The ability to decode words accurately is essential but not sufficient for efficient reading and comprehension. Most children, who decode well while reading, comprehend most of what they read. However, there are many children who do not understand what they are reading even though they appear to be reading fluently. Often these children are not detected in the early years of schooling because they generally sound like they are reading beautifully. It is not until the latter years of primary (or elementary school) when they are expected to read for understanding that they appear to be having problems with reading comprehension.
One of the problems is that these children do not normally connect emotionally with what they read. Emotions are usually associated with mental imagery. For example, the events of 9/11 were emotionally charged and the images of the planes crashing into the twin towers have been firmly etched into our long-term memories. It is difficult to read or talk about these events without replaying those horrific scenes in the 'mind's eye'. These images are vivid because they are emotionally charged and are often referred to as flash bulb memories. Not all mental images are as emotionally charged as this example but often readers make the comment that the book seemed to 'come alive'. What they are really saying is that they became emotionally involved with the book and the imagined scenes seemed to play like a movie. This is because mental imagery facilitates emotional associations and links reading to life experiences.
Watch this YouTube video to find out more about the role of mental imagery and reading.
Thus, the degree of involvement, enjoyment, and interest in reading are enhanced by the generation of images.
To find out more about mental imagery read 'Dual Coding Theory and Education' at http://www.umich.edu/~rdytolrn/pathwaysconference/presentations/paivio.pdf