A sequential analysis of relevant and irrelevant information in the Stroop task

The effect of repeating relevant (colour) and irrelevant (word) stimulus information is investigated in two Stroop tasks. Thomas (1977) observed that the Stroop effect is reduced when the irrelevant word is repeated from trial n -1 to trial n. A similar effect was observed in the Simon task (Notebaert, Soetens, & Melis, 2001; Notebaert & Soetens, 2003a). MacLeod (1991) interprets this effect as sustained suppression and relates it to negative priming. In this paper we investigate whether the reduced Stroop effect for word repetitions is indeed related to the negative priming effect. In Experiment 1 with a response-stimulus interval (RSI) of 50 ms, the Stroop effect is not influenced by the sequence of the word and there is no negative priming effect. In Experiment 2 with an RSI of 200 ms, the Stroop effect is reduced for word repetitions but there is still no negative priming effect. This does not support the sustained-suppression hypothesis. The reduced Stroop effect for word repetitions is explained in terms of response priming.