We agree with the authors that an adequate account of the perception-action interface is needed. However, we believe that the answer will not be found in a common representational structure encoding distal events, as the authors propose, but in Gibson's notion of ecological information, which, as we demonstrate, specifies not only perspective but also prospective and retrospective states of affairs.

For Gibson, sensory stimulation is neither the cause nor a component of perception, but merely incidental. Perception is based on the pickup of information, which occurs when purposeful observers actively seek information. I present a case in which only with the active sampling of the ambient optical flow field can observers extract the requisite information for the control of locomotion.