The correct response in the Grid task, which more faithfully ascertains the vividness of recognition, was 66% ± 5%, 46% ± 4%, 36% ± 5%, and 33% ± 5% after 15 min, 1 day, 1 week, and 3 weeks, respectively (bottom panel). There was no significant difference in performance between the 1 week group and the 3 weeks group. Thus, if the solution to a camouflage image is retained 1 week after seeing it, it is retained to essentially to the same degree Nutlin3a also 3 weeks afterwards. Might the performance during
the Test reflect a learning set or skill acquisition of the task, rather than stimulus-specific memory of the camouflage images and their associated solutions? This can be addressed by examining performance on the 10 camouflage images not seen during the Study session. In all four time-lag groups, performance was significantly PS-341 in vitro better on images that were presented in the Study versus novel images. This differential performance cannot be attributed to differences in the images’ attributes, since each participant saw a different subset of 30 camouflage images
during Study, drawn randomly from the total of 40 images. Moreover, no significant difference was found between the performance of the different time groups on the novel images (Figure 4, open symbols; Kruskal-Wallis ANOVA by ranks), indicating that the degradation in performance over time on the images seen at Study was not due to a general decline in task performance. The spontaneous recognition rate in the Study session was 34% ± 3%. There was no significant difference in spontaneous recognition Org 27569 between the four different time groups. This level is similar to the multiple choice correct recognition of novel images during Test (Figure 4), and a dependent samples t test showed no significant difference between the performances in the two tasks, suggesting that there was no general learning of the task above and beyond the stimulus-specific learning. Importantly, there was no subset of images that accounted for the majority of the remembered images. We calculated the frequency
distribution of the Grid task correct responses per image, and the resulted distribution did not significantly differ from the normal distribution (Shapiro-Wilk, p = 0.07). To test for possible effects of image content on subsequent memory, we performed a Kruskal-Wallis ANOVA on correct recognition per image, grouping images by their content (a human figure, an insect, an animal, an object, a face, or a complex scene). There was no effect of content on subsequent memory performance. On the basis of the results of Experiment 1, which showed similar memory performance after 1 week and 3 weeks, we decided to test subsequent memory 1 week after we performed fMRI scanning during the Study session in Experiment 2 (see Figure 3 for the protocol and the notation of its stages).