Jarvstad et al (2014) provide a worked illustration showing that it is not straightforward to declare perceptuo-motor decision making optimal, or even more optimal when compared to cognitive decisions.

They note that, in contrast to cognitive level decisions, that perceptuo-motor decisions have been described a optimal or near optimal (Seydell et al, 2008; Trommershäuser et al, 2006). But they also note that there are differences in the performance conditions and criteria of assessment as optimal between perceptuo-motor and cognitive decisions. Jarvstad et al (2013) demonstrated that when these differences are eliminated, claims about differences between domains are harder to substantiate.

In this paper, Jarvstad et al (2014) compare two reaching tasks to explore the notional optimality of human perceptuo-motor performance. They show that minor changes in task parameters can affect whether participants are classified as behaving as optimally or not (even if these changes in task parameters do not effect the level of performance of an optimal agent). Specifically they adjusted the size and distance of the reaching targets in their experiment, without qualitatively altering the experiment (nor the instructions and protocol at all).

The bound below which performance is classified as sub-optimal depends on a number of factors. The ease of task affects this (for easier tasks observed performance will be closer to optimal), but so does the variability in an optimal agent’s performance, or the accuracy of estimation around an optimal agent’s performance affect. Jarvstad et al conclude that, for this task at least, it is not straightforward to know how changes in an experiment will effect the bounds within which a subject is classified as optimal. They say (p.413):

That statements about optimality are specific and conditional in this way – that is, a behaviour is optimal given a task of this difficulty, and given these capacity constraints included in the optimal agent— may be appreciated by many, however the literatures typically do not make this explicit, and many claims are simply unsustainable once this fact is taken into account.


Jarvstad, A., Hahn, U., Warren, P. A., & Rushton, S. K. (2014). Are perceptuo-motor decisions really more optimal than cognitive decisions?. Cognition, 130(3), 397-416.

Seydell, A., McCann, B. C., Trommershäuser, J., & Knill, D. C. (2008). Learning stochastic reward distributions in a speeded pointing task. The Journal of Neuroscience, 28, 4356–4367.

Trommershäuser, J., Landy, M. S., & Maloney, L. T. (2006). Humans rapidly estimate expected gain in movement planning. Psychological Science, 17, 981–988.