Table 1.

Comparison of videography, optoelectronic, and EMG methods to Pixy

		Bermejo et al. (1996)	Knutsen et al. (2005)	Voigts et al. (2015)	Ritt et al. (2008)	O'Connor et al. (2010)	Gyory et al. (2010)	Perkon et al. (2011)	EMG	Pixy (our method)
1	Tracking principle	Opto	Video	Video	Video	Video	Video	Video	Muscle	Opto/video
2	Spatial element	Single point	Multiple points	Multiple points	Multiple points	Multiple points	Multiple points	Multiple points	NA	Multiple points
3	Real time	Yes	No	No	No	No	No	No	Yes	Yes
4	Individual whisker	Yes	Yes	Yes	Yes	Yes	No	No	No	Yes
5	Number of single identifiablewhiskers	One whisker on each side	One whisker on each side	One whisker on each side	Three whiskers	Five whiskers	N/A	N/A	NA	Two whiskers (up to seven in principle)
6	Whisker removal	Yes	Yes	Yes	Yes	Yes	N/A	N/A	No	No
7	Limitation	Whisker thickness	Contrast andresolution	Contrast and resolution	Contrast and resolution	Contrast and resolution	Contrast and resolution	Contrast and resolution	NA	Illumination and color
8	Method shows	Single whisker	Single row	C1-4 whiskers	Single whiskers	Multiple whiskers	Two rows	Full whisker pad	Whisker pad	Two whiskers/one whisker and two pad/two paws
9	Head tracking	No	Yes	Yes	Yes	No	Yes	Yes	Yes	Yes
10	Head tracking requirement	N/A	Additional light source for the eye	Tip of nose	Contour edge/whisker base	N/A	No requirement	No requirement	Wire in muscle	Marker glued to head
11	Compatible in IR	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes (single whisker)
12	Algorithm flexibility	Yes (not automatic)	No	No	No	No	No	No	Yes (with wires)	Yes
13	Unrestrained animal	No	Yes	Yes	Yes	No	Yes	Yes	Yes	Yes (whole animal)

Here we compare 13 different features of 7 earlier tracking methods, including optoelectronic (Opto), electromyography (EMG), and other whisker tracking algorithms combined with high-speed videography to our Pixy based method. The elements that we compared here: 1) Tracking principle: Tracking algorithms based on videography, optoelectronic methods like beam breaking, EMG or color. 2) Spatial coordinate system: Beam breaking has a distinct (single or multiple) spatial coordinate, while videography can track over multiple spatial locations. 3) Real-time at any frequency. 4, 5, 6) Number of objects tracked: A single whisker, or multiple individual whiskers, with or without plucking or removing whiskers. 7) Limiting element of each method: Lighting, contrast, resolution and length of whiskers for videography, or color and painting for Pixy, 8) Output: Single whisker, multiple whisker or whisker and whisker pad. 9, 10) Head direction tracking method: possibility, and whether the eye need or tip of the nose or a color needs to be tracked. 11) Ability to tack in infrared red light: All the high speed cameras can work with infrared light, as can EMG and optoelectronic methods. The pixy camera is limited in this context because it can only be used to track a single spatially distinct point with a pixy camera. 12) The flexibility in tracking multiple body parts: Cameras can be used for tracking any object, but optoelectronic methods, and EMGs, and even automated tracking video systems have to be optimized or positioned for tracking the object of interest. 13) The ability to use the system in unrestrained animals.