Figure 6. Exogenous, movement-unrelated ‘visual’ spikes affected movement metrics when they occurred within approximately ±30 ms from movement onset.

(A) For the different microsaccade amplitude ranges from Figure 5 (color-coded curves), we counted the number of exogenous spikes occurring from a recorded extra-foveal SC neuron (≤4.5 deg) within any given 5 ms time bin around movement onset (range of times tested: −100 ms to +100 ms from movement onset). The lowest two microsaccade amplitude ranges (0.1–0.2 and 0.2–0.3 deg) reflected baseline amplitudes during steady-state fixation (e.g. Figure 3), and they were not correlated with additional extra-foveal spiking activity around their onset (two darkest red curves). For all other larger microsaccades, they were clearly associated with precise timing of extra-foveal ‘visual’ spikes occurring within approximately ±30 ms from movement onset, regardless of movement size. The data shown are from experiment 1; similar observations were made from experiment 2 (Figure 6—figure supplement 1). The number of movements contributing to this figure is the same as in Figure 5. (B) Same as A but for movements opposite the recorded neuron’s RF locations. There were fewer spikes during the peri-saccadic interval, suggesting that it was easier to trigger eye movements when there was no activity present in the opposite SC. Figure 6—figure supplement 2 shows similar results from the far neurons (>4.5 deg eccentricity) of the same experiment (experiment 1).

Figure 6—figure supplement 1. Same analysis as in Figure 6 but for the neurons recorded during experiment 2 (≤4.5 deg).

Very similar observations could be made.

Figure 6—figure supplement 2. Same as Figure 6 but for the far neurons from experiment 1.

This figure is formatted similarly to Figure 6, but now using data from the far neurons of the same experiment (>4.5 deg eccentricity). Note how the same temporal alignment is seen as in Figure 6. Moreover, quantitatively, panel A shows that with proper temporal alignment, the same eye movement amplitude increases as in Figure 6A were expected to occur from the same numbers of injected ‘visual’ spikes, even with these far neurons with eccentricity >4.5 deg. Therefore, the weaker global behavioral effect with far stimuli (e.g. Figure 3—figure supplement 1) likely reflected more variability in the population temporal responses of the peripheral neurons’ visual bursts when compared to the central neurons’ visual bursts (see Discussion). Otherwise, within the proper time window, the spiking impact was similar in this figure as in the main Figure 6 with nearer neurons’ visual bursts.