REFERENTIAL CODING AND ATTENTION-SHIFTING ACCOUNTS OF THE SIMON EFFECT

Stoffer (1991) and Umilta and Nicoletti (1992) have proposed an attent ion-shifting account of the Simon effect. However, Hommel (1993) has p resented evidence suggesting that the effect can be explained in terms of referential coding, without invoking attentional shifts. Five expe riments are reported here, whose primary purpose is to test implicatio ns of the referential-coding account. All of the experiments compared conditions in which a noise stimulus was presented in the position opp osite the target stimulus with conditions in which it was not. Contrar y to the referential-coding account, (a) the basic Simon effect was la rger without a fixation point to serve as a referent than with one; (b ) the noise stimulus increased the magnitude of the Simon effect when a fixation point was used, but not when there was no fixation point; a nd (c) the magnitude of the Simon effect obtained in the presence of a noise stimulus was reduced substantially when the noise and the targe t (and, if present, the fixation point) were in different colors. The results, although counter to predictions of the referential-coding acc ount, can be accommodated by the attention-shifting account if it is a ssumed that a fixation point provides an anchor that minimizes attenti on shifts.