Bradley P Wyble
¹,
Howard Bowman
¹,
Dinkar Sharma
²
¹Computing Laboratory, University of Kent
²Psychology Department, University of Kent bw5@kent.ac.uk
The Stroop effect has long been a hallmark of competition between cognitive processes, in which the default tendency to report the name of a color word must be overridden in order to report its ink color. An excellent modelling effort by Botvinick et al (2001) suggests that a conflict-monitoring system, presumed to represent the Anterior Cingulate Cortex (ACC), enhances top-down cognitive control when the system detects competing activity within the response layer. This model provides a theoretical account for how frequent incongruent trials can bias the system towards processing future incongruent trials more rapidly. Recent work on the emotional Stroop paradigm (McKenna and
Sharma 2004) has provided evidence that using negatively valenced emotional words instead of color words has a slowing effect primarily on the subsequent trial. This is considered to be a slow effect, because the effect on the current trial is minimal, unlike the case of incongruent trials, which impair performance on the current trial. In this data, subjects perform 7 Stroop trials with no inter-trial delay. All of the words in the series are neutral words (e.g. Gate, Note, Clock) presented in one of 4 ink colors, with the exception of the second word, which has a negative emotional valence (e.g. Fail,
Fear, Grief). Emotional word trials were performed at the same speed as neutral words (~920 msec).
However, the following trial had a significantly larger reaction time (~980 msec, a 6.5% increase) despite being neutral. This effect decayed to baseline by the second post-emotional-word trial.
This paper describes an elaboration of the Botvinick et al (2001) model that accommodates this slow effect from emotional words. Recent theoretical and experimental work has demonstrated that the ACC may be divided into two halves, containing cognitive and emotional components (Drevets and Raichle 1998, Bush et al, 2000). FMRI evidence from a variety of tasks indicates that these two subdivisions may be mutually inhibitory, such that cognitive tasks tend to diminish activity in the emotional subdivision of the ACC and vice versa. This theoretical account is well suited to explain the slow effect of negative emotional words in the emotional Stroop task. In our reformulation of this model, emotional words cause elevated activity in the emotional subdivision of the ACC, suppressing activity in the cognitive subdivision. This suppression has the effect of reducing top down control and thus enabling the default behavior of identifying words rather than ink color, resulting in slower performance on the subsequent trial. These effects occur too slowly to affect performance on the current trial. In the model, presentation of an emotional word in the context of neutral words evokes a transient 6% increase in reaction time only on the subsequent trial. This model provides a concise link from current theories of ACC function, to existing data and models of both the Stroop effect and the Emotional Stroop effect.
Botvinick MM, Braver TS, Barch DM, Carter CS, Cohen JD (2001) Conflict monitoring and cognitive control. Psychol
Rev, 108(3):624-52.
Bush, Luu and Posner (2000) “Cognitive and emotional influences in anterior cingulate cortex”. Trends Cogn Sci,
4(6)215-222.
Drevets, WC and Raichle, ME (1998) “Reciprocoal Suppression of Regional Cerebral Blood Flow during Emotional versus Higher Cognitive Processes: Implications for Interactions between Emotion and Cognition.” Cognition and
Emotion , 12(3):353-385.
McKenna FP, and Sharma D (2004) “Reversing the emotional stroop effect reveals that it is not what it seems: the role of fast and slow components” J Exp Psychol Learn Mem Cogn, 30(2):382-92
65