Is apparent instability a guiding feature in visual search?

Humans are quick to notice if an object is unstable. Does that assessment require attention or can instability serve as a preattentive feature that can guide the deployment of attention? This paper describes a series of visual search experiments, designed to address this question. Experiment 1 shows that less stable images among more stable images are found more efficiently than more stable among less stable; a search asymmetry that supports guidance by instability. Experiment 2 shows efficient search but no search asymmetry when the orientation of the objects is removed as a confound. Experiment 3 independently varies the orientation cues and perceived stability and finds a clear main effect of apparent stability. Experiment 4 shows converging evidence for a role of stability using different stimuli that lack an orientation cue. However, here both search for stable and unstable targets is inefficient. Experiment 5 is a control for Experiment 4, showing that the stability effect in Experiment 4 is not simple side-effects of the geometry of the stimuli. On balance, the data support a role for instability in the guidance of attention in visual search. (184 words).