Figure 2.

The first stage of artifact removal removes shared structure recorded simultaneously across linear electrode array channels. (a) The electrical artifact evoked by a single pulse of a stimulus train is highly similar across the 24 channels of the array. (b) To identify the common artifact structure present across channels, we rearrange the artifact data into a matrix with dimensions time × pulses × trials (T × P × R) by channels (C), shown transposed. (c) The principal components of this matrix are linear combinations of the electrode channels. The projections of the recordings along these components clearly display artifact structure shared across channels. (d) Voltage recordings for the first pulse of the stimulus train, plotted separately for each channel with the responses on each trial superimposed. Raw voltage recordings are shown in black, with the artifact inferred via principal components regression shown in red. (e) Same presentation as in (d) but with the residual voltage recordings shown in blue, after the inferred artifact has been subtracted. (f) Cleaned voltage recordings for a single trial with the responses to each individual pulse superimposed. The top panel shows a superficial channel which had no detectable spontaneous neural activity, and the bottom panel shows a lower channel where a well-isolated single unit was spiking spontaneously.