Inhibitory motor control in stop paradigms: reply to McGarry and Franks (2000)

Two inhibitory mechanisms have been proposed to account for data obtained i n stop paradigms (De Jong, Coles, Logan, & Gratton, 1990; De Jong, Goles, & Logan, 1995). A central, cortically acting, mechanism was proposed to inte rfere with response preparation, and a more peripherally acting mechanism w ith response execution. In our recent review of inhibitory motor control in stop paradigms (Band & van Boxtel, 1999), we concluded that the evidence i n favor of the peripheral mechanism is scant and conflicting. We also reint erpreted behavioral and psychophysiological findings, and proposed that the available data can be more parsimoniously described by a single, central, mechanism. We argued that response activation continues as long as support from processes higher in the hierarchy continues, and that it grinds to a h alt as soon as the support stops (principle of response maintenance). Withi n this framework, inhibitory effects on measurements taken from levels peri pheral to the motor cortex do not necessarily imply a site of inhibition at that peripheral level. The reduced peripheral activity could result from c ortical activity that, albeit attenuated, was sufficient for producing some activation in peripheral structures. We further distinguished between the agent that instigates the inhibition, the sire onto which the inhibition is exerted, and their manifestations in observable measures.