Sensing fine skin movements with improved sensitivity

Abstract

A sensing device (20) is configured to fit on a head of a user (24) and includes an optical sensing head (28), including an emitter module (40) configured to direct coherent light toward a body surface of the user and an array (52) of sensors configured to sense a secondary speckle pattern due to reflection of the coherent light from an area of the body surface and to output a signal indicative of changes over time in the secondary speckle pattern. Objective optics (50) are configured to image the area of the body surface onto an image plane (64) between the objective optics and the array. Processing circuitry (36) is configured to process the signal to generate a speech output.

Description

[0001] SENSING FINE SKIN MOVEMENTS WITH IMPROVED SENSITIVITY

[0002] CROSS-REFERENCE TO RELATED APPLICATION

[0003] This application claims the benefit of U.S. Provisional Patent Application 63 / 726,559, filed December 1, 2024, whose disclosure is incorporated herein by reference.

[0004] FIELD

[0005] The present invention relates generally to physiological sensing, and particularly to methods and apparatus for sensing human speech.

[0006] BACKGROUND

[0007] The process of speech activates nerves and muscles in the chest, neck, and face. Thus, for example, electromyography (EMG) has been used to capture muscle impulses for purposes of speech sensing.

[0008] Secondary speckle patterns have been used for monitoring movement of skin on the human body. Secondary speckle typically occurs in diffuse reflections of a laser beam from a rough surface, such as the skin. By tracking both temporal and amplitude changes of secondary speckle produced by reflection from human skin when illuminated by a laser beam, investigators have measured blood pulse pressure and other vital signs. For example, U.S. Patent 10,398,314 describes a method for monitoring conditions of a subj ecf s body using image data that is indicative of a sequence of speckle patterns generated by the body.

[0009] Secondary speckle patterns on the skin can also be used in detecting speech. For example, PCT International Publication WO 2023 / 012527, whose disclosure is incorporated herein by reference, describes a sensing device, which includes a bracket configured to fit an ear of a user of the device. An optical sensing head is held by the bracket in a location in proximity to a face of the user and configured to sense light reflected from the face and to output a signal in response to the detected light. Processing circuitry processes the signal to generate a speech output.

[0010] As another example, PCT International Publication WO 2023 / 012527, whose disclosure is incorporated herein by reference, describes a method for generating speech that includes uploading a reference set of features that were extracted from sensed movements of one or more target regions of skin on faces of one or more reference human subjects in response to words articulated by the subjects and without contacting the one or more target regions. A test set of features is extracted from the sensed movements of at least one of the target regions of skin on a face of a test subject in response to words articulated silently by the test subject and without contacting the one or more target regions. The extracted test set of features is compared to the reference set of features, and based on the comparison, a speech output is generated, including the articulated words of the test subject.

[0011] SUMMARY

[0012] Embodiments of the present invention that are described hereinbelow provide improved devices and methods for detection of fine movements of the skin.

[0013] There is therefore provided, in accordance with an embodiment of the invention, a sensing device configured to fit on a head of a user. The device includes an optical sensing head, including an emitter module configured to direct coherent light toward a body surface of the user and an array of sensors configured to sense a secondary speckle pattern due to reflection of the coherent light from an area of the body surface and to output a signal indicative of changes over time in the secondary speckle pattern. Objective optics are configured to image the area of the body surface onto an image plane between the objective optics and the array. Processing circuitry is configured to process the signal to generate a speech output.

[0014] In some embodiments, the processing circuitry is configured to generate the speech output responsively to the signal due to movements of the body surface of the user during subvocalization by the user, and possibly without any utterance of sounds by the user.

[0015] In a disclosed embodiment, the emitter is configured to apply a temporal modulation to the coherent light.

[0016] Additionally or alternatively, the emitter module includes one or more emitters configured to emit beams of the coherent light and collimation optics, which are configured collimate the coherent light directed toward the body surface.

