The invention relates to a visual stimulator comprising a source of light stimuli connected with a control unit.

Background Art

Visual stimulators are used for activation of the visual system (a part of the central nervous system) by means of spatial and temporal modulation of light. They generate precise light stimuli and in case of need they also synchronize other devices enabling evaluation of functions of the eye and of the whole visual system up to the brain cortical areas - it means processes of the visual perception and cognition.

At present, computer monitor, array of light emitting diodes (LEDs) or various lamps are most frequently used as a stimulator/source of light stimuli. Such stimulators (usually computer controlled) are predominantly stationary. Existing mobile stimulators can be attached to the eye or they are fixed to the head in form of glasses or contact lenses.

More detailed information about variants of visual stimulation, so far used in clinical electrophysiology of vision and of the the central nervous system, are provided in the following publications:

Celesia, G.G., Bodis-Wollner, I., Chatrian, G.I., et al. Recommended standards for electroretinograms and visual evoked potentials. Report of an IFCN committee. Electroenceph. din. Neurophysiol., 1993, vol. 87, s. 421-436. (http://dx.doi.Org/10.1016/0013-4694(93)90157-Q)

Odom, J.V., Bach, M, Barber, C, Brigell, M., et al. Visual Evoked Potentials Standard (2004). Doc. Ophthalmol., 2004, vol. 108, s. 115-123. (http://dx.doi.Org/10.1023/B:DOOP.0000036790.67234.22) All variants of the visual stimulators used for diagnostic or other purposes (e.g. also for light stimulations in relaxation techniques - "psycho-walkmans") cover fully or significantly the visual field of the stimulated subject and such a stimulation requires also his/her attention. Thus, they do not allow any other activity - e.g. some employment during the stimulation. Therefore, they cannot be used continuously, e.g. for monitoring and evaluation of functional changes in brain reactions to visual stimuli - it means for continual assessment of visual perception (cognition). The required placement of such currently used stimulators into the center of the visual field (in front of eyes of the stimulated subject) is related to the type of the used stimuli and to the way of evaluation of the evoked brain reactions.

Disclosure of Invention

The above mentioned disadvantages are eliminated a visual stimulator, comprising a source of light stimuli, connected with the control unit, in accordance with the invention the principle of which is that the source of light stimuli is arranged on carrier/carriers for placement of the source of light stimuli in periphery of the visual field of a stimulated subject.

Visual stimulator according to the invention is a subtle, compact, eventually fully mobile device allowing long-term continuous testing of visual perception (cognition) and changes in brain functions. Since its using does not interfere with common human activities, it is possible to use it not only for standard diagnostic examinations in neuro-ophthalmological diseases but also for monitoring of attention changes or level of vigilance/fatigue in drivers or some other professions.

According to a preferred embodiment the carrier is adapted for placement on the head of a stimulated subject, e.g. a standard peak ( a part of a baseball cap) can serve as the carrier.

According to another preferred embodiment the carrier can be mounted by an upper inner edge of a front glass in a car or on an upper edge of a car dashboard. A row of light emitting diodes (LEDs) represents a preferred embodiment of the light stimuli for this purpose.

Brief Description of Drawings

The visual stimulator in accordance with the invention will be described in a more detailed way with the use of particular embodiments shown in the drawings where Fig. 1 presents an example of the visual stimulator which can be placed on the head of the stimulated subject. Fig. 2 provides the basic electrical diagram of the stimulator and Fig. 3 gives an example of a visual stimulator placed in a car.

Modes for Carrying Out the Invention

In Fig. 1 there is a first example of an embodiment of the visual stimulator according to the invention. The visual stimulator comprises a source 1 of light stimuli that is put on a carrier 3 for placement of the light stimuli in periphery of the visual field of the stimulated subject 4.

The carrier 3 according to this embodiment is a peak of a baseball cap enabling the placement of the stimulator on the head of the stimulated subject 4. The source 1 of light stimuli is a row of LEDs that are fixed in regular interspaces (span of about 1 cm) on the bottom outer edge of the peak to a flexible printed circuit board which follows the slightly convex shape of the peak.

