Decision-making in action: selecting among competing options
We often encounter situations in which we must decide which, of several target objects, to reach towards. According to the influential, but largely untested, affordance competition hypothesis, in such situations the brain prepares competing movement plans for each potential target (Cisek & Kalaska, Annual Review of Neuroscience, 2010).
Recent studies have shown that when required to initiate a reaching movement towards two potential targets, one of which is cued as the target after movement onset (resulting in a later corrective movement to that target), people initially aim their reach in the average direction of the two targets (see red arrow in panel A of the figure below). Although such spatial averaging is consistent with the idea that people simultaneously launch two prepared motor plans (and has been interpreted in this way), it is also consistent with the idea that people compute an average target position and then prepare and execute a single reach towards the average target.
In a recent study we tested between these two possibilities. By including an obstacle that affects the movement to the right target, but not a straight ahead movement, we were able to dissociate the visual position of the right target from its associated movement direction (panel B). If individuals, when presented with two potential targets, average prepared movements to each target, the initial direction of the movement towards the two potential targets should deflected to the left (panel B). In contrast, if they simply average the two target directions, the initial direction should be straight ahead (panel C).
We found that the initial movement direction is deflected to the left, providing direct support for the provocative idea that the brain prepares and integrates multiple competing movement plans in advance of deciding between targets. By representing competing options in terms of actions, the brain may be able to take movement related factors into account when deciding which option to execute.
For more information see: Stewart BM, Gallivan JP, Baugh LA, Flanagan JR (2014) Motor, not visual, encoding of potential reach targets Current Biology 24 (19): R953-4.
To read more about our work on decision making and action selection see Gallivan JP, Barton KS, Chapman CS, Wolpert DM, Flanagan JR (2015), Gallivan JP, Logan L, Wolpert DM, Flanagan JR (2016), and Gallivan JP, Stewart BM, Baugh LA, Wolpert DM, Flanagan JR (2017).