Recent evidence suggests that eye movements towards a laterally presented stimulus (prosaccades) are performed automatically, whereas eye movements in a direction opposed to the normal saccadic direction (antisaccades) are performed under attentional control. The antisaccade task was developed by Hallet, 1978 and Hallet and Adams, 1980 to investigate the mechanisms that underly the generation of automatic and voluntary eye movements. He found that antisaccadic eye movements typically have longer latencies (time between stimulus onset and the start of the eye movement), that inaccurate reflexive saccades towards the cue sometimes occur, and that practice does not result in an improvement of antisaccade performance.

Guitton, Buchtel and Douglas (1985) used the antisaccade task to investigate deficient inhibitory control in patients with prefrontal lesions. The Frontal Eye Field and the Colliculus Superior (CS) are two systems involved in the generation of saccadic eye movements. The CS is supposed to mediate automatic, reflexive movements, whereas the FEF is assumed to be involved in higher level control of saccadic eye movements. The results of the frontal patients were compared with those of a control group and a group with lesions in the temporal lobe. No differences between the groups were found in latencies or errors of prosaccades. In the antisaccade task, however, frontal patients made more reflexive saccades (i.e., incorrect saccades towards the stimulus). Moreover, some frontal patients only performed a reflexive saccade with stimulus presentation contralateral to the damaged hemisphere. The results suggest that the damaged structures are involved in the generation of the antisaccades. This strengthens the idea that the prefrontal cortex contributes to the generation of complex saccadic eye movement behaviour. The function of these lobes would then be the inhibition of reflexive oculomotor activity and the triggering of voluntary eye movements.

Other authors used the antisaccade task in populations where prefrontal dysfunctioning is hypothesised (e.g., schizophrenia, ADHD). Fukushima et al. (1988) studied prosaccade and antisaccade performance in schizophrenic patients. Compared to healthy control participants, no differences were observed in the prosaccade condition. However, half of the schizophrenic patients made more incorrect antisaccades, and the correct antisaccades had longer latencies.

Fukushima, J., Fukushima, K., Morita, N. and Yamashita, I., 1990. Further analysis of the control of voluntary saccadic eye movements in schizophrenic patients. Biological Psychiatry 28, pp. 943–958. Abstract | View Record in Scopus | Cited By in Scopus (74)Fukushima, Fukushima, Morita and Yamashita (1990) presented schizophrenic patients with a nosaccade task and a memory saccade task. In the nosaccade task, participants fixate a central point in spite of the presentation of a cue. In the memory saccade task, a cue is presented while the fixation point is still present. Only after the removal of the fixation point a saccade must be made to the point where the cue was previously presented. Schizophrenic patients made a high number of saccades in the nosaccade task, whereas the healthy controls made no mistakes. Moreover, the memory saccade latencies were longer in schizophrenic patients than in the controls. In view of this evidence it seems that schizophrenic patients, much like prefrontal patients, have difficulty inhibiting reflexive saccades and executing voluntary saccades when the target position is known but not visible. The connection with the frontal lobes is also supported by the work of Rosse, Schwartz, Kim and Deutsch (1993) who found a significant correlation between performance on the antisaccade task and the Wisconsin Card Sorting Task in schizophrenic patients. Crevits and De Ridder (1997) studied antisaccades and memory saccades in a large group of Parkinson’s patients. They demonstrated severe abnormalities suggesting a dysfunction in the striato-prefrontal lobe. However, previous reports in smaller groups of less severely affected patients could not show consistent abnormalities.

The multi-component working memory model proposed by Baddeley and Hitch (1974) and Baddeley, 1986 and Baddeley, 1990, has proven to be a very fruitful conceptualisation of short-term memory. It has earned its merits in various areas of cognitive psychology such as reading comprehension, mental arithmetic, imagery, reading development, problem solving and others. Moreover, the model has demonstrated its usefulness in the study of patients with neurological deficits. It has, for instance, been found that interference with attentional control in dual-tasks, results in patterns that are similar to those found in patients with prefrontal lesions.

Roberts et al. (1994) investigated the relationship between antisaccades and working memory. Like Gathercole (1994), these researchers assume two important functions of the prefrontal cortex: (1) the short-term retention of information in order to organise future actions, and (2) the inhibition of prepotent responses. In addition, the authors assume that a temporary increase in working memory load can result in patterns of errors similar to patterns of permanent dysfunction of working memory, like those observed in prefrontal patients. Roberts et al. (1994) compared the single-task and dual-task performance in a prosaccade and an antisaccade task. The secondary tasks used were mental arithmetic, a shadowing task (i.e. repeat a given number), or a repeat task (i.e. always repeat the same number). Logie, Gilhooly and Wynn (1994) have already shown that mental arithmetic loads the central executive and the phonological loop. In this experiment Roberts et al. (1994), used only healthy participants. In the prosaccade task, almost no errors were made and mental arithmetic did not affect saccade latency. In the antisaccade task, however, more directional errors (reflexive saccades towards the stimulus) occurred and saccade latencies increased, much like in the prefrontal patients of Guitton et al. (1985). These results suggest at least a behavioural similarity between frontal patients and non-patients under heavy working memory load.

Roberts et al. (1994) assumed that as long as working memory is able to intervene in response preparation, alternative responses can be inhibited. The CS, which takes part in reflexive saccades receives input directly (FEF–CS) and indirectly (FEF-caudate nucleus-substantia nigra-CS) from the dorsolateral prefrontal cortex. The working memory system can inhibit the CS, for instance to prevent reflexive saccades in the antisaccade task and it may also be involved in initiating a planned saccade. However, the more working memory resources are involved in other activities, the less resources are available for inhibitory control and planning, and the more probable it will be for directional errors to occur in the antisaccade task.

In order to show unequivocally that the central executive, rather than the entire working memory system, takes part in antisaccade preparation, the concurrent task should be specific: it should interfere with the central executive without loading the slave systems. The literature contains a large number of tasks that interfere with the central executive: e.g., random number generation, random digit generation, tapping a random key pattern, avoidance of automaticity in a verbal reaction task, random pursuit tracking, free recall, counting backwards, and generation of category members. All these tasks have the drawback of also interfering with either the visuo-spatial or the phonological slave subsystem, so that clear-cut conclusions are not easy to obtain. Vandierendonck, De Vooght and Van der Goten (1998) have developed and tested a central executive task that is allegedly pure in the sense that it does not load significantly either of the known slave systems. In this Random time Interval Generation (RIG) task, participants are to tap a randomly spaced sequence of time intervals on a key so as to produce a completely unpredictable “rhythm”. In order to tap randomly, automaticity has to be prevented, and so this task requires cognitive control, while there are no logical or empirical reasons to assume that it interferes with the slave systems. This task has already been shown to affect span, supraspan, stimulus independent thoughts, a dual content location span task and simple mental arithmetic. The reported experiments were inspired by the working memory model. However, because the concept of the “central executive” and its until recently presumed unitary nature stands to discussion, we prefer to use the more neutral term “executive functions”.