Patent Publication Number: US-2012029322-A1

Title: Processing a bio-physiological signal

Description:
FIELD OF THE INVENTION 
     The invention relates to the field of processing bio-physiological signals, and more specifically to an apparatus for processing a bio-physiological signal and to a method of processing a bio-physiological signal. In particular, the bio-physiological signal may be a brain wave signal. 
     BACKGROUND OF THE INVENTION 
     In the sleep of a human being, different sleep stages are distinguished by typical bio-physiological signals or signal patterns associated with the respective sleep stages. 
     In the context of this application, the term “sleep state” or “sleep stage” is considered to exclude an awake state. 
     Whereas in the brain of an awake and relaxed person, oscillations at about 10 Hz (alpha waves) are present in electroencephalography signals, other patterns of brain wave signals are observed in respective sleep stages. An alert person generates beta waves which are about twice as fast as alpha waves. 
     In stage 1 sleep, being a transition stage between wake and sleep, theta waves having a frequency typically in the range of 3.5 to 7 Hz are present. 
     In stage 2 sleep, so called sleep spindles having a frequency of 12 to 16 Hz and “K-complexes” are observed. 
     In slow wave sleep, also known as stage 3 and stage 4 sleep, delta waves, typically in the range of 0.5 to 4 Hz, are present. Moreover, the amplitude of the brain wave signal is increased as compared to other sleep stages. This sleep stage is also called delta sleep and is the “deepest stage of sleep”. 
     The sleep stages 1, 2, and slow wave sleep may be summarized as non-rapid eye movement (NREM) or “non-REM” sleep, and are distinguished from rapid eye movement (REM) sleep. During the REM sleep stage, rapid low amplitude brain wave signals are observed. This sleep stage is generally associated with the sleeping person experiencing dreams. 
     The REM sleep stage may also be distinguished from other sleep stages from the associated electro-oculogram signals and electro-myogram signals. During REM sleep, the sleeping person looses his ability to use postural or skeletal muscles, and this muscle inactivity can be determined from electro-myogram signals. The REM sleep stage is also characterised by rapid movements of the eyes, which clearly distinguishes REM sleep from NON-REM sleep in the electro-oculogram signals. 
     From WO2005/084538 A1, a device and a method for waking a user in a desired sleep state are known. The user&#39;s sleep state may be monitored during the night or sleep experience. Electrodes may be placed against the skin of the user to monitor an electro-encephalogram (EEG) signal, an electro-oculogram (EOG) signal and/or an electro-myogram (EMG) signal. The sleep state of the user is determined using a sleep state detection algorithm to process information from the electrodes. The device may predict an occurrence when the user will be in the desired sleep state, such as light sleep, and wake the user during that predicted occurrence. 
     U.S. Pat. No. 6,468,234 B1 discloses a method and an apparatus for measuring sleep quality. Sensors are incorporated in a sheet which laid on top of a conventional mattress on which the subject sleeps. The sensor can collect information about the subject&#39;s position, temperature, sound/vibration/movement, breathing and heart rate. Further the use of additional sensors is disclosed. With additional sensors information such as bedroom temperature, ambient light, brain wave changes and blood oxygen content can also be measured. 
     US 2008/0191885 discloses a device for monitoring the sleep cycles and for operating an alarm to awaken the user at an optimal time. 
     WO 97/49333A discloses a device and a method for detecting brain waves and supplying brainwave signals, wherein the brainwave signals are analyzed by a processor. A pattern generator means delivers an output in form of an pattern signal. 
     In US 2006/0258930 A1 device with uses frontal electrodes to detect the sleep stage of the user is disclosed. 
     WO 2005/084538 discloses a device and a method for waking a user in a desired sleep stage. Therefore the sleep stage of the user will be actively monitored. 
     SUMMARY OF THE INVENTION 
     It would be desirable for many people to be able to recognize a sleep state of another person. For example, it would be desirable to provide an apparatus or a method that is able to indicate whether a sleeping object is deep asleep or whether a person is dreaming. 
