Three experiments employed a discrete-trials version of the Stroop task to investigate further the claim that there are inhibitory mechanisms in selective attention (Neill, 1977). The results i~dicated that the evidence supporting the inhibitory theory (i.e., the diminished availability of distractor responses) cannot be explained by subjects' attempts to physically match successive stimuli (Lowe, 1979). In light of all the available evidence, it was suggested that the suppression effect does not index attentional inhibition, but may be attributed to a problem of code coordination (Keele & Neill, 1978).Deployment of selective attention permits an observer to respond optimally to chosen aspects of stimulation while excluding other, unwanted aspects. An important question concerns how this selective processing is achieved. Treisman (1964) hypothesized that selection of one message for analysis and response may sometimes involve the attenuation of others. According to this account, selection of some information may entail direct and specific inhibition of other information.Evidence for the existence of some form of inhibition in the context of selective attention comes from recent experiments (Neill, 1977) employing the Stroop (1935) color-word task. The Stroop task requires subjects to name the ink color of a letter display while overcoming the tendency to read a different color name spelled by the letters. Employing a series of discrete trials, Neill (1977, Experiment 1) found that when two successive Stroop stimuli were related such that the color name of the second item (~2) matched the distracting word of the first (Sl), observers took longer to respond than when the sequential inputs were unrelated (the suppression effect). Neill (1977) reasoned that when the color for Sl is named, the name of the conflicting color word is actively suppressed. Then, if that inhibited name is the correct response for S2, the inhibition slows responding, producing the suppression effect. However, subsequent results did not support a simple inhibitory account. For example, Neill (1977, Experiment 2) found that S1 distractor responses remained continuously available, and facilitated responses for S2, when manual responding was substituted for vocal color naming. Lowe (1979, Experiment 3) also demonstrated a facilitatory effect during related trials when color patches were substituted for color-word stimuli as S2. Lastly, results by Neill (1977Neill ( , 1979) also indicated that inhibition varied with the relative demands for speed versus accuracy. More pronounced inhibitory effects were obtained when instructions emphasized accuracy of responding. It is evident that the suppression effect is extremely sensitive to a number of variations in experimental context. This phenomenon can be influenced by the nature of the response requirements as well as by other sequences and stimuli that appear in the task.In light of these complications, Lowe (1979) suggested that subjects did not treat the successive stimuli as discrete, but employe...