Tuesday, 28 July 2015

Gestalt - The Limitations of G.I.S.S. (General Impressions of Size and Shape)

At the heart of any discussion around gestalt we have G.I.S.S., meaning the general impressions of size and shape, apparently derived from a WWII Royal Air Force term.  Curiously, there is also a valid association with a similarly sounding word JIZZ, apparently of Irish origin (HERE) and pre-dating WWII by some decades.  It is unclear what is implied by the Irish use of JIZZ in the context it was first used and whether it related to size, shape or the general 'gist' or 'energy' of a living species.  In any case, whether referring to the German term gestalt, the British term G.I.S.S. or the Irish term JIZZ, we are essentially dealing with the same concept.  We are referring to that almost indescribable uniqueness of a species in terms of its size, shape and how it carries itself, including it's behavior.  This is a much more complex concept than one derived solely from size and shape.

When the British Armed Forces came up with the concept of G.I.S.S. they were referring to the identification of fixed-wing aircraft.  Due to the limits of design, war planes of the 1940's would have all moved about in very much the same way.  So, realistically G.I.S.S. would have been mainly about the relative proportions of different aeroplanes.  It probably wasn't envisaged that such a concept would be adopted and applied to the general impression given by living creatures.  After all, there is far more to this subject then simply the size and general proportions of a bird.

Photographs represent an excellent opportunity to study a subject in fine detail and it is highly tempting to believe that we can take accurate measurements from photographs and use those to determine the accurate shape or proportions of a bird.  If we were going to start anywhere we might start with solid structures like the bareparts - consider perhaps the relative proportions of the eyes, bill and legs.  We might then include length of the primaries beyond the tertials, and the tip of the tail beyond the primaries at rest.  All these structures, on the face of it at least, seem like very valid and predictable measurements from photographs, and as birders we have become accustomed to studying these proportions in the field.  But, as I have demonstrated in recent postings (HERE, HERE and HERE) these are not reliable measurements from photographs.

At the heart of this challenge we have to accept that a photograph is merely a two-dimensional projection of a three-dimensional world.  We can only reasonably accurately measure objects which lie perfectly parallel to the plane of the lens and sensor, as discussed HERE.  When we try to measure something which is not parallel to that plane we run into the problem of perspective foreshortening.

And yet, even when we take away all field marks and leave only the simple outline of a bird the brain is quite good at interrogating general proportions along with our library of knowledge and beginning the process of identification.

If we are to approach gestalt in bird images from an objective, reasonably scientific perspective we may have to rethink some of our long held beliefs and discard some of the tools we have been using in the field and in our study of photographs.  We may have to come up with some new tools to work through this challenge of gestalt from bird images.

Link to quiz solution.

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