     To better address one or more of these concerns, in a first aspect of the invention, an apparatus for processing a bio-physiological signal is provided that comprises an image acquisition device for determination of the position and/or orientation of the head. In dependence of determined position, the sensor signals of at least one of the a plurality of sensors is used for capturing at least one bio-physiological signal of a sleeping object. A processing unit selects the at least one sensor in dependence of the input from the image acquisition device. Further the processing unit processes the at least one bio-physiological signal and thereby generating an output signal based on the at least one bio-physiological signal and based on a signal pattern stored or generated in the processing unit. The output signal comprises a temporally varying output signal pattern, wherein the output signal pattern depends on a current sleep state of the sleeping object. 
     For example, for at least two different sleep states of the sleeping object, different temporally varying output signal patterns of the output signal are generated. 
     In the context of the present application, the term “sleeping object” covers human beings and animals, in particular endotherms, and, more specifically, mammals. In particular, the sleeping object may be a sleeping person. 
     The bio-physiological signal is a brain wave signal or electroencephalography (EEG) signal, an electro-oculogram (EOG) signal or breathing rhythm. The term “brain wave signal” is to be understood to mean an electromagnetic signal produced by or correlated to electrical activity of the brain, i.e., the firing of neurons within the brain. For example, the brain wave signal may be an electroencephalography signal. 
     Further, the term “capturing a bio-physiological signal” covers measuring an electrical signal using electrodes with skin contact to sleeping object as well as contactlessly detecting an electromagnetic signal in the vicinity of the sleeping object. Since the bio-physiological signals are not captured for clinical applications, contactless measurements of the bio-physiological signals are possible. For example dry electrodes for EEG recording are described in Electroencephalogr Clin Nueropysiol. 1994 May; 90(5): 376-83. 
     The term “a temporally varying output signal pattern” is to be understood as an output signal or an output signal component having a temporally varying characteristic, for example a pattern of varying output signal intensity, a pattern of varying color and/or intensity at least one position of a two-dimensional graphical signal, or a two-dimensional graphical pattern that varies in time. However, the term is not limited to these examples. 
     Because the temporally varying output signal pattern depends on a current sleep state of the sleeping object, for example, different sleep states may be recognized or distinguished by an observer to which the output signal is reproduced in a human-perceptible form. Furthermore, for example, an observer may be entertained by or may enjoy perceiving the output signal. For example, for at least two different sleep states of the sleeping object, different temporally varying output signal patterns of the output signal are generated. For example, the output signal may reflect whether the sleeping object is dreaming or whether the sleeping object is deeply asleep. The output signal can be stored for further investigation. 
     The apparatus preferably is a consumer product, in particular an entertainment device. For example, the apparatus is a portable apparatus. 
     For example, the processing unit is adapted to permanently output the output signal and/or to permanently output the output signal at least during one sleep state of the sleeping object. 
     For example, the apparatus comprises an output unit for reproducing the output signal in human-perceptible form. The term “human-perceptible form” covers a signal that can be directly perceived by a person, e.g. an audible signal and/or a visible signal. For example, the output unit may visualize a bio-physiological signal in a form that provides meaning to a person that observes it. This may be done in an aesthetic manner. 
     For example, the output signal is synchronized to or correlated to at least one bio-physiological signal captured by at least one sensor. For example, the output signal may be synchronized or correlated with a brain wave signal in so far as a currently present main frequency of a brain wave signal, such as the frequency of theta waves or delta waves, may be present or detectable in the output signal. 
     The term “correlated” is to be understood as requiring that momentary slight variations of wave frequency of a currently present main frequency of the bio-physiological signal are reproduced as slight variations of wave frequency of that same frequency being present or detectable in the output signal. In particular, these variations may be concurrently reproduced in the output signal, wherein a time lag e.g. caused by digitalization of signals or digital processing may nevertheless be present. 
     For example, an intensity pattern of a brain wave signal, such as a wave pattern during slow wave sleep, may have a base frequency within a range of less than 3.5 Hz, and said frequency may also appear in the output signal. Thus, for example, a direct visualization of brain activity may be provided combined with aesthetic features of the output signal. 
