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with threshold; a temporal structuring of the background which interacts with
target interpretation; random noise or ‘intelligence’ structure which may change
the confidence level at which a decision is made. Considerable study has been
given to several of these areas. In this chapter what the author considers to be
some of the more important parts of the large body of data will be summarised.
It will be shown that certain of the phenomena observed may be tentatively
explained by considering the retinal image gradients associated with the complex
situations.
13.1 Local background structure
13.2 General background structure
13.3 Structured search
References
14. SURFACE REFLECTIVITY
To this point, in all considerations of object / background presentations, it has
been assumed, by implication, that whatever the surface luminance structure is,
it is invariant with time during presentation. Now, if one considers the laws of
reflection, this assumption must imply one of two things - either the viewing
and illumination conditions are invariant or all surfaces in the viewed scene are
diffuse reflectors*. In a practical situation it is relatively rare for one to be
looking at something from an invariant angle and with invariant illumination. On
the other hand it is convenient to assume that most natural objects and many
man-made objects, seen from a distance, will approximate to diffuse reflectors
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