Hunting the Snark: The contribution of the avian hippocampus to long-term visual memory and the representation of serial order.

Abstract

The study that forms the topic of this thesis was an investigation into the avian hippocampus’ contribution to visual memory and the representation of spatial information. Control and hippocampal lesioned pigeons (Colomba livia) learned a series of 2- and 3-item lists. After learning a block of 10 3-item lists pigeon’s memory for the lists was assessed. The delay between being trained on a 3-item list and being tested on that same list varied from just a couple of days to over 400 days. Following the second and final retention test pigeon’s ability to represent lists spatially was assessed. This was done by presenting pigeons with maintained and changed derived lists. All derived lists were composed of items drawn from the last five lists pigeons were trained on. On derived-maintained lists all items maintained the ordinal position (i.e., 1st, 2nd, 3rd) they occupied in the training lists. In contrast, on derived-changed lists no items maintained the ordinal position they occupied in the training lists. Finally, pigeons trained on derived lists in which one item maintained its ordinal position while the other two items were changed. With respect to the hypotheses, it was anticipated that control animals would display better memory for the training lists. In addition, it was predicted control animals would outperform hippocampal animals on the derived-maintained list but perform more poorly on the derived-changed list. This was predicted because of the robust literature describing the contribution that the hippocampus makes to spatial memory and more recent suggestions that lists like those used here are represented spatially. Neither hypothesis was supported, control and hippocamapal animals performed at a comparable level even at the longest delays. Similiarly, there was no difference in how control and hippocampal animals performed on the derived-maintained and derived-changed lists. We disscuss these findings in the context of whether the avian hippocampus plays a role in visual memory and whether pigeons represent the ordinal position of list items spatially.