     For example, the apparatus further comprises a pliable device that comprises said plurality of sensors. Such a pliable device may be positioned at, around or below the head of the sleeping object, for example, without causing discomfort to the sleeping object. In particular, for example, the apparatus may comprise a single pliable device for each sleeping object, said single pliable device comprising sensors for capturing a least one brain wave signal of the sleeping object. In contrast to the measuring of EEG signals for clinical applications, requirements on the quality of the captured brain wave signal(s) may be less strict for an apparatus of the invention. Therefore, wet electrodes placed on the scalp of the sleeping object can be dispensed with, and a more flexible positioning and usage of the at least one sensor is possible. Further the sensors can be used to detect the breathing rhythm of the sleeping person. 
     In one embodiment, the apparatus comprises a pillow that comprises said at least one sensor. The term pillow is to be understood to include any support for the head of a reclining sleeping object. For example, the pillow may be integrated in a bed or a couch. For example, the pillow is a pliable pillow. 
     In one embodiment, the sensors comprises contactless sensors. That is, the sensor is adapted to capture a bio-physiological signal of a sleeping object without electrical contact to the sleeping object, in particular, without electrical contact to the skin of the sleeping object. For example, the sensor allows to capture a bio-physiological signal of a sleeping object while there is a non-conducting space or gap between the sensor and the sleeping object. For example, the gap may contain hair. Thus, for example, the apparatus may allow to capture a brain wave signal through the hair of a sleeping object. For example, the at least one bio-physiological signal is captured through a non conductive space above the skin of the sleeping object. 
     Alternatively, the sensor may comprise an electrode for contacting the skin of the sleeping object. 
     In one embodiment, the at least one sensor is covered by a surface layer of the pliable device mentioned above. The surface layer is, for example, a lining, a pillow case, or a similar cloth, or a pliable sheet. Thus, the pliable device may provide increased comfort. 
     In one embodiment, the output signal is a two-dimensional graphical signal, e.g. a visual signal in analogue or digital form. For example, the output unit may comprise a display for displaying the output signal. Thus, the output signal may be visualized. Reproducing the output signal on a display of an output unit is one example of reproducing the output signal in a human-perceptible form. For example, the two-dimensional graphical signal may comprise a temporally varying color pattern and/or intensity pattern. For example, the graphical signal may be synchronized and/or correlated to at least one bio-physiological signal, such as a brain wave signal. 
     In one embodiment, the output signal comprises a color signal having a temporally varying intensity and/or hue. For example, such output signal may be reproduced in a human-perceptibly form by a light source. Thus, the output unit may be a light source. For example, the output unit may be adapted to control intensity and/or a hue of light emitted by the light source. For example, a color pattern and/or an intensity pattern of the signal may be synchronized and/or correlated to a bio-physiological signal, such as a brain wave signal. 
     In one embodiment, the output signal comprises an audio signal or is an audio signal. For example, the audio signal is an analog or digital audio signal. For example, the output unit may comprise a speaker, headset, earphone, headphone or similar. Thus, a bio-physiological signal may be made audible. 
     In one embodiment the image capturing device is not only used to detect the position and/or orientation of the sleeping object, the image capturing device is also use to detect the body movement of the sleeping object. 
     In one embodiment the image capturing device is an infrared camera, wherein the body motion of the sleeping person can easily be detected without the need of light in the room. Further the breath rhythm can be detected in the case the room temperature differs from the exhaled gas. 
     In a second aspect of the invention, a method of processing a bio-physiological signal is provided, the method comprising the steps of:
         taking an image of a part of a sleeping object,   capturing at least one bio-physiological signal of a sleeping object; and   processing the at least one bio-physiological signal using a processing unit ( 18 ), thereby generating an output signal ( 28 ;  38 ;  44 ) based on the at least one bio-physiological signal and based on a signal pattern stored or generated in the processing unit ( 18 ), the output signal ( 28 ;  38 ;  44 ) comprising a temporally varying output signal pattern, wherein the output signal pattern depends on a current sleep state of the sleeping object.       

     For example, the bio-physiological signal is a brain wave signal. 
     For example, the method comprises the step of reproducing the output signal in a human-perceptibly form. 
     For example, the output signal is correlated to at least one bio-physiological signal. 
