Liat Goldfarb

Evidence for task conflict in the Stroop effect.

C. M. MacLeod and P. A. MacDonald (2000) suggested that congruent and incongruent Stroop stimuli cause more task conflict than neutral stimuli because the anterior cingulate cortex is more activated with these stimuli. This study investigated behavioral expression for this pattern. Experiment 1 reduced task conflict control by increasing the proportion of nonword neutrals. Additionally, half the trials had conflict or neutral cues. The control reduction revealed the task conflict. For noncued trials, response time was longer for congruent stimuli than for neutral stimuli (reverse facilitation effect). In addition, response time for congruent stimuli was longer when stimuli were uncued vs. cued. Experiment 2 increased task conflict control by changing the neutral stimuli to noncolor words. Consequently, the task conflict expression disappeared.

Stop interfering: Stroop task conflict independence from informational conflict and interference.

Performance of the Stroop task reflects two conflicts—informational (between the incongruent word and ink colour) and task (between relevant colour naming and irrelevant word reading). This is supported by findings showing that the anterior cingulate cortex is more activated by congruent and incongruent stimuli than by nonword neutral stimuli. Previously, researchers demonstrated behavioural evidence for task conflict—a reverse facilitation effect under a reduced task conflict control condition. The boundary conditions of this Stroop reverse facilitation effect are not yet clear. The current study aimed to investigate whether task conflict arises, and task control is needed, whenever there are two possible tasks, even if the irrelevant task cannot mislead one to give erroneous responses (i.e., stimuli do not contain an informational conflict). To this end, in both experiments no incongruent stimuli were presented. In Experiment 1, participants conducted a Stroop task with a high proportion of nonword neutrals and with a neutral/congruent cue in 50% of the trials. In Experiment 2, the nonword neutral was replaced by a real non-colour-word. We found the reverse facilitation effect in the noncued trials of Experiment 1. Moreover, as expected, this effect was eliminated when a noncolour neutral word that induced task conflict was used (Experiment 2). We conclude that task conflict control is reactively activated whenever there are at least two possible tasks, even in the absence of any possibility of informational conflict.

New Data Analysis of the Stroop Matching Task Calls for a Reevaluation of Theory

In Stroop matching tasks, participants indicate whether the color of an object matches the meaning of a color word printed in color. Previously in this journal, Luo (1999) concluded that interference between two incongruent representations of the same attribute (ink color) occurs prior to the response stage. However, this conclusion was based on questionable data analysis. We suggest analyzing the data by separating “same” and “different” responses and then analyzing three congruency conditions within the “different” responses: (a) congruence between word color and word meaning, (b) congruence between word color and object color, and (c) incongruence between word color, word meaning, and object color. In an experiment similar to Luos, such an analysis revealed that responding was slowest in the first condition. This pattern of results does not fit with previous conclusions regarding this task, but rather indicates that task conflict and response competition contribute to interference. This analysis has implications for matching tasks other than the Stroop matching task.

The Effect of a Preceding Cue on the Conflict Solving Mechanism

In everyday life cues and signs are used in order to improve our performance and to modify and control our behavior. This study examines whether cues can improve the performance of the mental mechanism in charge of solving conflicts when the nature of the irrelevant task remains constant. In two experiments participants performed the Stroop task in which they were asked to name the color of a stimulus while ignoring its meaning. Half the trials were preceded by a conflict-cue containing information about an upcoming conflict. In addition, conflict trial proportions were manipulated. We found that only when the probability of conflict is low can cues alter the conflict solving mechanism. These findings are discussed in the context of the nature of the control mechanism and its tendency to minimize the cost of mental resources.

