Severe violations of independence in response inhibition tasks

Russell A. Poldrack

Abstract:

The stop-signal paradigm, a primary experimental paradigm for understanding cognitive control and response
inhibition, rests upon the theoretical foundation of race models, which assume that a go process races independently
against a stop process that occurs after a stop-signal delay (SSD). We show that severe violations of this indepen-
dence assumption at short SSDs occur systematically across a wide range of conditions, including fast and slow
reaction times, auditory and visual stop signals, manual and saccadic responses, and especially in selective stop-
ping. We also reanalyze existing data and show that conclusions can change when short SSDs are excluded. Last,
we suggest experimental and analysis techniques to address this violation, and propose adjustments to extant
models to accommodate this finding.