various embodiments are described hereinafter with reference to the figures . like reference numerals refer to like elements throughout . like elements will , thus , not be described in detail with respect to the description of each figure . it should also be noted that the figures are only intended to facilitate the description of the embodiments . they are not intended as an exhaustive description of the claimed invention or as a limitation on the scope of the claimed invention . in addition , an illustrated embodiment needs not have all the aspects or advantages shown . an aspect or an advantage described in conjunction with a particular embodiment is not necessarily limited to that embodiment and can be practiced in any other embodiments even if not so illustrated , or if not so explicitly described . the block schematic in fig1 illustrates a clinical setup 1 for testing and examining vestibular activity in a person . the clinical setup 1 comprises a computerized system 2 , an eye movement detector 6 for detecting movements of an eye 5 of the person being examined , an orientation sensor 4 for detecting the orientation of the person , and a display 3 for displaying orientation and vestibular activity in real time during an examination . the computerized system 2 comprises a data acquisition module 7 , a calculation module 8 , a memory 9 holding a three - dimensional model of a head and semi - circular canals of a person , and a graphic processor 10 for providing an output signal for the display 3 . the computerized system 2 may be embodied as a dedicated computing device or it may be embodied as an application designed for execution on a standard off - the - shelf personal computer . the eye movement detector 6 and the orientation sensor 4 may be built into a self - contained , head - mountable unit ( not shown in fig1 ), e . g . of the kind described in european patent application ep 14169653 . 4 . the head - mountable unit is a relatively small and lightweight piece of hardware allowing a person to move his or her head freely while wearing the unit . the head - mountable unit may preferably be embodied as a pair of goggles fixable to a person &# 39 ; s head by e . g . an adjustable headband . the eye movement detector 6 may be embodied as a small video camera constantly monitoring the eye of the person , e . g . via a semi - transparent mirror . the eye movement detector 6 may be doubled for the purpose of monitoring movement of both the left eye and the right eye of a person simultaneously . the orientation sensor 4 may be embodied as an accelerometer unit mounted on the head - mountable unit . during examination , the head - mountable unit is fixed to the head of the person being examined , and data regarding eye movements and spatial orientation are fed to the data acquisition module 7 of the computerized system 2 . prior to performing a proper examination of the person , an orientation calibration procedure is performed in order to be able to coordinate the data collected from the head - mountable unit correctly with a reference equilibrium position of the person . during an examination of the person wearing the calibrated , head - mountable unit , the person &# 39 ; s head is placed in a series of different positions or orientations by the physician performing the examination while the physician watches the display 3 of the clinical setup 1 . by looking at the display 3 during the examination the physician may monitor the actual orientation and the vestibular reactions of the person being examined . the vestibular reactions are reflected in involuntary movements of the eyeballs of the person and the data from the eye movement detector 6 are thus used by the calculating module 8 for calculating the corresponding vestibular reactions . the results of the calculations are provided to the graphic processor 10 and combined with a stored , three - dimensional model of a human head and a pair of associated semi - circular canals provided by the dedicated memory 9 for the purpose of generating a real time , two - dimensional perspective projection of a human head and semi - circular canals in a viewport of the display 3 for viewing by the physician performing the examination . an exemplary picture , as it may be provided by the display 3 of fig1 , is illustrated in fig2 . fig2 shows a main window 20 comprising a perspective projection of a human head 21 , a data window 28 , a set of operating controls 29 , 30 , 31 , 32 and a set of tabbed windows 33 , 34 , 35 and 36 . the perspective projection of the human head 21 further comprises a set of left semi - circular canals 22 l , a set of right semi - circular canals 22 r , a horizontal reference indicator 25 , e . g . constituting an example of the first reference indicator , a vertical reference indicator 26 , e . g . constituting an example of the second reference indicator , and an orientation indicator 27 . the orientation indicator 27 represents a two - dimensional projection of the head orientation of the person as determined by the orientation sensor 4 . in the perspective projection 21 , the left set of semi - circular canals 22 l has a posterior semi - circular canal 23 and an anterior semi - circular canal 24 emphasized by a dark color indicating vestibular activity in those canals . for clarity , the left and right sets of semi - circular canals 22 l and 22 r , respectively , are shown as floating in space some distance from the human head 21 in the main window 20 . during use of the system 1 , the physician initiates a data collection session by calibrating the head - mountable unit by activating the “ center ” button 29 in the main window 20 . this calibration is done with the person &# 39 ; s head carrying the head - mountable unit and facing straight forward . any subsequent movements the person &# 39 ; s head makes after calibration is then recorded and shown relative to the calibration point . when the person moves his or her head in space , the perspective projection angle of the human head 21 moves correspondingly in the main window 20 , the perspective projection angle of the set of left semi - circular canals 22 l and the set of right semi - circular canals 22 r moving along with the human head 21 while keeping their relative positions with respect to the human head 21 . when the calibration procedure has finished , the physician may start the acquisition of movement and vestibular response data by activating the “ start ” button 30 in the main window 20 . moving together with the perspective projection of the human head 21 is the orientation indicator 27 . when the person &# 39 ; s head moves , the orientation indicator 27 will move correspondingly with respect to the vertical reference indicator 26 and the horizontal reference indicator 25 , respectively . the positioning of the vertical reference indicator 26 and the horizontal reference indicator 25 is determined by the type of examination to be performed . in the case of e . g . the physician wishing to perform a dix - hallpike maneuver with the aid of the system 1 , the physician has to move the person &# 39 ; s head about an axis going vertically through the head of the person in a first move and about an axis going from ear to ear of the person in a second move . the orientation indicator 27 aids the physician in performing the dix - hallpike maneuver by making the physician move the person &# 39 ; s head in such a way that the orientation indicator 27 stays on the vertical reference indicator 26 during the first movement and the orientation indicator 27 stays on the horizontal reference indicator 25 during the second movement . preferably , orientation indicator 27 may light up or change color if the orientation indicator 27 is veering off track during the first or the second movement . an angle tolerance may be built into the system . in this way , the display 3 of the system 1 may provide positive feedback to the physician in real time during performance of e . g . the dix - hallpike maneuver , guiding the movements the physician has to perform on the patient &# 39 ; s head and / or torso in order to retrieve the desired examination or treatment results . the combination of the two - dimensional projection of the head 21 , the two sets of semi - circular canals 22 l and 22 r and the orientation indicator 27 with respect to the vertical reference indicator 26 and the horizontal reference indicator 25 provides for a high degree of precision in the movements of the person &# 39 ; s head . due to the fact that the eye movement detector 6 is monitoring the eyes of the person , the system may indicate e . g . the presence of nystagmus by making individual semi - circular canals of the two - dimensional projection of the semi - circular canals 22 l and 22 r light up or change color in the window 20 , thus indicating vestibular activity in those semi - circular canals . this is indicated in fig2 as the left posterior semi - circular canal 23 and the left anterior semi - circular canal 24 being dark in color indicating activity in the left posterior semi - circular canal and the left anterior semi - circular canal of the person being examined . some types of examination may require the person being tested to be vision denied , i . e . blindfolded . this is due to the fact that it is natural to most people to use their eyesight in order to determine their orientation in space . in order to exclude this sensory modality from the examination , the person being examined may wear dark or opaque eye coverings on one or both eyes during examination or treatment . the eye coverings are preferably placed beneath the goggles when worn by the person and are manufactured from a material blocking all light but the infrared range of the electromagnetic spectrum , thus rendering the person without any visual cues for the duration of the examination . the eye movement detector 6 of the system 1 is configured to be sensitive in the infrared range of the spectrum , thereby permitting detection of eye movements even though the person being examined cannot see anything . since the balance reflex of the eyes is present even if the person does not see anything , this strategy of examination effectively excludes visual cues from the examination , thus effectively isolating the signals from the balance organs for detailed analysis during or after the examination . during an examination , the data acquisition module 7 of the computerized system 2 in fig1 provides the calculation module 8 with streams of real time data representing gaze direction and spatial orientation of the head of the person being examined . these data are sorted , filtered and recorded by the calculation module 8 and converted into a vector representing spatial orientation and vestibular activity in both sets of semi - circular canals 22 l and 22 r , respectively . this vector is provided to a first input of the graphic processor 10 for the generation of the real time two - dimensional projection of a human head 21 shown in fig2 . simultaneously , the stored three - dimensional model of a human head and associated semi - circular canals provided by the dedicated memory 9 is applied to a second input of the graphic processor 10 for calculating the projection of a proper two - dimensional representation of a human head 21 and corresponding left and right sets of semi - circular canals 22 l and 22 r , respectively , suitable for being shown on the display 3 . a three - dimensional