Many perceptual stimuli are cross-modal, processed by more than one sensory modality.
Human perceptual processing tends to interpret covarying visual and auditory information as originating from one stimulus event, and this interpretation is adaptive for organizing or guiding one's perceptions. Researchers of cross-modal perception traditionally have chosen static stimuli over dynamic stimuli. Further, horizontal or vertical placements have been chosen over placements in depth. It can be argued that two-dimensional experimental conditions are somewhat restricted in ecological validity and generalizability to the natural world. The lack of dynamic conditions also limits generalizability.