Finally we mention connectionist  models of parsing, which perform syntactic analysis using layered (artificial) neural nets (ANNs, NNs) (see Palmer-Brown et al. 2002; Mayberry and Miikkulainen 2008; and Bengio 2008 for surveys). There is typically a layer of input units (nodes), one or more layers of hidden units, and an output layer, where each layer has (excitatory and inhibitory) connections forward to the next layer, typically conveying evidence for higher-level constituents to that layer. There may also be connections within a hidden layer,  implementing cooperation or competition among alternatives. A linguistic entity such as a phoneme, word, or phrase of a particular type may be represented within a layer either by a pattern of activation of units in that layer (a distributed representation) or by a single activated unit (a localist representation). 