     For example, the at least one bio-physiological signal is captured using a pillow comprising at least one sensor. 
     For example, the at least one bio-physiological signal is captured using at least one contactless sensor. That is, the sensor is adapted to capture a bio-physiological signal of a sleeping object without requiring contact to the sleeping object. 
     For example, the output signal is a two-dimensional graphical signal. 
     For example, the output signal comprises a color signal having a temporally varying intensity and/or hue. 
     For example, the output signal is an audio signal. 
     For example, the method is a method of processing a bio-physiological signal using an apparatus as described above, wherein said at least one sensor captures said at least one bio-physiological signal of a sleeping object, and wherein the processing unit performs the processing step. 
     In a further aspect of the invention, there is provided a computer program or computer program product for performing the steps of the method as described above when executed on a computer. In particular, the computer program or computer program product may be adapted for performing the processing step and, optionally, the output step, when executed on a computer, at least one sensor for capturing at least one bio-physiological signal of a sleeping object being connected to the computer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  schematically shows an apparatus for processing a bio-physiological signal, having a processing unit and devices comprising sensors; 
         FIG. 2  schematically shows a pillow comprising sensors; 
         FIG. 3  schematically shows a wireless transmission of bio-physiological signals from a device comprising sensors to the processing unit; 
         FIG. 4  schematically shows a transmission of bio-physiological signals from a device comprising sensors through a wire connection to the processing unit; 
         FIG. 5  schematically shows a pliable headband comprising sensors; 
         FIG. 6  schematically shows pliable headbands having integrated sensors and processing units; and 
         FIG. 7  schematically shows a baby cap having sensors. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Various embodiments of the apparatus and method of the present invention will now be described with reference to the figures. 
     A method of processing a bio-physiological signal will now be described in conjunction with an apparatus for processing a bio-physiological signal shown in  FIG. 1 . In  FIG. 1 , signal paths and/or signal connections are indicated by arrows. 
     The apparatus comprises a pliable device in the form of a pillow  10  that comprises multiple sensors  12  for capturing brain wave signals of a sleeping person, whose head rests on the pillow  10 . The sensors  12  are contactless sensors, so that it is not required that the sensors  12  are in direct contract with the skin of the person. The sensors  12  are arranged in rows and columns below a cloth surface layer  14  of the pillow  10 . 
     The pillow  10  further comprises a communication unit  16  to which the sensors  12  are connected. For example, the communication unit  16  is a wireless communication unit adapted to transmit the brain wave signals captured by the sensors  12  to a processing unit  18  of the apparatus. For example, the processing unit  18  may comprise a computer or may be a computer. 
     Further, electro-myogram sensors  20 , for example in the form of conducting foils, are integrated in a pliable device in the form of a bed sheet  22 . The electro-myogram sensors  20  are adapted to capture electro-myogram signals of a person sleeping on the bed sheet  22 . For example, the electro-myogram sensors  20  are contactless sensors. For example, the sensors  20  are covered by a cloth surface layer  24  of the bed sheet  22 . For example, the bed sheet  22  comprises a communication unit  26 , to which the electro-myogram sensors  20  are connected. For example, the communication unit  26  is adapted to transmit electro-myogram signals to the processing unit  18  by wireless communication. Alternatively, a wire connection may be provided between the communication unit  26  and the processing unit  18 . Thus, the communication unit  26  may be connected to the processing unit  28  via a wireless connection or a wired or wire connection. 
     The pillow  10  and the bed sheet  22  are two examples of devices comprising sensors for capturing at least one bio-physiological signal of the sleeping object. Other devices and sensors may be provided additionally or alternatively for capturing a bio-physiological signal of the sleeping object. Moreover, in a modified embodiment only brain wave signal sensors may be present, or only electro-myogram sensors  20  may be present, optionally combined with at least one sensor for capturing a different bio-physiological signal. 
     The processing unit  18  is adapted to process the at least one bio-physiological signal captured by the sensors  12  and/or the sensors  20  and generate an output signal as will be described below. 
