Fish use of geometric and non-geometric properties of an environment for spatial reorientation

When disoriented in a novel environment, rats and young children reoriented themselves in accord with the large-scale shape of the environment, but not in accord with non-geometric properties of the environment such as the colour of a wall or the patterning of a distinct featural panel placed in a corner. In contrast to young children and mature rats, human adults conjoined geometric and non-geometric information. It has been claimed that their performance suggests that some representational systems become more accessible and flexible over development and evolution. However, other species (e.g. chicks, pigeons, monkeys) also conjoined geometric and non-geometric information. We tested fish (Xenotoca eiseni) in a rectangular environment constructed to eliminate external orientation cues. Ways to escapes from the environment were located in some corners that fish had to find out. When tested in an all-white tank, fish proved able to reorient them- selves using purely geometric information: in accord with the shape of the environment, they searched the correct and the rotationally equivalent corners equally often. On the other hand, when tested in a tank with one blue wall, fish searched only at the correct corner thus demonstrating that they also encoded non-geometric information. Moreover, when trained with four distinct panels located at the corners and then tested in the absence of the panels, chicks chose the two geometrically correct corners, thus indicating that they encode geometric information even when featural information alone would suffice for orientation. Possible reasons for species differences in the encoding and integrating of geometric and non-geometric information are discussed.