First published online April 17, 2009
Journal of Experimental Biology 212, 1344-1350 (2009)
Published by The Company of Biologists 2009
doi: 10.1242/jeb.021881
Fast learning but coarse discrimination of colours in restrained honeybees
C. Niggebrügge1,
G. Leboulle1,
R. Menzel1,
B. Komischke1 and
N. Hempel de Ibarra1,2,*
1 Department of Neurobiology, Institute of Biology, Free University of Berlin,
14195 Berlin, Germany
2 Centre for Research in Animal Behaviour, School of Psychology, University of
Exeter, Exeter EX4 4QG, UK
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Fig. 1. Colour discrimination and generalisation after absolute conditioning. Bees
were exposed to either a blue or yellow spot and rewarded with sucrose
solution during 10 training trials. The graph depicts the rate of proboscis
extensions to the trained stimulus before delivering the reward. Following
acquisition, each bee trained with the blue stimulus (triangles) was tested
subsequently with a yellow, dim blue (d. blue), green and white unrewarded
stimulus (black bars). Similarly, bees trained to a yellow stimulus (diamonds)
were tested with a blue, dim yellow (d. yellow), green and white test stimulus
(chequered bars). Bars for test responses are arranged according to the
chromatic distance between the test stimulus and the respective rewarded
colour stimulus (CS+) (descending order). Asterisks depict significant
differences between responses during the last acquisition trial and the test
trial (Wilcoxon matched-pairs test, P<0.05). Differences in
responses to test stimuli were assessed for the groups trained to blue (black
bars) and yellow (checkered bars) separately (McNemar  2 test;
bars with different letters differ significantly from each other,
P<0.05). PER, proboscis extension response.
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Fig. 2. Colour discrimination and generalisation after differential conditioning.
(A) Some bees were trained to the yellow stimulus as rewarded colour stimulus
(CS+) (closed diamonds) versus the blue stimulus as unrewarded colour
stimulus (CS–) (closed triangles) and tested with dim yellow (d. yellow)
and green stimuli (black bars). Other bees were also trained to the yellow
stimulus as CS+ (open diamonds) but experienced a green CS– (open
circles). They were tested with blue, dim yellow and dim green (d. green) test
stimuli (white bars). (B) In the reversal group, bees were exposed to a yellow
CS– versus a blue CS+ (closed diamonds and triangles, respectively) or a
green CS+ (open circles) (corresponding yellow CS–: open diamonds). The
former bees were tested with a green and dim blue (d. blue) stimulus (black
bars). Bees rewarded on the green stimulus were tested with a dim green, dim
yellow and blue stimulus (open bars). Asterisks depict significant differences
between responses during the last acquisition trial and the test trial
(Wilcoxon matched-pairs test, P<0.05). PER, proboscis extension
response.
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Fig. 3. Differential conditioning of different intensities. Bees were trained to
discriminate a dim yellow (d. yellow) rewarded colour stimulus (CS+) (closed
diamonds) from a yellow unrewarded colour stimulus (CS–) (closed
squares; N=14) or vice-versa (open symbols; N=16).
Response rates are depicted separately for CS+ (solid lines) and CS–
(broken lines). After training, they were tested with a similar and dissimilar
colour, green and blue, respectively (black bars, bees trained to dim yellow
CS+; white bars, bees trained to yellow CS+). Asterisks depict significant
differences between responses during the last acquisition trial and the test
trial (Wilcoxon matched-pairs test, P<0.05). PER, proboscis
extension response.
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Fig. 4. Differential conditioning of intermediate colours. Bees were trained to
discriminate a blue rewarded colour stimulus (CS+) (closed triangles) against
a white unrewarded colour stimulus (CS–) (closed squares) or a yellow
CS– (open diamonds) (corresponding blue CS+: open triangles),
respectively. The first group was tested with a yellow and dim blue (d. blue)
test stimulus (black bars), while the other group that experienced the yellow
CS– was tested with a white and dim blue test stimulus (open bars).
Asterisks depict significant differences between responses during the last
acquisition trial and the test trial (Wilcoxon matched-pairs test,
P<0.05). PER, proboscis extension response.
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Fig. 5. Memory test and extinction trials after absolute conditioning. The memory
recall for a previously rewarded yellow stimulus was tested after one hour of
rest following a three trial conditioning period (grey circles). To test the
response to extinction trials, bees were trained during three (black
triangles) or seven learning trials (black squares) with a yellow stimulus.
The training was followed by nine or five subsequent unrewarded stimulus
presentations (open symbols), respectively. The asterisk depicts significant
differences between responses during the last acquisition trial and unrewarded
trials (Wilcoxon matched-pairs test, P<0.05).
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© The Company of Biologists Ltd 2009
