Abstract
Intuitive physics has traditionally been associated with higher-level cognition, but recent work has also focused on the exciting possibility that properties such as physical *stability* may be rapidly and spontaneously extracted as a part of seeing itself — as when you look at a tower of blocks, and can appreciate at a glance that it is about to topple. Much of this work has contrasted towers that appear stable vs. unstable, in terms of whether they would fall as a result of external physical forces (such as gravity) alone. But the ‘perception of physics’ in block towers seems richer than a binary stable/unstable state. Even when a tower is (and appears to be) stable, for example, we might still readily perceive how *precarious* it is — in terms of how much force would be required in order to knock it over. Here we explored perceived ‘precariousness’ using change detection. Observers viewed pairs of block-tower images (one at a time, separated by a mask), and simply reported whether the second image was different. The towers were always stable, but could be differentially precarious. On More-Precarious trials, a single block was shifted slightly so that the tower became less resistant to falling (as quantified by physics-based simulations with variable amounts of spatial jitter). On corresponding Less-Precarious trials, that same block was shifted slightly so that the tower became *more* resistant to falling. We expected greater attention to (and memory for) changes that introduced a greater likelihood of collapse. But we obtained exactly the opposite pattern: observers were far better at detecting changes on Less-Precarious trials, compared to More-Precarious trials. We explore the possibility that this surprising result may be explained by the ‘perception of history’, in terms of appreciating how such towers were constructed in the first place.