Measures
Swim speed
Not a memory measure, but you'll want it before you interpret one.
Swim speed doesn't measure memory, but it guards against misreading the measures that do. Dr Roger Morris's 1999 essay notes that general locomotory activity "is monitored in the watermaze as swimming speed".
Why it matters
Speed is a check that slower or faster results are about memory, not about how well the subject can move.
More detail
Latency, path length and platform crossings are strongly affected by swim speed. If one group is much slower, longer latencies and fewer crossings may reflect motor or motivational issues rather than cognitive ones. SPEEDmts includes floating; ACTIVEms excludes slow periods; both are in metres per second.
Escape from water is relatively immune from activity or body mass differences (Vorhees and Williams, 2006), but speed still needs checking. A slow speed may itself be informative, for example in ageing or lesion models; in some studies slow swimmers should be included and in others excluded to maintain data quality, so decide which applies to yours.
Average and active speed (SPEEDmts, ACTIVEms)
Average speed is path divided by trial duration, so it includes stationary time. Active speed leaves out slow floating periods. Both are in metres per second.
More detail
SPEEDmts is overall average speed including floating; ACTIVEms excludes slow floating periods. If speeds look too fast, check the pool diameter you entered at calibration first: if larger than the real water surface, all distances and speeds are inflated.
Mouse swim speed varies with water temperature, pool size, strain and treatment, so use speed as a control when comparing latency between groups. One web page states swim speed in centimetres per second; the software outputs metres per second.
Questions people ask
Swim speeds look too fast. How is speed calculated and what should I check?
Check the pool diameter you entered at calibration first: if larger than the real water surface, all distances and speeds are inflated. 1) Average speed = path / trial duration (includes stationary time). 2) Check duration against a stopwatch and path against a printout. 3) Look for outlying points.
More detail
All distances use the calibrated pool diameter. SPEEDmts is overall average speed including floating; ACTIVEms excludes slow floating periods; both in metres per second. Mouse swim speed varies with water temperature, pool size, strain and treatment.
Going deeper
The software outputs speed in metres per second, not centimetres per second. A path ending just short of the platform can also mean the pool or platform diameter entered differs from the real one.
See also swim speed in Morris water maze analysis on hvsimage.com.
Spotted a mistake, or know a better source? Tell us and we'll fix it and say so on our corrections page.