[0017] In a disclosed embodiment, the optical sensing head is configured to direct the coherent light toward an ear canal of the user and to sense the secondary speckle pattern due to the reflection of the coherent light from the ear canal. Additionally or alternatively, the device includes a pressure sensor configured to sense pressure changes in an ear of the user, wherein the processing circuity is configured to apply the sensed pressure changes in generating the speech output.

[0018] There is also provided, in accordance with an embodiment of the invention, a sensing device configured to fit on a head of a user and including an optical sensing head, which includes an emitter module configured to direct temporally modulated coherent light toward a body surface of the user. An array of sensors is configured to sense a secondary speckle pattern due to reflection of the temporally modulated coherent light from an area of the body surface and to output a signal indicative of changes overtime in the secondary speckle pattern. Processing circuitry is configured to process the signal to generate a speech output.

[0019] In a disclosed embodiment, the coherent light is temporally modulated at a frequency of at least 1 kHz. Additionally or alternatively, the emitter includes a laser diode, and the coherent light is temporally modulated by applying a temporal modulation to a drive voltage applied to the laser diode.

[0020] There is additionally provided, in accordance with an embodiment of the invention, a sensing device configured to fit on a head of a user and including an optical sensing head. The optical sensing head includes an emitter module, which includes one or more emitters configured to emit beams of the coherent light and collimation optics, which are configured collimate the coherent light and to direct the collimated coherent light toward a body surface of the user. A receiver module is configured to sense a secondary speckle pattern due to reflection of the coherent light from an area of the body surface and to output a signal indicative of changes over time in the secondary speckle pattern. Processing circuitry is configured to process the signal to generate a speech output.

[0021] There is further provided, in accordance with an embodiment of the invention, a method for sensing, which includes directing coherent light toward an area of a body surface of the user. The area of the body surface is imaged, using objective optics, onto an image plane between the objective optics and an array of sensors configured to sense a secondary speckle pattern due to reflection of the coherent light from the area of the body surface. A signal from the array that is indicative of changes over time in the secondary speckle pattern is output from the array and is processed to generate a speech output.

[0022] There is moreover provided, in accordance with an embodiment of the invention, a method for sensing, which includes directing temporally modulated coherent light toward a body surface of the user. A secondary speckle pattern due to reflection of the temporally modulated coherent light from an area of the body surface is sensed, and a signal indicative of changes over time in the secondary speckle pattern is output and processed to generate a speech output.

[0023] There is furthermore provided, in accordance with an embodiment of the invention, a method for sensing, which includes directing collimated coherent light toward an area of a body surface of the user and sensing a secondary speckle pattern due to reflection of the collimated coherent light from an area of the body surface. A signal indicative of changes over time in the secondary speckle pattern is output and processed to generate a speech output. The present invention will be more fully understood from the following detailed description of the embodiments thereof, taken together with the drawings in which:

[0024] BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Fig. 1 is a schematic pictorial illustration of a system for speech sensing, in accordance with an embodiment of the invention;

[0026] Fig. 2 is a schematic sectional view of an optical sensing head, in accordance with an embodiment of the invention;

[0027] Fig. 3 is a schematic side view of a defocused optical sensing scheme, in accordance with an embodiment of the invention;

[0028] Fig. 4 is a schematic plot showing the autocorrelation over time of optical speckle patterns created by laser light at different temporal modulation frequencies, in accordance with an embodiment of the invention;

[0029] Fig. 5A is a schematic image of an optical speckle pattern created on the skin by unmodulated laser radiation; and

[0030] Fig. 5B is a schematic image of an optical speckle pattern created on the skin by temporally modulated laser radiation.

[0031] DETAILED DESCRIPTION OF EMBODIMENTS

[0032] The widespread use of mobile telephones in public spaces creates a cacophony of noise and often raises privacy concerns, since conversations are easily overheard by passersby. At the same time, when one of the parties in a telephone conversation is in a noisy location, the other party or parties may have difficulty in understanding what they are hearing due to background noise. Text communications provide a solution to these problems, but text input to a mobile telephone is slow and interferes with the users’ ability to see where they are going.

