The role of observers' gaze behaviour when watching object manipulation tasks: predicting and evaluating the consequences of action.

When watching an actor manipulate objects, observers, like the actor, naturally direct their gaze to each object as the hand approaches and typically maintain gaze on the object until the hand departs. Here, we probed the function of observers' eye movements, focusing on two possibilities: (i) that observers' gaze behaviour arises from processes involved in the prediction of the target object of the actor's reaching movement and (ii) that this gaze behaviour supports the evaluation of mechanical events that arise from interactions between the actor's hand and objects. Observers watched an actor reach for and lift one of two presented objects.

The role of uncertainty in the systematic spatial mislocalization of moving objects.

It only makes sense to talk about the position of a moving object if one specifies the time at which its position is of interest. The authors here show that when a flash or tone specifies the moment of interest, subjects estimate the moving object to be closer to where it passes the fixation point and further in its direction of motion than it really is. The authors propose that these biases arise from a combination of a large temporal uncertainty, a temporal asymmetry related to sampling the moving object's position, and a bias toward believing that one is looking at what one sees.

Eye movements when observing predictable and unpredictable actions.

We previously showed that, when observers watch an actor performing a predictable block-stacking task, the coordination between the observer's gaze and the actor's hand is similar to the coordination between the actor's gaze and hand. Both the observer and the actor direct gaze to forthcoming grasp and block landing sites and shift their gaze to the next grasp or landing site at around the time the hand contacts the block or the block contacts the landing site. Here we compare observers' gaze behavior in a block manipulation task when the observers did and when they did not know, in advance, which of two blocks the actor would pick up first.

Flashes are localised as if they were moving with the eyes.

Targets that are flashed during smooth pursuit are mislocalised in the direction of the pursuit. It has been suggested that a similar mislocalisation of moving targets could help to overcome processing delays when hitting moving objects. But are moving targets really mislocalised in the way that flashed ones are? To find out we asked people to indicate where targets that were visible for different periods of time had appeared.

Mislocalization of targets flashed during smooth pursuit depends on the change in gaze direction after the flash.

Subjects mislocalize the position of a target that is flashed while they are making pursuit eye movements. This mislocalization is in the direction of pursuit. However, it is not clear whether it is the movement of the eyes or the movement of the pursuit target that matters.

Quickly tapping targets that are flashed during smooth pursuit reveals perceptual mislocalisations.

In various studies subjects have been shown to misperceive the positions of targets that are flashed during pursuit eye movements. They mislocalise them in the direction of pursuit. Nevertheless, Hansen (1979) found that subjects accurately hit targets that are flashed during pursuit with a quick hammer blow.

Spatial but not temporal cueing influences the mislocalisation of a target flashed during smooth pursuit.

Human subjects misjudge the position of a target that is flashed during a pursuit eye movement. Their judgments are biased in the direction in which the eyes are moving. We investigated whether this bias can be reduced by making the appearance of the flash more predictable.