Evidence Supporting the Computational Framework

Evidence Supporting the Computational Framework Some evidence supports Logan and Sadler’s (1996) decomposition of apprehension into the constituent steps (e.g., Carlson & Logan, 132 Laura A. Carlson2001; Carlson-Radvansky & Logan, 1997; Carlson-Radvansky & Irwin, 1993, 1994; Logan & Compton, 1996; Logan, 1995). However, the evidence comes from separate experiments with diVerent methodologies that target each step in isolation. In order to generalize across these diVerences, one must rely on the untested assumptions that the steps are independent and operate similarly across tasks. In addition, these tasks use measures that are tied to the final response of the subject, making it diYcult to locate the influence of a given factor at a particular step. To overcome these potential diYculties, Carlson, West, Taylor, and Herndon (2002) examined the constituent processes in apprehension (finding the relevant objects, assigning directions to space, and computing and comparing the spatial relation) using event-related potentials (ERPs). ERPs provide a continuous online measure of cognitive processing with real-time temporal resolution that enables one to obtain independent evidence for each step within the same task (e.g., Coles & Gratton, 1986; Donchin & Coles, 1988; Meyer, Osman, Irwin, & Yantis, 1988). In this study, participants performed a speeded sentence/picture verification task in which they were shown a sentence such as ‘‘The ball is above the watering can’’ followed by a picture containing two objects (e.g., a ball and a watering can) in some spatial relation. The task was to determine whether the sentence was an acceptable description of the picture as quickly and accurately as possible. Particular manipulations that targeted the constitu- ent processes were employed, and distinct modulations of the ERPs were observed that were associated with these manipulations