Representations of perception models developed for object recognition exhibit typical spatial cell-like firing profiles.
Active units were classified across model layers based on standard criteria used to identify place cells (P), head-direction cells (D), and border cells (B). Example units from VGG-16 (see Appendix for more examples from other models). (A) Pie charts illustrating the proportion of “spatial” cell types identified in DNNs, including units that are inactive. Many units satisfied the criteria for place, head-direction and border cells irrespective of layer depth. Many units exhibited mixed selectivity, with a significant amount of units displaying strong place and directional tuning. (B-E) Spatial firing profiles of model units in spatial activation maps and polar plots . For activation maps, each unit’s activation was plotted at each location in the two-dimensional area irrespective of heading direction. For direction selectivity, polar plots show the average activity of the activity map across location at a given angle, which reflects the tuning magnitude to each heading direction). (B) Example place cell units that show strong spatial selecitivity with little direction selectivity. (C) Examples of head-direction cell units that show strong direction selectivity but weak location selectivity. (D) Examples of border cell units that respond strongly to boundaries of the environment. (E) Examples of mixed-selective place and head-direction cell units with strong spatial and directional tuning. Examples presented are from VGG-16. See Appendix for more examples.