The EyeLink II machine has been used by Dr. Russell at the Macquarie Centre for Cognitive Science to study how individuals with schizophrenia process the facial expressions of other people [see Schizophrenia Research Institute (SRI)]. The machine records two eye movement parameters; fixations and saccades. Fixations are the location in space (or on an image) where the individual stops their eye. During fixations, the foveae remain directed at that particular point and the fine detail can be processed by the brain. Saccades are the paths between fixations, moving the eye rapidly between targets.
Work by Dr. Melissa Green at Macquarie demonstrated that people with schizophrenia have fewer fixations to the feature areas of faces (e.g. eyes, nose, mouth), with greater difficulties seen for negative emotions such as fear and anger. They also have longer and more-wide ranging saccades. These deviations in visual scanning have a negative impact on the accurate detection of facial emotion. Recent studies conducted by Drs. Russell and Green have shown that following a short computer-based training package the visual scan paths of people with schizophrenia can change, and in some respects, start to look more 'normal'. See Tamara Russell's biography if you would like more information about this research.
Saccades are when the eye is moving between fixations and are very rapid (700 degrees per second or faster). They appear as output in the EyeLink II software as a path or trace between the successive fixations. A phenomena called saccadic suppression means that when the eye is moving like this, visual information uptake is essentially shut down. This is demonstrated very aptly in the 'Did you see the gorilla?' experiment (currently being used with live audiences by Derren Brown). In this experiment, saccades are required to count the number of times two individuals pass a basket-ball to and fro. Because the movement of the eye makes the viewer effectively blind during that transition, viewers fail to spot a man in a gorilla suit who enters the frame and stands for 9 seconds between the two players. Typically this experiment is done by showing a video however it is now being conducted with live audiences in Derren Brown’s stage show!
These saccades are important later on, as in 'the art' part of our work, we use the saccadic output as a way to create a mark with our eye movements. Remember though that we are producing something for you to admire that stems entirely from a time when we were in fact almost blind, see the eye movement chapter in Methods in Mind.
