We end this section by noting that although ERP parameters are sensitive to psychological variables they are neither generally nor readily reducible to psychological constructs. Ultimately it is the brain’s “view” of cognitive processing that we seek to characterize. ERPs provide a particularly apt inroad to this, by being a direct measure of neocortical activity that tracks brain states continuously and instantaneously. The N400’s relationship to other measures (e.g., RTs) whose functional sensitivities had been better mapped out was important as a starting point, but, ultimately, where ERPs are more direct, selective, and sensitive, the direction of influence must shift and, correspondingly, the field must be willing to rethink the pool of available cognitive constructs it has developed, largely from end-state measures. As we will show, in some cases the questions we ask about cognitive processing via the N400 have relatively clear answers; in other cases, however, our failures to converge upon an answer after intensive investigation raises the distinct possibility that the question itself may be ill-posed – either insufficiently clear or based on faulty assumptions.
