Do Task Sets Compete in the Stroop Task and Other Selective Attention Paradigms?

Age-related changes in attentional selection: revealing processes underlying the degradation of task set quality

The present study further explored the age-related changes in attentional selection, first reported by Jackson and Balota Jackson and Balota (Psychology and Aging 28:3, 2013). To this end, response stimulus interval (RSI) was manipulated in in a Stroop paradigm that allows to isolate different components of the overall Stroop effect. The originally reported reduction of the overall Stroop effect in short (vs. long) RSI was successfully replicated. In line with the original claim that the ability to maintain the relevant task set consistently across time is preserved in older adults, this reduction failed to interact again with age - a null result that was uniquely supported in the present study with Bayesian evidence. Although healthy aging affected all components of the overall Stroop effect, the present study further identified interference and a disproportionally larger semantic conflict effect, as being the primary mechanisms behind the larger overall Stroop effect that older adults produce compared to younger adults. These results therefore directly fuel the original conclusion of Jackson and Balota Jackson and Balota (Psychology and Aging 28:3, 2013) that age-related differences in attentional selection are due the degradation of task set quality, namely a lesser ability of older adults to control interference. The present study additionally showed this reduced control of interference directly and identified where in the processing stream it occurs. The immediate implication that challenges the dominant unitary models of Stroop performance, is that future interventions designed to boost interference control in older adults should most likely target semantic, as opposed to response conflict.

Age-related differences in information, but not task control in the color-word Stroop task

Older adults were found to struggle with tasks that require cognitive control. One task that measures the ability to exert cognitive control is the color-word Stroop task. Almost all studies that tested cognitive control in older adults using the Stroop task have focused on one type of control - Information control. In the present work, we ask whether older adults also show a deficit in another type of cognitive control - Task control. To that end, we tested older and younger adults by isolating and measuring two types of conflict - information conflict and task conflict. Information conflict was measured by the difference between color identification of incongruent color words and color identification of neutral words, while task conflict was measured by the difference between color identification of neutral words and color identification of neutral symbols and by the reverse facilitation effect. We tested how the behavioral markers of these two types of conflicts are affected under low task control conditions, which is essential for measuring task conflict behaviorally. Older adults demonstrated a deficit in information control by showing a larger information conflict marker, but not in task control markers, as no differences in task conflict were found between younger and older adults. These findings supported previous studies that work against theories that link the larger Stroop interference in older adults to a generic slowdown or a generic inhibitory failure. We discussed the relevancy of the results and future research directions in line with other Stroop studies that tested age-related differences in different control mechanisms.

Distributional analyses reveal the polymorphic nature of the Stroop interference effect: It's about (response) time

The study addressed the still-open issue of whether semantic (in addition to response) conflict does indeed contribute to Stroop interference (which along with facilitation contributes to the overall Stroop effect also known as Congruency effect). To this end, semantic conflict was examined across the entire response time (RT) distribution (as opposed to mean RTs). Three (out of four) reported experiments, along with cross-experimental analyses, revealed that semantic conflict was absent in the participants' faster responses. This result characterizes Stroop interference as a unitary phenomenon (i.e., driven uniquely by response conflict). When the same participants' responses were slower, Stroop interference became a composite phenomenon with an additional contribution of semantic conflict that was statistically independent of both response conflict and facilitation. While the present findings allow us to account for the fact that semantic conflict has not been consistently found in past studies, further empirical and theoretical efforts are still needed to explain why exactly it is restricted to longer responses. Indeed, since neither unitary nor composite models can account for this polymorphic nature of Stroop interference on their own, the implications for the current state of theory are outlined.

The Stroop legacy: A cautionary tale on methodological issues and a proposed spatial solution

The Stroop task is a seminal paradigm in experimental psychology, so much that various variants of the classical color-word version have been proposed. Here we offer a methodological review of them to emphasize the importance of designing methodologically rigorous Stroop tasks. This is not an end by itself, but it is fundamental to achieve adequate measurement validity, which is currently hindered by methodological heterogeneity and limitations. Among the several Stroop task variants in the literature, our methodological overview shows that the spatial Stroop task is not only a potentially methodologically adequate variant, which can thus assure measuring the Stroop effect with the required validity, but it might even allow researchers to overcome some of the methodological limitations of the classical paradigm due to its use of verbal stimuli. We thus focused on the spatial Stroop tasks in the literature to verify whether they really exploit such inherent potentiality. However, we show that this was generally not the case because only a few of them (1) are purely spatial, (2) ensure both all the three types of conflicts/facilitations (at the stimulus, response, and task levels) and the dimensional overlaps considered fundamental for yielding a complete Stroop effect according to the multiple loci account and Kornblum's theory, respectively, and (3) controlled for low-level binding and priming effects that could bias the estimated Stroop effect. Based on these methodological considerations, we present some examples of spatial Stroop tasks that, in our view, satisfy such requirements and, thus, ensure producing complete Stroop effects.

