Configural sensitivity to inter-letter spacing in visual word perception

The word superiority effect refers to the phenomenon that people have better recognition of letters presented within words as compared to recognition of isolated letters. Although many previous research on how the spatial relations between letters in words affect the perceptual processing through the inversion paradigm, a significant amount of effort goes into setting the default inter-letter spacing when designing new fonts. Our current research examines the effect of manipulating letter spacing on the processing efficiency, as a measure of the word superiority effect. First, we tested multiple different words instead of fixed word stimuli to show that measures of efficiency can be generalized; second, we disrupted default inter-letter spacing by increasing, decreasing, and randomizing letter spacing to explore the extent to which the efficiency was sustained with the assessment functions. Our results indicate that participants are limited capacity only in the extreme spacing scenario. Additionally, the principle component (PC) analysis shows that highest PC values occur at normal spacing with degradation with increased disruption—spreading or narrowing. These results appear to confirm the configural nature of perceptual processing with normally-spaced words between identifiable tracking and kerning boundaries, and agree well with the ideas about optimal spacing by type designers and typographers implicit in general notion of "rhythmic spacing''. This work is also notable in that we demonstrate the use of assessment functions as a standardized tool for assessing the capacity benefits and efficiency of configural processing.