Figure 4. Simulated selections.

An arbitrary visual input (a) representing four images characterised by different brightness, that change luminance pattern every 5 seconds. The first control simulation (b) shows the ideal behaviour: the artificial agent chooses in each interval the position associated to the brightest image (in this example, the correct sequence is: up, left, down, right). The condition of control is characterised by a set of parameters allowing quick initiation of selections as a response to the sensory input and continuous maintenance for the duration of the luminance pattern. The same parameters as the control, but for the reduced DA drive have been used to show the agent exhibits distinct behaviours, depending on the strength of the sensory stimulus. (c) Weak stimuli result in motor suppression; (e) conversely, strong sensory stimuli are associated with selections continuously changed with ambitendency among the strongest competitors. In both cases, the agent shows short perseverance after each change of luminance pattern. Finally, the simulated selections associated with Parkinson’s disease treated with subthalamic DBS (d) show the agent is again capable of performing correct choices and maintain a chosen selection. On the downside, the perseverance increases significantly as the agent shows problems in disengaging after a change in luminance pattern.