Measures
Path length and path ratio
Distance travelled is less sensitive to swim speed than latency.
Path length is the distance the animal swims before it reaches the platform. Because it doesn't depend on speed, it helps when groups swim at different speeds. The path ratio goes a step further and compares the actual path with the straight line from start to platform.
Why it matters
Path length shows how far the subject travelled; shorter paths over training usually mean the platform location is being learned.
More detail
Shorter paths over learning trials indicate learning of the platform location. Path length is confounded by start-to-platform distance, so when start positions vary use the path efficiency ratio.
Path length gives only minimal insights into strategy: a long path may reflect thigmotaxis, scanning the whole pool or looping close to the platform, and procedural strategies such as chaining can shorten paths in a way that looks like spatial learning. Combine it with strategy measures.
Why it matters
Path ratio compares the route taken with the straight line, so you can compare trials fairly even when start points change.
More detail
Path ratio is the actual path length divided by the shortest possible path between start and platform; a perfectly direct swim has a ratio of 1 and higher values mean less efficient paths. It is not affected by start-to-platform distance.
Because it normalises for the ideal path, path ratio supports comparisons across moving start points, reversal trials and different pool sizes, including across different set-ups. In the Direct Path definition a ratio of 1.2 or less is classed as direct.
Path length
Path length is how far the subject travelled, in metres. Shorter paths to the platform usually mean a more direct search, but path length depends on start distance, so compare like with like or use the path ratio.
More detail
Path length is the sum of distances between scaled coordinates from release to arrival. Because path length depends on start distance and pool size, the path efficiency ratio is better for comparing moving starts, reversal and different pool sizes. The suffix mt means metres.
All distances use the calibrated pool diameter, so a diameter entered larger than the real water surface inflates path length; check calibration before comparing studies.
Path efficiency ratio
The path ratio is the actual path divided by the shortest direct path. A ratio of 1 is perfectly direct and lower is better, so well-trained subjects approach 1.
More detail
Unlike path length, the ratio does not depend on start distance. Tick one box to include it in single and batch analysis. A path counts as direct for the Direct Path classifications when actual path / shortest path is no more than 1.2.
No Direct Path classification but a low path ratio means an efficient route that did not meet the criteria. The Direct Path classifications are described in the HVS Image Direct Path Measures documentation.
Questions people ask
Why use path efficiency ratio rather than path length?
Path length depends on start distance; the ratio (actual path / shortest direct path) does not. A ratio of 1 is perfectly direct and lower is better, so well-trained subjects approach 1. Tick one box to include it in single and batch analysis.
More detail
Path length is the total distance travelled from release to arrival, the sum of distances between scaled coordinates; the path efficiency ratio is that path divided by the shortest direct path. Because path length depends on start distance and pool size, the ratio is better for comparing moving starts, reversal and different pool sizes. A ratio of 1 is perfectly direct and lower is better.
Going deeper
The ratio still rises with tracking noise and with very short trials, where small deviations weigh heavily, so smooth the data (HVS uses 100 ms) and read the ratio with heading angle and Direct Path classifications.
HVS Image has a page on path length in Morris water maze analysis.
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