Table 1.

Spatial characteristics of the mean-increasing and mean-decreasing subunits

Parameters	0.25 Hz	1 Hz	4 Hz
KE	26 ips	42 ips	52 ips
	(23 ± 4)	(42 ± 5)	(58 ± 6)
RE	0.58°	0.61°	0.53°
	(0.66 ± 0.06)	(0.68 ± 0.07)	(0.49 ± 0.05)
KIc	27 ips	26 ips	15 ips
	(24 ± 4)	(25 ± 5)	(20 ± 6)
RIc	0.15°	0.15°	0.15°
	(0.16 ± 0.01)	(0.16 ± 0.01)	(0.16 ± 0.01)

Listed are parameter values estimated from fitting the dual-subunit model (Fig. 5) to the average spatial frequency curves of the mean rate in Figure 4d. Because firing rate cannot be negative, averaging the curves of many cells will lead to an underestimate of the integrated strength of the mean-decreasing mechanism. For this reason the mean values of the parameters (± SD) estimated from the 13 tuning curves used to construct the average ones are given in parentheses. Recall that integrated excitatory strength is the sum of the strengths of large (mean-increasing) subunits and small (mean-decreasing) subunit surrounds.