Cartoon depiction of the direction-dependent interaction rules in submodels M1 through M5.

<p>A right-moving reference individual at <i>x</i> receives signals from distant individuals, to the right at <i>x</i> + <i>s</i>, and from the left at <i>x</i> − <i>s</i>. Arrows at <i>x</i> + <i>s</i> and <i>x</i> − <i>s</i> indicate whether the reference individual will receive stimuli from distant right-moving (right arrow) and distant left-moving (left arrow) neighbours. For example, the direction-dependent interaction rules in submodel M1 describe how a right-moving reference individual at <i>x</i> receives signals from distant individuals, to the right at <i>x</i> + <i>s</i> and from the left at <i>x</i> − <i>s</i>. For attraction and repulsion (a), this individual uses all information from neighbours regardless of their direction of travel. Arrows pointing left and right indicate this. For alignment (b), the reference individual only uses information from neighbours heading toward it, as indicated by the arrows heading toward the reference individual. The submodels illustrated here are the same as those considered in [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0198550#pone.0198550.ref022" target="_blank">22</a>–<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0198550#pone.0198550.ref024" target="_blank">24</a>].