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Light Perception - Material & Methods
2.3 The Light Perception Threshold
2.3.1 Study rationale
Now that we knew the mole-rats could perceive light, and that even at low daylight intensities,
we wanted to narrow down their perception threshold of white light. As conditional training
based on a strong white light stimulus connected to a food reward was unsuccessful (R.
Wegner & P. Dammann, unpublished data), we tested spontaneous reactions to several graded
intensities of white light in a T-maze to find out down to which light intensity Zambian mole-
rats can learn (i.e. perceive) the location of a light source in order to find a food reward.
Preceding the threshold study, we trained the same animals to find a food reward in front of a
white light stimulus in a different set-up than the unsuccessful one to confirm the mole-rats’
ability to perceive light and to create a basis of well-learned intensities for the threshold
examination procedure.
2.3.2 Study procedure
Five mole-rats of the species Fukomys kafuensis (4 females, 1 male) were tested in the preceding
light learning experiment and three individuals of this group (3 females) were consecutively
tested in the light perception threshold study.
In the preceding learning experiment, the mole-rats were trained to reach a food
reward connected to a light stimulus in a maze (for details, see fig. A5) using operant
conditioning. The maze was made from thick, light-impervious plastic material with a non-
reflective, black inner side. Two coldlight lamps (KL 150B, Schott, Mainz; light source
Xenophot 15V 150W) were inserted into both terminal tunnels of the T-shaped maze and
both were switched on to prevent unilateral auditory, lamp-generated cues. The illuminated
side, that the animals were trained to, was determined in a randomized pattern for each run of
the experimental series. A food reward (sunflower seeds) was placed at the end of the
iluminated tunnel. On the dark side, light was blocked by an inserted metal plate; sunflower
seeds were also placed on this side, behind the metal plate, to exclude that the animals were
guided by the odour of the reward rather than by the light stimulus. As the metal plate was not
tight regarding the food smell, placing seeds on both sides ensured that the animals chose the
illuminated side to reach their reward. Olfactory orientation would have resulted in a random
choice independent of the illuminated side.
The learning experiments comprised eight learning series with eight different light
intensities, beginning with a light intensity that was assumed to be definitely perceivable by the
mole-rats and then by reducing the intensity gradually down in the following learning series in
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