WO2013012315A1

WO2013012315A1 - Method and apparatus to determine a degree of visuomotor coordination

Info

Publication number: WO2013012315A1
Application number: PCT/NL2011/050530
Authority: WO
Inventors: Johannes VAN DER STEEN; Johannes Jacob Mient Pel
Original assignee: Erasmus University Medical Center
Current assignee: Erasmus University Medical Center
Priority date: 2011-07-21
Filing date: 2011-07-21
Publication date: 2013-01-24
Anticipated expiration: 2014-01-21

Abstract

The invention relates to a method for determining a degree of visuomotor coordination in a patient, comprising the steps of automatically tracking a movement of a patient's eye pursuant to a presented visual stimulus; automatically tracking a movement of a patient's limb pursuant to the presented visual stimulus; computing respective parameters associated with the said movements. The invention further relates to a system 10 for enabling determination of a degree of visuomotor coordination in a patient, comprising an electronic display 2 connected to a processor 3, an eye tracker 4 and a motion tracker 5.

Description

Title: Method and apparatus to determine a degree of visuomotor coordination

FIELD OF THE INVENTION

The invention relates to a method for determining a degree of visuomotor coordination. In particular the invention relates to a method for determining a degree of visuomotor coordination of goal- directed eye/hand coordination tasks.

The invention further relates to a system for enabling determination of a degree of visuomotor coordination.

BACKGROUND OF THE INVENTION

In daily life one combines visual and spatial orientation for executing numerous motor tasks. The normally functioning brain is able to handle multiple sensory inputs, such as visual information, spatial memory and motor assessment. This highly specialized brain function is defined in medical science as visuomotor integration. Processing of visual information starts at the retina in a human eye. Here, different features, such as form, motion and colour are coded into neural signals that project via different neural lines to the visual cortex. The neural inputs is further segregated and processed in specialized cortical areas to recognise shape and to determine the spatial coordinates between objects. Subsequently, a hand movement is coded and planned by supplementary motor area and can either be internally (unconscious) or externally (conscious) triggered.

Unconscious hand movements are usually learned motor programs which are stored in different association cortices. The prefrontal cortex is assumed to be the most important.

A conscious hand movement requires planning of the movement which requires access to (visual and spatial) working memory for retrieving information about external cues. The working memory does not exist as a sole identity or as a separate brain function. It is a complex feature of different cognitive processes.

Many primate and human studies show that part of the integration of visuomotor information lies in the parietal cortex for the brain. This area is suggested to be the original of motor function. In the posterior parietal cortex (PPC) spatial information from the visual system is being processed and transformed into a motor plan. This motor plan leads to the motor command for the necessary muscles by projections to the dorsal premotor areas and the primary motor cortex. The PPC is subdivided into functional and anatomical different areas by intraparietal sulcus (IPS). The IPS generally contains clusters of neurons with specific functions. The anterior part is involved in eye- hand coordination as it transforms visual coordinates into motor programs, e.g. finger pointing. The superior part of the IPS is involved in visual working memory. The parietal eye field (PEF) is located along the posterior part of the IPS and is involved in attention processes as well as triggering reflexive visually guided saccades. The PEF projects both to the superior colliculus and the frontal eye field (FEF). Together with the dorsolateral prefrontal cortex (DLPFC), FEF is involved in preparation and triggering of all intentional saccades, e.g. an eye movement in the opposite direction of the appearing target (anti-saccade).

Inhibition of an unwanted reflexive misdirected saccade (DLPFC) and concomitant triggering of an intentional correct antisaccade (FEF) are important for this performance. The FEF projects directly to the superior colliculus (SC). The supplementary eye field (SEF) is suggested to be involved in motor programs comprising a sequence of several successive saccades. The basal ganglia also play an important role in successive saccades, in particular the caudate nucleus and the substantia nigra pars reticulate (SNpr) .These structures are especially involved in selecting targets and programming saccades that will be rewarded. The pathway comprises two serial inhibitory links. First, the caudate nucleus receives excitatory input from frontal projections of the FEF, DLPFC or SEF and sends a phasic inhibitory signal to the SNpr. Subsequently, phasic inhibition of the SNpr temporarily removes the tonical inhibition of the SC. This enables the SC to generate a saccadic eye movement. In contrast, neurons of the subthalamic nucleus receive excitatory input from the same frontal projections and excite the SNpr, which in turn inhibits the SC. The basal ganglia also provide initiation of other voluntary movements (such as hand movements) and simultaneously inhibition of competitive, unwanted (reflexive) movements. It is likely, that damage to structures like parietal cortex results in impaired integration of sensory information and execution of motor tasks and as a consequence reduces the quality of life significantly.