[0033] The above-mentioned PCT publications address these problems by using optical sensing of secondary laser speckle patterns cast on the face of a subject to detect minute movements of the skin surface and thus reconstruct the sequence of words articulated by the subject. By sensing fine movements of the skin (indicative of activation of subcutaneous nerves and muscles), occurring in response to words articulated by the subject with or without vocalization, a speech output is generated. The term “speech output” refers to modalities that are typically conveyed by speech, such as text, voice, identity, and emotions.

[0034] Further techniques of this sort are described in PCT International Publication WO 2024 / 018400, whose disclosure is also incorporated herein by reference. This publication describes systems for detecting and utilizing facial skin micromovements. In some non-limiting embodiments, the detection of the facial skin micromovements occurs using a speech detection system that may include a wearable housing, a light source (either a coherent light source or a noncoherent light source), a light detector, and at least one processor. One or more processors may be configured to analyze light reflections received from a facial region to determine the facial skin micromovements, and extract meaning from the determined facial skin micromovements. Examples of meaning that may be extracted from the determined facial skin micromovements may include words spoken by the individual (either silently spoken or vocally spoken), an identification of the individual, an emotional state of the individual, a heart rate of the individual, a respiration rate of the individual, or any other biometric, emotion, or speech-related indicator.

[0035] Using the systems and methods described in WO 2024 / 018400 and the other PCT publications cited above, facial skin micromovements may be detected during subvocalization. The term “during subvocalization” refers to any speech-related activity that takes place without utterance, before utterance, or preceding an imperceptible utterance. In one embodiment, the speech-related activity may include silent speech (i.e., when air flow from the lungs is absent but the facial muscles articulate the desired sounds). In another embodiment, the speech-related activity may include speaking soundlessly (i.e., when some air flows from the lungs, but words are articulated in a manner that is not perceptible using an audio sensor). In yet another embodiment, the speech-related activity may include prevocalization muscle recruitments (i.e., subvocalization that occurs prior to an onset of vocalization). In some cases, the prevocalization facial skin micromovements may be triggered by voluntary muscle recruitments that occur when certain craniofacial muscles start to vocalize words. In other cases, the prevocalization facial skin micromovements may be triggered by involuntary facial muscle recruitments that the individual makes when certain craniofacial muscles prepare to vocalize words.

[0036] Embodiments of the present invention that are described herein may similarly be applied in sensing fine movements of the skin during subvocalization, irrespective of lip movements by the speaker, by sensing light reflected from areas of the user’s body surface, such as the face, neck, or ear canal (including but not limited to the eardrum). The term “light,” as used in the present description and in the claims, refers to electromagnetic radiation, which may be coherent or incoherent, in any or all of the infrared, visible, and ultraviolet ranges. Specifically, the disclosed techniques enable sensing of such fine movements by detecting changes in laser speckle patterns with enhanced sensitivity and reduced noise. Although the disclosed embodiments relate to the use of these techniques in sensing subvocalization, the principles of the present invention may alternatively be used, mutatis mutandis, in other applications of sensing speckle patterns, not only for sensing of speech-related activity, but also for other sorts of physiological measurement and monitoring, as well as in other fields.

[0037] Fig. 1 is a schematic pictorial illustration of a system 18 for speech sensing, in accordance with an embodiment of the invention. System 18 is based on a sensing device 20, in which a bracket, in the form of an ear clip 22, fits over the ear of a user 24 of the device. An earphone 26 attached to ear clip 22 fits into the user’s ear. An optical sensing head 28 is connected by an arm 30 to ear clip 22 and thus is held in a location in proximity to the user’s face. In the pictured embodiment, device 20 has the form and appearance of a clip-on headphone, with optical sensing head 28 in place of (or in addition to) the microphone.

