Eye tracking technology is frequently utilized to diagnose eye and neurological disorders, assess sleep and fatigue, study human visual perception, and enable novel gaze-based interaction methods. However, traditional eye tracking methodologies are constrained by bespoke hardware that is often cumbersome to wear, complex to apply, and demands substantial computational resources. To overcome these limitations, we investigated the application of Electrooculography (EOG) eye tracking using 14 electrodes positioned around the ears, integrated into a custom-built headphone form factor device. In a controlled laboratory experiment, 16 participants tracked a series of on-screen stimuli designed to induce smooth pursuits and saccades. Data analysis identified the optimal electrode pairs for tracking vertical and horizontal eye movements, benchmarked against gold-standard EOG and camera-based eye tracking. The electrode montage closest to the eyes provided the best results for horizontal eye movements. One-dimensional smooth pursuit eye movements measured via earEOG exhibited a high correlation with the gold-standard for horizontal 1D pursuits spanning \(2.5^{\circ }\) to \(15^{\circ }\) visual angle for the best performing electrode pair ( \({\textrm{r}}_{\textrm{EOG}} = 0.81, {\textrm{p}}=0.01\) ; \({\textrm{r}}_{\textrm{CAM}} = 0.56, {\textrm{p}}=0.02\) ). Vertical 1D smooth pursuits were only weakly correlated for the best performing pair ( \({\textrm{r}}_{\textrm{EOG}} = 0.32, {\textrm{p}}=0.03\) ; \({\textrm{r}}_{\textrm{CAM}} = 0.31, {\textrm{p}}=0.05\) ). Voltage deflections of earEOG and gold-standard EOG for saccades from \(2.5^{\circ }\) to \(15^{\circ }\) in the four cardinal directions are highly correlated for horizontal eye movement ( \({\textrm{r}}_{\textrm{left}} = 0.99, {\textrm{p}}<0.001\) ; \({\textrm{r}}_{\textrm{right}} = 1.0, p<0.001\) ) but not for vertical eye movements ( \({\textrm{r}}_{\textrm{up}} = 0.79, {\textrm{p}}=0.06\) ; \({\textrm{r}}_{\textrm{down}} = 0.35, {\textrm{p}}=0.53\) ). A regression model was employed to predict absolute gaze angle changes of horizontal saccades using earEOG and gold-standard EOG. In the left and right directions, the earEOG model achieved a mean absolute angular error of \(3.99 ^\circ \pm 3.45 ^\circ\) , for saccades ranging from \(2.5^{\circ }\) to \(15^{\circ }\) . In comparison, gold-standard EOG attained mean absolute angular error of \(2.98 ^\circ \pm 2.44 ^\circ\) . Overall, horizontal earEOG demonstrated strong performance, indicating its potential effectiveness in our setup. On the other hand, vertical earEOG showed significantly poorer results, suggesting that it may not be feasible with our current configuration.
