will provide new insights into the corresponding neural mechanisms, with possible implications for clinical populations with reading impairments.

• Subjects / Keywords

  • Reading
  • Sentence context
  • Aging
  • N400
  • PNP
  • Event-related potentials

• Graduation date

  Fall 2016

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3FB4WX35

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.