No unique magnocellular facilitation in parafoveal processing: A combined EEG and eye-tracking study

Rapidly processed magnocellular (M) information may facilitate visual object recognition but its role in reading is unclear. A previous study with Chinese characters and masked foveal primes did not find a unique role of the M-system as compared to the parvocellular (P) system in mediating repetition effects. As M cells are better represented in the parafoveal visual field, the present study tested whether the M- and P-systems contribute differentially to parafoveal processing during reading. We combined EEG recordings and eye-tracking to measure parafoveal preview effects in fixation-related potentials (FRPs), using the boundary paradigm. In two experiments, we contrasted high versus low spatial frequency previews and luminance versus color contrast previews and also included standard previews as a manipulation check. As expected, the N250 component was diminished after valid as compared to invalid normal previews, especially over the left hemisphere. We also obtained left-lateralized preview effects for the N250 component for both M- and P-biased previews in both experiments. In the experiment involving a spatial frequency manipulation, P-biased preview effects tended to be larger than M-biased preview effects over the left hemisphere, but not the right hemisphere. No interactions with preview validity were found for the luminance contrast manipulation. This null effect was supported by a Bayesian analysis. Taken together, these results indicate that the M pathway does not exclusively mediate the preview effect, even for stimuli presented in the parafovea. Instead, both M- and P-based information appear to contribute to early, left-lateralized neural processes underlying visual word recognition.