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Fig. 2. Test trials and expected homing directions in experiment I. The large
circles with a small rectangle represent the experimental arena and peripheral
nest box, respectively. The dotted arrows along the arena circle indicate that
the arena has been rotated before the start of the trial. The continuous lines
with an arrow within arena circles represent the outward journey to the food
source. The small circles indicate that the animal walks in circles
(diameter 30 cm). Trials without a fix (left) take place under infrared
light only, and the subjects can only home through path integration (PI) that
is anchored to the current nest position (dotted arrows). In trials with a fix
(right), the room lights are turned on for 10–12 s during or at the end
of the outward trip, when the subject is located at P1. During a fix, the
homing directions based on PI on the one hand, and on visual references on the
other hand, diverge by 98°. The arrows starting at P1 or P2 represent the
expected homing directions depending on PI that is reset by a visual fix
(dashed arrows) or is not reset (dotted arrows). (In controlled reference
trials, the two expected homing directions lead to the nest at 0°). In
uncontrolled reference trials, the arena is not rotated and the animal is
guided from the nest exit at 0° to any point on the arena floor, where it
is offered food, and then returns to the nest. In controlled reference trials,
the arena and nest box are rotated by 180° and then rotated back to the
standard 0° position. From the nest exit at 0°, the hamster is led to
one of five different locations (dots), where it walks along 2.5 full circles
(small circle) in the dark, and then along a further circle in the opposite
direction, the room lights being turned on. The animal is then offered food
and returns home, in darkness. In both reference trials, homing is considered
to be successful if the animal deviates by no more than 45° from the
correct homing direction when reaching the arena periphery. Before the start
of each experimental trial, the arena (with nest box) is rotated by 135°
clockwise or counterclockwise. Only clockwise trials are presented here. In
baseline trials, the hamster is guided to P1, where it picks up some food, and
then to P2, where it fills its pouches completely and initiates the homing
trip. Baseline-with-circling trials follow the same pattern, but the animal
walks along 2.5 full circles near P1 instead of pouching food. In
fix-without-translation trials, the animal is led to P1, walks along 2.5 full
circles in the dark and then along a further circle in the opposite direction
in the fully lit environment, fills its cheek pouches at P1 and returns
towards the arena periphery. Fix-with-translation trials follow the same
procedures; however, after the fix interval, the animal is led from P1 to P2,
where it fills its pouches and starts the homing trip.
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67°. A full
resetting would lead to the standard nest location N0°, and a partial
(direction only) resetting to the virtual nest location NDR. The theoretical
homing directions based on a full or a partial resetting differ by 72° at
P1 and by 125° at P2.
