Pioneering a New Method for Investigating the Neural Correlates of Ageing Effects during Natural Reading

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Reading is vital for people to function effectively in modern societies. Furthermore, good reading abilities are important for social inclusion and often essential for individuals to work productively, access educational opportunities and acquire new skills. However, numerous studies show that, compared to young adults (aged 18-30 years), older adults (aged 65+ years) experience considerable difficulty reading even when their visual and mental abilities appear normal. Surprisingly little is known about the underlying cause of this age-related reading difficulty or how it might be combated. However, this issue is likely to be increasingly socially important as the proportion of older people in society increase due to population ageing, as well as the likelihood that they will have extended working lives, often in jobs requiring good reading abilities. Scientific investigations of ageing effects on reading are therefore very important.When we read, our eyes move in a series of high-velocity jumps (saccades) separated by brief pauses (fixations) lasting about a quarter of a second. Readers visually and linguistically process a small portion of text during each fixation, before making a saccade to inspect a new portion. Quantitative measures of these eye movements have been the preferred way to study natural reading, and led to the development of detailed theoretical models of the mental processes that govern this behaviour, including how these might change with age. However, a major limitation of this approach is that eye movements are not directly informative about underlying brain processes, although such knowledge is essential if we are to more fully understand the fundamental mechanisms responsible for ageing effects on reading behaviour.Our project addresses this issue by pioneering a new method that permits the examination of brain processes in real-time during natural reading. This is achieved by simultaneously recording eye movements using a high-precision eye-tracker and electroencephalographic (EEG) measures of brain activity from electrodes placed on the scalp. We then synchronise these signals so that the EEG record is time-locked to individual fixations on specific words in sentences, thereby allowing us to quantify patterns of brain activity that take place as these words are processed visually. Once averaged (over trials in an experiment), the resulting EEG recording (the fixation-related brain potential, or FRP) exhibits a stereotypical waveform with components (peaks and troughs) that are selectively sensitive to factors that influence a word's recognition.The co-registration method is difficult to implement. Our first objective, therefore, is to demonstrate the viability of using this method with older adult participants. We propose then to conduct three experiments to establish the utility of this new method for revealing age differences in word recognition during natural reading. To do this, we will assess ageing effects on two key factors that affect word recognition during reading. The first is the frequency of a word's written usage (and so its familiarity to readers), and the second is the predictability of a word from its prior sentence context. Theoretical accounts of ageing effects predict larger effects of both word frequency and word predictability for older than young adults, due to slower lexical processing and greater reliance on context in older age. It will be important, therefore, to establish if our new method can detect age differences in the influence of these factors on brain processes during reading. There is a significant degree of risk to this project. But if we are successful, the approach we are pioneering is likely to produce a paradigm shift in psychological research on ageing effects on visual cognition (including reading) by providing the tools to develop new theories and obtain new evidence about brain processes that underlie socially-important everyday functions.