Discrimination of movement and visual transfer abilities in cichlids (Pseudotropheus zebra)

摘要

Fish rival birds and mammals in many of their cognitive skills, and have been shown to successfully discriminate between a range of stationary and moving objects. The present study tested the ability of Pseudotropheus zebra to recognize unique movement patterns shown in the form of a single moving dot, point displays (PDs), point-light displays (PLDs), and videos of moving organisms in two alternative forced-choice experiments. Cichlids successfully distinguished between (1) different directions of movement, (2) a biological vs. a random movement, (3) a biological (humanwalking) vs. a scrambled motion pattern, and (4) two biological motion patterns (human walking to the left vs. to the right). Following training in (3), it was tested if the walking human was also correctly identified when either the positive, the alternative, or both stimuli were altered or presented inverted; following training in (4), stimuli were presented inverted or moving backwards. With the exception of the presentation of inverted and backwards-moving stimuli, fish excelled at these tasks. Furthermore, cichlids successfully discriminated between videos of different organisms such as eel vs. trout, human vs. dog, eagle vs. bat, and dolphin vs. shark. Following each training, a series of transfer tests elucidated whether P. zebra could also recognize these organisms when shown in transfer test trials (a) from a different perspective (front or sideways), (b) enlarged or downsized, or (c) as PDs. With few exceptions, all individuals learned all tasks and significantly often chose the previously reinforced (but altered) training stimulus over the alternative one during transfer tests. This indicates that cichlids have the ability to recognize a familiar organism under new conditions, for example, based on its movement alone, which may be helpful in recognizing approaching predators early on.