Place versus cued trial

The question

Here's a puzzle worth a few minutes: How do we know an animal is using a map, and not just swimming towards something it can see? You're watching Morris Water Maze Software Guide, over at morriswatermazesoftware.com.

Meet the place versus cued trial

In a place trial the platform is hidden, so the animal has to use room cues to find it. In a cued trial the platform is visible, or marked with a beacon, so the animal can swim straight to what it sees. A 1981 paper used the visible platform as a control for vision, swimming and motivation. If an animal can find a visible platform but not a hidden one, the problem is more likely to be spatial memory than sight or the will to escape.

How it runs

Here's the routine, in order. First, run hidden-platform training from varied start points, with stable room cues. Next, add a cued session, often on a different day, with the platform visible or flagged, and preferably in a new place so the animal cannot just revisit the old spot. Then, keep trial limits, water and handling the same in both conditions. Finally, compare hidden and cued scores in the same animals.

Strengths and limits

What's it good for? It separates place learning from vision and motivation. It is a short add-on to a standard protocol. A spared cued performance makes a hidden-platform deficit much more convincing. Now, the small print. A cue in the same place as the old hidden platform can still be solved with a memory of that place. Some animals are wary of a newly visible platform at first, which can slow the first cued trials.

What to measure

What should you actually measure? Hidden-platform latency and path length: the place-learning scores. Cued-platform latency and path length: the vision and motivation control. First heading on hidden versus cued trials: whether the animal sets off towards a place or towards a seen cue. Cued success rate: how often the visible platform is found within the trial limit. A group looks lost in hidden-platform training. On the cued day they swim straight to the flag in a few seconds. They can see, they can swim, and they want to get out. What they lack is the hidden place.

The takeaway

If you remember only one thing, make it this: cued-platform latency and path length and its neighbours tell you how the task was done, not just how fast. Everything we covered is written up below.