Previous studies have shown that responses can be partially activated by irrelevant stimuli in focused-attention tasks. In two experiments, such response activation was used to investigate the organization of keypress responses. Stimuli were rows of three letters, with a relevant target letter in the middle of the row and irrelevant flanker letters on the outside. There were four target letters, and these were assigned to four keypress responses made with the index and middle fingers of the two hands. Irrelevant flankers were parentheses, a neutral letter, or one of the four target letters. Responses were fastest when flankers were identical to the target, indicating facilitation of a response activated by both relevant and irrelevant letters. When flankers were response-incompatible target letters, responses were faster if these were target letters assigned to a response finger on the same hand as the correct response than if they were target letters assigned to a response finger on the opposite hand. The latter result is consistent with the hypothesis that simultaneous activation of two response fingers on the same hand produces faster responses than simultaneous activation of two response fingers on different hands, as assumed by Miller (1982). In Experiment 2, flankers were presented slightly before targets, and flankers that were same-hand target letters sometimes facilitated responses relative to the neutral parentheses flankers.In a series of papers concerning visual selective attention, C. W. Eriksen and his coworkers have documented a sizable response-compatibility effect of unattended stimuli. In one series of experiments, for example, subjects were presented with rows of letters and told to respond to the identity of the middle letter, ignoring the flanker letters on either side (C. W. Eriksen & Schultz, 1979). Even though the flankers were to be ignored, responses were faster when flankers were targets assigned to the same response as the relevant middle letter (response-compatible trials) than when flankers were target letters assigned to the opposite response (responseincompatible trials). Reaction time (RT) was intermediate when the flankers were response-neutral letters, indicating that target flankers produced both facilitation and inhibition.Two recent studies indicate that much or all of this response-compatibility effect is produced by competition in response activation processes. C. W. Eriksen, Coles, Morris, and O'Hara (1985) measured electromyographic (EMG) activity as an index of response activation. They found that response-incompatible displays caused more This research was supported by NIMH Grant PHS-MH40733. I would like to thank C. W. Eriksen, Patricia Haden, Roland Schaffer, and two anonymous reviewers for helpful comments on earlier drafts of the paper, particularly suggestions leading to Experiment 2. I would also like to thank Grace Fang, Alann Lopes, Brent Roberts, and Thomica James