Constraints on Letter-in-String Identification in Peripheral Vision: Effects of Number of Flankers and Deployment of Attention

Myriam Chanceaux,Jonathan Grainger

doi:10.3389/fpsyg.2013.00119

Abstract

Effects of non-adjacent flanking elements on crowding of letter stimuli were examined in experiments manipulating the number of flanking elements and the deployment of spatial attention. To this end, identification accuracy of single letters was compared with identification of letter targets surrounded by two, four, or six flanking elements placed symmetrically left and right of the target. Target stimuli were presented left or right of a central fixation, and appeared either unilaterally or with an equivalent number of characters in the contralateral visual field (bilateral presentation). Experiment 1A tested letter targets with random letter flankers, and Experiments 1B and 2 tested letter targets with Xs as flanking stimuli. The results revealed a number of flankers effect that extended beyond standard two-flanker crowding. Flanker interference was stronger with random letter flankers compared with homogeneous Xs, and performance was systematically better under unilateral presentation conditions compared with bilateral presentation. Furthermore, the difference between the zero-flanker and two-flanker conditions was significantly greater under bilateral presentation, whereas the difference between two-flankers and four-flankers did not differ across unilateral and bilateral presentation. The complete pattern of results can be captured by the independent contributions of excessive feature integration and deployment of spatial attention to letter-in-string visibility.

Highlights

What factors influence our ability to identify a single letter presented in a random string of letters? Answering this question is important because it will help develop our understanding of the very first phase of the reading process during which visual feature information is mapped in parallel onto position-coded letter identities in both central and peripheral vision (Grainger and van Heuven, 2003; Marzouki et al, 2013)
CROWDING AND NON-ADJACENT FLANKERS Effects of lateral interference on letter identification is a well-studied phenomenon in experimental psychology, with resultsshowing that target letters flanked by other letters to the left and to the right, are harder to identify than isolated letter targets (e.g., Bouma, 1970; Huckauf and Nazir, 2007; Grainger et al, 2010)
The main findings of the present study can be summarized as follows: (1) number of flanking stimuli continued to affect letter identification beyond the two-flanker conditions of standard crowding experiments; (2) homogeneous × flankers facilitated letter identification compared with different letter flankers; (3) unilateral presentation facilitated letter identification compared with bilateral presentation; and (4) the interfering effects of adjacent flankers were reduced under unilateral compared with bilateral presentation and with X flankers compared with different letter flankers, whereas differences between the two-flanker and four-flanker conditions were not affected by these manipulations

Summary

Introduction

What factors influence our ability to identify a single letter presented in a random string of letters? Answering this question is important because it will help develop our understanding of the very first phase of the reading process during which visual feature information is mapped in parallel onto position-coded letter identities in both central and peripheral vision (Grainger and van Heuven, 2003; Marzouki et al, 2013). CROWDING AND NON-ADJACENT FLANKERS Effects of lateral interference on letter identification is a well-studied phenomenon in experimental psychology, with resultsshowing that target letters flanked by other letters to the left and to the right, are harder to identify than isolated letter targets (e.g., Bouma, 1970; Huckauf and Nazir, 2007; Grainger et al, 2010) These effects of lateral interference have been integrated within the wider perspective of crowding effects on the processing of various kinds of visual stimuli (e.g., Pelli et al, 2004; Pelli and Tillman, 2008; see Levi, 2008; Whitney and Levi, 2011, for reviews). Natural cluttered environments in general, and printed text in particular, nearly always involve situations where there are non-adjacent flanking elements

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Discussion

Conclusion