Prospective Sky Guides (Fixed Wing Aircraft)

The Ecological Approach to Motion Perception

The primary sense utilised by humans to guide themselves through their environment is sight.  Sight has evolved into a precision system that enables light rays impinging on the 2-dimensional retinal surface to be interpreted instantly (‘at-a-glance’), intuitively and in three dimensions.  When moving through that environment, the visual field must not only provide information concerning where the observer is now, but where the observer will be in the near future.

A number of theories exist as to how what we see is interpreted and hence perceived.  The Ecological Theory, pioneered by J. J. Gibson [11,12], maintains that the information in the observer’s field of vision, particularly when the observer moves, is rich.  The observer and its environment are inextricably linked (hence ecological).  A number of key concepts exist within the theory:

  1. The world is comprised of surfaces under illumination;
  2. Because light travels in straight lines, it can carry information (e.g. holographic images);
  3. When an observer moves, the motion is perceived by the way that the optic field changes from moment to moment – this changed is termed optic flow.
  4. The flow of the visual scene is not random but follow lawful progressions or patterns of stimulation that remain constant during the motion e.g. motion perspective (objects close to the moving observer appear to be moving more quickly than objects in the distance).  These are known as invariants

The first question that an observer must be able to answer when moving is ‘where am I heading ?’.  Once this can be established, the next question must be ‘will I collide with anything ?’.  If the answer to this question is ‘yes’, then the question ‘how long will it be until a collision occurs ?’ must be addressed if if timely corrective action is to take place.  Any theory regarding a living organism’s perception of self-motion must be able to explain how those questions are answered.  The ecological approach, using optic flow as a basis, provides explanations for how each of these questions can be answered directly from the motion itself. 

In the context of engineering display design, any theory used must be amenable to mathematical manipulation and analysis.  The theory must also provide relevance to the research subject matter.  Ecological psychology places the environment at the heart of perception [13] and does not rely on experiments involving isolated stimuli in a laboratory (organisms did not evolve under such conditions).  This ‘real-world’ approach is compelling to an engineering mind that must deal with ‘real-world solutions’.  From a mathematical perspective, ecological psychology and the use of optic flow has been developed into a simple but elegant theory known as ‘Tau Theory’.  As such, this branch of psychology, or, perhaps more correctly, psychophysics, was considered suitable to guide the research described in these pages.