Figure 4.

A comparison between non-synaesthetes and synaesthetes according to the cross-activation model, disinhibited feedback model and the stochastic resonance model. ‘M’ indicates modulatory effects, symbol ‘+’ indicates excitatory input, and symbol ‘−’ represents inhibitory input. According to the cross-activation model, synaesthetes have additional connections between the inducer and concurrent, while the disinhibited feedback model suggests the absence of inhibitory signal from higher areas to the concurrent in synaesthetes. The stochastic resonance model suggests that synaesthetes have higher levels of noise in the concurrent, which leads to stochastic synchronization between the inducer and the concurrent. (Online version in colour.)