Eye tracking is unobtrusive and both time and cost effective compared with other neurological analysis methods. A growing number of researchers therefore use eye tracking to investigate for instance developmental aspects of visual and neurological functions, neurological diseases and brain damage.
Eye tracking - a window into neurological function and processes
Human vision solves two main tasks. Firstly, it transmits the image via the eye, retina, and second cranial nerve (optical nerve) into the brain passing the chiasm, thalamus, and visual cortex. Research indicates a link to many more parts. Secondly, it tries to control both eyes, directing them to the most relevant position at that point of time. This task is performed by the oculomotor system that controls the six muscles attached to each eye via the third cranial nerves.
Eye tracking gives access to both tasks. Data first shows the image shown to the retina followed by the response of the oculomotor system, including response time and exact saccade characteristics. Scientists can also access data regarding blink frequency and pupil size, which can indicate cognitive load changes.
Automated processes and quantifiable data
Eye tracking provides a method for researchers to study and quantify gaze patterns and eye movements in an objective and automated way that increases reliability and reduces variability. Video-oculography eye tracking provides a more comfortable method than electro-oculography eye tracking (using search coils).
Neuroscience studies, in which eye tracking is used include studies of:
- Eye movements, such as saccades, fixations and smooth pursuit
- Visual processing
- Interaction between eye movements, vision, and performance tasks
- Object-by-object search mechanisms in change blindness studies
- Mechanisms of visual neglect
- Conditions under which external visual-stimuli of moderate intensity capture spatial attention
- Neurological functions involved in perceptual decision making
- Neurological networks involved in covert spatial orienting of attention across visual and auditory modalities
- Head impulse tests
Eye tracking in research of neurological diseases and brain damage
Eye tracking is used in research to acquire a better understanding of neurological functions and related diseases and impairments. For instance, investigating scan patterns and control mechanisms of eye movements can provide early indicators for such diseases as autism, Alzheimer’s and schizophrenia. Clinical areas of research include:
- Autistic spectrum disorder (ASD) and attention deficit hyperactivity disorder (ADHD)
- Cognitive decline such as dementia, Alzheimer’s, Lewy body and Parkinson’s
- Reading and learning difficulties such as dyslexia
- Stroke and non-traumatic brain injury
- Amyotrophic lateral sclerosis (ALS)
- Receptive language, expressive language, or cognitive functioning
In research aimed at developing new means of screening and diagnosing neurological diseases, eye tracking paves the way for areas of new markers (parameters that can indicate normal function or disease). Automated assessment processes and the ability to quantify data provide new therapeutic follow-up opportunities that make it possible to follow disease or rehabilitation progression in an objective and quantifiable way.
There are three different ways of using eye tracking data in assessments:
- Analyze eye and head movement
- Analyze gaze patterns
- Use gaze data as an response or input method
Tobii eye trackers allow for large head movements, which enables and facilitates research that involves new groups of people, such as very young children and non-verbal adults.
Eye tracking combined with EEG
Real-time integration of eye tracking and EEG has become a more frequently requested feature. Combined use of these two methods enables simultaneous examination of brain activity and eye movements, giving information about what regions of the brain are activated while people engage in cognitive tasks or when faced with emotionally loaded images. Attention, time-on-task pupillometry, and eye blinks can be linked to the ongoing EEG.
Tobii eye tracking solutions
The Tobii TX300 Eye Tracker is designed for eye tracking studies that require a higher sampling rate; e.g. the need to study eye movements such as saccadic movements, large micro saccades, antisaccades, fixations, fixation stability, smooth pursuit, pupil size changes and blinks. Sophisticated technology allows head movements to be subtracted from gaze direction data, thus measuring real eye movements.
The Tobii TX300 combines 300 Hz sampling rate, very high precision and accuracy, robust tracking, and compensation for large head movements, thereby extending the possibilities for unobtrusive research of minute eye movements in neuroscience studies.
Eye tracking studies can be conducted without positioning the subject in an unnatural chinrest, which enable and facilitate research that involves children. The display closely fills a subject’s field of view and enables automated preferential looking paradigms. A latency of 10msec allows for gaze-contingent paradigms.
The system can be synchronized with most EEG systems, including Brain Products, EGI and ANT via E-Prime, for instance.
A wide range of research software applications are compatible with the Tobii TX300, including Tobii Toolbox for MATLAB, E-Prime Extensions for Tobii and Tobii Studio eye tracking software. Researchers can download the Tobii Software Development Kit at no cost, allowing their own applications to calibrate and retrieve gaze and pupil information from the Tobii eye tracker.