Attention to action: Securing task-relevant control in spoken word production

Attention to Action: Securing Task-Relevant Control in Spoken Word Production Ardi Roelofs ( ardi@mpi.nl ) Max Planck Institute for Psycholinguistics Wundtlaan 1, 6525 XD, Nijmegen, The Netherlands Performance on the Stroop task is of direct relevance to theories of language production and comprehension. The basic modes of language use, namely speaking, listening, reading, and writing, all seem to make use of overlapping sets of basic processing components (e.g., Caplan, 1992; Levelt, 1989; Shallice, 1988). Whereas language percep- tion occurs automatically, hearing or reading a word does not automatically lead to its production but this is under the control of a language user. Similarly, seeing an object does not automatically lead to the naming of it. Further- more, words do not occur in isolation, but are typically part of a spoken discourse, a text on a page, or appear on ob- jects in the real world. This points to the need to deal with the issue of selectivity. It is generally assumed that per- formance on the Stroop task can provide evidence on how language is controlled, that is, how a speaker secures task- relevant control over the basic language processes under- lying naming and oral reading (e.g., Allport, 1993). Since Stroop’s (1935) experiments in the 1930s, over 700 articles have appeared using his task (reviewed by Mac- Leod, 1991), which established the following basic empiri- cal picture. Color naming is inhibited by incongruent color words, but word reading not by incongruent color patches. For example, saying “red” to a red color patch on which the word “green” is superimposed proceeds slower than saying “red” in a control condition consisting of a string of Xs. The stimulus onset asynchrony (SOA) between color patch and word has an important effect. Maximal inhibi- tion of incongruent words on color naming is obtained when the words are presented within 100 msec of the col- ors (e.g., Glaser & Glaser, 1982). Preexposed congruent words yield facilitation, which is constant over SOAs. Whereas color naming is affected by incongruent words, Introduction The Stroop phenomenon is the finding that color naming is inhibited by incongruent color words but word reading not by incongruent colors. When the stimulus onset asynchrony (SOA) is manipulated, maximal inhibition of incongruent words on color naming is obtained when the words are pre- sented within 100 msec of the colors, whereas facilitation of preexposed congruent words is constant. These finding are obtained both with and without task certainty. Whereas ex- isting models explain the basic Stroop effects, they fail to account for the time course findings and for performance under task uncertainty. In this paper, I extend and apply the WEAVER ++ model of spoken word production (Roelofs, 1992, 1993, 1997c; Levelt, Roelofs, & Meyer, 1999) to perform- ance on the Stroop task and show that the model accounts for the key findings. reading aloud words (e.g., “red”) is not influenced by in- congruent colors (e.g., green). The asymmetry in effect is not due to a difference in processing speed between words and colors (i.e., reading is some 200 msec faster than color naming), as evident from manipulating the SOA. When a color patch is presented 300 or 400 msec before the word to be read, still no effect of incongruent colors is obtained (e.g., Glaser & Glaser, 1982). LATENCY EFFECT (msec) Abstract SOA (msec) Figure 1: Time course of the Stroop effects (relative to control) in color naming under task uncertainty as meas- ured by Glaser and Glaser (1989): = incongruent, = congruent In a standard Stroop experiment, participants are certain about what task to perform. Typically, one group of par- ticipants is asked to name the color and to ignore the word, and another group of participants is asked to read aloud the word and to ignore the color patch. Thus, trials are blocked by task. However, in examining the effect of task uncer- tainty, Glaser and Glaser (1989) asked a single group of participants to perform both tasks. They instructed their participants to respond to the second stimulus component (in the condition with negative SOAs) or the first compo- nent (in the condition with positive SOAs). Words had to be read aloud and colors had to be named. Participants can perform this task up to differences in presentation time of 50 msec. The experiment was run with SOAs of -300, -200, -100, -50, 50, 100, 200, and 300 msec (a minus sign indi- cates preexposure of the irrelevant stimulus). With task uncertainty, Glaser and Glaser obtained the normal patterns of inhibition and facilitation observed with task certainty, for example, with the instruction to name the color and ignore the word. Inhibition increased when the SOA be-