Disentangling the Number of Letters Effect and the Influence of Visual Crowding

Abstract

We transferred the approach of Hautala et al. (2011) and Hautala & Loberg (2015) from Finnish to German to dissociate the confound word length components number of letters (NrL) and spatial width (SpW) inherent to the majority of reading research. The aim was to disentangle the NrL-effect from the influence of visual crowding (cf. Levi et al. 2002). We applied the crossed NrL × SpW manipulations from Hautala & Loberg (2015) to German nouns, expecting results congruent with Finnish: positive correlations of NrL with (summative) fixation durations, and crowding effects of SpW. Despite the inherent correlation of NrL and SpW, we constructed a 2×2 orthogonal design: embedded target words were short (mode 8 letters) or long (10) by NrL, and narrow (mean 52.2 pixels) or wide (58.1) by SpW. 32 German native speakers read 32 sentences. Using LMMs for analysis, we found no NrL main effects. Our NrL manipulation was less distinctive than in the Finnish stimuli (4 vs. 7 letters). But we found first and single fixation durations negatively correlated with SpW – agreeing with the crowding effects uncovered by Hautala & Loberg (2015). While further methodological refinement remains needed, our results support a crowding effect independent of NrL.