Neural correlates of sparse coding and dimensionality reduction
Fig 5
Identification of retinal ganglion cell subunits with STNMF.
(A) Samples of a ganglion cell’s effective spike-triggered stimulus ensemble (top), whose average corresponds to the cell’s STA. For easier visual comparison with the subunits, STAs are displayed with negative pixel values set to zero and with zero corresponding to white in the grayscale image. STNMF decomposes this ensemble into a set of modules and hidden coefficients (bottom). The example here shows four modules that were identified for a sample ganglion cell. (B) Modules obtained for another sample ganglion cell by applying STNMF with 20 modules (bottom two rows). Some modules have a strongly localized structure (blue frames); others are more noise-like (red frames). These modules make up the subunits within a ganglion cell RF. The top row shows the cell’s RF, given by the spatial component of the STA, as well as the fitted RF outline (GC RF, black ellipse), together with outlines of the localized subunits (blue ellipses). Scale bars, 100 μm. GC, ganglion cell; RF, receptive field; STA, spike-triggered average; STNMF, spike-triggered nonnegative matrix factorization. Adapted with permission from [44].