Dynamic differences in letter contrast polarity improve peripheral letter string and word recognition performance

[摘要] Letter crowding (the inability to identify a letter when surrounded by other letters) is reduced when target and flankers are dissimilar. This release is particularly strong when target and flankers have different contrast polarities (Kooi et al, 1994), but peripheral word recognition does not benefit from this release because observers need to simultaneously report target and flankers of different contrasts (Chung et al, 2010). Here, we investigate if the sequential uncrowding of successive letters using a dynamic contrast polarity difference could improve peripheral letter string and word recognition performance. Three subjects participated in two experiments with letters presented horizontally at 10° in the lower visual field in white or black on a gray background (same absolute contrast value) while eye position was controlled. Subjects identified trigrams (Experiment 1) and 5-letter words (Experiment 2) using three different displays (4 blocks of 50 trials for each experiment and each display): (a) Basic display (Black letters), (b) Static contrast polarity variation (SCPV) display (letters with static alternate contrast polarity) and (c) Dynamic contrast polarity variation (DCPV) display (each letter successively changing from black to white for 200 ms from left to right). Presentation duration was 800 ms in Experiment 1, and depended on subjects in Experiment 2 (3.54±1.26 s). Letter print-size was adjusted so that letter recognition rate was at 50% for the basic display in Experiment 1. For each subject, results for Experiments 1 and 2 show the best recognition rate for the DCPV display (average: 64±4% (Exp1) and 72±5% (Exp2)) compared to the SCPV (40±2% (Exp1) and 57±3% (Exp2)) and basic (42±3% (Exp1) and 49±6% (Exp2)) displays. These results suggest that peripheral letter string and word recognition can be improved using letter contrast polarity differences if word letters are successively uncrowded.

[学科分类] 眼科学