Using Brain Potentials to Functionally Localise Stroop-Like Effects in Colour and Picture Naming: Perceptual Encoding versus Word Planning

Abstract

The colour-word Stroop task and the picture-word interference task (PWI) have been used extensively to study the functional processes underlying spoken word production. One of the consistent behavioural effects in both tasks is the Stroop-like effect: The reaction time (RT) is longer on incongruent trials than on congruent trials. The effect in the Stroop task is usually linked to word planning, whereas the effect in the PWI task is associated with either word planning or perceptual encoding. To adjudicate between the word planning and perceptual encoding accounts of the effect in PWI, we conducted an EEG experiment consisting of three tasks: a standard colour-word Stroop task (three colours), a standard PWI task (39 pictures), and a Stroop-like version of the PWI task (three pictures). Participants overtly named the colours and pictures while their EEG was recorded. A Stroop-like effect in RTs was observed in all three tasks. ERPs at centro-parietal sensors started to deflect negatively for incongruent relative to congruent stimuli around 350 ms after stimulus onset for the Stroop, Stroop-like PWI, and the Standard PWI tasks: an N400 effect. No early differences were found in the PWI tasks. The onset of the Stroop-like effect at about 350 ms in all three tasks links the effect to word planning rather than perceptual encoding, which has been estimated in the literature to be finished around 200–250 ms after stimulus onset. We conclude that the Stroop-like effect arises during word planning in both Stroop and PWI.

Control adjustments in speaking: Electrophysiology of the Gratton effect in picture naming

“…Finally, the planned picture name is articulated. As we discussed in detail elsewhere (Shitova, Roelofs, Schriefers, Bastiaansen, & Schoffelen, 2016), the locus of the interference effect has been linked either to perceptual and conceptual encoding (Dell'Acqua, Job, Peressotti, & Pascali, 2007;Dell'Acqua et al, 2010;Van Maanen, Van Rijn, & Borst, 2009) or to word planning (Piai, Roelofs, & Schriefers, 2014;Schnur & Martin, 2012). The dual-task findings by Van Maanen and Van Rijn (2010) would suggest that the locus is in perceptual and conceptual encoding or word planning depending on the previous trial type.…”

“…For the Stroop task (in various adaptations), a prominent negative-going deflection at approximately 400e450 msec post-stimulus onset, an N400 component, is typically larger on incongruent than on congruent trials (Hanslmayr et al, 2008;Liotti, Woldorff, Perez, & Mayberg, 2000). Some of these previous studies referred to this component as an "N450", but we take it to be an N400 (see Piai, Roelofs, Jensen, Schoffelen, & Bonnefond, 2014;Piai, Roelofs, & Van der Meij, 2012;Roelofs, Piai, Garrido Rodriguez, & Chwilla, 2016;Shitova et al, 2016). Contrary to the N2 effect in the Eriksen flanker task, the N400 effect has not been consistently shown to follow the Gratton pattern of control adjustments in the Stroop task.…”

“…Moreover, Larson, Clayson, Kirwan, and Weissman (2016) reported control adjustment effects on the N400 component in a novel primeprobe Stroop-like task. The N400 effect has also been reported to reflect the semantic and Stroop-like effects in the PWI task (e.g., Piai, Roelofs, Jensen, et al, 2014;Piai et al, 2012;Shitova et al, 2016). Based on the N400 findings, it has been argued that the semantic and Stroop-like effects in the PWI task arise during word planning rather than during perceptual and conceptual encoding.…”

“…However, there is an alternative interpretation of the empirical results reported in the Van Maanen and Van Rijn (2010) study, which does not assume that the locus of the interference effect shifts depending on the previous trial type. Rather, the alternative interpretation holds that there is a single fixed locus of semantic and Stroop-like effects (i.e., in word planning, see Piai, Roelofs, & Schriefers, 2014;Shitova et al, 2016). The behavioral effects reported by Van Maanen and Van Rijn may also have resulted from a change in strategic task scheduling depending on the previous trial type, in order to optimally perform in the dual-task setting.…”

“…As indicated before, the perceptual and conceptual encoding stage is completed around 200 msec post stimulus-onset, which is well before the moment that the Stroop-like effects occurs in the eventrelated potentials (ERPs). For example, in the study of Shitova et al (2016), the onset of the Stroop-like effect was around 350 msec after stimulus onset. This indicates that the effect occurred during word planning, which starts 200 msec post stimulus-onset.…”