coordinate system is defined as a standard right - hand coordinate system , where the x - axis goes from ear to ear in a person &# 39 ; s head , the y - axis goes from the top of the person &# 39 ; s parietal bone through the neck , and the z - axis goes from the back of the person &# 39 ; s head to the tip of the nose . this coordinate system will be referred to in the following . orientation angles of a human head about the three axes x , y and z may be expressed as tait - bryan chained rotations using three rotational matrices , where the three rotational angles α , β , and γ expressed in radians , describe the rotation of a human head about the three axes with respect to the origin ( set at calibration time ). data provided by the rotation sensor 4 in fig1 is used to calculate the rotation angles of the head of the person being examined . at calibration time , the rotational angles α , β , and γ are zero , and the data from the rotation sensor 4 is expressed as a vector , thus : during examination . the vector { right arrow over ( m )} x , y , z is generated from data from the rotation sensor 4 by the data acquisition module 7 , and is used as input for the calculation module 8 . anatomically , the three semi - circular canals of a human being are denoted the lateral semi - circular canal ( operating around a vertical axis in the transversal plane ), the anterior semi - circular canal ( operating around an anterial - posterial axis in the coronal plane ) and the posterior semi - circular canal ( operating around a lateral axis in the sagittal plane ). as stated in the foregoing , the activity of the semi - circular canals cannot be monitored directly . instead , the vestibulo - ocular reflex is used for detecting vestibular activity during examination using the eye movement detector 6 . if , for instance , the head of the person being examined moves from left to right in the transversal plane , the person &# 39 ; s eyes will move in the opposite direction from right to left thanks to the vestibulo - ocular reflex . the eye movement detector 6 records this behaviour and interprets it as a horizontal movement vector { right arrow over ( e )} h . if the person &# 39 ; s head instead is moved up and down in the sagittal plane , the person &# 39 ; s eyes will move down and up , respectively . the eye movement detector 6 records and interprets this behaviour as a vertical movement vector finally , if the person &# 39 ; s head is tilted and rotated in the coronal plane , the person &# 39 ; s eyes will rotate in the opposite direction . the eye movement detector 6 records these eye movements and interprets the behaviour as a rotational movement vector { right arrow over ( e )} r . the way that the movement vectors { right arrow over ( e )} h , { right arrow over ( e )} v and { right arrow over ( e )} r are derived from the eye movement detector 6 is beyond the scope of this application . the vectors { right arrow over ( e )} h , { right arrow over ( e )} v and { right arrow over ( e )} r are also used as inputs for the calculation module 8 for the purpose of deriving a set of vectors indicating the presence of a vestibular stimulus to a particular semi - circular canal . this set of vectors may be derived in the following manner : similarly , for the right eye , a stimulus vector { right arrow over ( r )} is derived : the constants k 1 , k 2 and k 3 are chosen in such a way that the individual values of l lateral , l anterior , l posterior , r lateral , r anterior and r posterior may take on the value of 0 or 1 , respectively . the vectors { right arrow over ( m )}, { right arrow over ( l )} and { right arrow over ( r )} are used by the calculation module 8 as inputs for the graphic processor 10 . during use , the graphic processor 10 takes the three - dimensional representation of a human head provided by the dedicated memory 9 and generates a two - dimensional representation of it by applying the vector m to the three - dimensional representation , generating a two - dimensional projection angle for the representation . next , the graphic processor 10 takes the stimulus vectors { right arrow over ( l )} and { right arrow over ( r )}, respectively , and uses them to determine the color of the individual semi - circular canals of the set of semi - circular canals 22 l and 22 r of the projection of the human head shown in the main window 20 of fig2 . when there is no significant activity in the semi - circular canals of the person being examined , as derived from the vectors { right arrow over ( e )} h , { right arrow over ( e )} v and { right arrow over ( e )} r provided by the eye movement detector 6 , the semi - circular canals are depicted in a neutral color . upon detection of vestibular activity in one or more of the semi - circular canals of the person being examined , in the manner described above , the graphic processor 10 changes the color of the semi - circular canals where activity is detected into a color deviating from the neutral color used to illustrate no vestibular activity , as illustrated by the semi - circular canals 23 and 24 in fig2 . in this way , the head orientation and the vestibular activity may be monitored simultaneously on the display 3 of the system 1 during examination of a person wearing the rotation sensor 4 and the eye movement detector 6 . in order to provide a more secure and precise indication of the person &# 39 ; s head during the performance of e . g . a dix - hallpike maneuver , additional indicators are provided in the main window 20 of the display 3 in the form of the horizontal reference indicator 25 , the vertical reference indicator 26 and the orientation indicator 27 . the orientation indicator 27 is a two - dimensional projection of a