The peak is provided with a fixing belt 5 for placement on the head of the stimulated subject 4. A case 6 covering a control unit 2 (see Fig. 2) for switching of individual LEDs and for generating of synchronizing pulses (to EEG signal analyzer accomplishing evaluation of visual evoked potentials) is attached to the fixing belt 5. In the demonstrated embodiment the control unit 2 is composed of microprocessor PIC16F628A with accumulator cells 9, connector 10 for connection with an EEG analyzer (e.g. PC), with selector 8 for changing of stimulus type and with switcher 7 for switching on/off of the stimulator. The control unit 2 is connected via shielded cable 11 with the source 1 of light stimuli on the peak.

The peak 3 is attached with the use of the fixing belt 5 to the head of the stimulated subject 4 in such a way that his/her view is not significantly limited and that he/she has sufficient perception of the LED stimulation. The set of LEDs is located about 20° from the center of the stimulus field. Assembly of LEDs forms ca 15 cm long, about circular arc with diameter of about 10 cm, which makes in the visual field of the observer the angle of about 80°. The color of light emitted by LEDs in the used example of construction is yellow-green (with dominant λ = 588 nm - nanometer) and typical luminous intensity is 20 mod (milicandela). However, the color and luminosity of the used LEDs are not critical; described variant only represents a compromise between effectiveness of the stimulation and minimal interference with subject's activity during a long-term use.

After switching-on of the stimulator with the use of the switcher 7, it is possible to choose via the selector 8 one of stimulation programs saved in the control unit 2. Programs of the microprocessor enable to generate visual motion stimuli (sequential switching-on/off of single LEDs in the row from the center to both margins or from margins to the center with random changes of directions) and flash stimuli (simultaneous switching-on/off of all LEDs with a selected frequency). There are several variants of stimulation available because there are significant inter-individual differences in reactivity of subjects to particular stimuli and thus, it is possible to choose an optimal stimulus for each subject.

In the described example, the stimuli are generated with the period of 1.2 s. Duration of motion stimuli with velocity of 200 - 400 s is 100 - 200 ms, the flash stimulation with the same duration has frequency of 14 Hz. Parameters of stimulation are resettable in a wide range by the microprocessor program. In the described example, the motion stimuli have similar parameters as stimulations used for clinical diagnostic purposes - see Kuba, M., Kubova, Z., Kremlacek, J., et al. Motion-onset VEPs. characteristics, methods, and diagnostic use. Vision Res., 2007, vol. 47, s. 189-202. mttp://dx.doi.orq/10.1016/i.visres.2006.09.020). In the case of need a simple change of the program will enable using of different variants of stimulation according to individual characteristics of the stimulated subject.

Another example of the visual stimulator according to the invention is depicted in Fig. 3. The carrier 3 with the source 1 of light stimuli is arranged by the upper inner margin of the front glass 12 in a car. The case 6 with the control unit 2 is mounted in this example to a car dashboard. The source 1 of light stimuli is again a row of LEDs. The arrangement of the LED set and control of their function is dependent in this case on the particular type of a car and on the distance of the visual stimulator from eyes of the stimulated subject. It is important that the stimulus parameters should be about adequate to the first above described example.

In another, not presented example, the carrier 3 with the source of light stimuli is arranged on the upper margin of a car dashboard.

In all described examples of embodiments, there are currently available repeated intervals of motion stimulation (motion velocity ca 200 - 400 s) and flash stimulation (with frequency of 14 Hz that displays the lowest interference with spontaneous EEG) with duration of 100 - 200 ms. These stimulation intervals are interrupted by intervals without stimulation lasting 1s to reduce a possible adaptation of the brain to the stimulation. It allows evaluating repeatedly differences between average reactions of the brain to the visual stimuli (cortical visual evoked potentials) and the spontaneous EEG activity during the non- stimulation time. Recording of the electric activity of the brain (EEG) is not a subject of this invention and it is possible to do it with the use of any known method, e.g. only with one forehead electrode against a reference point.

It is evident for the person skilled in the art that besides the described examples of embodiments it is possible to suggest a lot of other variants of the visual stimulator in accordance with the invention that will follow the same inventive idea according which the source of convenient light stimuli is arranged on a carrier in periphery of the visual field of a stimulated subject. The visual stimulator according to the invention can be used not only for standard diagnostic examinations in neuro-ophthalmological diseases but it enables also a long-term continual observation of brain functions during activities in which a monitoring of brain functions is highly advisable, e.g. level of vigilance/fatigue in drivers and many other professions.