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Robert Green, Edwin Dickinson, David Badcock; Convergent evidence for global processing of shape. Journal of Vision 2018;18(10):412. doi: 10.1167/18.10.412.
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© ARVO (1962-2015); The Authors (2016-present)
There is an ongoing debate over whether there is convincing evidence in support of global contour integration in shape discrimination tasks, particularly when using radial frequency (RF) patterns as stimuli (Baldwin, Schmidtmann, Kingdom, & Hess, 2016). The objection lies in the previous use of high-threshold-theory (HTT), rather than signal detection theory (SDT) to analyse the change in observer thresholds with increasing cycles of modulation. Here we use a discrimination at threshold method to determine whether there is evidence of global processing around the contour of RF patterns. This provided strong experimental evidence for global integration occurring around RF3 and RF5 patterns. To provide a bridge between current and past research we examined the two proposed methods, finding that HTT produced probability summation estimates which were more conservative than SDT (when an appropriate number of channels was used to generate estimates). We found no difference in performance when an RF pattern was presented as the only test stimulus in a block of trials or when two RF patterns were interleaved. For SDT probability summation estimates to account for this it would be necessary for the number of monitored channels to either remain the same for both patterns, or be so high that changing patterns has no observable effect. We reject the idea that probability summation can describe the data. Our results demonstrate the importance of using random phase RF patterns while measuring integration around a contour and provides strong evidence for global shape processing around low frequency RF patterns.
Meeting abstract presented at VSS 2018
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