Table 3.
Types of eye movements and experimental paradigms to elicit them.
| Type of eye movement | Paradigm | Description |
|---|---|---|
| Spontaneous | In the dark | Movement not triggered toward a visual target |
| Reflexive (triggered by the sudden appearance of a visual target in space) | Simultaneous | The fixation point switches off and the target appears simultaneously |
| Gap (facilitates the most reflexive saccades) | The fixation point switches off and the target appears after a gap period typically lasting a few hundred milliseconds. Such gap period is believed to facilitate fixation disengagement and movement preparation. Typically leads to the gap effect (shorter latency in the gap than the simultaneous paradigm) and express saccades (with latency < 120 ms in humans) | |
| Overlap | The fixation point remains on the screen after the target appears, for an overlap period in which the two are simultaneously present for a few hundred milliseconds. In such paradigm, there is an enhanced competition between maintaining fixation and preparing a saccade. Typically leads to the overlap effect (i.e., longer latency in the overlap than in the simultaneous paradigm) | |
| Flashed | The movement is triggered by briefly flashed visual targets toward the location in which they had appeared | |
| Voluntary (the target was already present, is already gone, or was never present) | Visually-guided voluntary | Typically triggered by endogenous cue (such as an auditory signal or a central arrow prompting a saccade toward a lateral target) |
| Memory-guided | Participants are required to make an eye movement when a fixation point extinguishes (go signal) toward a target that was flashed before | |
| Anti-saccade | Participants are required to perform a saccade away from a visual target, which involves the inhibition of a reflexive pro-saccade and the generation of a voluntary, non-visually-guided anti-saccade | |
| Predictive | Repetitions allowing the participant to predict the direction, amplitude and timing of the next target | Movement triggered toward a stimulus not present yet (i.e., with latency < 80 ms in humans) |