     One or more brain wave signals may be captured by the sensors  12 . For example, signal readings of more than one sensor  12  may be combined to provide a combined brain wave signal. Additionally or alternatively, one or more sensors  12  may be selected on the bases of on image captured by an IR camera, not shown in  FIG. 1 , for providing at least one brain wave signal transmitted to the processing unit  18 . Further, for example, the processing unit  18  may select and/or combine signal readings from different sensors  12  and/or different sensors  20  for processing. For example, sensors or sensor readings/signals may be selected depending on their respective signal amplitude or intensity. 
     For example, the processing unit  18  may generate an output signal  28  in the form of a two-dimensional graphical signal that is transmitted to an output unit  30  comprising a display  32 . For example, the output signal  28  comprises, for at least one position or for a subset of spatial positions in the two-dimensional signal, a color signal having a temporally varying intensity and/or hue. For example, brain wave signals captured by the sensors  12  may be transformed into the output signal  28  and visualised on the display  32  using a visualisation algorithm similar to visualisation algorithms for visualising music, which are known from current music players, e.g. software music players. For example, the graphical output signal may be synchronized with a brain wave signal, so that the graphical output signal is at least partially correlated with a brain wave signal captured by the sensors  12 . For example, graphical patterns may be generated in the processing unit and may be synchronised with the brain wave signal. Thus, the output signal is generated based on at least one brain wave signal captured by the sensors  12  and the signal pattern generated in the processing unit  18 . Because the output signal is synchronised or correlated with a brain wave signal, a temporally varying output signal pattern depends on the brain wave pattern and, thus, on a current sleep state of the sleeping person. By generating the two-dimensional graphical signal and displaying it on the display  32 , the output signal and, thus, the brain wave signal(s) captured by the sensors  12  are reproduced in a human-perceptible form. For example, during non-REM sleep, steadily evolving or substantially uniformly repeating signal patterns may be generated by the processing unit  18 , whereas during REM sleep, rather irregular or uneven animated patterns may be generated, reflecting, for example, a vivid dream activity. 
     Additionally or alternatively to the output unit  30  having the display  32 , an output unit  34  having a speaker  36  may be provided, and additionally or alternatively to generating the output signal  28 , the processing unit  18  may generate an output signal  38 , which may be transmitted to the output unit  34 . For example, the output signal  38  is an audio signal and is reproduced by the output unit  34  in a human-perceptible form by making it audible. 
     One example for generating an audio output signal based on at least one brain wave signal captured by the sensors  12  and based on a signal pattern stored in the processing unit  18  is modulating a noise signal by at least one brain wave signal captured by the sensors  12 . For example, pink noise, which may be generated in the processing unit  18  or which may be stored as a digital sound in the processing unit  18 , may be multiplied with a brain wave signal, thereby generating the output signal. Thus, an output signal pattern, e.g. an amplitude pattern or intensity pattern of the pink noise may directly correspond to a temporally varying brain wave signal pattern. Because the brain wave pattern depends on a current sleep state of the sleeping person, the audio output signal pattern also depends on the current sleep state. In particular, the audio output signal is synchronised and correlated with a brain wave signal. 
     For example, during a deep sleep stage, the audio output signal may be a slowly changing waveform, similar to the sound of waves in the sea, with a deep modulation of the resulting envelope. While the person is awake, there is, for example, a faster modulation. For example, the amplitude of the output signal  38  may be controlled in amplitude and/or in dynamic range etc. 
     Additionally or alternatively to providing the output unit  30  and/or the output unit  34 , an output unit  40  comprising at least one light source  42  such as a lamp may be provided. Further, additionally or alternatively to providing the output signal  28  and/or the output signal  38 , an output signal  44  may be generated by the processing unit  18  as follows and transmitted to the output unit  40 . For example, the output signal  44  may be a color signal and/or intensity signal for controlling the hue and/or intensity of light emitted by the light source(s)  42  of the output unit  40 . For example, the output signal  44  may comprise RGB values. For example, the light source  42  may comprise one or more LEDs. The output unit  40  is, for example, a device for creating ambient light. 
     For example, a color and/or intensity signal component of the output signal  44  will be generated in a manner similar to generating the output signal  28  as described above. For example, the color and/or intensity may correspond to an instantaneous average color or intensity of the output signal  28 , e.g. a mean color or intensity of a two-dimensional image or video frame. 
