Figure 3.

Visually evoked potentials (VEP) and stimulation thresholds. (a) Example VEP waveforms with flat and pillar 55 μm implants at various irradiances and pulse durations. The traces were averaged over 500 trials. The double-headed arrow indicates the primary peak located at ~17 ms post stimulus. The purple arrow indicates the secondary negative peak that has high irradiance threshold. The green arrows indicate a VEP component that is highly sensitive to pulse duration but not irradiance. (b) Variation of the VEP amplitudes with irradiance. Stars indicate the lowest irradiance at which p < 0.05 (unpaired t-test, n = 5 for each implant type). Thresholds are summarized in table 1. (c) Variation of the VEP amplitude with pulse width. Stars indicate the shortest duration at which p < 0.05 (same as (b)). Thresholds are summarized in table 2. (d) Variation of the VEP amplitude with frequency for all 4 implant types and for normal vision (n = 5). For the plot clarity, we used one-sided error bars offset horizontally by the line width in order to avoid overlapping with adjacent bars. All error bars are shown in terms of s.e.m.