Reading‐related wavelength and spatial frequency effects in visual spatial location

Abstract

SummarySpecific deficits in the processing of transient visual stimuli have been identified in reading‐disabled children, and it has been shown that the filtering out of some medium to high spatial frequencies and some visible wavelengths impacts on their performance in a number of visual tasks. To assess further how these light diffusing and colour filtering manipulations might mediate visual processing, this study compared the letter‐naming accuracy and visual spatial location judgements of eighteen poor readers with those made by eighteen good readers of the same age. Naming and spatial discrepancy measures were recorded for briefly displayed target letters at varying eccentricities, for each child, under a normal (NI) condition and wearing blue (Be), yellow (Yw), diffusion (Dn), blue with diffusion (BeDn), and yellow with diffusion (YwDn) optical framed lenses. A preliminary analysis of the data detected larger spatial discrepancies for the poor readers, and this finding was consistent with the presence of a deficit in transient (or magnocellular) activity in these children. Both the naming accuracy data and the spatial location data showed filter‐dependent differences in reading ability. The letter‐naming data showed that the addition of the blue filter to the diffusion lens significantly depressed performance only for the good readers, and that the addition of the yellow filter to the diffusion lens significantly improved performance only for the poor readers. Comparison of the spatial discrepancies showed that the rate at which location accuracy declined with increasing target eccentricity was smaller for the blue and yellow lenses than for normal viewing in the case of the good readers but not in the case of the poor readers. Some of these effects are consistent with the proposition that increased stimulation of the blue cones relative to the red and green cones reduces tonic inhibition in the magnocellular pathways and increases the level of transient activity, but others are more problematical. It is cautioned, therefore, that while the short‐wavelength lenses show some differentiation between good and poor readers, this should not be interpreted as supporting the efficacy of prescribed, coloured or diffusing optical filters as a remediation technique.