Metameric Colors

Individual Results in Color Recognition Experiments

Nest 4. Great tit.
In the color recognition experiment for training the birds were offered the stimuli different by two features simultaneously: both by their relative spectral reflectance (FePb vs CoCd) and by lightness, dark FePb stimulus being the conditioning one and light CoCd stimulus being the reference. By the way, such organization of the experiment made easier the work of experimenters, who saw the difference between the stimuli now.
The male great tit (that did learned to use the perch, but did not distinguishe metameric stripes by orientation in the form discrimination experiment) learned to discriminate new stimuli in two days. After that it was tested with another pair of stimuli with opposite spectrum-lightness relation: the section with nestlings was marked with dark CoCd and the empty section - with light FePb one. Though the lightness might be used here as a guide as well, the male was guided by the spectral properties of the stimuli and preferred FePb stimulus. From the point of view of human observer its behavior looked unreasonable, for the nestlings were in the section marked with dark stimuli as before, while the bird changed its preference and became to bring the food to the empty section marked with light stimuli.

Experimental conditions and discrimination scores
for male great tit from the nest 4

last training session

test session

+
dark FePb

-
light CoCd

+
dark CoCd

-
light FePb

19 :  5

 2 :  9

Nest 5. Flycatcher.
Four pairs of metameric stimuli were prepared that differed in lightness and even in color for human observers. Both female and male flycatchers learned to distinguish the CoCd (reinforced) stimulus from the FePb one of the 1st pair of the metamers rather quickly. Being tested with new specimens cut from the same painted papers, the birds showed correct discrimination with confidence. During the subsequent tests with new pairs of metameric stimuli the female chose also CoCd stimuli. With 3rd and 4th pairs (not shown at the table) the scores were 7:0 and 12:3 respectively. The male in these test sessions flied less regularly. So, only a cumulative score reaches confidence, namely, 19:8 in favour of CoCd stimuli for all 3 new metameric colors.

Experimental conditions and discrimination scores
for female and male flycatcher from the nest 5

last training session

first test session

second test session

+
1st CoCd