Figure 17.

Loss of SNR for neurons in a converging pathway. (A), (B) Contrast sensitivity compared for a ganglion cell (neuron 2) and its converging presynaptic array of bipolar cells (array 1). When probed with a small flashed spot across the receptive field (A), and with different diameter centered spots (B), the converging bipolar cell array has a larger optimal stimulus and greater performance than the ganglion cell. The ganglion cell’s non-specific loss comprises the bipolar array’s non-specific loss plus the loss in synaptic transmission to the ganglion cell. (C), (D) Contrast sensitivity compared for the ganglion cell and a single presynaptic bipolar cell (neuron 1). The bipolar cell (dotted black) has the same optimal stimulus position as the ganglion cell because it is centered in the ganglion cell receptive field. (C) Bipolar cells have greater non-specific loss than the ganglion cell because they collect fewer inputs. Bipolars with offset position (dotted gray) show the same non-specific loss, but differ in their optimal stimulus (gray dashed arrow). Note that for the same stimulus, some of the bipolar cell performances are greater than the ganglion cell performances. (D) the optimal stimulus for a bipolar cell is smaller than for the ganglion cell. For small spots the bipolar cell performance is greater than the ganglion cell’s because the ganglion cell receives noise from bipolars outside the stimulus. Figure omits inhibition from amacrine cells that will modify performance of ganglion cell center and surround. As in the previous figure, the neural performances are shown magnified relative to ideal for clarity.