Table 2. Equivalent eccentricity conversion.

The target in the complex-display (colored symbols) and simple-display tasks (open symbols) is big enough to not be limited by acuity. The complex (colored symbols) displays are limited by crowding, which is eccentricity dependent. The acuity test (line symbol) is limited by acuity, which is also eccentricity dependent. The simple-display tests (open symbols) are not affected by crowding or acuity limits and are independent of eccentricity. For each test, the table provides the slope m of the regression line

$$p=1+m\phi$$ (7)

describing how the standard observer’s performance p drops with eccentricity φ in deg, where m is the slope in deg⁻¹. For each task, the performance p is measured proportion correct, except for the acuity index p_acuity (Eq. 5). Solving Eq. 7 for the equivalent eccentricity yields the conversion formula

$${\phi }_{\text{eq}}=\frac{p-1}{m},$$ (8)

using the value of m corresponding to the task for which p was measured. (For acuity, Eq. 8 is equivalent to Eq. 4.)

Symbol	Test	Slope m (deg−1)	Stimulus
	Similar flanker	−0.100
	VOSP cube	−0.060
	BORB double objects	−0.059
	BORB triple letters	−0.030
	BORB triple shapes	−0.025
	BORB single objects	−0.025
	Dissimilar flanker	−0.022
	Boston Naming Test	−0.022
	Snodgrass & Vanderwart	−0.020
	VOSP incomplete letter	−0.020
	BORB double letters	−0.005
	VOSP visual detection	−0.000
	BORB single shape	−0.000
	BORB single letter	−0.000
	Acuity	−0.029