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N. S. Yeotikar, S. K. Khuu, L. J. Asper, J. Alexander, C. M. Suttle; Configuration Effects of Chain Lateral Gabor Stimuli on Parafoveal Crowding. Invest. Ophthalmol. Vis. Sci. 2010;51(13):5173.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate the configuration effects of flanking Gabor stimuli (GS), arranged laterally in a row (chain) on parafoveal crowding under three flanker conditions using an orientation discrimination task.
A random double staircase psychophysical procedure was used to obtain orientation discrimination thresholds (ODT) in ten normally-sighted subjects (6 females, 24-38 years). Two basic flanker configurations, ISO and CROSS (horizontal and vertical orientation, relative to the horizontally oriented reference GS) were employed under three subset conditions namely, viewing eccentricities (EC: 0, 3, 6 and 9o), number of flankers (NF: 1, 3 and 5), and flankers’ contrast (FC: 30, 50 and 70%). The target GS contrast was kept constant at 50% and the initial orientation offsets were 24o and 15o for the two staircases. The observers’ task was to judge the target orientation with respect to horizontal (spatial 2AFC). The non-dominant eye (sighting dominance) was tested monocularly in an otherwise dark room. A ‘no flanker’ condition at 6o EC was considered as baseline and subtracted from all the ODT measures to yield relative threshold (RT). RT elevation above baseline was considered as crowding.
Linear mixed models were used for statistical analysis and posthoc comparisons were adjusted with Bonferroni correction. In both ISO and CROSS configurations, the RT was significantly higher than baseline at 9o (p<0.001) but not at 0o or 3o EC. RT was significantly higher than baseline in the ISO configuration but not in the CROSS configuration, for all the subsets of both NF (p=0.01) and FC (p<0.01) conditions. However, the RT measures within three subsets of NF and FC conditions were not significantly different compared to baseline, in both ISO and CROSS configurations.
These results demonstrate typical dependencies of crowding on eccentricity, independent of flanker configurations. The NF and FC conditions produced significant crowding in ISO configuration, but not in the CROSS configuration. This configurational difference suggests that ‘target saliency’ and ‘perceptual grouping’ are factors in parafoveal crowding of chain lateral Gabor stimuli in orientation discrimination.
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