     In another example, the processing unit  18  may perform a frequency analysis of brain wave signals captured by sensors  12 , and, depending on the occurrence of frequencies that are characteristic for a specific sleep stage, the processing unit  18  may select a color and/or intensity output signal pattern assigned to that sleep state. For example, a frequency of an intensity variation of the output signal  44  may be selected depending on a detected sleep state. For example, a deep sleep stage may be indicated by green or blue light of a slowly varying intensity, whereas, when an REM sleep stage is detected, the output signal  44  may comprise a color-changing pattern. 
     By the use of this invention it is possible that further person sleeping in the same room, but have different sleep cycles, enters the at a time where the sleeping person is in a deep sleep phase. 
     The frequency analysis or sleep stage detection may be performed by a sleep stage detection unit  46  of the processing unit  18 , such as a sleep stage detection algorithm in the processing unit  18 . Detecting the sleep stage may be based on characteristic features of brain wave signals detected by the sensors  12  and/or characteristic features of electro-myogram signals detected by the sensors  20  and/or characteristic features of other suitable bio-physiological signals captured by other sensors. As described above, the output signal  44  comprising a temporally varying output signal pattern is selected depending on a current sleep state of the sleeping person. Thus, the output signal  44  is generated based on at least one bio-physiological signal and based on a signal pattern stored or generated in the process unit  18 . 
     Other examples of generating a two-dimensional graphical output signal  28  or an audio output signal  38  based on a detected sleep stage are described in the following. 
     For example, depending on a detected sleep state, the processing unit  18  may select a two-dimensional graphical output signal  28 , which is stored or generated in the processing unit  18 . For example, pre-defined patterns or pattern generating algorithms may be selected by the processing unit  18  dependent on the detected sleep stage. Thus, a temporally varying output signal pattern of the output signal  28  depends on a current sleep state of the sleeping person. However, the output signal is not necessarily synchronised or correlated with a bio-physiological signal. In a similar manner, the processing unit  18  may select an audio signal pattern stored or generated in the processing unit  18  depending on a detected sleep stage. Again, a temporally varying output signal pattern of the audio output signal  38  depends on the current sleep state of the sleeping person, whereas, however, the output signal  38  is not necessarily synchronized or correlated with a bio-physiological signal. 
     The output signals  28 ,  38 ,  44  may be transmitted via a wireless connection or a wire connection to the respective output unit. Further, for example, an output unit, such as the output unit  30 ,  34  or  40 , may be integrated into the processing unit  18 . 
     In the embodiment shown in  FIG. 1 , a contactless respiration and/or heart rate sensor  47  is provided and is connected by a wire connection or a wireless connection to the processing unit  18 . For example, due to the respiratory sinus arrhythmia, the heart rate may be determined from the respiratory signal. 
     For example, the respiration and/or heart rate sensor  47  is a photoplethysmographic imager (PPGI) including an infrared light source and, for example, a camera with an IR filter. Thus, the respiration rate may be captured even if the person lays with his mouth on a pillow. For example, the sensor  47  determines a bio-physiological signal in the form of the heart rate and/or a bio-physiological signal in the form of the respiratory rate for processing by the processing unit  18 . The heart rate and the respiratory rate may depend in a characteristic manner on a sleep state. For example, when entering REM sleep, respiration and heart rate increases substantially. Thus, the processing unit  18  may, for example, be adapted to process the at least one bio-physiological signal captured by the sensor  47  and generate an output signal as described above, similar to processing the signals from the sensors  12  and/or  20 . For example, detecting the sleep stage may be based, in addition to or alternatively to the signals mentioned above, on characteristic features of the heart rate signal and/or characteristic features of the respiratory rate signal captured by the sensor  47 . For example, the heart rate and/or the respiratory rate may be used as input or as additional input to the sleep stage detection unit  46 . As described above, an output signal  44  comprising a temporally varying output signal pattern may be selected depending on a current sleep state of the sleeping person. In a modified embodiment, the sensor  47  may be present instead of the sensors  12  and/or  20 , optionally combined with at least one sensor for capturing a different bio-physiological signal. 