[0038] Optical sensing head 28 directs one or more beams of coherent light toward different, respective locations on the face of user 24. In the pictured embodiment, these beams create an array of spots 32 extending over an area 34 of the face (and specifically over the user’s cheek). In the present embodiment, optical sensing head 28 does not contact the user’s skin at all, but rather is held at a certain distance from the skin surface.

[0039] Optical sensing head 28 senses the secondary speckle patterns that are created due to reflection of the coherent light from spots 32 from the face and outputs a signal that is indicative of changes in the speckle patterns. Device 20 may sense and process the signals due to all of spots 32 or of only a certain subset of spots 32. In the embodiments that are described hereinbelow, sensing head 28 implements one or more of a number of techniques for strengthening the signals and reducing the effects of noise in the varying speckle patterns that arise due to subvocalization.

[0040] These techniques may include, for example, defocusing the image of the skin received by sensing head 28 and / or temporally modulating the coherent light that is used in creating the speckle patterns. The defocus may be chosen to image the skin onto an image plane between the objective optics and an array of sensors in sensing head 28 (as shown in Fig. 3, for example) or onto an image plane behind the array of sensors. Details of the structure and operation of optical sensing head 28 that are used in implementing these techniques are described below. These techniques may be integrated with the sensing modalities described in the above-mentioned PCT publications.

[0041] Additionally or alternatively, to improve speckle tracking using coherent light and enable measurement of the micro-movements of the skin, optical sensing head 28 collimates the wavefront of the coherent light impinging on the skin surface. Coherent light reflected from the skin scatters from sites not only on the surface of the epidermis, but also within the inner layers of the skin, generating an image of speckles that is different from the image that would be formed by surface scattering alone. For at least this reason, it is desirable that the coherent light that is incident on the skin be as close to a plane parallel wavefront as possible, to enhance correlation between consecutive images of speckles and thus enable speckle tracking over larger distances and at high velocities of skin motion.

[0042] In alternative embodiments (not shown in the figures), an optical sensing head may direct light toward and sense light reflected from spots on other areas of the body, such as the neck or the ear canal. Specifically, fine motions in the ear canal, such as motions of the eardrum, can be indicative of contraction of facial muscles, as well as pressure changes due to movements of the mouth, and sensing these fine motions can be helpful in improving the fidelity of detection of subvocal speech.

[0043] Processing circuitry in system 18 processes the signal that is output by optical sensing head 28 to generate a speech output. As noted earlier, the processing circuitry is capable of sensing movements of the skin of user 22 and generating the speech output even without vocalization of the speech or utterance of any other sounds by user 22. The functions of the processing circuitry in system 18 may be carried out entirely within device 20, or they may alternatively be distributed between device 20 and an external processor, such as a processor in a smartphone 36 running suitable application software. Smartphone 36 may also access a server 38 over a data network, such as the Internet, in order to upload data and download software updates, for example.

[0044] In the pictured embodiment, device 20 also comprises a pressure sensor 35, which is connected to ear clip 22 and inserted into the user’s ear. For example, pressure sensor 35 may comprise a piezoelectric sensor or strain gauge, which may be integrated with earphone 26. Pressure sensor 35 senses pressure changes due to muscle movements (including micromovements) associated with subvocalization, including movements of the user’s tongue, for example. The sensed pressure changes can be used in conjunction with the signals output by optical sensing head 28 in generating the speech output from sensing device 20.

[0045] Fig. 2 is a schematic sectional view of optical sensing head 28 of device 20, showing components and functional details of the optical sensing head in accordance with an embodiment of the invention. Optical sensing head 28 comprises an emitter module 40 and a receiver module 48.

[0046] Emitter module 40 comprises a light source, such as an infrared laser diode 42, which emits an input beam of coherent radiation. A beamsplitting element 44, such as a Damman grating or another suitable type of diffractive optical element (DOE), splits the input beam into multiple output beams 46, which form respective spots at a matrix of locations extending over area 34. In one embodiment (not shown in the figures), emitter module 40 comprises multiple laser diodes or other emitters, which generate respective groups of the output beams 46, covering different respective sub-areas within area 34 of the user’s face. To optimize speckle tracking performance, collimation optics, such as a collimating lens 45, collimate output beams 46 so that the optical wavefronts that are incident on area 34 are approximately planar.

