Influences of additional external noise on neuronal responses in our model.

<p>We carried out simulations at 4 different noise levels. We computed the discriminability index <i>d'</i> for L2/3 (<b><i>A</i></b>) and L5 (<b><i>B</i></b>) of the model responding to a vertical or a horizontal bar. The dashed line shows the magnitude of <i>d'</i> in the neutral condition. Solid gray and black lines indicate the results of spatial and feature-based modes of attention, respectively. L2/3 and L5 showed similar changes in discriminability with changes in the noise level. Only at a low noise level, spatial attention increased <i>d'</i> compared to <i>d'</i> in the neutral condition, whereas feature-based attention increased it at any noise level tested in this study.