     The respiration and/or heart rate sensor  47  may, for example, alternatively or additionally include a micro wave Doppler radar sensor adapted to provide a heart rate signal and/or a respiration rate signal, for example, by non-contact, through-clothing measurement of chest wall motion of the sleeping person. 
     In the embodiment shown in  FIG. 1 , optionally, an image acquisition device in the form of a camera  48  is provided and is connected by a wire connection or wireless connection to the processing unit  18 . For example, the camera  48  is arranged above the pillow  10 . The processing unit  18  may be adapted to determine, from an image signal of the image acquisition device, whether there is a head on the pillow  10 , and/or to determine an orientation and/or position of the head. For example, the processing unit  18  may select sensors  12 , the sensor readings of which are to be processed, based on a detection of an orientation and/or position of a head on the pillow  10 . In case the sensor  47  includes a camera, this camera may as well form the image acqusition device and may be used instead of the camera  48 . 
       FIG. 2  shows another example of a pillow  10 ′ which, for example, may be provided instead of the pillow  10  in the embodiment of  FIG. 1 . The pillow  10 ′ is similar to the pillow  10  described above and comprises, for example, the same sensors  12 , cloth surface layer  14  and communication unit  16  arranged and connected as described above. However, the pillow  10 ′ comprises pressure sensors  50  connected to the communication unit  16 . Pressure signals of the pressure sensors  50  may be transmitted to the processing unit  18 . The processing unit  18  is, for example, adapted to determine whether there is a head on the pillow  10 ′ based on the pressure signals. Further, for example, the processing unit  18  may be adapted to determine an orientation and/or position of a head on the pillow  10 ′ based on the pressure signals. Thus, additionally or alternatively to an image signal of the camera  48 , pressure signals of the pressure sensors  50  may be used to determine an orientation and/or a position of a head on the pillow  10 ′. Thus, sensors  12 , the captured signals of which are to be processed, may be selected based on the determined orientation and/or position of a head. 
       FIGS. 3 and 4  schematically show a device  52  comprising at least one sensor  54  for capturing at least one bio-physiological signal of a sleeping object, and a connection of said device  52  to the processing unit  18 . The sensors  54  are connected to a communication unit  56  for transmitting the bio-physiological signals to the processing unit  18 . In  FIG. 3 , the connection is a wireless connection, and in  FIG. 4 , the connection is a wire connection. More than one device  52  may be connected to the processing unit  18 . For example, the device  52  may be the pillow  10  and the sensors  54  may be the sensors  12 , and the communication unit  56  may be the communication unit  16 . Further, for example, the device  52  may be the bed sheet  22 , the sensors  54  may be the sensors  20 , and the communication unit  56  may be the communication unit  26 . The processing unit  18  may also be included in the device  52 . For example, the processing unit  18  may be included in the pillow  10 . 
       FIG. 5  shows an example of a pliable device  52  in the form of a head band  58  comprising sensors  12  for capturing at least one brain wave signal of a sleeping person wearing the headband  58 . Further, the headband  58  comprises at least one electro-oculogram sensor  60  for capturing an electro-oculogram signal of the person. For example, the person places the headband  58  such that the EOG sensor  60  is positioned above an eye. 
     For example, the sensors  12  and the at least one EOG sensor  60  are connected to a communication unit  56  integrated in the head band  58  for transmitting the signals captured by the respective sensors  12 ,  60  to the processing unit  18  similar to the example of  FIG. 3 . The headband  58  is one example of pliable headgear containing at least one sensor for capturing at least one bio-physiological signal of a sleeping object. For example, the sensors  12  and  60  are contactless sensors. For example, the sensors  12  and  60  are covered by a cloth surface layer  62  of the pliable headband  58 . 
