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7.5 Peripheral thresholds
7.6 Sign of contrast
7.7 The effect of edge sharpness
7.8 Dynamic thresholds
7.9 The scotopic regime
7 .1 0 Colour thresholds
7 .1 1 Discussion
References
8. RUDIMENTARY SEARCH MODELLING
In the preceding chapters the processes of acquisition have been limited to the
detection of objects in a known position in the visual field. Whilst such
knowledge is a necessary foundation from which to develop an appreciation of
the practical functions of vision, the visual task is frequently more complicated.
If detection of the presence of an object somewhere in the visual field is the task
one is concerned with - as, for instance, in the task of detecting the presence of
an aircraft in the sky or of a vehicle in open country - then the important
difference between this task and basic detection threshold studies discussed so
far is the need to search for the object over an extended field. The search process
is discussed at length by Koopman, Krendel & Wodinsky and Bloomfield,
amongst others.
During a search process the eye scans the scene in a series of jumps, dwelling
for a fraction of a second on each area. Such a series of jumps and dwells are the
search equivalent of the involuntary saccades and inter-saccadic intervals
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