Perceptual Degradation Affects Stop-Signal Performance in Normal Healthy Adults

During stop-signal task performance, little is known how the quality of visual information of the go stimuli may indirectly affect the interplay between the go and stop processes. In this study, we assessed how perceptual degradation of the visual go stimuli affect response inhibition. Twenty-six healthy individuals (mean age 33.34 {+/-} 9.61) completed a modified 12-minute stop-signal task, where V and Y letters were used as visual go stimuli. The stimuli were subjected to four levels of perceptual degradation using Gaussian smoothing, to parametrically manipulate stop difficulty across low, intermediate-1, intermediate-2 and high difficulty conditions. On 33% of trials, the stop-signal (50ms audio tone) followed a go stimulus after a stop-signal delay, which was individually adjusted for each participant. As predicted, we found that with increased level of stop difficulty (little perceptual degradation), reaction times on go trials and the proportion of successful behavioural inhibitions on stop trials (P(i)) decreased in normal healthy adults. Contrary to our predictions, there was no effect of increased stop difficulty on the number of correct responses on go trials and reaction times on stop trials. Overall, manipulation of the completion time of the go process via perceptual degradation has been partially successful, whereby increased stop difficulty differentially affected P(i) and SSRT. These findings have implications for the relationship between the go and stop processes and the horse-race model, which may be limited in explaining the role of various cortico-basal ganglia loops in modulation of response inhibition. HighlightsO_LIManipulation of the completion time of the go process is partially successful C_LIO_LIPerceptual degradation differentially affects stop-signal performance C_LIO_LIIncreased stop difficulty (easy go) results in lower P(i) C_LIO_LIIncreased stop difficulty (easy go) has no effect on SSRT C_LIO_LIHorse-race model does not fully explain basal ganglia involvement in inhibition C_LI