Abstract
Deficits in magnocellular stream activity have been implicated as a factor in individuals with developmental dyslexia. While many investigations direct efforts at understanding magnocellular processing as it applies to dyslexia, its role in skilled adult readers remains relatively unexplored. Using diffuse red light, which is known to suppress activity in the magnocellular channel (e.g., Breitmeyer & Breier, 1994), we examined how this pathway affects lexical processing as reflected in eye movements. Our investigation explored the role of the magnocellular stream in extrafoveal vision during skilled adult reading by employing a gaze-contingent moving window paradigm (McConkie & Rayner, 1975, 1976). We predicted that readers would have difficulty efficiently using extrafoveal information when the magnocellular stream is suppressed. As a result, when text is presented on a red background, readers should exhibit slower reading rates, an increased number of fixations, and increases in time per fixation. Additionally, magnocellular stream suppression might result in a reduction in the number of characters useful to readers in extrafoveal vision. We employed a within-subjects factorial design in which readers viewed sentences on either grey or red backgrounds while the number of characters available to the right of a reader's fixation (4, 8, 12, 16, or open) varied across sentences. Not surprisingly, window size reliably affected eye movement measures up to 12 letters to the right of fixation. In addition, readers required additional time per fixation when viewing sentences on a red background compared to when readers viewed sentences on a grey background. Readers may have required additional time at each fixation due to a reduction in the quality of extrafoveal visual information during the previous fixation. These findings warrant further investigation in order to determine the specific lexical information processed by the magnocellular stream.
Meeting abstract presented at VSS 2018