Because one usually looks at what catches our attention (overt shift of attention), the question of how the eye finds the goal for the next saccade has often been answered by assuming that attention allocation precedes the shift in gaze direction. This leaves the question of how covert attention shifts are guided from one location to the next.
With prosaccades and procues one indeed obtains more express saccades and a shortening of reaction times.
However, with procues and antisaccades the reaction times become longer and the error rate increases. The subject behaves as if the precue was also treated as indicating the opposite side, eventhough it indicated the correct side. In other words: the subject is unable to use the instruction anti for the stimulus and the instruction pro for the cue.
|spatially selective||direction selective|
|sustained time course||transient time course|
|top down||bottom up|
Unrecognized errors are corrected faster: On trials with unrecognized errors the corrections occurred after an average of 95ms as compared to 145ms on trials with recognized errors. The reaction times of the errors were the same.
Even more surprising, when the subjects were asked to produce a sequence of saccades equivalent to an error and a corrective saccade on purpose almost all of them were unable to return the eyes from the first saccade target as quickly as they did when this first saccade happened as an unvoluntary error: a saccade made on purpose implies that the fovea spends a minimum of time (about 200 ms on average) at its goal and there is nothing the subject can do.
When the antisaccade task was combined with a dicrimination task it turned out that on trials with unrecognized errors the subjects had allocated their attention to the "wanted" side although they made saccades to the "unwanted" side. This was the first time a dissociation of saccade direction and attention direction could be demonstrated.