Abstract
Unexpected responses of physical systems to external stimuli can be observed when the stimuli are organized into spatial patterns and, especially, when stimuli of different physical origins are involved, leading to the pattern interaction problem. Combinations of weak stimuli-individually only capable of producing marginal local responses-can produce a global response without involving any bifurcations. Its existence is demonstrated by the interaction of properly tuned topography and temperature patterns. When these patterns overlap in a symmetry preserving manner, the resulting convection has the form of local rolls. When these patterns are misaligned, the resulting convection involves global horizontal particle movement with direction depending on the type of misalignment.