Neutral stimuli and pupillometric task conflict

The contribution of difficulty of an irrelevant task to task conflict

In the standard colour-word Stroop task, participants are presented with colour words and required to respond to their colour while ignoring their meaning. Two types of conflict might occur in such experiments: information conflict and task conflict. Information conflict reflects the processing of two contradicting pieces of information and is indicated by shorter reaction times (RTs) in congruent than in incongruent trials. Task conflict reflects the additional effort associated with performing two tasks, as opposed to one, and is indicated by shorter RTs in neutral trials than in congruent trials (termed reverse facilitation). While information conflict is commonly seen in Stroop and Stroop-like tasks, task conflict is rarely observed. In the present study, participants were presented with coloured segments that, by applying Gestalt principles, could be perceived as colour words. We found that incongruent trials were slower than congruent trials, suggesting that participants successfully perceived the colour words, which led to involuntary reading. In addition, reversed facilitation was found so that neutral trials (i.e., trials that only consist of one task) were faster than congruent trials (as well as incongruent trials; both consist of two tasks). The presence of both interference from the incongruent trials and reverse facilitation suggests that involuntary reading could also occur in scenarios requiring cognitive effort.

Resting Stroop task: Evidence of task conflict in trials with no required response

In the typical Stroop task, participants are presented with color words written in different ink colors and are asked to respond to their color. It has been suggested that the Stroop task consists of two main conflicts: information conflict (color vs. word naming) and task conflict (respond to color vs. read the word). In the current study, we developed a novel task that includes both Response trials (i.e., trials in which a response is required) and Rest trials (i.e., trials in which no response is required or available) and investigated the existence of both information and task conflicts in Rest trials. We found evidence for task conflict in Response and also in Rest trials, while evidence for information conflict was only observed in Response trials. These results are in line with a model of task conflict that occurs independently of and prior to information conflict in the Stroop task.

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

Task sets have been argued to play an important role in cognition, giving rise to the notions of needing to switch between active task sets and to control competing task sets in selective attention tasks. For example, it has been argued that Stroop interference results from two categories of conflict: informational and task (set) conflict. Informational conflict arises from processing the word and is resolved by a late selection mechanism; task conflict arises when two task sets (i.e., word reading and colour identification) compete for activation and can be construed as involving an early selection mechanism. However, recent work has argued that task set control might not be needed to explain all of the switching cost in task switching studies. Here we consider whether task conflict plays a role in selective attention tasks. In particular, we consider whether S-R associations, which lead to informational conflict, are enough on their own to explain findings attributed to task set conflict. We review and critically evaluate both the findings that provided the original impetus for proposing task conflict in selective attention tasks and more recent findings reporting negative facilitation (longer RTs to congruent than to neutral stimuli) - a unique marker of task conflict. We then provide a tentative alternative account of negative facilitation based on poor control over informational conflict and apply it to a number of paradigms including the Colour-Object interference and Affordances tasks. It is argued that invoking competition between task sets in selective attention tasks might not be necessary.

The contribution of temporal analysis of pupillometry measurements to cognitive research

Reaction time (RT) is one of the most frequently used measures to detect cognitive processes. When tasks require more cognitive processes/resources, reaction is slower. However, RTs may provide only restricted information regarding the temporal characteristics of cognitive processes. Pupils respond reflexively to light but also to cognitive activation. The more cognitive resources a task requires, the more the pupil dilates. However, despite being able to use temporal changes in pupil size (advanced devices measure changes in pupil diameter with sampling rates of above 1000 samples per second), most past studies using pupil dilation have not investigated temporal changes in pupil response. In the current paper, we discuss the advantage of the temporal approach to analyze pupil changes compared to a more traditional perspective, specifically, singular value methods such as mean value and peak amplitude value. Using data from two recent studies conducted in our laboratory, we demonstrate the differences in findings arising from the various analyses. In particular, we focus on the advantage of temporal analysis in detecting hidden effects, investigating temporal characterizations of the effects, and validating the experimental manipulation.