three - dimensional point p onto an imaginary plane f in front of the two - dimensional representation of a human head 21 . the plane f is perpendicular to the vector { right arrow over ( m )} cal . the point p is defined as the point where the vector { right arrow over ( m )} x , y , z intersects with the imaginary plane f . this may be expressed as : in other words , the orientation indicator 27 follows the direction of the head of the person being examined closely whenever the head is turned about one of its three axes . during setup of a dix - hallpike maneuver , the horizontal reference indicator 25 and the vertical reference indicator 26 are projected onto the plane f in such a way that the orientation indicator 27 coincides with the vertical reference indicator 26 during a first correct movement of the dix - hallpike maneuver , and the orientation indicator 27 coincides with the horizontal reference indicator 25 during a second correct movement of the dix - hallpike maneuver . the horizontal reference indicator 25 and the vertical reference indicator 26 both have an elongated shape when displayed in the main window 20 , and this feature makes it easy for the physician to follow with the movements of the head of the person being examined . by providing the system 1 with a tolerance of e . g . five degrees in either direction , the physician may be easily alerted whenever a movement diverts too much from the correct movement , e . g . by having the orientation indicator 27 change color , texture or general appearance in such cases , allowing the physician to perform corrections of the movements in a secure and easy manner . the way an examination is performed using the system 1 is described in greater detail in the following . if the dix - hallpike maneuver is chosen for detecting e . g . bppv in the left set of semi - circular canals in a person being examined , this choice may be input to the system 1 in the test setup tab 33 in the main window 20 in fig2 . the system 1 now shows the horizontal reference indicator 25 and the vertical reference indicator 26 in the main window 20 . the person being examined is sitting upright on an examination couch and in a first step of the dix - hallpike maneuver has his or her head turned 45 ° to the side being tested ( i . e . the left side in this case ). with the head still turned in this fashion , the person is laid down on the back on the examination couch rather quickly in such a way that the head is tilted further 20 °- 30 ° backwards . during this part of the dix - hallpike maneuver , the physician performing the maneuver watches the main window 20 on the display 3 , especially keeping an eye on the orientation indicator 27 . the orientation indicator 27 moves about in the main window 20 when the head of the person being examined moves , and usually represents the gaze direction of the person . if the head angle differs too much from the expected 45 °, or if the movement of the person being examined into the lying position is too slow , the orientation indicator 27 in the main window 20 changes color , e . g . to a red color , in order to guide the physician to a proper execution of the movement . during a second step of the dix - hallpike maneuver , the person being examined is returned to an upright sitting position while keeping the head turned 45 ° to the left , the physician still keeping an eye on the orientation indicator 27 in order to provide the right velocity and angles for the second step of the dix - hallpike maneuver . during the performance of the dix - hallpike maneuver , the system 1 records and displays the movements and reactions of the person being examined . the head angle is reflected in the two - dimensional representation of a human head 21 in the main window 20 allowing the physician to follow the head orientations in a precise manner during examination . the reactions of the vestibular systems of the person being examined are being reflected in the two - dimensional representation of the semi - circular canals 22 l and 22 r displayed along with the human head representation 21 , allowing the physician to monitor the vestibular reactions of the person being examined in real time during examination . the horizontal reference indicator 25 and the vertical reference indicator 26 provides a guidance for the physician performing the movements of the dix - hallpike maneuver , using the positioning and coloring of the orientation indicator 27 as an aid in the movements . when the dix - hallpike maneuver has been performed , the physician may browse through the recorded data by selecting the “ collection ” tab 35 of the main window 20 and perform subsequent analyses aided by the recorded data set in order to establish accurate diagnoses , e . g . of bppv . the mechanism of the aid provided by the system 1 is described more closely with reference to fig3 a and 3 b . in fig3 a is illustrated an orientation indicator 27 right after performance of a first step in a dix - hallpike maneuver . as stated in the foregoing , the first step of a dix - hallpike maneuver involves turning the head of the person being examined 45 ° from the origin about the vertical axis towards the suspected affected side , in this case the left side , while keeping the head straight up . the orientation indicator 27 will move about in the display 3 as the head is turned , in this case to the left side . in fig3 a , the orientation indicator 27 is at the 45 ° mark on the horizontal axis and at 0 ° on the vertical axis . also shown in fig3 a is a vertical box v and a horizontal box h . as indicated in fig3 a , these boxes represents the horizontal reference indicator 25 and the vertical reference indicator 26 in fig2 and illustrate the limits