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4.8 Effect of retinal position
4.9 Flicker thresholds
4.10 Effects of motion
4.11 Effects of colour
4.12 Effect of state of eye focus
4.13 Positive versus negative contrast
4.14 Contrast sensitivity
4.15 Orientation effects
4.16 Other factors
References
5. RECOGNITION THRESHOLDS
In the preceding chapter we have been concerned with laboratory performance
at the most basic level of acquisition - that of detecting the presence of an
object. By definition such detection must always imply no ability to extract
detail information about an object such that it can be recognised as of a
particular type. In real life it is rare indeed that the visual task involves nothing
more than simple detection. Much more frequently it is necessary for an
observer to recognise that an object is of the correct class - a square rather than
a circle, a Landolt ‘C’ rather than an annulus, a given letter out of a possible set
of letters, a vehicle rather than a bush. For any of these tasks it is not enough to
be aware of the presence of the object - one must be able to see some of the
structure. What is by no means obvious is exactly what structure it is necessary
to see in order to effect recognition in a given situation. Nor is it obvious how
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