Table 1.
Pilot data comparing various freezing measures
| Algorithm | Thr | BL% | Test% | Noise% | Thr/25 % | |
|---|---|---|---|---|---|---|
| A. Human | visual sampling | subj. | 0.4 | 32.1 | (empty chambers) | |
| B. Density [mean (μ) optical density for each frame] | ||||||
| |(μ1–μ2)| | 0.05 | 9.6 | 31.2 | 62.5 | 48.1 | |
| |(μ1–μ2)| & adj | 0.08 | 5.6 | 34.2 | 77.3 | 65.6 | |
| σ(μ1, μ2) | 0.04 | 10.2 | 34.9 | 55.0 | 42.5 | |
| σ(μ1, μ2) & adj | 0.05 | 4.4 | 30.1 | 72.9 | 59.6 | |
| σ(μ1, μ2, μ3) | 0.06 | 3.8 | 31.9 | 87.1 | 69.2 | |
| σ(μ1, μ2, μ3) & adj | 0.07 | 2.0 | 31.2 | 92.1 | 75 | |
| C. Disturbance [standard deviation (σ) of density for each frame] | ||||||
| |(σ1–σ2)| | 0.05 | 7.1 | 33.1 | 90.2 | 80.6 | |
| |(σ1–σ2)| & adj | 0.06 | 1.6 | 31.0 | 94.8 | 85.4 | |
| σ(σ1, σ2) | 0.03 | 6.3 | 29.2 | 93.1 | 84.2 | |
| σ(σ1, σ2) & adj | 0.05 | 2.5 | 33.4 | 97.1 | 91.0 | |
| σ(σ1, σ2, σ3) | 0.06 | 2.7 | 31.9 | 100 | 98.5 | |
| >> σ(σ1, σ2, σ3) & adj | 0.07 | 0.8 | 31.4 | 100 | 100 | |
Table 1 depicts data from the Pilot experiment using NIH Image to score movement and index freezing behavior. (A) Average measurements taken by visual sampling by two human observers. (BL%) Freezing during the 122-sec baseline prior to any shock. (Test%) Freezing during the 122-sec contextual fear test. (B) Measurements using changes in mean optical density from video frame to frame. (Algorithm) Comparison made of successive frames [(μ) mean optical density; (σ) s.d. of the optical density; subscripts 1, 2, 3 refer to successive frames]. (Thr) Threshold for this algorithm that yielded the best fit with human-scored freezing during the context test. (Noise%) Ability to reject noise as nonmovement, from video taken of the chambers without any mice in them. (Thr/25%) Ability to still reject noise if the threshold value is arbitrarily decreased by 25%. (C) Measurements using changes in the disturbance (s.d. of the optical density) from frame to frame. The measure (disturbance) and algorithm chosen [σ(σ1, σ2, σ3) & adj)] for use in experiment 1 yielded equivalent context scores to human observers, exhibited low baseline, and robustly rejected noise.