[0047] When multiple emitters are used, the processing circuitry in device 20, such as a controller 56, may select and actuate only a subset of the emitters, without actuating all the emitters. Additionally or alternatively, controller 56 may adjust the power of the emitters to compensate for differences in the reflected light intensity, for example due to differing distances. Further additionally or alternatively, controller 56 may implement a feedback loop to adjust laser power or exposure time, and specifically to enable individual adjustment of laser and sensor array parameters. As yet another option, the illumination pattern may be adjusted to suit the anatomy of the user.

[0048] Receiver module 48 comprises an array 52 of optical sensors, for example, a CMOS image sensor, with objective optics 50 for imaging area 34 onto array 52. An optical filter 54 passes light to array 52 at the wavelength of output beams 46 while filtering out ambient light at other wavelengths.

[0049] Fig. 3 is a schematic side view of a defocused optical sensing scheme implemented in receiver module 48, in accordance with an embodiment of the invention. Objective optics 50 are configured and positioned so that the image of a body surface 58, such as the skin surface of the user, is defocused on array 52 of optical sensors in the receiver. More specifically, objective optics 50 image an area of body surface 58 onto an image plane 64 that is located between the objective optics and array 52. (Equivalently, an object plane 62 of objective optics 50 with respect to an image plane at the surface of array 52 is located between the objective optics and the body surface.)

[0050] As explained above, fine movements of body surface 58 cause corresponding changes in the secondary speckle pattern reflected from the body surface, which are processed in system 18 (Fig. 1) to generate a speech output. The defocus of the image of the body surface that is formed by objective optics 50 on array 52 enhances the sensitivity of receiver module 48 to the changes in the locations and amplitudes of the speckles and thus improves the precision of measurement of the fine movements that are associated with subvocalization.

[0051] Another factor that can reduce the sensitivity of device 20 in sensing fine movements of body surface 58 is noise in the speckle pattern, i.e., rapid variations over time in the speckle pattern that are not indicative of subvocalization. A part of this noise is due to minute movements of tissues and fluids in deeper layers 60 of the dermis and subcutaneous tissues. To reduce the noise in the speckle pattern, in some embodiments, controller 56 applies a temporal modulation to the coherent light that is output by emitter module 40, for example by modulating the drive voltage that is applied to laser diode 42 (Fig. 2). The inventors have found that temporal modulation at a frequency of at least 1 kHz is effective in reducing the noise in the speckle pattern, although lower or higher modulation frequencies may alternatively be applied. It is understood that the physiological layers of body surface 58 have a depth (thickness) which can vary over different areas of the body. The image of body surface 58 that is obtained from the reflection of coherent light from the spots on the body surface may be from different depths in the body surface and depends on the depth to which the light source penetrates.

[0052] Fig. 4 is a schematic plot showing the autocorrelation over time of optical speckle patterns created by emitter module 40 at different temporal modulation frequencies, in accordance with an embodiment of the invention. A plot 70 shows the autocorrelation over time at a temporal modulation frequency of 2 kHz. At this modulation frequency, a high level of autocorrelation is maintained over tens to hundreds of milliseconds, i.e., periods substantially longer than the variations in the speckle pattern due to subvocalization and longer than the frame time of array 52. A plot 72 shows that adequate (if lower) autocorrelation over time is still maintained at a temporal modulation frequency of 1 kHz.

[0053] On the other hand, a plot 74 shows the autocorrelation over time when laser diode 42 is driven with a DC voltage, and the coherent light output by emitter module 40 is unmodulated. In this case, the temporal autocorrelation drops rapidly, indicating that most of the speckles in the pattern are varying rapidly for reasons unrelated to subvocalization.

