Peeking into the Mind’s Eye: Electrooculography in Text Comprehension Research
A Century of Research
For over 100 years, investigators have documented the binocular eye movements (EMs) known as saccades that reposition a reader’s fixation field to successive words or phrases in a sentence. The visual perception of text is limited to the fixation time between EMs. Nineteenth century experimenters reported the sequence of stops and starts during reading tasks by direct observation with handheld mirrors. Decades later, custom-built mechanical devices attached to the eyeballs became the preferred data collection method to record the roving eyes of readers. One experimenter even resorted to dosing his subjects with cocaine to reduce the discomfort of such invasive procedures. The first non-invasive EM recorder was devised in 1901 and relied on a light beam reflected from the reader’s cornea to project images on a moving photographic plate.
Vacuum tube technology led to instruments with sufficient signal amplification to detect bioelectric activity. Studies comparing EOG recordings to the more established photographic methods of data collection demonstrated the utility of this new technology. Biomedical recorders configured with amplifiers for monitoring brain wave activity (EEG), cardiac rhythms (ECG), muscle activity (EMG) as well as ocular dynamics (EOG) evolved into the polygraphs used by sleep technologists and research-driven educators. These analog workhorses could generate ink-on-paper tracings to produce interpretable graphic records when properly calibrated and maintained.
Incidentally, biomedical recorders built to assess an individual’s credibility by the detection of deception predated the use of clinical and research polygraphs. Generally, these “lie detectors” were limited to recordings of cardiovascular activity, respiration and sweating as measured by electrodermal activity. Another interesting fact in polygraph history concerns the first continuous, electrographic recording of nocturnal REM sleep. The study was conducted at the University of Chicago on a polygraph that used vacuum tube EOG/ EEG amplifiers.
The computerization of EOG in addition to other physiologic measures emerged in the 1960s from research in motion sickness related to air and space travel. Digitized systems helped relieve human scoring technicians from the time consuming chore of manually reducing big data sets with minimal scoring bias.
To learn more about electrooculography in text comprehension research, view the entire article in the A2Zzz Q2 2020 issue.