Dementia is a neurodegenerative disease which is defined as an overall decline in intellectual function. Dementia causes neurodegeneration of brain tissues, which is also associated with aging. Dementia does not originate suddenly or at short notice. Usually it takes an intermediate state between normal aging and dementia, which is regarded as mild cognitive impairment. Alzheimer's disease (AD) is the most common sub form of dementia. Both prevalence as incidence increase strongly with age. Other sub forms, such as Frontotemporal dementia (FTD), Parkinson Disease Dementia (PDD) and Lewy Body Dementia (LBD) contribute to a smaller part of the overall prevalence.

AD is characterized by neuronal atrophy, synapse loss, and the abnormal accumulation of amyloid plaques and neurofibrillary tangles in median temporal lobe limbic structures and the association cortices of the frontal, temporal, and parietal lobes. It progresses from mild forgetfulness to widespread neurological impairment and ultimately death and affects approximately 27 million people worldwide. The cognitive decline is characterized by prominent amnesia with additional deficits in language and semantic knowledge, executive functions, abstract reasoning, attention, and visuospatial abilities. The onset of these symptoms are usually around ages 60 up to 70. These cognitive deficits are the core features of the AD syndrome and are the focus of clinical assessment of the disease.

Parkinson's disease (PD) is a debilitating neurodegenerative disease of frequent occurrence in people of 50 years and older. PD is characterized by impairment of dopaminergic nigrostriatal projections. Similar pathological features are present in dementia with Lewy-Bodies. In addition to impaired motor function, these patients show in particular deficits in visuoperceptual and visuospatial abilities, frontal executive functions, attention and cognition.

According to recent studies, visuomotor performance may be impaired at an early stage of dementia. This may provide a new approach in early stage differential diagnosis between different sub-forms of dementia

Impairment of the PPC in early stage AD could explain an early disrupted visuomotor integration. It is also found that AD is characterized by a strong correlation between antisaccade performance and general cognitive status. In a number of clinical studies it has been demonstrated that visuomotor integration is impaired in early stage of AD even before the onset of memory deficit.

A method for diagnosing Alzheimer's disease is known from US 6 475 161. In the known method a computer-based system is used for assessing impairment of some cognitive and motor functions. For investigating motor functions the known method uses a mechanical input devise, such as a joystick or a keyboard.

It is a disadvantage of the known method in at least that it may be subjective because the known method does not provide reliable data for assessing a degree of impairment in the visuomotor coordination.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a method for assessing a degree of visuomotor coordination in an accurate and reliable way. To this end the method according to the invention comprises the steps of:

automatically tracking a movement of a patient's eye pursuant to a presented visual stimulus;

- automatically tracking a movement of a patient's limb pursuant to the presented visual stimulus;

computing respective parameters associated with the said eye and limb movements.

It is found that by enabling an automatic tracking of both the eye movement and a limb movement suitable data analysis may be carried out for establishing due parameters associated with the nature of such movements. It will be appreciated, that although a patient's arm may be a preferable embodiment for practicing the method according to the invention, other extremities may be used as well.

In accordance with the method of the invention, the said parameters are selected from the group consisting of: a visual or motor latency, a velocity, a displacement, a task error, a type of the task error.

Due to the fact that the eye and hand movements may be tracked and recorded, the method according to the invention enables determination of the movement-related parameters, characteristic to the patient with a high degree of certainty.

In an embodiment of the method according to the invention the visual stimulus is provided on a display. Preferably, the display is touch sensitive.

It is found to be particularly advantageous to use a suitable electronic display for feeding back the stimulus or stimuli used for the examination of the patient. One of the advantages of the electronic display is that a contrast, a colour and a dimension of the stimulus may be changed on demand. Preferably a routine is used for generating suitable stimuli. In an advantageous embodiment the routine is adaptive and self-learning, such as the reaction of the patient to a particular stimulus is used for generating a further stimulus or stimuli.

In a still further embodiment of the method according to the invention the stimuli presented before the patient may have a specific task, such as to tap the stimulus or stimuli with a finger. However, the tasks may have different degrees of difficulty, such as a pro-tapping task (reflex based), an anti-tapping task (planning based) a colour tapping test (memory based) and anti-saccade tapping task (planning based) or the memory-guided tapping task (memory and planning based). It may also be envisaged that the patient is requested to practice the task prior to carrying out the experiment.

