Cite as:
Zdravkovic S, Gilchrist A L, 2000, "Lightness determination for an object under two illuminations" Perception 29 ECVP Abstract Supplement

Lightness determination for an object under two illuminations

S Zdravkovic, A L Gilchrist

When a shadow is cast across half of an object, observers can make a separate lightness match for (a) the whole object, (b) the shadowed region, and (c) the nonshadowed region.

We tested three hypotheses concerning whether matches for the whole object agree most closely with: (i) matches for the region in higher illumination, (ii) matches for the region within the larger field of illumination, or (iii) whichever matches show the least error. A row of five adjacent rectangles, ranging from black to white, was suspended in mid-air. A shadow with a blurred edge was cast across this row so that only part of each rectangle was under the shadow. Previously we reported object matches for the black-and-white targets only, and these were closer to veridical values than to the matches obtained for either higher illumination or larger field size. In order to understand how the visual system could minimise the error we tested intermediate shades of gray as well as a truncated range of grays.

The results show object matches to agree with target regions that appear to lie in the prevailing illumination, even if this entails a significant shift away from veridicality.

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