Proportion Manipulation of the Emotional Stroop

Abstract

The Stroop effect is commonly demonstrated by measuring the time required to identify the colour of the ink (e.g. blue) in which a colour word (e.g. RED) is printed and illustrates a strong interference effect when the prepotent response of processing the word must be inhibited to respond correctly to the colour of the ink. Longer response latencies in colour-identification tasks involving emotional words versus neutral words, an effect dubbed the Emotional Stroop (ES), is often likened to the type of interference found in the Stroop task. However, research has suggested that the effect of attentional modulation in Stroop tasks may be very different from the kind of emotional interference found when comparing reaction times to emotional versus neutral words (McKenna & Sharma, 2004). Proportional congruency experiments using the Stroop task manipulate the amount of incongruity present in a block of trials (Logan & Zbrodoff, 1979), and demonstrate attentional modulation as a change in the size of the Stroop effect such that a greater amount of Stroop interference in a block is associated with a smaller Stroop effect. Manipulating the proportion of interference trials may inform understanding of the differences between Stroop colour-word interference and emotional-word interference. In three experiments, we manipulated the proportion of emotional words in a mixed-list design to study the effect of proportion manipulation on the ES. An enlarged ES was found in blocks of trials that contained more emotional interference; a finding contrary to attentional modulation seen for proportion manipulations of congruency in the Stroop task. The differences between the ES effect and the Stroop effect are discussed, including the role of response incongruity as one possible reason for the discrepancy.