Fig. 12.

Spatial selectivity of utricle and saccule stimulation. To examine spatial selectivity, the direction of eye movements elicited from stimulation can be grouped based on the magnitude ratio between the right and left eyes. From the ocular countertilt data collected from normal chinchillas detailed and shown in Fig 11, bottom, in the companion paper (Hageman et al. 2020) and using the trends in this manuscript’s Table 1, the ratio of right/left eye magnitude gives an indication of the tilt axis in the following groups: A: ratio < 0.8 (right eye magnitude < left eye magnitude); B: right and left eye magnitudes approximately equal (0.8 ≤ ratio ≤1.2); and C: ratio>1.2 (right eye magnitude > left eye magnitude). Each stimulation electrode used to elicit eye movements are circled and grouped based on the magnitude ratio of eye position between the right and left eye. Data shown are from all chinchillas during 300 pps pulse train of 40-s duration, focusing on stimulation that elicited a change in angular eye position >2° for both eyes. Focusing on Ch133 only, for the utricular electrodes, the majority of eye movements showed a ratio <0.8 and were elicited more with the lower half of electrodes, circled in red. While only a few examples for Ch133 where the ratio ≈1 or ratio >1.2, the examples for ratio>1.2, cluster toward the top right. Additionally, for the saccule of Ch133, clusters of red and blue sit on opposite sides of the array. This indicates that some level of selectivity may be achievable with proper placement. However, a similar pattern was not seen with Ch128 and Ch132.