Academic journal article Attention, Perception and Psychophysics

Exploring the Differences in Distributional Properties between Stroop and Simon Effects Using Delta Plots

Academic journal article Attention, Perception and Psychophysics

Exploring the Differences in Distributional Properties between Stroop and Simon Effects Using Delta Plots

Article excerpt

Stroop and Simon tasks are logically similar and are often used to investigate cognitive control and inhibition processes. We compare the distributional properties of Stroop and Simon effects with delta plots and find different although stable patterns. Stroop effects across a variety of conditions are smallest for fast responses and increase as responses slow. Simon effects across a variety of conditions, however, are largest for fast responses but decrease, and even reverse, as responses slow. We show in three experiments that these diverging patterns hold within participants and even when the stimulus materials are identical across the tasks. These stable differences in time course serve as bedrock phenomena for building and testing theories of cognitive control and inhibition. The results of two additional experiments suggest that the determinant of time course is not simply whether the distracting information is location.

Psychologists have long known that judgments about stimuli are affected by the surrounding context. A classic context effect occurs in the Stroop task, in which a judgment about the ink color of a color term is affected by the identity of the color term (Stroop, 1935). In this case, word identity serves as task-irrelevant context information, and judgments about color are faster when color and word identity match than when they mismatch. Another context effect occurs in the Simon task (Simon, 1969), in which participants judge the color of a target square by pressing left- and right-hand response keys. Responses are faster when the stimulus is displayed on the same side as the response than when it is displayed on the opposite side. Other examples of context-effect tasks include priming tasks (Scarborough, Cortese, & Scarborough, 1977), flanker tasks (Eriksen & Eriksen, 1974), and identification tasks with nested letters (Navon, 1977). Because these and similar tasks can be described as assessing the effects of task-irrelevant context information on judgments about a target, we refer to them generically as context tasks (see also Kornblum & Lee, 1995).

Context effects have been interpreted as evidence for cognitive control (Botvinick, Braver, Barch, Carter, & Cohen, 2001), selective attention (Spieler, Balota, & Faust, 2000), response inhibition (Ridderinkhof, 1997), and spreading activation (Neely, 1991), depending on the task and specifics of the experimental conditions. Differences in context effects across populations have been used to make claims about the effects of aging (Spieler, Balota, & Faust, 1996), schizophrenia (Baving, Wagner, Cohen, & Rockstroh, 2001), autism (Christ, Holt, White, & Green, 2007), and attention deficit disorder (Ridderinkhof, Scheres, Oosterlaan, & Sergeant, 2005) on cognitive control, selective attention, and inhibition. In fact, the robustness of the context effect across several tasks, as well as the logical similarity of these tasks, has led to a general perception that these tasks are more or less interchangeable in measuring cognitive control, selective attention, or inhibition.

In this article, we examine the time course of context effects in Stroop and Simon tasks. On the basis of the robustness of these context effects, as well as the logical similarity of the tasks, it might be expected that the time courses follow the same qualitative patterns. In fact, we report here dramatic differences. In Stroop tasks, the context effect is minimal for the fastest responses and increases as responses slow. The opposite pattern is found for Simon tasks: The context effect is maximal for the fastest responses, decreases as responses slow, and may even reverse for the slowest responses.

Distributions and Delta Plots

The dynamics of the time course of an effect are determined by the underlying response time (RT) distributions. Figure 1A shows two hypothetical distributions for congruent and incongruent conditions. …

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