     The headband  58  may be provided instead of or additionally to the pillow  10  and/or the bed sheet  22  of the embodiment of  FIG. 1 . For example, alternatively to or additionally to processing the signals of the sensors  12  of the pillow  10 , the signals of the sensors  12  of the headband  58  and/or the signals of the at least one EOG sensor  60  may be processed by the processing unit  18 , thereby generating an output signal as described above. Providing a headband  58  has the advantage that the capturing of the signals is less dependent on the sleeping object&#39;s position on a pillow. When the output signal  28 ,  38  and/or  44 , for example, is generated based on an EOG signal from an EOG sensor  60  and on a signal pattern stored or generated in the processing unit  18 , the rapid eye movements of the sleeping person may be made visible and/or audible. For example, a varying output signal pattern may reflect the varying eye movements during the REM sleep stage. By generating an output signal based on a brain wave signal of the sensor(s)  12  and/or the electro-oculogram signal of the sensor(s)  60 , in some respects, dreams of the sleeping person may be visualised and/or made audible. 
     In one example, the processing unit  18  may be integrated in the device  52 , such as the headband  58 . For example, the device  52 , such as the headband  58 , may comprise the processing unit  18  as well as an output unit, such as the output unit  34 . For example, the headband  58  may comprise speakers  36  in the form of earphones or headphones in order to make an audio output signal audible. For example, there is a wire connection between the sensors  12 ,  60  and the processing unit  18 . Thus, the apparatus for processing a bio-physiological signal may be a headband  58  comprising the processing unit  18  and, optionally, an output unit. For example, the headband  58  may comprise batteries for powering the apparatus. The headband  58  is one example for a portable apparatus for processing a bio-physiological signal. 
     In  FIG. 6 , a system for processing bio-physiological signals is shown comprising two headbands  58 ,  58 ′, each having the sensors  12  and  60  as described for the embodiment of  FIG. 5 . In the embodiment of  FIG. 6 , the communication unit  18  for processing the signals of the sensors of the headband  58  is included in the headband  58 ′. Correspondingly, a processing unit  18 ′ for processing the signals of the sensors of the headband  58 ′ is included in the headband  58 . The sensor signals are transmitted via a wireless connection between respective communication units  56  of the respective headbands  58 ,  58 ′. Further, for example, output units  34  and/or output units  40  may be included in the respective headbands  58 ,  58 ′. Thus, brain wave signals and/or electro-oculogram signals of a sleeping person wearing a headband  58  may be wirelessly transmitted to a headband  58 ′ of a partner in order to visualise them or make them audible. 
     In an alternative example, the processing unit  18 ,  18 ′ for processing the sensor signals of the respective headband  58 ,  58 ′ may be included in said headband  58 ,  58 ′, and the output signal generated by the respective processing unit may be wirelessly transmitted to an output unit  34  or  40  included in the other headband  58 ′,  58 . 
     Thus, in the examples of  FIG. 6 , a system for processing bio-physiological signals is provided, said system comprising two processing units for processing at least one bio-physiological signal captured by a respective at least one sensor associated with said processing unit. In this sense, the system combines two apparatuses for processing a bio-physiological signal as described above in conjunction with  FIG. 1 . 
       FIG. 7  shows an embodiment where the device  52  is a pliable baby cap  64  comprising sensors  12  for capturing at least one brain wave signal of a sleeping baby wearing the baby cap. For example, the sensors  12  are covered by a cloth surface layer  66  of the baby cap  64 . Similar to the example of  FIG. 3 , a communication unit  56  may be included in the baby cap  12  for communication with the processing unit  18 . For example, the processing unit  18  and at least one output unit, such as an output unit  40 , may be included in a baby crib. This is an example of the embodiment of  FIG. 1 , wherein the baby cap  64  may be provided additionally or alternatively to the pillow  10 . For example, the visualisation of an output signal of the processing unit  18  may be done by using lighting elements of the output unit  40  embedded in the crib. Thus, for example, if the baby was sleeping well, the crib could light up a green glow light pattern, and if the baby is restless, the crib could light up in a different pattern and/or a differently colored pattern. 
     As described above, for example, the invention may allow to visualise a sleep state, make it audible or, in general, produce a human-perceptible output signal related to a sleep state or dream of the sleeping object. For example, the invention may enable people to see that their baby, child or loved-one is sleeping well. Further, for example, the invention may allow making their sleep and/or dreams tangible in some way. For example, an apparatus for consumer use that enables a person to monitor another person&#39;s sleep in an interesting and/or entertaining manner is provided.