Technical specification of the JAZZ-novo system

Principle of Operation

The key functions of the Jazz-novo Multisensor system are aimed at monitoring visual attention processes, reflecting the management of the operator’s conscious attention. From the point of view of the overall operator’s performance, it allows detection of anomalies in attention management.

Eye movement measurement

JAZZ-novo measures the Eye Movements (EM) by utilizing the method of Direct Infra Red Oculography, which is embedded in the Cyclop ODS sensor. Its design is optimized for easy set-up and minimal intrusiveness, which are crucial for monitoring the oculomotor functions in the non-laboratory settings.

Unlike other IR-Oculography systems, which require to place the infrared emitters/sensors around the eye in its direct vicinity, the Cyclops-ODS opto-electronic transducers, are located between the eyes, thus hiding the sensor assembly behind the „shadow” of the nose. Such ergonomically optimized sensor arrangement, does not limit the visual field and the measuring system can work without interfering with the subject’s visual functions. It does not require any kind of mechanical adjustments of the sensor position in relation to the eye. All necessary adjustments are performed automatically by the JAZZ-novo control system.

The Cyclops-ODS sensor measures the resultant rotations of the left and the right eye taken together. Due to the conjugacy and synchronicity of the saccadic eye movements, the rotation of left and right eyes, can be added and averaged. The inner canthi of the left and right eyes are illuminated with the low intensity (see the safety considerations) IR light. The difference between the amounts of IR reflected back from the eye surfaces, carries the information about the eye position changes. (relative eye position measurement requires to define the initial fixation position). In the Cyclop ODS, both eyes contribute equally to the generation of the EM signal. The measurements of the left and right eye rotations average, are used as the standard EM measurement procedure in the clinical electro-nystagmography. The values acquired by this method are the sum of electro-oculographic potentials, received from the temple parts of the left and the right eye (Oculus Dexter Sinister - ODS). The Cyclop-ODS is equipped with the Automatic Gain Control (AGC) system, which compensates the differences of anatomical shapes of the nose and eye cavities. It allows to measure the eye movements with the same physical gain, equal for all subjects, without influencing the signal to noise ratio (constant gain of the photo-detecting circuitry).

Eye movement measurement

Measuring range

• along the horizontal axis ±35 deg
• along the vertical axis ±20 deg

Sampling frequency

• 1000 Hz

Instrumental noise (sensor on the test-bed)

• Horizontal axis point to point: 2 a.u.
• Horizontal axis peak to peak: 8 a.u.
• Vertical axis point to point: 2 a.u.
• Vertical axis peak to peak: 7 a.u.

Instrumental noise pick-up caused by placing sensor on the subject forehead

• Horizontal axis point to point: 2 a.u.
• Horizontal axis peak to peak: 7 a.u.
• Vertical axis point to point: 2 a.u.
• Vertical axis peak to peak: 6 a.u.

Start-up drift (sensor on the test-bed)

• Horizontal axis 22 a.u. over 600 ms (afterwards stable signal)
• Vertical axis 22 a.u. over 600 ms (afterwards stable signal)

Noise level (measured over 20 degrees range)

• Horizontal axis peak to peak value: 0.51% of the reference range, what gives 0.1 degree
• Horizontal axis signal to noise ratio (SNR): 45 dB

Vestibulo option

Two-axial Analog Devices accelerometer

• measurement range ±2 g
• sensitivity 12.5% / g

Two one-axis Analog Devices gyroscopes

• measurement range ±300 deg/s
• sensitivity 5mv / deg / s

Pletyzmography

Infrared Emitter

• wavelength at peak emission 950 nm
• typical radiant intensity at 1mA current 5.0 mW/sr

Photodiode

• range of spectral bandwith 430 nm to 1100 nm
• wavelength of peak sensitivity 900 nm

Voice signal

Microphone

• omnidirectional
• sampling frequency 8 kHz
• signal to noise ratio 59 dB
• bandwidth 100 Hz to 8000 Hz

Safety Considerations

JAZZ-novo system was designed following the strict rules of safety, as specified for medical instrumentation.

Electrical Hazard

The system is battery powered and the voltage in the system does not exceeds 3V. The mechanical arrangement of terminal sockets on the JAZZ-novo control unit excludes the possibility to connect erroneously another plugs-in. Ones the sensor, which is attached to the patient, has been connected to the control unit, the only sockets left free, are the one provided for accommodating the optical fibber plug It makes the connection, between the subject and the computer, galvanically isolated by 1.5m plastic optical fibber.

Level of IR irradiance of the eye surface

According the calculations and direct measurement the IR irradiance does not exceeds 0.6 mW/cm2 and is well below the level accepted as the safe for the eyes (10 mW/cm2) Please refer to the measurement protocol (Saccadometer eye surface irradiation report).

The level of irradiance depends on the output of IR illuminators, as well as on the distance between the IR source and the illuminated surface (eye cavity). The irradiance level,was calculated assuming the average distance of 10 mm. This distance can vary depending on the anatomical shapes of the nose and the eye cavity. Normally it cannot be excluded that the sensor will be placed closer to the eye, what will cause the increase of the eye IR irradiance. In the JAZZ-novo due to implementation of the active adjustment of the IR illumination,such situations are excluded. The JAZZ-novo control system automatically compensates the varying distance by adjusting the intensity of IR source. When the IR illuminator comes closer to the eye surface, its intensity is automatically reduced, thus the IR irradiance can be held constant on the calculated level.

Certification

At this stage of development, the JAZZ-novo can be considered as the custom made, experimental device. It was designed and manufactured to fulfill the highest standards of SAFETY, which are required for the medical diagnostic device.