Some recent models of learning and adaptation invoke multiple processes with different timescales. These theories postulate that learning occurs at more than one timescale concurrently, and the final product of the learning—that which is measured in most experiments—is a combination of these processes. Such models have been introduced for saccade gain control (Kording, Tenenbaum, & Shadmehr,
2007), motor adaptation (Smith, Ghazizadeh, & Shadmehr,
2006), dark adaptation (Lamb,
1981), and habituation (Staddon & Higa,
1996), to name a few, and can explain a number of peculiar phenomena in learning, including savings, spontaneous recovery, and spacing effects. Furthermore, adaptation in cortical neurons reflects multiple timescales (from 30 msec to several minutes; Kohn,
2007; Wark, Lundstrom, & Fairhall,
2007). While a number of results suggest that models with multiple timescales of learning provide a better fit to physiology and behavior, as of yet, no results have isolated individual timescales of concurrent cortical learning. We investigated the time course of adaptation in the visual domain using the McCollough effect (McCollough,
1965) as a test case and psychophysically isolated two distinct timescales of learning.