Measures
Gallagher proximity: average distance to the platform
How close, on average, did the animal stay?
Gallagher, Burwell and Burchinal (1993) developed a learning index for aged rats based on how close the animal stayed to the platform location during probe trials. It is the basis of what are now called the Gallagher proximity measures.
Why it matters
Proximity is the average distance from the target, so it shows how close the search stayed even without exact hits.
More detail
Global proximity (mean distance to the learned location) suits probe trials; cumulative proximity (summed over time) suits training trials and is read with latency and path length. Raw and start-point-corrected values are given; lower values mean closer.
Gallagher et al. (1993) introduced proximity measures describing the spatial distribution of search in training and probe trials, in work on spatial learning impairment in ageing, and Maei et al. (2009) found mean proximity consistently outperformed quadrant, zone and crossing measures in detecting group differences. Proximity describes closeness to one target only, so use it with close encounters, heading, path ratio, speed and inactivity.
Gallagher proximity (PROXIMmt, PROXmt00 etc.)
Global proximity is the average distance from the target over the trial or slice: lower means closer, and it is used for probes. Cumulative proximity sums one-second average distances: higher means more search error, and it is used for training.
More detail
Cumulative proximity should be read with latency and path length because escape time sets the summing window. By segment shows early close approach then distancing, or late focusing; the first few seconds of a probe are often most informative.
Proximity describes closeness to one target only: it does not identify strategy, count near-goal visits, measure initial intent or path efficiency. The corrected version excludes the time to swim the straight-line start-to-target distance at the subject's mean active speed; report raw and corrected values together (Gallagher et al., 1993).
Questions people ask
What is the difference between Gallagher Global, Cumulative and by-segment?
Gallagher measures describe how close the subject stayed to the target, using its average distance from the target. Global is the average distance over the trial or slice (lower means closer; used for probes). Cumulative is the sum of one-second average distances (higher means more search error; used for training). By segment is the one-second distance series itself.
More detail
Gallagher proximity measures are distance-to-target measures: they summarise how close the subject stayed to the target throughout the trial, which makes them less dependent on a single crossing than counts or quadrant time. Global is the mean distance (PROXIMmt for the target, PROXmt00 etc. for each calibrated position) and suits probe trials; Cumulative sums the one-second mean distances and suits acquisition trials, but read it with latency and path length because escape time sets the summing window. By segment (tick the checkbox) shows the one-second series, revealing early close approach then distancing, or late focusing; the first few seconds of a probe are often most informative.
Going deeper
Proximity describes closeness to one target only: it does not identify strategy, count near-goal visits, or measure initial intent or path efficiency. Use it with close encounter measures, heading, path ratio, speed and inactivity. The measures follow Gallagher, Burwell & Burchinal (1993), doi:10.1037/0735-7044.107.4.618.
What are the start-point-corrected Gallagher measures, and why are they sometimes 'not applicable'?
Start-point-corrected Gallagher measures are proximity scores that remove the time a direct swim from the start would take, so unequal start distances do not bias the score. They are 'not applicable' when there is no valid target, too little path data, no active speed, or no samples left after correction.
More detail
Start-point-corrected Gallagher measures are versions of the Gallagher proximity measures (distance to target over time) that discount the unavoidable time spent travelling from the start, so subjects released at different distances can be compared. The correction estimates the time to cover the straight-line start-to-target distance at the subject's mean active speed (speed excluding inactive or floating periods) and excludes that initial interval. They are 'not applicable' when there is no valid target, too little path data, no active speed, or no samples left after correction. Report raw and corrected values together, with swim-speed context.
Going deeper
Very short remaining records after correction may limit interpretation even when a value is produced, so check the trial length left after the correction and treat values from very short remainders with caution.
See also the Gallagher proximity measures on hvsimage.com.
Sources
- Gallagher et al. (1993). Severity of spatial learning impairment in aging: Development of a learning index for performance in the Morris water maze. Behavioral Neuroscience 107(4):618-626. doi:10.1037/0735-7044.107.4.618
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