Neuropsychological Model of the Stroop Effect

Virzi & Egeth (Memory & Cognition, 1985) developed a model of the Stroop effect using the concept of a translation mechanism. In this mechanism parallel processing systems coded different aspects of the Stroop stimuli (e.g., word vs. color). If an output channel is selected that is processed by the same analyzers that process the stimulus then no translation is required. On the other hand, if different analyzers are used to process the stimulus versus the response then translation is required and processing is slowed. For example, if a manual (right hemisphere) response is required to respond to a verbal stimulus than processing is slower than if a spatial stimulus is processed.

This mechanism explained well the reaction time data in a Stroop task. Unfortunately, little about the neural substrate of this cognitive model is offered. Thus, the Virzi & Egeth (1985) model is expanded in the diagram below to delineate the localization of the neural processors involved in the Stroop effect. The neural levels are labeled at the extreme left edge of the figure.

  1. Perceptual refers to secondary visual cortex;
  2. Symbolic refers to posterior tertiary cortex (i.e., inferior parietal lobule);
  3. Memorial refers to Papez' limic ring that connects memory encoding of posterior perceptual information to frontal motor systems;
  4. Motor refers to medial-frontal/striatal connections (i.e., basal ganglia & supplementary motor cortex, inclusive of cingulate gyrus motor areas);
  5. Executive refers to anterior tertiary cortex that plans and programs the response which evenuates in output through the motor cortex

In addition, the model includes lateralized processors which make testable the differences in reaction time associated with posterior analyzers. A controversy about the locus of interference has resulted in the current position that interference occurs at the output stage. However, some evidence in favor of interference occurring at the encoding stage remains, necessitating the current model's ability to test posterior analyzers. Posterior analyzers are the most likely locus of encoding interference. The Semantic box is the locus of verbal meaning processing while the Spatial boxes are the locus of spatial meaning, one for position-mediated spatial information in the right hemisphere and one for verbally-mediated information in the left hemisphere.

The present "synaptic distance" model can be tested by using a Stroop task in which the words UP and DOWN are shown in a top or bottom position either in the left or right visual field (RVF and LVF boxes). The participant is then required to respond either to the verbal or position information by either a vocal or manual response. The various hypothesized pathways of the processing are indicated by the numbers in the figure, representing their relative synaptic distances in ascending order. A graphic illustration of the hypothesized relationships are represented in a linked document.

Return to Osmon home page