Table 3.
Factor loadings
| Factor 1 | Factor 2 | Factor 3 | Factor 4 | Factor 5 | Rep score | ||
|---|---|---|---|---|---|---|---|
| Maximum of radial velocity (with respect to operandum) | 0.94 | 0.25 | 0.16 | 0.01 | −0.03 | 0.55 | |
| SD of radial velocity (with respect to operandum) | 0.92 | 0.14 | 0.13 | 0.30 | 0.00 | 0.36 | |
| SD of speed | 0.88 | 0.10 | 0.37 | 0.22 | 0.00 | 0.18 | |
| Maximum speed | 0.88 | 0.24 | 0.39 | −0.02 | 0.02 | 0.25 | |
| Move duration | 0.09 | 0.95 | 0.06 | −0.07 | 0.08 | 0.78 | |
| Path length | 0.34 | 0.82 | 0.29 | 0.33 | 0.05 | −0.18 | |
| Latency to maximum speed | 0.04 | 0.77 | 0.09 | −0.08 | −0.02 | 0.73 | |
| Latency to maximum acceleration | 0.04 | 0.75 | 0.08 | −0.09 | 0.00 | 0.72 | |
| Maximum deviation from direct path | 0.21 | 0.66 | 0.28 | 0.58 | 0.10 | −0.50 | |
| SD of angular velocity (with respect to operandum) | 0.39 | 0.12 | 0.87 | 0.17 | 0.00 | 0.19 | |
| Maximum of angular velocity (with respect to operandum) | 0.45 | 0.23 | 0.82 | −0.02 | 0.19 | −0.02 | |
| Mean of angular velocity (with respect to operandum) | 0.18 | 0.23 | 0.74 | 0.45 | −0.38 | 0.26 | |
| Turn efficiency | 0.01 | 0.04 | 0.04 | −0.20 | 0.02 | NA | |
| Mean radial velocity (with respect to operandum) | 0.54 | 0.20 | 0.14 | 0.77 | 0.20 | −0.30 | |
| Mean speed | 0.49 | 0.24 | 0.37 | 0.75 | 0.01 | −0.36 | |
| Path efficiency | −0.03 | −0.02 | 0.11 | 0.48 | −0.02 | 0.43 | |
| Movement onset latency | −0.12 | 0.01 | −0.04 | −0.15 | 0.01 | NA | |
| Net change in heading | −0.01 | −0.03 | 0.00 | −0.01 | 0.01 | NA |
PCA followed by FA was used as the basis to select a subset of variables for subsequent use as regressors in GLMs to detect correlation with neuronal activity. Variables used as regressors are shown in bold. We selected a representative variable for each factor based on high loading onto its representative factor and low co-loading onto other factors (which together are represented by the rep score, the variable’s highest factor loading minus the sum of its loadings onto all other factors). These representative variables were: factor 1, maximum of radial velocity with respect to operandum; factor 2, move duration; factor 3: SD of angular velocity with respect to operandum; factor 4, path efficiency. Additionally, we selected three “independent” variables that did not load strongly onto any one factor (turn efficiency, net heading change, and movement onset latency). NA, not applicable.