Table 2.
Scaling equations proposed by various authors (modified from Strasburger, 2003b).
| Equation | Source | Comment | Equation number |
|---|---|---|---|
| M −1 = M0−1 · (1 + aE) | For example, Cowey and Rolls (1974)† | Simple and useful | (1) |
| M −1 = M0−1 · (1 + E/E2) | Levi et al. (1985) | Same as above using E2. Caution: E2 alone does not predict slope (a foveal value is needed) | (2) |
| M −1 = M0−1 · (1 + aE + bE3) | Rovamo and Virsu (1979) | Third-order term adds little precision | (3) |
| M −1 = M0−1 · (1 + aE)α | van Essen et al. (1984), α = 1.1; Tolhurst and Ling (1988), α = 1.1; Sereno et al. (1995), α = 1.26 | Another way to introduce a slight non-linearity; α is close to 1 | (4) |
| M −1 = a + bsin(E) | Virsu and Hari (1996), Näsänen and O'Leary (1998) | Only 1/8 of the sine period is used | (5) |
†
Using the data of Wertheim (1894).