What is word? The boundary conditions of task conflict in the Stroop task

The Stroop task is characterized by two types of conflicts-information conflict (between the incongruent word and ink color) and task conflict (between the relevant color-naming task and the competing, irrelevant, stimulus-driven, word reading task). It is not yet clear what stimuli trigger the task of reading, and thus task conflict, and to what extent. In the current study, we applied a novel low-control (high neutral proportion) between-subject design to test the effect of different neutral conditions (symbols, same-letter strings, illegal-letter strings, pseudo-words, and real-words) on task conflict, in both manual and vocal response-types. Results indicated that in the manual task, a reverse facilitation effect, a signature of task conflict, appeared in all non-word conditions in a similar magnitude, but did not appear in the real-words condition. In the vocal task, reverse facilitation was found only in the symbols condition, regular facilitation was exhibited in all other neutral conditions, and larger facilitation appeared in the real-words condition. Our results indicate that the reading process and the activation of task conflict, depend on response-types (manual vs. vocal). In both response-types we found support for a word superiority effect, such that words trigger task conflict to a greater extent, however, we only observed an orthographic effect in the vocal response-type where stimuli consisting of letters triggered the reading task. We concluded that in the manual response-type, conflict arises only in the lexical route, whilst in the vocal response-type, conflict arises in the lexical and orthographic routes.

Conflict monitoring or multi-tasking? Tracking within-task performance in single-item and multi-item Stroop tasks

Cognitive control is applied in situations that require overriding a habitual and automatic response. The conflict monitoring hypothesis and the Expected Value of Control (EVC) theory as its extension posit a control system responsible for detecting conflicting occasions and adapting to them dynamically within a task. Here we evaluate this prediction in two versions of one of the most popular tasks in cognitive control, namely the Stroop task. We hypothesized that nearby-items interference combines with task interference in the multi-item version effectively turning it into a multi-task that may challenge cognitive control. Adopting an alternative methodology tracking within-task performance, we compared the classical multi-item version of the Stroop task and its single-item counterpart in adults and children. The results revealed a within-task performance decline only in the multi-item version of the task, in both incongruent and neutral conditions, modulated by the presumed maturity of the control system. These findings suggest capacity constraints in control implementation and allocation under conditions requiring parallel execution of multiple cognitive tasks. Task complexity and demands seem to modulate effects on performance. We discuss implications for cognitive control as well as substantial concerns regarding the calculation and use of indices of interference based on the commonly used multi-item version of the Stroop task.

Publication guidelines and recommendations for pupillary measurement in psychophysiological studies

A variety of psychological and physical phenomena elicit variations in the diameter of pupil of the eye. Changes in pupil size are mediated by the relative activation of the sphincter pupillae muscle (decrease pupil diameter) and the dilator pupillae muscle (increase pupil diameter), innervated by the parasympathetic and sympathetic branches, respectively, of the autonomic nervous system. The current guidelines are intended to inform and guide psychophysiological research involving pupil measurement by (1) summarizing important aspects concerning the physiology of the pupil, (2) providing methodological and data-analytic guidelines and recommendations, and (3) briefly reviewing psychological phenomena that modulate pupillary reactivity. Because of the increased ease and tractability of pupil measurement, the goal of these guidelines is to promote accurate recording, analysis, and reporting of pupillary data in psychophysiological research.

Task and information conflicts in the numerical Stroop task

Studies of the Stroop color‐word task have provided evidence for the existence of two conflicts: (1) an early task conflict between noting the relevant color and reading afforded by the irrelevant word (or word‐like stimuli), and (2) a late information conflict between the information provided by the word and the information provided by the color. Measurements of pupil changes, in addition to reaction time (RT), have extended understanding regarding these two conflicts. The current work examines the generalizability of such understanding. We ask whether similar processes work in the comparative judgment of numbers (e.g., in the numerical Stroop task). We present two experiments that support and extend the knowledge gained in the word‐color context to numerical processing. Similar to results with the Stroop color‐word task, we found a dissociation between RT and pupillometry and an early task conflict followed by an information conflict.

Recent Stroop color‐word studies have indicated the existence of an early task conflict followed by an information conflict. The current experiments used pupillometry to show the existence of these two conflicts in a numerical Stroop‐like task. Accordingly, our research extends and generalizes the two‐conflict notion beyond color‐word processing.

