Spatial primes produce dissociated inhibitory effects on saccadic latencies and trajectories.

In masked priming, a briefly presented prime can facilitate or inhibit responses to a subsequent target. In most instances, targets with an associated response that is congruent with the prime direction speed up reaction times to the target (a positive compatibility effect; PCE). However, under certain circumstances, slower responses for compatible primes are obtained (a negative compatibility effect; NCE). NCEs can be found when a long pre-target delay is used. During the delay, inhibition is assumed to take place, and therefore an effect on saccade trajectories may also be expected. In a previous study, we found the effects of inhibition on response times and trajectories to be dissociated, but this experiment varied the timing of several aspects of the stimulus sequence and it is therefore unclear what caused the dissociation. In the present study, we varied only one aspect of the timing, but replicated the dissociation. By varying just the pre-target delay, we found a PCE for a short delay, and an NCE for a long delay, but saccade trajectories deviated away from prime directions in both conditions. This suggests dissociated inhibitory effects of primes on response times and saccade trajectories

The relation between attention and tic generation in Tourette syndrome

OBJECTIVE: Many neuropsychiatric disorders involve abnormal attentional processing. Systematic investigations of how attention may affect tic frequency in Tourette syndrome are lacking.METHOD: Patients performed rhythmic finger movements, approximately once every 2 s. Each movement triggered a unique visual color stimulus. Patients were asked to monitor and remember their finger actions, the external colors caused by their actions, or their tics. Sixteen adult Tourette syndrome patients performed each task twice: once while inhibiting tics, and once without inhibiting tics.RESULTS: During the "freely tic" condition, patients had significantly fewer tics when attending to finger movements, or to the ensuing colors, compared with when attending to their tics. Attention to fingers produced the fewest tics overall. During tic suppression, tic frequency was reduced to an equal level in all conditions.CONCLUSIONS: Focusing attention away from tics significantly reduces tic frequency. This attentional process may operate by regulating motor noise.</p