j *@ - Sociedade Brasileira de Psicologia

OPPO NENT CO LO R COD ING A ND CO LO R PERCEPTIO N IN BEES
1. N chophysical scaling melods
WERNER BACKHAUS
Universidade Livre de Berlim
Psychophysics measures the responses of subjects with respect to one or more
stim tli. The responses are directly related to the stimuli (preferences) or related to
judgments when stimuli are compared with reference stimuli. The results of the experiments
depend in general on the design of the experiment and the instructions given to
the artimnl by trnining. Bees can be instruqted by training to prefer one stimulus from
others. The bees confuse the stimuli more or less depending on their discriminability.
If the trained stim ulus is absent, they show graded preferenc:s for the other stimuli
according to the similarity with the remembered trained stimulus even if all Zternatives
are wel discriminqble from the trained stimulus (Backhaus et al., 1987). The choice
behavior of bees is based on similarity judgments. Htlmans show two diferent kinds of
similarity judgments: the similarity value pf two stimuli is reported diredly or
indirectly in the ondimensional case as distance diferences (n urstone, 1927) or
ratios (ratio scnling, Torgerson, 1958 Ekmnn, 1963) of the scale values of two stimuli.
In the case of multidimensional stimuli, the jude el!t is performed as diference between
the distances of each of two test stimuli to the reference stimulus (method of
triads, Tôrgerson, 1958) or as ratio of the length of one stimulus vecior to the projec-
'
tion o ? t he other stimulus vectoy onto it (Ekman , 1963).
Tlw lmits of perçeption are thought to be simultaneously present. Thus,
differences between scale values or vectors representing stimuli in a multidimensional
space are symmetrical, i.e. the distance from A to B has the same value as the distancç
from B to A. n ere jore,
diference judpnents lead to symmetrical data mntrices, but
the mntrices of ratiojudment! are asymmetrk in general.
2. S- lm' g of color sim larity in humnnm
Differçnce and ratio scaling methods have been applied to hlxmnn color vision
(Torgerson, 1958; Indow and Ohslxmi, 1972; Helm, 1964). Multidimensional srmling
of difference judm ents showed that color vision is three dimensional and the m int
configurations are very similar to the corifigtrations in the subjective Munsel color
order system. Helm (1964) has Sven an interpretation of the derived scales to be two
opponent color scales representing blue/yelowness and red/peennes of the stimuli
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