Figure 9.

Excitation elicited by negative contrast stimulation of the subfields is mediated by the ON pathway. The stimulus was a negative contrast (−80%) bar flashed at two locations 100 and 150 μm above and below the center of the RF. Data show average results from 6 cells. The format for the panels is identical to Figure 8A–J. Responses to dark bar stimulation in the center were largely suppressed by blocking the ON pathway. K–O, Negative contrast activated both “A/K” and NMDA inputs from the subfields, with little evidence for activation of inhibition. P–T, Subfield responses were completely suppressed when the ON pathway transmission was blocked with 50 μm l-AP4.