Fig. 4.

Invariant responses over the geometric shapes, physical appearances, colors, construction materials, etc. (A) Invariant responses of Cell #1 to the geometric shapes of nests. As shown by both the perievent spike rasters and perievent spike histograms, Cell #1 exhibited a significant firing increase in response to a new circular nest made out of the top part of a cardboard coffee cup with a wall height of 2.5 cm and a diameter of 7.5 cm (Left), a square cardboard nest (Center), and a triangular cardboard nest (Right). (B) Invariant responses of Cell #1 to nests made from different materials. A metal nest (Left), plastic nest (Center), and porcelain nest (Right) were tested. (C) The cell also increased its firing when the mouse encountered natural cotton nests (Left and Center) but not to five cotton balls that were simply lumped together (Right). The bin width in the perievent spike histogram is 250 ms.