Item-only simulation assumed that the magnitude of error for each item memory would remain the same but the direction of error would not be systematically influenced by the gist. [We generated 1000 simulations for each participant. Each simulation consisted of all simulated retrieved items, corresponding to all the landmark locations. For each location, we randomly generated a retrieved location based on the participant’s true error for this specific location, allowing angle to vary randomly across the simulations. Then, we computed the center for these locations to get the simulated estimated gist for each simulated participant. The error for such simulated estimated gist was the Euclidean distance between the true center and the simulated gist. The simulated estimated gist error for each real participant was the average value of simulated estimated gist error for their corresponding 1000 simulated participants]. Aligned rank transformed ANOVA analysis with three gist memory error type revealed a main effect of delay, F(2, 381) = 42.93, p < 0.001, memory type, F(2, 381) = 15.17, p < 0.001, and an interaction between delay and memory type, F(4, 381) = 3.83, p < 0.01, suggesting that the error increase over time was not the same for these gist memory types. For reported gist error (Gr) and simulated estimated gist error (sGe), we found a significant interaction between delay group and gist memory error type, F(2, 254) = 6.68, p = 0.001. For estimated gist error (Ge) and simulated estimated gist error, we also found a significant interaction between delay group and gist memory error type, F(2, 254) = 3.28, p = 0.039. Gist error and estimated gist error both increased less over time compared to the simulated estimated gist error under this simple item-only simulation over time, suggesting that participants’ data are not compatible with this simple item-only simulation. We did not find a significant interaction between Gr and Ge across time, F(2, 254) = 1.18, p = 0.31, consistent with the idea that Ge was calculated from item memories influenced by the center after delay. **** indicates p < 0.0001 and ns indicates p > 0.05 by ANOVA (top left). The band indicates the median, the box indicates the first and third quartiles, the whiskers indicate ± 1.5 × interquartile range, and the solid points indicate outliers.