Table 3.

The slope of the cone detection, z-transformed ROC curve (σ_N/σ_SN) for each stimulus strength, and the exponent values (ρ) describing the rate of change of discriminability (Δm) with the stimulus strength (Δm ∝ S^ρ) for cone and rod detection. Cone and rod values reported for subject 1 are the mean and standard deviation across 6 and 4 data sets, respectively. Rod values reported for subject 4 are the mean and range for 2 data sets. Cone ROC slopes for subject 1 only and averaged across all subjects were significantly less than 1 (p < 0.05*, p < 0.005**; unpaired, 2-tailed t-test). ρ was greater for cone than rod detection, but in both cases significantly higher than 1 (p = 0.03, cones; p = 0.02, rods). High Intensity ROC slope for subject 5 could not be calculated due to 100% seeing frequency. Also shown is the average ρ value calculated for Sakitt's three subjects from the detection data reported in Sakitt (1972).

	ROC slope = σN/σSN (cone detection)			Exponent (ρ) (where Δm ∝Sρ)
Condition	Low intensity	Medium intensity	High intensity	Cones	Rods
Subject 1	0.77 ± 0.19*	0.62 ± 0.17**	0.56 ± 0.12**	2.99 ± 0.99*	1.60 ± 0.37
Subject 2	0.60	0.28	0.50	3.36	1.64
Subject 3	0.52	0.31	0.41	5.91	n/a
Subject 4	0.69	0.55	0.65	2.51	1.99 (1.52 - 2.47)
Subject 5	0.73	0.28	n/a	2.03	n/a
Subject 6	n/a	n/a	n/a	n/a	1.33
Average	0.66 ± 0.10**	0.41 ± 0.16**	0.53 ± 0.10**	3.36 ± 1.51*	1.64 ± 0.27*
Sakitt, 1972	n/a	n/a	n/a	n/a	1.18 ± 0.22