Balkenius, C., Holmqvist, K. & Holsanova, J. (2001) Implicit Learning of Anticipatory Saccades. Poster presented at the ECEM 11, Turku.
What is the relation between visual expectations and voluntary eye movements? To investigate whether anticipatory saccades depend on explicit expectations of target location or if an implicit learning strategy is sufficient we tested 12 subjects in a visual expectation task while their eye-movements were recorded. After the experiment, subjects were interviewed to see whether their experience with the task had lead to explicit expectations or rules that described the regularities of the task. The subjects were given a number of trials where a cue stimulus (a red or blue dot) was followed by a target stimulus (a yellow dot) to the right or the left of the cue. Each trial lasted for 1000 ms. The cue stimulus was shown for 250 ms at a pseudo random location followed by a pause of 250 ms before the target stimulus appeared. The target was presented for 250 ms followed by a pause of 250 ms before the next trial. Depending on the color of the cue, the target was presented either to the right or to the left of the cue. The eye movements were recorded by the SMI iView remote eye-tracker. The subjects were instructed to look at all yellow dots that appeared but they were not told about the correlation between the red or blue cues and the location of the target. Analysis of the recorded eye-movement data showed that all subjects learned to make anticipatory saccade toward the target location before the target appeared. However, when asked after the experiments whether they had found any correlation between the colored cues and the targets, the subjects had very different theories. All subjects had tried to find a structure in the scene but surprisingly their hypotheses were not correct. Although all subjects reported seeing some pattern in the sequence and nine (75%) reported having seen repetitions of the same sequences, only one (8%) had recognized that the targets occurred in close proximity to the cues. Even in this case, the subject did not realize that the color of the cue indicated the direction to the target. Interestingly, one subject reported having a feeling of knowing where the target would appear without having any idea of how he could know it. The results clearly show that learning of anticipatory saccades can occur without explicit rules or expectations. This implies that expectation based eye-movements need not be voluntary in the sense that they are driven by explicit expectations.