Table 1.

Features of Brinley Functions

Feature	Slowing Interpretation	Ratcliff et al. (2000) Interpretation
Slope greater than 1	Cognitive processes are slowed for older subjects relative to young subjects by a factor that is the slope of the Brinley function	The slope of the Brinley function is the ratio of the SD of condition means for older subjects to the SD of condition means for young subjects; the SD for older subjects is typically larger
Linearity	Rarely addressed; if serial or parallel processing is assumed, linearity derives from all processes slowing by a constant amount	A Brinley function will be linear if the distributions of condition means for the older and young subjects have (at least approximately) the same shape
Negative intercept	Processing can be divided into peripheral and central components, and there is more slowing with age in the central components	Intercept = μO −μY(σO/σY); typical values of μs and σs produce negative value of intercept
Negative correlation between slopes and intercepts	Given more slowing with age in the central components, random variation across experiments in central and peripheral components leads to negative correlation	Variation in μs and σs across experiments produces the negative correlation
Target for modeling	Brinley slope	Distributions of mean RTs across conditions, plus all other dependent variables in the task