Figure 5.

Human reaction times (RTs) for different levels of variation in two-class invariant object categorization tasks with plain and natural backgrounds. The RTs were almost equal across all levels of variation when objects were presented on plain backgrounds (except for the higher levels of variation, see p-values for all comparisons at the right insets. We made all possible comparisons between RTs across different levels to find out whether the differences between the RTs are statistically significant. Here we only showed matrices for motorcycle vs. car. Animal vs. car gives similar p-value matrices). In contrast, when objects were presented on natural backgrounds, the RTs in all levels of variation increased significantly compared to the plain background condition. Error bars are s.e.m. See p-values on the top of the figure show comparisons between natural and plain background conditions.