Summation characteristics of the detection of compound gratings

S. Plainis, N. R A Parry, A. Panorgias, P. Sapountzis, I. J. Murray

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    Many classical experiments have shown that two superimposed gratings are more easily detected than a single grating, in keeping with probability theory. Here we test the rules for the detection of 2-component compound gratings by extending the range of parameters used in previous experiments. Two complementary methods of deriving summation indices are described. Data are presented so that the conditions for the transition from probability to neural summation are easily identified. True probability summation occurs only when grating contrasts are carefully perceptually equalised and spatial frequency differs by more than a factor of 2. A wide range of contrast ratios of the component gratings were explored such that gratings were at different contrasts, relative to respective thresholds. We find clear evidence of suppressive interactions when the compound gratings are composed of a close to threshold low frequency component and a below-threshold higher spatial frequency component. © 2009 Elsevier Ltd. All rights reserved.
    Original languageEnglish
    Pages (from-to)2056-2066
    Number of pages10
    JournalVision Research
    Issue number16
    Publication statusPublished - 12 Aug 2009


    • Compound gratings
    • Contrast
    • Interactions
    • Probability summation
    • Spatial frequency channels


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