The system for enabling determination of a degree of visuomotor coordination in a patient, according to the invention comprises:

- a first automatically tracking system for tracking a movement of a patient's eye pursuant to a presented visual stimulus;

- a second automatically tracking system for tracking a movement of a patient's limb pursuant to the presented visual stimulus;

- a processor coupled to the said first automatically tracking system and the second automatically tracking system for computing respective parameters associated with the said movements.

Preferably, the system further comprises a display for generating the said stimulus, which may be implemented as a touch sensitive display.

These and other aspects of the invention will be discussed in more detail with reference to figures wherein like reference numerals refer to like elements. It will be appreciated that the figures are presented for illustrative purposes and may not be used for limiting the scope of the appended claims.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 presents in a schematic way a system according to an aspect of the invention. Figure 2 presents in a schematic way an embodiment of stimuli presented on an electronic display of the system according to the invention.

DETAILED DESCRIPTION

Figure 1 presents in a schematic way a system according to an aspect of the invention. The system 10 according to an aspect of the invention comprises an electronic display 2 arranged for feeding back visual stimuli generated by a suitable program (not shown). The display 2 may be connected to an external processor 3 adapted to execute a suitable routine for generation visual stimuli in a visual field defined by the active area of the display 2.

Preferably, the active area of the display 2 is at least virtually sub-divided into different areas in which the stimuli appear. The stimuli may have different contrast, different size and different colour.

In accordance with a method of the invention the patient whose visuomotor coordination is being examined is positioned in front of the display 2 preferably with the head fixed.

The patient may be requested to carry out a plurality of tasks. For example:

- pro-tapping task: appearance of a peripheral dot may be used as a trigger for touching this dot as fast and as accurate as possible.

This task relates to a reflex based process;

- anti-tapping: two dots having different colours appear on the display at opposite positions with respect to the display's centre. The patient is requested to make a saccade towards the first dot and to touch the second dot. For example, the first dot may be blue and the second dot may be red. This task relates to memory and decision making processes;

- colour-tapping: this task may be divided in four following sections. In the first section, two dots of different colours appear on the display, which have to be touched as accurate as possible in the known order. Continuously, in each section two other colours may be added to the previous known order. The final order of colours may be blue, yellow, green, orange, pink, purple, red and brown;

- anti-saccade-taping task: a red dot appears on the touch screen. A patient has to inhibit an eye movement towards this dot and have to make a saccade in the opposite direction. Furthermore, the patient may be requested to touch this opposite location on the display. This test relates to spatial memory.

- Memory-guided-tapping task: at starting position a peripheral green dot may be flashing for a time period, for example 50 ms at a randomly selected location on the display. After disappearance of the white dot and blue bar, the subject may be requested to touch the remembered location of the green dot as fast and as accurate as possible. This task relates to spatial memory.

It will be appreciated that although the above tasks have been explained with respect to dots of a certain colour, different colours may be used. In addition, the dot may be replaced by an area, which may be regular in shape, such as a square or rectangle or irregular.

The tasks set forth above are not exhaustive. Many variants may be designed and pre-programmed on demand. In addition, the routine for generating the stimuli may be adapted to be self-learning for increasing the difficulty level of the task.

The described exemplary sequence of fixating and touching initial targets (stimuli) and subsequent fixating and/or touching peripheral targets (stimuli) may be repeated until the batch of eye/hand coordination tasks has been completed.

Simultaneously with projection of the central and peripheral targets, the eye movements may be recorded using a suitable eye tracking technology and the hand movements may be recorded using motion capturing technology. For example, the system 10 may be adapted with a suitable eye tracker 4 and a suitable motion tracker 5. The eye tracker 4 and the motion tracker 5 may be connected to the processor 3 for recording the movement data.

It will be further appreciated that although the display 2 may be a touch sensitive display thereby defining a coordinate of a touch moment executed by the person, it is also possible to use a simple electronic display and to record the coordinates of the touch moment by the motion tracking system 5. Those skilled in the art readily appreciate how the motion tracking system may be calibrated in world or other coordinates for carrying out this task. It will be appreciated that the position of the display 2 may be adjusted in 3D. If necessary, the display 2 may be horizontally positioned for enabling

determination of 3D eye/hand coordination. For a vertical arrangement of the display 2 a 2D eye/hand coordination may be determined.