[0054] Figs. 5A and 5B are schematic images 80 and 82 of optical speckle patterns created on the skin by unmodulated and temporally modulated laser radiation, respectively, in accordance with an embodiment of the invention. Image 80 shows the noisy pattern generated by unmodulated laser radiation, while image 82 shows the smoother pattern achieved when the output of emitter module 40 is modulated.

[0055] The embodiments described above are cited by way of example, and that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described hereinabove, as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not disclosed in the prior art.

Claims

CLAIMS1. A sensing device configured to fit on a head of a user and comprising: an optical sensing head, comprising: an emitter module configured to direct coherent light toward a body surface of the user; an array of sensors configured to sense a secondary speckle pattern due to reflection of the coherent light from an area of the body surface and to output a signal indicative of changes over time in the secondary speckle pattern; and objective optics configured to image the area of the body surface onto an image plane between the objective optics and the array; and processing circuitry configured to process the signal to generate a speech output.

2. The device according to claim 1, wherein the processing circuitry is configured to generate the speech output responsively to the signal due to movements of the body surface of the user during subvocalization by the user.

3. The device according to claim 2, wherein the processing circuitry is configured to generate the speech output without any utterance of sounds by the user.

4. The device according to claim 1, wherein the emitter is configured to apply a temporal modulation to the coherent light.

5. The device according to any of claims 1-4, wherein the emitter module comprises: one or more emitters configured to emit beams of the coherent light; and collimation optics, which are configured collimate the coherent light directed toward the body surface.

6. The device according to any of claims 1-4, wherein the optical sensing head is configured to direct the coherent light toward an ear canal of the user and to sense the secondary speckle pattern due to the reflection of the coherent light from the ear canal.

7. The device according to any of claims 1-4, further comprising a pressure sensor configured to sense pressure changes in an ear of the user, wherein the processing circuity is configured to apply the sensed pressure changes in generating the speech output.

8. A sensing device configured to fit on a head of a user and comprising: an optical sensing head, comprising:an emitter module configured to direct temporally modulated coherent light toward a body surface of the user; and an array of sensors configured to sense a secondary speckle pattern due to reflection of the temporally modulated coherent light from an area of the body surface and to output a signal indicative of changes over time in the secondary speckle pattern; and processing circuitry configured to process the signal to generate a speech output.

9. The device according to claim 8, wherein the coherent light is temporally modulated at a frequency of at least 1 kHz.

10. The device according to claim 8, wherein the emitter comprises a laser diode, and the coherent light is temporally modulated by applying a temporal modulation to a drive voltage applied to the laser diode.

11. The device according to claim 8, wherein the processing circuitry is configured to generate the speech output responsively to the signal due to movements of the body surface of the user during subvocalization by the user.

12. The device according to claim 11, wherein the processing circuitry is configured to generate the speech output without any utterance of sounds by the user.

13. The device according to any of claims 8-12, wherein the emitter module comprises: one or more emitters configured to emit beams of the coherent light; and collimation optics, which are configured collimate the coherent light directed toward the body surface.

14. The device according to any of claims 8-12, wherein the optical sensing head is configured to direct the coherent light toward an ear canal of the user and to sense the secondary speckle pattern due to the reflection of the coherent light from the ear canal.

15. The device according to any of claims 8-12, further comprising a pressure sensor configured to sense pressure changes in an ear of the user, wherein the processing circuity is configured to apply the sensed pressure changes in generating the speech output.

16. A sensing device configured to fit on a head of a user and comprising: an optical sensing head, comprising: an emitter module, comprising: one or more emitters configured to emit beams of the coherent light; andcollimation optics, which are configured collimate the coherent light and to direct the collimated coherent light toward a body surface of the user; and a receiver module configured to sense a secondary speckle pattern due to reflection of the coherent light from an area of the body surface and to output a signal indicative of changes over time in the secondary speckle pattern; and processing circuitry configured to process the signal to generate a speech output.

17. The device according to claim 16, wherein the processing circuitry is configured to generate the speech output responsively to the signal due to movements of the body surface of the user during subvocalization by the user.

