The Simon Effect
We tend to associate responses on the right with movements to the right and vice versa. When this pattern is violated, it takes effort to coordinate movements. If you have ever driven a vehicle with a trailer attached, you know the difficulty of backing up, where in order to make the trailer go left in reverse you must turn the steering wheel to the right and vice versa.
Spatial Location and Response Selection
In this lab activity, you will generate results that show the relationship between spatial relationship and response selection. You will complete 10 practice trials and 60 experimental trials. At the beginning of each trial, you will see a fixation +. To begin, press the spacebar and then your task is to respond to red squares using the “D” key and to green squares using the “K” key. Position your left hand over the “D” key and your right hand over the “K” key. Make responses as quickly and accurately as possible. You will receive feedback only on practice trials.
Congruent vs. Incongruent Results
First described by Simon (1969), the first key finding is participants respond fastest when the stimulus is located in the same spatial location as the required response. In the first graph, you will see that red/left is faster than red/right, and green/right is faster than green/left. When the stimulus is on the left and a response with the left hand is required, participants are faster than when the stimulus is on the left and a response with the right hand is required. The second graph shows that trials with congruent spatial position have responses that are faster than trials with incongruent spatial position. The third graph shows that participants tend to be equally accurate at responding to stimuli of each color and with each hand but tend to make more errors in the incongruent than the congruent condition.
An Information Processing Perspective
If the Simon paradigm involves three stages of processing—stimulus identification (i.e., determine color), response selection (i.e., choose left or right response), and response execution (i.e., make the selected response)—then it can be argued that the experiment manipulates the duration of the response selection stage of processing such that processing for incongruent trials is slower than processing for congruent trials. That error rates are similarly low for different stimulus types suggests that the Simon effect is not a result of a delay in perceptual processing on incongruent trials. That response times are similar for left- and right-hand responses also suggests that the Simon effect is not the result of a delay in response execution on incongruent trials. This leaves the response selection stage as the source of the effect.
Practical Implications
There are numerous real-world considerations that are informed by the Simon effect. In the world of manufacturing, the results suggest it would be unwise to require machine operators to reach to their left to respond to something on their right, or vice versa, because doing so could lead to errors and worse an accident. Virtual training scenarios for driving and piloting have been updated so that students are deliberately presented with stimuli in their path and trained to turn away from the stimuli to avoid collision. Training like this is important because the Simon experiments show that we have a natural tendency to turn toward a stimulus.