Express Eye - Saccade Analysis

Quick and easy test of a subject's quality of fixation, reflexive gaze control and ability to produce voluntary saccades.
Reaction time measurements.

Document Index:

Introduction
Features
Description
Built-In Visual Tasks
Applications
Scientific Background

Introduction

This device with its new unique combination of included target generation, eye movement measurement and data analysis makes it easy to test a subject's quality of fixation, reflexive gaze control and ability to produce voluntary saccades and do reaction time measurements.

Express Eye was developed in cooperation with the Express Saccade Laboratory of the University Freiburg, Germany.

Prof. Dr. B. Fischer, the discoverer of Express Saccades, has over a decade of experience in measuring and interpreting eye movements.

The normative database of this research group is available to customers of Express Eye for interpretion of individual measurements.

The group of Prof. Fischer has done research in the area of anti saccades, development of voluntary control over eye movements with age and the interpretion of this data in the context of various brain dysfunctions, dyslexia and diseases, e.g. schizophrenia. For example in many dyslexic children their voluntary control over their eye movements seems to be not fully developed.

Features

quick and easy to use:
performs several standard oculomotor tests automatically
completely stand-alone:
no additional equipment required because target display and data analysis are built in: mini-lasers project three visual targets, a hand-held controller analyses the eye movements and presents the numerical results on a LCD display or optionally transfers the data to a PC.
small and easily transportable
All you need is the head-band and the hand-held controller.
can operate under normal room light conditions
no need for a special room, background light is filtered out electronically
touch-free
eye movements are measured by infrared light reflection
automatic head movement compensation
There is no need to fixate the head. The new unique mounting of the target projection on the head band (in form of three mini-lasers) ensures that the relative positions of the targets as seen from the subject are not changed by head movements.
high precision
Express Eye analyses the eye position 1000 times a second with 0.1 degree resolution
easy mechanical adjustment
the position of the measuring elements can be easily adjusted with three degrees of freedom for optimal signal quality. The calibration program assists you semi-automatically in finding the optimum position very quickly and easily.
easy calibration
a quick procedure of looking at three points provides the controller enough information for automatic calibration in a given subject.

Description

Express Eye consists of

a lightweight head-band holding the detector unit and preamplifier. The size of the head-band can be adjusted in two dimensions to fit comfortably on almost every head, even of children.

a detector unit in front of the subjects eye. The position of the detector can be easily adjusted with three degrees of freedom for optimal signal quality.

a small hand-held controller with included target control, data analysis software and a LCD display, see built in saccade tasks and results.
three mini lasers are mounted on top of the helmet for target projection on almost any surface. They can be adjusted to project three points in either 4, 8 or 12 degrees distance from each other. The beams cross above the subjects eyes such that changes in head position and viewing distance are largely compensated. The lasers do conform to laser class 2 (i.e. they are not dangerous unless someone stares directly into the beam).
a serial port to transfer eye position data to a PC or to print the numerical results on a printer. The data being sent to the PC is 10 bit digitized data with a resolution better than 0.1 degrees.
optionally a PC program to receive and store the data, display the eye movements graphically and print a reaction time histogram.

Built-In Saccade Tasks

Express Eye controls three mini-lasers to provides gap and overlap tasks. The spatial and temporal parameters of the tasks are configurable by the user.

A measurement typically consists of 100 or 200 trials. In each trial the center laser (fixation point) apprears first. After one second the left or right target appears in random order. Right/left ratio of random selection can be chosen between 0/100 and 100/0.

The subject can be instructed to either look towards (pro-task) or away from (anti-task) the target.

Results

Express Eye interprets reaction time and direction according to the instructions to either generate prosaccades (to the stimulus) or antisaccades (to the opposite side).

After a selected number of trials EXE will display the %-number of correct and incorrect saccades, the respective reaction time mean values and their standard deviations, separately for left and right stimuli. These tasks have been selected because they provide information on the quality of fixation, reflexive gaze control, and the ability to produce voluntary saccades.

Applications

Express Eye can be used in basic science laboratories (Neurosciences, Psychophysics, Psychology), for clinical application (Neurology, Psychiatry, Ophthalmology), in public health service or wherever the efficiency of gaze control is of importance (dyslexia, aging, drug abuse, medication, sports, driver's license,...).

measure saccadic latencies
control fixation
determine ability to produce voluntary saccades

Scientific Background

The human brain has an elaborate system to coordinate visual functions and gaze direction. Gaze can be stabilized by active fixation provided by a separate neural system (tectum and parietal cortex). Quick changes of gaze direction (saccades) occur 3-5 times a second and are generated either automatically or on the subjects voluntary decision. The fixation system and the voluntary control system develop during different time periods in life, with the latter being completed not before the age of 15-20 years (Fischer et al., 1997. Brain Research).

Voluntary saccade generation is impaired after lesions of the frontal cortical system (Guitton et al., 1985. Exp Brain Res. 58, 455) while stable fixation is lost after tectal inactivation (Munoz and Wurtz, 1993. J. Neurophysiol. 70, 576). A subject with an impaired fixation system is also impaired on an antisaccade task producing high %-numbers of reflexive prosaccades. A subject with a selective impairment of voluntary control may be able to suppress the reflexes but is unable to look to the opposite side. Other subjects may be impaired on both aspects of the antisaccade task.

Patients with schizophrenia (Matsue et al., 1994. Jpn J Psychiatry & Neurology 48, 13), Alzheimer's disease (Currie et al., 1991. Arch Neurol 48, 644), or advanced Parkinson's disease (Kitagawa et al., 1994. Neurology 44, 2285), or lesions in the prefrontal cortex are impaired on the antisaccade task, while patients with posterior parietal lesions (Pierrot - Deseilligny et al., 1991. Brain 114, 1473) or affective disorders (Fukushima et al., 1990. J Psychiatric Res. 24, 9) can perform this task sufficiently well. Abnormal numbers of express saccades and significant changes in saccade latencies have been described in different neurological and psychiatric disorders. Corresponding normative data are available for healthy subjects of different ages between 10 and 60 years.

The quality and the developmental state of fixation and automatic vs voluntary saccade control can be accessed by reaction time measurements and counting the number of direction errors as provided by EXE: an extra diagnostic tools in the diagnosis of various abnormalities of the central nervous system.

If you have any questions, please contact us!

address:
  Optomotor Laboratory
  c/o B.B.L. Fischer
  Tivolistraße 11
  D-79104 Freiburg
  Germany

email: info@optom.de
web: www.optom.de
phone +49 761 2922600
fax +49 761 2922699