Retinotopic selectivity of adaptation-based compression of event duration: Reply to Burr, Cicchini, Arrighi, and Morrone

There are two points at issue here. The first is whether there is a robust adaptation-based duration compression in a spatiotopic frame of reference (when the eye moves and the stimulus is placed in the same screen position as the adaptor). The second is whether there is perceived duration compression in a retinotopic frame of reference (when the eye moves and the stimulus is placed in the same retinal position). The first issue is the robustness of the spatiotopic effect reported by Burr, Tozzi, and Morrone (2007). We reported a trend in the spatiotopic direction when the standard was presented first but not when the standard was presented second (Bruno, Ayhan, & Johnston, 2010). We used a twotailed test because for a one-tailed test it would have been necessary to ignore a significant difference in the direction opposite to the expectation. We have previously found expansion after adaptation in regions surrounding the test (Ayhan, Bruno, Nishida, & Johnston, 2009) and after 5-Hz adaptation in dyslexics (Johnston et al., 2008), therefore apparent duration expansion is possible, and if we found expansion, we would want to report it. We should also report that the number of subjects was set before the start of the experiment, there were no outliers, and no subjects were removed from the analysis. Burr et al. (this issue) invited us to report the results of Experiment 6 (Bruno et al., 2010) for the spatiotopic conditions with the authors removed.We used a bootstrapped one-sample t-test (PASW) given the smaller N. With the authors, the p-values are Standard First p = 0.072, Standard Second p = 0.172, and Standard Random p = 0.108. Without the authors, we have Standard First p = 0.097, Standard Second p = 0.223, and Standard Random p = 0.034. With Bonferroni correction (criterion 0.016 for 3 tests), the trend, reported in our paper in the spatiotopic conditions, just fails to reach significance, with or without the three practiced observers. We do not deny the possibility of finding a significant spatiotopic effect using Burr’s laboratory paradigm; they indeed have reported such effects; however, in our study, the trend we saw in that direction did not reach significance on a two-tailed test and did not occur robustly in all conditions. We do not see a spatiotopic trend in trials in which the standard (in the adapted region) is presented second. Presenting the standard second introduces a delay between switching off the adaptor and switching on the standard of an additional 700–1500 ms. Burr et al. attribute this to a decay of the spatiotopic effect within this period.We attribute the difference to a switch in strategy in the standard first adaptation trials with observers choosing to ignore the standard and simply comparing duration on any given trial relative to the mean of the set. Burr et al. point out that in some of their experiments trials were mixed and in other trials were blocked, so subjects could not use a running average of stimuli as a standard. However, Morgan (1992) Journal of Vision (2011) 11(2):21a, 1–3 http://www.journalofvision. org/content/11/2/21a 1