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. Highlights Manipulation of the completion time of the ‘go’ process is partially successful Perceptual degradation differentially affects stop-signal performance Increased stop difficulty (easy ‘go’) results in lower P (i) Increased stop difficulty (easy ‘go’) has no effect on SSRT Horse-race model does not fully explain basal ganglia involvement in inhibition