A volunteer demonstrates the eye tracking apparatus (ASL 504 system). Stimuli are presented on the computer monitor, and the position of the subject's eye using the infrared videocamera at the lower right of the computer monitor.
An example of a letter cancellation task. The subject is instructed to scan the image (which fills the width and height of the monitor) to locate occurrences of a target letter (the letter 'P' for instance), then to press a switch while looking at that letter each time they locate it. The eye tracking system allows us to analyze scanning patterns, make accuracy determinations, and examine the timing features (decision latency, duration of fixation, etc.) related to decision making.
An example of the text stimuli. We are concerned with measuring eye movements associated with the target word ('hedge'), which typically is not the word most people would expect to be used in this particular sentence. Regressions (shifting the eyes to a prior position in the sentence) and unusually long fixations (the time the eyes actually look at a word) often take place when an unexpected word appears in a sentence.