Figure 2.

Latency and precision of the earliest visual responses. Latency and precision of dLGN cells were calculated from the first spike times in response to whole-field flashed stimuli. The optimal stimulus polarity of the cell was used (bright flashes for On-dominated or dark flashes for Off-dominated). A, dLGN cells were ranked by latency, and for the cells at the 20th, 55th, and 80th percentiles, two plots are shown: the first spike raster plot (top) and the first spike histogram (bottom). Each raster shows the times of the first spikes. Each histogram was constructed from all first spike times and was smoothed using an adaptive filter (widened from each 1 msec time step to capture 10 action potentials) (Mainen and Sejnowski 1995) and plots the probability (in arbitrary units and calculated as the inverse of the width of the window required to capture 10 spikes) that a first spike was recorded at a particular time after the onset of the flash. The latency was defined as the time of the peak of the histogram, the precision as the minimum width of a window about the latency that captured half of the first spikes. B, Cumulative probability plot of latency and precision of dLGN cells recorded during the first 2 weeks of visual responsiveness. The distribution reveals the range of response latencies (minimum, 36 msec; median, 268 msec; maximum, 891 msec) and precision values (minimum, 2.3 msec; median, 53 msec; maximum, 424 msec). C, D, Scatter plots comparing age against latency (C) and precision (D). The population includes cells recorded through the naturally closed eyelids (closed symbols) and cells recorded just after natural eye opening (open symbols). Latency and precision showed a statistically significant trend over this developmental period, with both measures decreasing with age (latency Spearman r = -0.55; p < 0.0001; precision Spearman r = -0.24; p < 0.05). For presentation purposes, overlapping data points in the scatter plots were offset along the x-axis.