Reaction times of manual responses to a visual stimulus at the goal of a planned memory-guided saccade in the monkey

Monkeys demonstrate improved contrast sen- sitivity at the goal of a planned memory-guided saccade (Science 299:81-86, 2003). Such perceptual improve- ments have been ascribed to an endogenous attentional advantage induced by the saccade plan. Speeded reac- tion times have also been used as evidence for attention. We therefore asked whether the attentional advantage at the goal of a planned memory-guided saccade led to speeded manual reaction times following probes pre- sented at the saccade goal in a simple detection task. We found that monkeys showed slower manual reaction times when the probe appeared at the memorized goal of the planned saccade when compared to manual reaction times following a probe that appeared opposite the saccade goal. Flashing a distractor at the saccade goal after target presentation appeared to slow reaction times further. Our data, combined with prior results, suggest that a spatially localized inhibition operates on the neural representation of the saccade goal. This inhibi- tion may be closely related or identical to the processes underlying inhibition-of-return. We also found that if the same detection task was interleaved with a difficult perceptual discrimination task, manual reaction times became faster when the probe was at the saccade goal. We interpret these results as being an effect of task dif- ficulty; the more difficult interleaved task may have en- gaged endogenous attentional resources more effectively, allowing it to override the inhibition at the saccade goal. We construct and discuss a simple working hypothesis for the relationship between the effects of prior attention on neural activity in salience maps and on performance in detection and discrimination tasks.