The color phi phenomenon: Not so special, after all?
Fig 4
An abstract one-dimensional three-pixel visual system, illustrating the phi phenomenon.
(A) The circuit. Outputs ya, yb and yc separately respond to inputs xa, xb and xc respectively, corresponding to perception when above a certain threshold. Weights and τ-values of the a and c-chains are identical as those indicated in the b-chain. (B) Long distance weakly coupled feedforward priming units pa, pb and pc (middle graph) with fast activation and slow decay enable sensitivity to recent inputs to be carried to adjacent output units. (C) If the input pulses on xa and xc are temporally sufficiently separated, the decayed priming signals pa and pc are unable to evoke a response from the middle output yb. (D) When inputs xa and xc are stimulated adequately fast after one another, the priming signals combine and a ghost percept on yb appears. This ghost happens after ya and before yc cross the threshold in opposite directions. The ghost appears without the presence of an input stimulus on xb.