within which the orientation indicator 27 is deemed to be ‘ correctly ’ positioned horizontally and vertically . as long as the center of the orientation indicator 27 is within those limits , the orientation indicator 27 is assigned a pale , or neutral color by the system when shown in the main window 20 in fig2 . the rotational tolerance limits of a first step of a dix - hallpike maneuver is from about 42 ° to approximately 47 ° from the origin in the horizontal plane and from approximately − 3 ° to around 3 ° from the origin in the vertical plane . these limits are selected for illustrative purposes only and are chosen arbitrarily in the examples shown in fig3 a and 3 b . in fig3 b is illustrated an orientation indicator 27 right after performance of a first step in a dix - hallpike maneuver . in this case , however , the physician has not turned the head of the person being examined sufficiently far to the left , but only to about 41 ° from the origin . the orientation indicator is still at 0 ° along the vertical axis in fig3 b . since the orientation indicator 27 is now outside the predetermined limits defined by the vertical box v , the feedback condition is now met and the orientation indicator 27 is assigned a darker , contrasting color by the system when shown in the main window 20 in fig2 , thus providing a clear feedback signal to the physician that the head of the person being examined has not been turned sufficiently far to the left in the first step of the dix - hallpike maneuver . as soon as the physician turns the head of the person being examined sufficiently further to the right to have the orientation indicator 27 fall within the limits of the vertical box v , the feedback condition ceases to be met and the orientation indicator 27 will therefore change back to a neutral color in the main window 20 again . if the turn of the head is overshot , for instance by turning the head of the person being examined further than approximately 47 °, the feedback condition is met once again and the orientation indicator 27 will again change to a contrasting color indicating a maneuver error by the physician . a variety of vestibular conditions may be diagnosed or alleviated using the system 1 . an example of a procedure which alleviates bppv is the epley repositioning maneuver , which works by allowing free - floating particles located within the affected semi - circular canal to flow back from the semi - circular canal to the utricle of the inner ear by the straightforward means of gravity . the epley maneuver involves a sequence of manipulations with a patient similar to the dix - hallpike maneuver , but is a bit more involved and thus more difficult to perform correctly . having used the system 1 and e . g . the dix - hallpike maneuver to determine the extent and location of the cause of bppv in a person , the physician may set up the system 1 in a similar manner in order to perform the epley maneuver while observing the main window 20 for guidance during the various steps of the epley maneuver . the physician may subsequently perform the dix - hallpike maneuver again in order to determine if , and to what degree , the epley maneuver have provided an improvement to the patient . thanks to the elaborate guidance means provided by the main window 20 of the display 3 of the system 1 , the physician may perform a wide range of different , vestibular examinations quickly and securely , without worrying if the movements performed of the person being examined or treated are sufficiently accurate to be effective . in a preferred embodiment , the eye movement detector 6 and the rotation sensor 4 of the system 1 are built into a pair of lightweight goggles , e . g . of the kind described in european patent application ep 14169653 . 4 . the processing of data from the sensors of the goggles may be executed on a standard personal computer running suitable software providing the functionality of the computerized system 2 of the system 1 . data acquisition , recording and storage may be provided by the standard storage means provided by the personal computer , and means for subsequent analysis of the data recorded during the examinations may also be provided by the software . the system according to one or more embodiments described herein provides an improvement of diagnosis and treatment of a variety of ailments in the vestibular system of a person and is especially useful in diagnosing and treating people suffering from bppv . although particular features have been shown and described , it will be understood that they are not intended to limit the claimed invention , and it will be made obvious to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the claimed invention . the specification and drawings are , accordingly to be regarded in an illustrative rather than restrictive sense . the claimed invention is intended to cover all alternatives , modifications and equivalents .
a system for detecting and recording head orientations of a person includes : a first sensor device capable of providing sensor data regarding a head orientation of a person in a three - dimensional space ; a medical data acquisition system configured for storing and outputting the sensor data from the first sensor device ; and a processor configured for processing the sensor data from the medical data acquisition system , outputting a first signal representing the head orientation , and generating an image for presentation by a graphical display ; wherein the image comprises : a first reference indicator ; an orientation indicator , wherein a position of the orientation indicator in the image is determined based on the first signal from the processor , and a feedback indicator when a first condition is met .