Early Auditory Event Related Potentials Distinguish Higher-Order From First-Order Aversive Conditioning

Stimuli in reality rarely co-occur with primary reward or punishment to allow direct associative learning of value. Instead, value is thought to be inferred through complex higher-order associations. Rodent research has demonstrated that the formation and maintenance of first-order and higher-order associations are supported by distinct neural substrates. In this study, we explored whether this pattern of findings held true for humans. Participants underwent first-order and subsequent higher-order conditioning using an aversive burst of white noise or neutral tone as the unconditioned stimuli. Four distinct tones, initially neutral, served as first-order and higher-order conditioned stimuli. Autonomic and neural responses were indexed by pupillometry and evoked response potentials (ERPs) respectively. Conditioned aversive values of first-order and higher-order stimuli led to increased autonomic responses, as indexed by pupil dilation. Distinct temporo-spatial auditory evoked response potentials were elicited by first-order and high-order conditioned stimuli. Conditioned first-order responses peaked around 260 ms and source estimation suggested a primary medial prefrontal and amygdala source. Conversely, conditioned higher-order responses peaked around 120 ms with an estimated source in the medial temporal lobe. Interestingly, pupillometry responses to first-order conditioned stimuli were diminished after higher order training, possibly signifying concomitant incidental extinction, while responses to higher-order stimuli remained. This suggests that once formed, higher order associations are at least partially independent of first order conditioned representations. This experiment demonstrates that first-order and higher-order conditioned associations have distinct neural signatures, and like rodents, the medial temporal lobe may be specifically involved with higher-order conditioning.

Degree and pattern of dual-task interference during walking vary with component tasks in people after stroke: a systematic review

QUESTIONS

What are the degree and pattern of dual-task interference during walking in people after stroke? How do these vary with disease chronicity and different component tasks in people after stroke? How does dual-task interference differ between people after stroke and people without stroke?

DESIGN

Systematic review with meta-analysis of studies reporting gait-related dual-task interference.

PARTICIPANTS

People after stroke and people without stroke.

OUTCOME MEASURES

Measures of walking and secondary (cognitive or manual) task performance under dual-task conditions relative to those under single-task conditions.

RESULTS

Seventy-six studies (2,425 people after stroke and 492 people without stroke) were included. Manual and mental tracking tasks imposed the greatest dual-task interference on gait speed, although there was substantial uncertainty in these estimates. Among mental tracking tasks, the apparently least-complex task (serial 1 subtractions) induced the greatest dual-task interference (-0.17 m/s, 95% CI -0.24 to -0.10) on gait speed, although there was substantial uncertainty in these estimates. Mutual interference (decrement in both walking and secondary component task performances during dual-tasking) was the most common dual-task interference pattern. The results of the sensitivity analyses for studies involving people with chronic stroke were similar to the results of the primary analyses. The amount of dual-task interference from a mental tracking or manual task during walking was similar between people with or without stroke.

CONCLUSIONS

The degree and pattern of dual-task interference vary with the choice of component tasks. When evaluating limitations to functional mobility during dual-tasking conditions and in planning interventions accordingly, clinicians should select dual-task assessments that correspond to the daily habits and physical demands of people after stroke.

REGISTRATION

CRD42017059004.

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.

eStroop: Implementation, Standardization, and Systematic Comparison of a New Voice-Key Version of the Traditional Stroop Task

The Stroop effect is a well-documented phenomenon, demonstrating both interference and facilitation effects. Many versions of the Stroop task were created, according to the purposes of its applications, varying in numerous aspects. While many versions are developed to investigate the mechanisms of the effect itself, the Stroop effect is also considered a general measure of attention, inhibitory control, and executive functions. In this paper, we implement "eStroop": a new digital version based on verbal responses, measuring the main processes involved in the traditional effect. eStroop features four categories of stimuli in four different colors: (1) geometrical shapes, (2) neutral words, (3) congruent words, and (4) incongruent words. The results of the administration to 307 University students confirm the Stroop effect and offer baseline data for future research and clinical testing. Direct comparisons with other recent versions of the task are discussed, offering insights into differences and similarities between different task variables.

The contribution of meaning to the detection of task conflict

The colour-word Stroop task produces both information conflict (detection of the ink colour vs word meaning) and task conflict (respond to the ink colour vs read the word). In this study, we measured both reaction time and pupil dilation, and the neutral stimuli in our study were non-readable letter strings as well as meaningless non-readable stimuli (i.e., coloured patches and abstract character strings). Our results showed slowest responses in the incongruent trials and fastest responses in the congruent trials. However, no differences were found between the investigated neutrals. In contrast, pupil dilation was largest in the incongruent trials and smallest in the neutral trials. Moreover, the more the neutral stimuli were meaningless, the less the pupil dilation that was observed. Our results suggest that non-word meaningless stimuli reduced task conflict (compared with all the investigated conditions). Neutral equivalence should be taken into consideration in Stroop and Stroop-like tasks.