Interference in the shared-stroop task: a comparison of self- and other-monitoring

Co-acting participants represent and integrate each other’s actions, even when they are not required to monitor one another. However, monitoring the actions of a partner is an important component of successful interactions, and particularly of linguistic interactions. Moreover, monitoring others may rely on similar mechanisms to those that are involved in self-monitoring. In order to investigate the effect of monitoring on shared linguistic representations, we combined a monitoring task with the shared Stroop task. In the shared Stroop task, one participant named the colour of words in one colour (e.g., red) while ignoring stimuli in the other colour (e.g., green); the other participant either named the colour of words in the other colour or did not respond. Crucially, participants either had to provide feedback about the correctness of their partner’s response (Experiment 3) or did not (Experiment 2). The results showed that interference was greater when both participants responded than when they did not, but only when partners provided feedback. We argue that feedback increased joint task interference because in order to monitor their partner, participants had to represent their target utterance, and this representation interfered with self-monitoring of their own utterance.

Methods
Verbal responses were collected using DMDX and onset latencies were measured using CheckVocal (see references below). To prepare the data for analyses, after removing all incorrect responses, onset latencies below 200 milliseconds were removed (1 trial) before we conducted a recursive trimming procedure in which the criterion cut-off for outlier removal was established independently for each participant in each condition, by reference to the sample size in that condition. Error totals used in accuracy analysis do not include the removed outliers.

Forster, K. I., Forster, J. C. 2003 DMDX: A windows display program with millisecond accuracy. Behavior Research Methods, Instruments, & Computers. 35, 116-124.  (10.3758/BF03195503)

Protopapas, A. 2007 CheckVocal: A program to facilitate checking the accuracy and resposne time of vocal responses for DMDX.