The timing of stimulus localisation and the Simon effect: an ERP study

Area of Science:

• Cognitive psychology
• Neuroscience
• Human motor control

Background:

• The Simon effect is an observed acceleration of responses when a stimulus appears on the same side as the response location.
• It is hypothesized to result from automatic response activation due to irrelevant stimulus location processing.
• Previous evidence for the temporal decay of the Simon effect is indirect, leaving its initiation and timing unclear.

Purpose of the Study:

• To directly investigate the temporal dynamics of the Simon effect decay.
• To determine when automatic response activation begins and what initiates it.
• To examine the influence of visual spatial processing on response activation.

Main Methods:

• Combined a localization task with a Simon task within an electroencephalography (EEG) study.
• Measured the Simon effect's size in relation to the time interval between localization and manual response.
• Controlled for the unequivocal encoding of relevant stimulus features following localization.

Main Results:

• Demonstrated that response activation is indeed evoked by visual spatial processing.
• Found a steady decrease in the magnitude of the Simon effect as the time between localization and response increased.
• This decay pattern was contingent upon the clear encoding of relevant stimulus features after localization.

Conclusions:

• The study provides direct evidence for the temporal decay of the Simon effect.
• Visual spatial processing initiates automatic response activation, which diminishes over time.
• The findings clarify the timing and underlying processes of the Simon effect's decay under specific encoding conditions.