A. Percept electrodes (green) that produced a phosphene upon electrical stimulation and non-percept electrodes (red) that did not in three subjects. Subject 1 (s1) shows a posterior view of the right hemisphere; s2: posterior view of left hemisphere; s3: medial view of left hemisphere. Electrodes were implanted only in a single hemisphere for each subject (right for s1, left for s2 and s3). OP: occipital pole.
B. Maps showing the difference in gamma power between percept electrode stimulation and non-percept electrode stimulation in three subjects (same subjects as A). For each subject, one percept electrode and the nearest non-percept electrode in the implanted hemisphere was repeatedly stimulated, and the significance of post-stimulation difference in gamma power at each electrode (except for the stimulation electrodes) was calculated and mapped to the cortical surface. Black spheres show electrode locations. TPJ: temporoparietal junction.
C. TPJ response during electrical stimulation of occipital electrodes that did (left) or did not (right) produce a phosphene, averaged across subjects. Color scale indicates power at each frequency. Dark gray bar centered at t = 0 indicates stimulation artifact. Dashed white line at f = 30 Hz indicates boundary between two different frequency estimate techniques. Dashed black line indicates gamma band f-t window used to estimate power for single-trial analysis.
D. TPJ gamma responses for every trial during stimulation of a percept (left) or non-percept (right) electrode. Each horizontal line (raster) shows the power in a single trial over time, collapsed across 60–150 hz. Same color scale as C.
E. Receiver-operating curve analysis of single trial data.

A. The average TPJ response during electrical stimulation of three percept electrodes in occipital lobe in s1 at varying stimulation currents (2–8 mA).
B. Psychometric (blue) and neurometric (red) functions for subjects s1, s2 and s3. The psychometric curve (left y-axis) shows the behavioral performance during the two-interval forced choice (2-IFC) task at different stimulation currents; performance was near chance (50%) at low currents and near ceiling (100%) at high currents (error bars show 75% confidence interval from the binomial distribution). The neurometric curve (right y-axis) shows the TPJ gamma power at the same currents (error bars show standard error of the mean).
C. TPJ response during percept electrode stimulation with near-threshold currents, averaged across subjects. Data averaged from trials in which subjects correctly (left) or incorrectly (right) discriminated which of two intervals contained electrical stimulation. Stimulation current was the same for correct and incorrect trials (4 mA for s1 and s2, 0.65 mA for s3).
D. TPJ response in the gamma band for single correct (left) and incorrect (right) trials of electrical stimulation at the same current. Each horizontal line (raster) shows the power in a single trial over time, collapsed across the gamma band.