18. The device according to claim 17, wherein the processing circuitry is configured to generate the speech output without any utterance of sounds by the user.

19. The device according to any of claims 16-18, wherein the optical sensing head is configured to direct the coherent light toward an ear canal of the user and to sense the secondary speckle pattern due to the reflection of the coherent light from the ear canal.

20. The device according to any of claims 16-18, further comprising a pressure sensor configured to sense pressure changes in an ear of the user, wherein the processing circuity is configured to apply the sensed pressure changes in generating the speech output.

21. A method for sensing, comprising: directing coherent light toward an area of a body surface of the user; imaging the area of the body surface, using objective optics, onto an image plane between the objective optics and an array of sensors configured to sense a secondary speckle pattern due to reflection of the coherent light from the area of the body surface; outputting a signal from the array that is indicative of changes over time in the secondary speckle pattern; and processing the signal to generate a speech output.

22. The method according to claim 21, wherein processing the signal comprises generating the speech output responsively to the signal due to movements of the body surface of the user during subvocalization by the user.

23. The method according to claim 22, wherein the speech output is generated without any utterance of sounds by the user.

24. The method according to claim 21 , wherein directing the coherent light comprises applying a temporal modulation to the coherent light.

25. The method according to any of claims 21-24, wherein directing the coherent light comprises collimating the coherent light that is directed toward the body surface.

26. The method according to any of claims 21 -24, wherein the coherent light is directed toward an ear canal of the user, and wherein imaging the area comprises sensing the secondary speckle pattern due to the reflection of the coherent light from the ear canal.

27. The method according to any of claims 21-24, further comprising sensing pressure changes in an ear of the user, wherein processing the signal comprises applying the sensed pressure changes in generating the speech output.

28. A method for sensing, comprising: directing temporally modulated coherent light toward a body surface of the user; sensing a secondary speckle pattern due to reflection of the temporally modulated coherent light from an area of the body surface; outputting a signal indicative of changes over time in the secondary speckle pattern; and processing the signal to generate a speech output.

29. The method according to claim 28, wherein the coherent light is temporally modulated at a frequency of at least 1 kHz.

30. The method according to claim 28, wherein directing the coherent light comprises applying a temporal modulation to a drive voltage applied to a laser diode, which emits the coherent light.

31. The method according to claim 28, wherein processing the signal comprises generating the speech output responsively to the signal due to movements of the body surface of the user during subvocalization by the user.

32. The method according to claim 31, wherein the speech output is generated without any utterance of sounds by the user.

33. The method according to any of claims 28-31, wherein directing the coherent light comprises collimating the coherent light that is directed toward the body surface.

34. The method according to any of claims 28-31 , wherein the coherent light is directed toward an ear canal of the user, and wherein sensing the secondary speckle pattern comprises sensing the secondary speckle pattern due to the reflection of the coherent light from the ear canal.

35. The method according to any of claims 28-31, further comprising sensing pressure changes in an ear of the user, wherein processing the signal comprises applying the sensed pressure changes in generating the speech output.

36. A method for sensing, comprising: directing collimated coherent light toward an area of a body surface of the user; sensing a secondary speckle pattern due to reflection of the collimated coherent light from an area of the body surface; outputting a signal indicative of changes over time in the secondary speckle pattern; and processing the signal to generate a speech output.

37. The method according to claim 36, wherein processing the signal comprises generating the speech output responsively to the signal due to movements of the body surface of the user during subvocalization by the user.

38. The method according to claim 37, wherein the speech output is generated without any utterance of sounds by the user.

39. The method according to any of claims 36-38, wherein the coherent light is directed toward an ear canal of the user, and wherein sensing the secondary speckle pattern comprises sensing the secondary speckle pattern due to the reflection of the coherent light from the ear canal.

40. The method according to any of claims 36-38, further comprising sensing pressure changes in an ear of the user, wherein processing the signal comprises applying the sensed pressure changes in generating the speech output.

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