Montani, V. 1 , Facoetti, A. 2 & Zorzi, M. 2
1 Department of Developmental Psychology and Socialization-University of Padua
2 Department of General Psychology-University of Padua
The reading rate depends on the number of letters we take in at each fixation (visual span). This span seems limited by crowding: beyond some eccentricity the reader’s critical spacing exceeds the spacing of the text and the letters crowd each other, spoiling recognition. We used the progressive demasking task, a degraded stimulus presentation procedure, to study the crowding effect during reading of isolated words. Stimuli were familiar words or pronounceable non-words, and spacing between letters was manipulated. We used standard letter and decreased letter spacing (1,03 x letter length). Our results show that the identification of decreased spaced strings was slower than normally spaced strings (crowding effect). More importantly, decreasing the lateral distance between letters impaired non-word more than word identification, thereby revealing a top-down modulation of the crowding effect. Lexical, whole-word representations would convey top-down signals that interactively help to extract spatial details in the reduced spacing condition. This feedback mechanism is not available for unfamiliar letter strings. Since sub-lexical information and phonological decoding are crucial for reading development, increased crowding could be an important factor underlying reading difficulties in dyslexic children.