Evidence for Automatic, Stimulus Driven, Arithmetic Processing of Single-digit Multiplication Problems

Certain stimuli can automatically trigger different behaviors in a stimulus-driven manner. To investigate whether mathematical equations automatically trigger the tendency to engage in arithmetic processing, we asked whether the presentation of multiplication equations in an irrelevant dimension can trigger the automatic task of arithmetic processing and if so, which processes are involved. To that end, we employed a color-naming task in which participants had to name the color of different stimuli, such as: mathematical equations (e.g., 4 × 6 = 24), neutral-symbols (e.g., ####), neutral-words (e.g., building), and same-number strings (e.g., 11111), which appeared as one of four different colors. We found that mathematical equations and regular words in the irrelevant dimension triggered more task conflict (i.e., color naming's reaction time was longer) as compared to same-number strings. In addition, we found evidence for the automatic activation of different numerical processes; such that large-size equations (7 × 9 = 63) triggered more conflict as compared with small-size (2 × 3 = 6) equations and same-parity incorrect equations (3 × 2 = 8) triggered more conflict as compared to different-parity incorrect equations (4 × 2 = 9). We found no evidence indicating a distinction between the correct and incorrect equations. We discussed the relevance of the findings to the automaticity of arithmetic abilities and other domains in numerical cognition.

Onset complexity and task conflict in the Stroop task

The present study examined the extent to which a key marker of task conflict, negative facilitation, is modified by onset complexity. Negative facilitation, slower reaction times (RTs) to congruent stimuli than to non-lexical neutral stimuli in the Stroop task, is thought to reflect competition between the task sets of colour naming and word reading in the Stroop task (also known as task conflict). That is, it reflects competition between whole task sets, over and above any competition between specific responses associated with a stimulus. An alternative account of negative facilitation argues that it reflects the specific phonological processing differences between pronounceable (e.g., congruent) and non-pronounceable (e.g., xxxx) stimuli that are magnified by the specific task contexts that produce negative facilitation (a mostly non-lexical trial context). Here we used onset complexity to manipulate pronounceability of the irrelevant words in the Stroop task to test this alternative account. However, before applying manipulations that produce negative facilitation, we initially tested whether there was an effect of onset complexity on Stroop task performance. The results from Experiment(s) 1 (and 3) showed that complex onsets led to larger positive facilitation and congruency effects relative to simple onsets, but did not modify incongruent or neutral-word RTs. Experiment 2 directly tested whether onset complexity modifies negative facilitation and provided strong evidence for no effect of onset complexity, contrary to the alternative account predictions. The implications of the results for task conflict theory, selective attention, and phonological processing in the manual response Stroop task are discussed.

Proactive control affects task conflict beyond contingency learning

Various models of the Stroop task suggest that proactive task control adaptation accounts for the modulation of task conflict in different conditions of the Stroop task, for example, when task conflict is very frequent or very infrequent. Other researchers have argued that a contingency learning of colour-word associations is the main contributor to the modulations of the Stroop effect. In this work, we constructed a design that controls for confounds that are suspected to rule out the role of control adaptation in the Stroop task. We focused on one type of conflict-task conflict and tested whether colour-naming of neutral-words (where task conflict is present) differed from colour-naming of neutral-symbols (where task conflict is not present) in four different conditions: mostly words-congruent, mostly words-incongruent, mostly words-neutral, or mostly non-words-shape. Importantly, the conditions used for the task conflict marker were identical in all four conditions. We found that the marker of task conflict (reaction time [RT] for neutral-words > RT for neutral-symbols) was significant in the mostly non-words-shape condition, where proactive task control is relaxed, but not in the mostly words conditions, where proactive task control is activated, with no difference between these three words conditions. These findings suggest that control adaptation is the main contributor to the modulations of the Stroop effect. The relevance of the results to the current literature is discussed and the results are explained in light of the proactive control-task conflict (PC-TC) model.