Figure 8.

MSE in the corticotectal model depends on unimodal modulatory inputs. Responses of the bimodal, visual-auditory DSC unit from Figure 7 are computed, to targets of visual (V), auditory (A), both (V, A), or neither (spont) modality. Active primary inputs were assigned a value of six, because this value was found to produce maximal MSE for this DSC unit. Responses are shown for the intact model (A) and after interruption of modulatory connections of the visual (B), auditory (C), or both (D) modalities. Interruption of modulatory connections has little effect on modality-specific responses but greatly decreases cross-modal responses and reduces MSE. The reduction in MSE is greatest when modulatory connections of both modalities are interrupted (D). This result is a consequence of training with the correlation-anti-correlation rule in stage two, which produces cross-modal but not modality-specific modulatory connections. The amount of MSE in the model is affected by both the magnitude of modulatory weights and the primary input spontaneous activation probability. In E-H, the modulatory weights have been increased by seven times (v large), and the spontaneous activation probability for the primary inputs has been reduced to zero (p_x0 = 0). Active primary inputs are assigned a value of three, because this value now produces maximum MSE. Responses are shown for the intact model (E) and after interruption of the modulatory connections of the visual (F), auditory (G), or both (H) modalities. The effect of the modulatory connections is qualitatively the same as before (p_x0 = 0.1, v normal), but maximal percentage enhancement is higher. Also, the effect of removal of modulatory connections is greater than before for cross-modal responses and nil for modality-specific responses.