Knowledge Base

Analyze Data

Phase Dispersions Parameters

• Target Start (T-Start) – Initial Contact of the target paw.
• Peculiarities – Displays the abbreviations for a number of potential error conditions that can occur:
  • ANT – Anchor but no valid target. This is not considered an error with the placement of the first anchor paw, when the target has not been placed yet.
  • AMT – Anchor with multiple targets. This occurs when the target paw is placed more often than the anchor paw.
  • TNA – Target no anchor. This is not considered to be an error with the placement of the last target, when the anchor is not placed on the glass plate anymore.
• Mismatches – This row displays the number of Peculiarities that occurred.
• CStat Mean / AD / SD / R – Phase Dispersions and Couplings are more correctly described as a circular variable where a value of 0% (that is, the Target paw starting exactly at the same time as the Anchor paw) is equivalent to a value of 100% (that is, the Target paw starting at the end of the previous step cycle of the Anchor paw). In order to generate meaningful averages, special procedures are followed. The values derived in this way are labeled as CStat.
  • Mean is the circular mean, expressed as percentage. For Phase Dispersions, it ranges between -50% and +50%. For Couplings, it ranges between 0% and 100%.
  • AD is the Angular Deviation, expressed as percentage. AD is the same as the Standard Deviation in CatWalk 10.6 and earlier versions.
  • SD is the circular Standard Deviation, expressed as percentage. AD and SD are measures of spread and are calculated with similar formulas.
  • R is the length of the vector that represents the mean direction, that is, the mean percentage projected on a circle. It measures the degree of concentration of values around the mean, and is therefore a measure of directedness. R is dimensionless and ranges between 0 (no dominant direction) and 1 (full directedness).

In the Phase Dispersions sheet, when you click a row with a target and an anchor pair, the Print View highlights both the target and the anchor paw, and the Timing View graphically displays the interval between Initial Contact of the anchor and target paw and the Anchor Duration.

Notes on Phase Dispersions

The values of Phase Dispersions are, by definition, limited in the range -50% to +75%. Values between 50% and 75% are equivalent to those between -50% and -25%. Therefore, if the average is greater than 50%, it is expressed as the complementary (negative) value. For example, if the points are around 52%, the CStat Mean reported by CatWalk is -48.

If you are not familiar with circular statistics, take a look at the Excel sheet Calculate Circular Statistics of Phase Dispersions and Couplings.xlsx in the CatWalk XT documentation folder.

Applications

Kloos et al. (2005) use the Phase Dispersions parameter to study the effect of locomotor and sensory recovery from spinal cord injury (SCI) on inter-paw coordination in rats. In normal animals, for the diagonal paw pairs (RF-LH, LF-RH) the target paw typically moves synchronously with the anchor so the Initial Contacts occur simultaneously, resulting in a Phase Dispersions value of 0%. Girdle pairs (RF-LF, RH-LH) usually yield a Phase Dispersions value of 50% when walking at a moderate speed. Kloos et al. found that depending on the severity of SCI, recovery of inter-paw coordination followed different patterns.

Couplings

Couplings describe the temporal relationship between placement of two paws within a step cycle. It is used as a measure of inter-paw coordination. In the Couplings sheet, Couplings values are displayed for all 12 pairs of paws.

Calculation

Couplings are computed the same way as Phase Dispersions. However, in the case of Couplings a target can never precede an anchor. Therefore, the value of Couplings ranges between 0 and 100%.

Assuming that the step cycle is constant, Phase Dispersions and Couplings are related to each other. For example, if the Phase Dispersion value of a single Anchor-Target pair A-B is -20% of the step cycle of A (B occurring earlier than A), for Couplings the value is +80% because the previous paw B is taken as an anchor.

Statistics

For a description of the statistics displayed in the Couplings sheet, see the Phase Dispersions section. The main difference between Couplings and Phase Dispersions is that the average of Couplings is always positive in the range 0%–100%, while the average of Phase Dispersions is in the range -50% to 50%.

Notes on Couplings

If you are not familiar with circular statistics, take a look at the Excel sheet Calculate Circular Statistics of Phase Dispersions and Couplings.xlsx in the CatWalk XT documentation folder. See also the Circular Distributions section.

Support

The Support sheet shows the following parameters:

• Start Time – Displays the start time of the different sections. A section is a time segment in which the same paws make contact with the glass plate. A section starts every time a paw is placed on the glass plate or lifted from the glass plate.
• Duration – Duration of a section.
• Support Formula – This is the number of paws that are simultaneously on the glass plate in a section. The Support Formula starts at Initial Contact of the left hind paw after all paws have been placed on the glass plate once. A new Support Formula row is started with the next Step Cycle of left hind.
• Footfall Formula – Contains information about which paws are touching the glass plate during each section.
• Standing On % – This parameter displays the relative duration of simultaneous contact with the glass plate of all combinations of paws. The combinations are: zero paws, a single paw, diagonal pair of paws (RF-LH or LF-RH), lateral paws (RF-RH or LF-LH), girdle paws (RF-LF or RH-LH), three paws, and four paws.

When you click a Support Formula, the Print View highlights all paws in the section that touch the glass plate, and the Timing View graphically displays the section interval.