In a 2002 Nature paper, Bruce measured the response of disparity-tuned cells in V1 to a full range of two-dimensional disparities. This was unusual, because previous work had either used horizontal disparity (in awake animals), or disparity orthogonal to the preferred orientation of the cell (in anaesthetised animals). Bruce found that the 2D disparity-tuning surfaces of the cells tended to be elongated along the horizontal direction, no matter what the preferred orientation of the cell was. This was a very surprising result, as it completely contradicts the predictions of all existing models. Everyone had always assumed that the tuning to 2D disparity would reflect the cell's orientation tuning. So, my next project was to investigate what sort of model could account for this result.

We came up with two models. The first simply postulated that the cells Bruce recorded from were composed of many subunits, and these were scattered more widely horizontally than vertically. The second involved monocular normalization by appropriately elongated units.