You can readily see at a glance how two objects spatially relate to each other. But seeing how 20 objects all relate seems impossible, due to computational explosion (with 190 pairs). Such situations require visual routines: dynamic visual procedures that efficiently compute various properties 'on demand' -- e.g. whether two points lie on the same winding path, in a busy scene containing many points and paths ('path tracing'). Some surprisingly foundational questions about visual routines remain unexplored, including: what (if anything) remains in visual memory after the execution of a visual routine? Does path tracing result in a memory of the traced path itself? Or just of whether there was a path? Or nothing at all, after the moment has passed? We explored this for spontaneous path tracing in 2D mazes. Observers saw a maze in which two probes appeared in positions connected by a path. They were then shown two mazes, and had to select which was the initially presented maze. Across experiments, the incorrect maze could be (1) a Path-Obstruction maze, where a new contour blocked the initial inter-probe path; (2) an Irrelevant-Obstruction maze, where a new contour was introduced elsewhere; or (3) an Alternative-Path maze, where the same new Path-Obstruction contour was accompanied by the removal of an existing contour, providing an alternative inter-probe path. Performance on Path-Obstruction trials was much better than on Irrelevant-Obstruction trials (always controlling for lower-level contour properties across trial types). But Alternative-Path trials entirely eliminated this advantage. This suggests that a visual memory is formed by spontaneous path tracing, but that its content is not the path itself, but only whether a path existed. If visual routines exist to answer on-demand questions during perception, then the resulting memories may consist only of the answers themselves, and not the processing that generated them.

Visual processing usually seems both incidental and instantaneous. But imagine viewing a jumble of shoelaces, and wondering whether two particular tips are part of the same lace. You can answer this by looking, but doing so may require something dynamic happening in vision (as the lace is effectively 'traced'). Such tasks are thought to involve 'visual routines': dynamic visual procedures that efficiently compute various properties on demand, such as whether two points lie on the same curve. Past work has suggested that visual routines are invoked by observers' particular (conscious, voluntary) goals, but here we explore the possibility that some visual routines may also be automatically triggered by certain stimuli themselves. In short, we suggest that certain stimuli effectively afford the operation of particular visual routines (as in Gibsonian affordances). We explored this using stimuli that are familiar in everyday experience, yet relatively novel in human vision science: mazes. You might often solve mazes by drawing paths with a pencil -- but even without a pencil, you might find yourself tracing along various paths mentally. Observers had to compare the visual properties of two probes that were presented along the paths of a maze. Critically, the maze itself was entirely task-irrelevant, but we predicted that simply seeing the visual structure of a maze in the first place would afford automatic mental path tracing. Observers were indeed slower to compare probes that were further from each other along the paths, even when controlling for lower-level visual properties (such as the probes' brute linear separation, i.e. ignoring the maze 'walls'). This novel combination of two prominent themes from our field -- affordances and visual routines -- suggests that at least some visual routines may operate in an automatic (fast, incidental, and stimulus-driven) fashion, as a part of basic visual processing itself.