When the tasks have been executed by the patient and the corresponding data related to eye and hand movements are recorded, the data may be analyzed for determining at least the following parameters associated with the said movements:

- calculate time delays or latencies of the eye and hand movements; the eye latency is defined as the time between presentation of the stimulus and the start of the saccade towards it;

- hand latency, defined as the time between presentation of the stimulus and the time the patient releases the finger from the (touch sensitive) display to execute the touching of stimuli ;

- hand execution time, defined as the moment the patient touches the stimulus minus the time the patient releases his or her finger from the (touch sensitive) display;

- eye-hand latency, defined as hand latency minus eye latency;

- total reaction time, defined as the time between presentation of the stimulus and the moment the patient touches the stimulus; - hand total distance, defined as the total distance covered by the patient's hand between starting point of the finger and the touched location on the (touch sensitive) display;

- eye maximum velocity, defined as the maximum eye velocity during saccades;

- hand maximum velocity, defines as the maximum hand velocity during hand movements.

It is found that different time delays or latencies between eye and hand movements represent precisely the specific steps of multiple sensory integration in the brain during each task, such as visual processing, visuomotor integration and motor planning and execution. For example, the latency between peripheral target presentation and onset of eye movement to that target reflects processing of visual information by the brain. The latency between peripheral target presentation and the onset of hand movement reflects planning of motor tasks. It is further found that latencies may be used as accurate markers for impaired cortical connectivity and may be used for determining a degree of visuomotor integration in patients. The system according to the invention enables to assess parameters associated with the eye and hand movements with a high degree of accuracy and reliability thereby increasing the overall accuracy of the assessment of a patient's condition in a quantitative way.

Figure 2 presents in a schematic way an embodiment of stimuli presented on an electronic display of the system according to the invention. The display 20 is presented in three conditions (view a, view b, view c), meeting three particular test situations.

View "a" relates to a pre-test display condition wherein the patient is requested, for example, to touch the area 22 and to fixate stimulus 21. Such pre-test is useful for setting the eyes and the hand of the patient is a predefined position prior to carrying out the substantive testing. In view "b" a further situation is schematically depicted wherein two peripheral stimuli are presented and the patient is requested to either fixate or touch these targets.

In view "c" a plurality of targets (stimuli) is presented, wherein the stimuli have a comparable size yet a different contrast. The patient may be requested to fixate or touch the stimuli which he has detected.

In response to these tasks the eye tracker, discussed with reference to Figure 1, may generates the coordinates of the patient's alternating gaze position between central and peripheral targets and simultaneously the motion tracker, discussed with reference to Figure 1, generates coordinates of the patient's hand when he is touching these stimuli. From these signals eye/hand movements and timing characteristics may be calculated, for example, velocities, directions, accelerations, latencies en so forth may be determined.

It will be appreciated that while specific embodiments of the invention have been described above, the invention may be practiced otherwise than as described.

Claims

A method for determining a degree of visuomotor coordination in a patient, comprising the steps of:

- automatically tracking a movement of a patient's eye pursuant to a presented visual stimulus;

- computing respective parameters associated with the said eye and limb movements.

The method according to claim 1, wherein the said parameters are selected from the group consisting of: a visual or motor latency, a velocity, a displacement, a task error, a type of the task error.

The method according to any one of the preceding claims 1 - 2, wherein for tracking the movement of the patient's eye an eye tracker is used.

The method according to claim 3, wherein the eye tracker is affixed to the patient's body.

The method according to any one of the preceding claims, wherein for tracking the movement of the patient's limb a motion tracking system is used.

The method according to any one of the preceding claims, wherein the visual stimulus is provided on a display.

7. The method according to claim 6, wherein the display is touch sensitive.

8. The method according to any one of the preceding claims, wherein the stimulus forms part of a series of stimuli.

9. The method according to claim 8, wherein the series of stimuli is compiled in accordance with a pre-defined rule.

10. The method according to claim 8, wherein the series of stimuli is generated using an automatic routine in dependence of a patient response.

11. The method according to claim 10, wherein the routine is self- learning.

12. A system for enabling determination of a degree of visuomotor coordination in a patient, comprising:

a second automatically tracking system for tracking a movement of a patient's limb pursuant to the presented visual stimulus; a processor coupled to the said first automatically tracking system and the second automatically tracking system for computing respective parameters associated with the said movements.

The system according to claim 12, further comprising a display for generating the said stimulus.

14. The system according to claim 13, wherein the display is touch sensitive.

15. The system according to claims 12, 13 or 14, wherein a stimulus generating routine is adaptive or self-learning.