The numerical distance effect is task dependent

Number comparison tasks produce a distance effect e.g., Moyer & Landauer (Nature 215: 1519-1520, 1967). It has been suggested that this effect supports the existence of semantic mental representations of numbers. In a matching task, a distance effect also appears, which suggests that the effect has an automatic semantic component. Recently, Cohen (Psychonomic Bulletin & Review 16: 332-336, 2009) suggested that in both automatic and intentional tasks, the distance effect might reflect not a semantic number representation, but a physical similarity between digits. The present article (1) compares the distance effect in the automatic matching task with that in the intentional number comparison task and suggests that, in the latter, the distance effect does include an additional semantic component; and (2) indicates that the distance effect in the standard automatic matching task is questionable and that its appearance in previous matching tasks was based on the specific analysis and design that were applied.

Is size perception based on monocular distance cues computed automatically

The study reported here examined whether size perception based on monocular distance cues is computed automatically. Participants were presented with a picture containing distance cues, which was superimposed with a pair of digits differing in numerical value. One digit was presented so as to be perceived as closer than the other. The digits were of similar physical size but differed in their perceptual size. The participants’ task was to decide which digit was numerically larger. It was found that the decision took longer and resulted in more errors when the perceptual size of the numerically larger digit was smaller than the perceptual size of the numerically smaller digit. These results show that perceived size affects performance in a task that does not require size or distance computation. Hence, for the first time, there is empirical support for the working assumption of the visual perception approach that size perception based on monocular distance cues is computed automatically.

Counting Multidimensional Objects Implications for the Neural-Synchrony Theory

It has been suggested that a neural instantiation of the temporary multidimensional representations of objects might be synchrony of firing between the neurons representing the features that co-occur in a given location. In this article, we direct attention to a logical problem that arises when certain synchrony assumptions are applied to real situations in which multiple multidimensional objects are presented. We demonstrate a new behavioral effect that shows that this logical problem coincides with a genuine behavioral problem. Even when a display contains only a small number of objects characterized by features on two dimensions, the representation of the display becomes difficult when, according to our described assumptions, the object representations cannot be simultaneously synchronized on both features. This article outlines a new principle that governs object representation, and the experimental results might be unique behavioral evidence for a neural-based theory of feature binding.

Does a color difference between parts impair the perception of a whole? A similarity between simultanagnosia patients and healthy observers

In three experiments, participants decided whether a Star of David shape was present among distractors. Although the participants were instructed to ignore the colors in the display, detection was slower when each triangle of the Star of David was printed in a different color than when the Star of David was printed in a uniform color or when each triangle was in two colors. Extending the object file theory, we suggest that when the parts of an object are distinguished by a color difference and are perceived as separate objects, the perception of the whole object, which is composed of these same parts, is damaged. One interpretation within object file theory is that when the visual system represents the location of a complex object as occupied by identity tags for its different parts, it cannot also link the same location to the identity of the complex object. A new object file must then be created.

The cause of the within-language Stroop superiority effect and its implications

This study examines the causes for the within-language Stroop superiority effect (WLSSE; larger Stroop effect for words appearing in the response language than in another language). Participants named in their first language (L1) or second language (L2) the colour of colour-words or colour-associated words appearing in L1 or in L2. The WLSSE was limited for colour-words. It was concluded that for colour-words, the cause for the WLSSE is that words appearing in the within-language condition belong to the response set, whereas words in the between-language condition do not. This finding challenges previous suggestions that a nonrelevant stimulus language can be suppressed.

Repetition blindness: The survival of the grouped

The repetition blindness (RB) effect demonstrates that people often fail to detect the second presentation of an identical object (e.g., Kanwisher, 1987). Grouping of identical items is a well-documented perceptual phenomenon, and this grouping generally facilitates perception. These two effects pose a puzzle: RB impairs perception, while perceptual grouping improves it. Here, we combined these two effects and studied how they interact. In a series of three experiments, we presented repeated items in a simultaneous string, while manipulating the organization of the repeated items in groups within a string. We observed an interaction between RB and grouping that we summarize with a rule that we call “the survival of the grouped”: In essence, the ability to group repeated elements protects them from RB. These findings are discussed within the framework of the object file theory.