Fig. 2.

Habituation model structure, implementing the hierarchical nature of visual processing. Each grey rectangle is a node that simulates the activity of a large number of neurons with similar inputs and outputs. The first layer represents retinotopic visual features; the prime node, representing the features of the doubled-up prime word, either connects to the target node (if the prime matches the target) or the foil node (if the prime does not match the target) in the visual objects layer. The retinotopic target node represents the features of the target display, and also the response display, when it is the same as the target. The retinotopic foil node represents the response display when it is different from the target. The perceptual decision making portion is a new addition to the model, capturing the maintenance of each word’s semantic identity in working memory during the course of the trial sequence for comparison with the response word. Updating into this maintained semantics layer is assumed to underlie the N400, and the degree of residual activation for the response word in this layer is assumed to underlie the same/different decision (i.e., more residual activation indicates that this response word was previously seen in the trial, and thus the correct answer is ‘same’).