The loci of Stroop effects: a critical review of methods and evidence for levels of processing contributing to color-word Stroop effects and the implications for the loci of attentional selection

Despite instructions to ignore the irrelevant word in the Stroop task, it robustly influences the time it takes to identify the color, leading to performance decrements (interference) or enhancements (facilitation). The present review addresses two questions: (1) What levels of processing contribute to Stroop effects; and (2) Where does attentional selection occur? The methods that are used in the Stroop literature to measure the candidate varieties of interference and facilitation are critically evaluated and the processing levels that contribute to Stroop effects are discussed. It is concluded that the literature does not provide clear evidence for a distinction between conflicting and facilitating representations at phonological, semantic and response levels (together referred to as informational conflict), because the methods do not currently permit their isolated measurement. In contrast, it is argued that the evidence for task conflict as being distinct from informational conflict is strong and, thus, that there are at least two loci of attentional selection in the Stroop task. Evidence suggests that task conflict occurs earlier, has a different developmental trajectory and is independently controlled which supports the notion of a separate mechanism of attentional selection. The modifying effects of response modes and evidence for Stroop effects at the level of response execution are also discussed. It is argued that multiple studies claiming to have distinguished response and semantic conflict have not done so unambiguously and that models of Stroop task performance need to be modified to more effectively account for the loci of Stroop effects.

When it’s harder to ignorar than to ignore: Evidence of greater attentional capture from a non-dominant language

Aims and Objectives: Imagine you’re driving and you become so distracted by the radio that you miss your turn. Which is more likely to have caught your attention, a broadcast in your native tongue or one in your second language? The present study explores the effect of language proficiency on our ability to inhibit irrelevant phonological information. Methodology: Participants were asked to identify which of two drawings changed color while ignoring irrelevant words in either their native language, English, or a less proficient language, Spanish. The drawings appeared on screen for either 200 or 2000 ms prior to word-onset, which was followed 200 ms later by a color-change. On critical trials, the irrelevant word shared phonological features with the label of the non-target drawing. Trials were blocked by preview time and language. Data and Analysis: Reaction time data from 19 bilinguals were analyzed utilizing generalized linear mixed-effects models, with fixed effects of Competition (competitor vs. control), and Language (English vs. Spanish) and random effects for Subject and Item within each preview window. Findings/Conclusions: No interference was observed when participants heard their native tongue in either preview condition. However, participants in the long-preview condition were significantly slower to respond when there was phonological competition in their less proficient language, despite the fact that the task required no language processing. Originality: Past work has indicated that languages are processed more automatically and cause greater interference as proficiency increases. We propose that though higher-proficiency languages may receive greater activation overall, lower-proficiency languages may be more likely to exogenously capture attention due to both relatively greater salience, and relatively less control. Significance: The present findings have implications for how we understand the dynamic relationship between language proficiency, activation, and inhibition, suggesting that the salience of the less familiar influences our ability to ignore irrelevant information.

Response Modality and the Stroop Task

A long-standing debate in the Stroop literature concerns whether the way we respond to the color dimension determines how we process the irrelevant dimension, or whether word processing is purely stimulus driven. Models and findings in the Stroop literature differ in their predictions about how response modes (e.g., responding manually vs. vocally) affect how the irrelevant word is processed (i.e., phonologically, semantically) and the interference and facilitation that results, with some predicting qualitatively different Stroop effects. Here, we investigated whether response mode modifies phonological facilitation produced by the irrelevant word. In a fully within-subject design, we sought evidence for the use of a serial print-to-speech prelexical phonological processing route when using manual and vocal responses by testing for facilitating effects of phonological overlap between the irrelevant word and the color name at the initial and final phoneme positions. The results showed phoneme overlap leads to facilitation with both response modes, a result that is inconsistent with qualitative differences between the two response modes.

Strategic Allocation of Attention Reduces Temporally Predictable Stimulus Conflict

Humans are able to continuously monitor environmental situations and adjust their behavioral strategies to optimize performance. Here we investigate the behavioral and brain adjustments that occur when conflicting stimulus elements are, or are not, temporally predictable. ERPs were collected while manual response variants of the Stroop task were performed in which the SOAs between the relevant color and irrelevant word stimulus components were either randomly intermixed or held constant within each experimental run. Results indicated that the size of both the neural and behavioral effects of stimulus incongruency varied with the temporal arrangement of the stimulus components, such that the random-SOA arrangements produced the greatest incongruency effects at the earliest irrelevant first SOA (−200 msec) and the constant-SOA arrangements produced the greatest effects with simultaneous presentation. These differences in conflict processing were accompanied by rapid (∼150 msec) modulations of the sensory ERPs to the irrelevant distractor components when they occurred consistently first. These effects suggest that individuals are able to strategically allocate attention in time to mitigate the influence of a temporally predictable distractor. As these adjustments are instantiated by the participants without instruction, they reveal a form of rapid strategic learning for dealing with temporally predictable stimulus incongruency.

Irrelevant Words Trigger an Attentional Blink

It has been argued that salient distractor items displayed during rapid serial visual presentation (RSVP) trigger an attentional blink (AB) when they share features with the target item. Here we demonstrate that salient distractor words induce an AB independently of feature overlap with the target. In two experiments a color-highlighted irrelevant word preceded a target by a variable lag in an RSVP series of false font strings. Target identification was reduced at short relative to long temporal lags between the distractor word and the target, irrespective of feature sharing with the distractor word. When the target shared features with the distractor word, target accuracy was reduced across all lags. Accordingly, feature sharing between the distractor word and the target did not amplify the AB, but had an additive effect on attentional capture by the distractor word.