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Albert Ahumada, Lauren Scharff; Lines and dipoles are efficiently detected. Journal of Vision 2007;7(9):337. doi: 10.1167/7.9.337.
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Watson, Barlow, & Robson (1983 Nature) rated patterns by contrast energy threshold and found a 7 cpd Gabor to be best. Watson (2000 Optics Express) plotted the contrast energy thresholds for the 43 Modelfest stimuli and found a Gaussian spot with a standard deviation (SD) of 2.1 arc min was best. When he compensated for contrast sensitivity, the best spot was the smallest one (SD = 1.05 min) and the overall best stimulus was the “one octave” (window SD = 2.1 min) 16 cpd Gabor. When he accounted for spatial summation in addition to contrast sensitivity, the spots and the Gabors were similar in performance and the best stimulus (but not significantly different) was the long (window SD = 30 min), narrow (1 pixel = 0.5 min) line. Using Modelfest-like methods, we have measured the detectability of lines as a function of length (2, 6, 18, 54 min) and width (0.5, 1, 2 min) and also have compared the detectability of lines (8 × 0.5 min) with that of dipoles (2 adjacent 8 × 0.5 min lines of equal and opposite contrast). We found that short lines can have contrast energy thresholds as low as those of spots, and that when contrast sensitivity is taken into account, dipole thresholds can be as low as those of lines. We also found that the introduction of fixation marks close to the small patterns could lower the thresholds as much as 3 dB, suggesting that spatial uncertainty may have played an important role in the detection of small patterns in the Modelfest experiments.
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