Fig. 1.
L-2-amino-4-phosphonobutyric acid (L-AP4) decreases the accuracy with which excitatory currents in the OFF α-cell detect a dark flash. A: the top traces show a 100-ms dark flash at three example contrasts. Below are excitatory currents from an OFF α-cell in control and L-AP4 conditions. B: currents from each trial were divided into n = 12 time bins, and the current averaged for each bin to give xn. The top graph shows xn for a sham trial (0% contrast) and a trial with 4% contrast. The bottom graph shows the Fisher discriminant λn (materials and methods). C: the probability distributions of the Fisher measure F = ∑n xnλn for 0% and 4% contrasts. The two probability distributions were well separated in control but overlapped in L-AP4 (shaded region). D: the neurometric curves for excitatory currents in control and L-AP4 conditions. To construct neurometric curves, the data points were fit with a cumulative Weibull function: accuracy = 1 − 0.5 exp [−(contrast/a)b] (Quick 1974), where a is a scaling factor and b determines the slope. Error bars in this and subsequent figures indicate standard error of the mean. a.u., Arbitrary units.