The Parietal Cortex in Sensemaking: The Dissociation of Multiple Types of Spatial Information

Figure 3

The parietal cortex module for computing target values on Numerosity, Radius, DistanceFly, and DistanceWalk (represented on the target layer “PC_Value”). The hidden layer “PC_HL2” is “sliced” into 4 groups, each responsible for a different type of target values. The competition on PC_HL2 is achieved by a kWTA function (k-Winners-Take-all, [26]), which is a combination of within-group inhibition (only the most active units within a group can contribute as the layer output) and entire-layer inhibition (units within a relatively weaker group are more likely to be inhibited). Such a function allows both of the dissociation and interference between different types of target computations. In the bottom-up information flow, input for both Numerosity and Radius is represented on PC_Attn (group attacks on visual field); Input for DistanceFly is based on a direct comparison of PCWM_POI (point of interest) and PCWM_GC (group center). Input for DistanceWalk is represented on PCWM_RS (road segment between POI and group center). The top-down control from layer PFCcPC represents 4 types of magnitude computation (Numerosity, Radius, DistanceFly, DistanceWalk) (the fifth unit is tentatively reserved for topological comparison). At any time, only one type of the magnitude values is available at the output level. The example shown here illustrates the case when the top-down demand is to compute Numerosity (second unit on PFCcPC), such that the bottom-right section on PC_HL2 is more likely to win over other sections in kWTA inhibition.