Stroboscopic image modulation to reduce the visual blur of an object being viewed by an observer experiencing vibration

The invention described herein was made in the performance of work under a NASA contract and by employees of the United States Government and is subject to the provisions 51 U.S.C. § 20135, and may be manufactured and used by or for the Government for governmental purposes without the payment of any royalties thereon or therefore.

Not Applicable

1) Field of the Invention

The present invention relates generally to method and apparatus for reducing the visual blur of an object (particularly elements of a display) being viewed by an observer experiencing vibration. More particularly, stroboscopic image modulation is used to reduce the visual blur due to effects of the vibration.

2) Description of Related Art

When an object is experiencing vibration, an observer trying to focus on the object may see a blurred image of the object. This becomes particularly problematic when the perceived object is a display having text or characters that the observer needs to read or focus particular attention on. It is known in the art that illuminating an object (experiencing vibration) with a strobe light can decrease the perceived blur of the object for a stationary observer, if the light is strobed at or near the frequency (or integer factors [divisors] of) of the vibration.

U.S. Pat. No. 4,167,877 by Avery discloses the use of a strobe and accelerometer to analyze the resonant frequency(s) of a structure.

U.S. Pat. No. 5,591,972 by Noble et al, discloses strobing LED(s) at a predetermined frequency to read optical information from a distant object.

For situations where the observer is experiencing vibration and the object is stationary, or both the observer and object are experiencing vibration, the situation is more complex. When a vibrating object is viewed by a stationary observer, certain biological eye-movement mechanisms help the observer compensate for the shifting position of the viewed object. “Smooth pursuit” movements help to keep the image of a moving object on the foveal region of the retina. Saccadic eye movements help to rapidly shift the line of sight between successive points of fixation. When an observer is experiencing vibration, (in particular the observer's head), additional biological eye-movement mechanisms come into play. Vibration that cause rotation of the observer's head can trigger the vestibulo-ocular reflex, which in turn results in rotation of the eyes seeking to maintain an object's image on the foveal region of the retina. In addition the optokinetic reflex is triggered to assist the vestibulo-ocular reflex. If the object being viewed is shifting in position (near to far, or vice versa) due to relative motion between the observer and the viewed object, vergence eye movements (that coordinate rotations of the eyes for accurate binocular imaging) can come into play. For low temporal frequencies, all of these mechanisms help to mitigate the effects of observer vibration. However, these mechanisms are unable to accurately track higher temporal frequencies, and in fact can exacerbate the detrimental effects of vibration on human vision.

An aspect of the present invention provides for reducing the visual blur of an object (particularly elements of a display) being viewed by an observer experiencing vibration (“observer vibration”). In various embodiments of the present invention, the visual image of an object viewed by the observer is stroboscopically modulated to reduce the visual blur of the viewed object. Stroboscopic image modulation (SIM) serves to reduce visual blur by “freezing” (or reducing to a slow drift) the viewed object's visual image. The SIM manner of operation comprises operating a device (“SIM device”) in an alternating “on/off” temporal pattern (on/off states) according to a SIM drive signal (SDS) derived from the observer vibration. In various embodiments, the SDS comprises a pulsed signal with two-state logic (on/off) generated by the SIM control system. In various embodiments, the SIM control system generates the SDS that causes a SIM device (illuminator, shutter, display, and combinations of the foregoing [including the use of multiple illuminators, shutters, and displays]) to operate in the SIM manner. In various embodiments, the SIM control system is separate from the SIM device it is controlling. In various embodiments, the SIM control system is incorporated into the SIM device.

FIGS. 1A-1D illustrate various aspects of embodiments of a SIM control system with respect to measurement and analysis of the observer vibration, and generation of a “stroboscopic image modulator” (SIM) drive signal. In the figures, like or similar elements (such as strobe signal generator 15 ) utilize the same reference characters throughout the various views.

FIGS. 2A-2E illustrate various aspects of embodiments of the present invention with respect to the observer vibration and SIM drive signal.

FIG. 3 illustrates various aspects of embodiments of the present invention with respect to a SIM illuminator that stroboscopically modulates the visual image of an object being viewed by the observer.

FIG. 4 illustrates various aspects of embodiments of the present invention with respect to a SIM display control system that stroboscopically modulates the visual image of a display being viewed by the observer.

FIG. 5 illustrates various aspects of embodiments of the present invention with respect to use of a SIM drive signal to drive a SIM shutter that stroboscopically modulates the visual image of an object being viewed by the observer.

Acronyms

DSP Digital Signal Processor

DC sim SIM duty cycle—percentage of time that the SIM device is “on” during one cycle of the SDS frequency period (1/F sds ), expressed as a proportion (e.g., 35%) of a vibration cycle, in embodiments where the SDS is characterized by an SDS frequency F sds

DISAB sim SIM device “disabled” mode—mode wherein the SIM device is not operating in any “enabled” modes (i.e., no stroboscopic image modulation).

EMG Electromyography

ENAB sim SIM device “enabled” mode—mode wherein the SIM device is operating in one of various modes:

a) constant firing mode (SDS characterized by F sds ); b) episodic firing mode; c) automatic mode (ability to switch between constant firing and episodic firing modes)

EOG Electrooculography

FPGA Field Programmable Gate Array

FFT Fast Fourier Transform

F objv Viewed object vibration frequency—frequency selected as representative of the viewed object vibration, where the viewed object's vibration is deterministic

F objvd Viewed object vibration frequency/dominant—dominant frequency (e.g., sinusoidal component with the largest amplitude) selected from a frequency range of interest, where the viewed object vibration is deterministic and characterized by a composite of multiple sinusoids with different frequencies

F objvs Viewed object vibration frequency/single—where the viewed object vibration is deterministic and characterized by a single sinusoid at this frequency

F ov Observer vibration frequency—frequency selected as representative of the observer's vibration, where the observer's vibration is deterministic

F ovd Observer vibration frequency/dominant—dominant frequency (e.g., sinusoidal component with the largest amplitude) selected from a frequency range of interest, where the observer vibration is deterministic and characterized by a composite of multiple sinusoids with different frequencies

F ovs Observer vibration frequency/single—where the observer vibration is deterministic and characterized by a single sinusoid at this frequency

F sds SIM drive signal frequency—in various embodiments, a frequency characterizing the SDS, wherein the frequency is derived from the observer vibration (or combinations of observer vibration and viewed object vibration)

OTM sim SIM onset trigger mechanism—the trigger mechanism that initiates an individual SDS “on” pulse

IC integrated circuit

rms root mean square

SDS SIM drive signal—signal according to which a SIM device is driven in an alternating on/off temporal pattern. In various embodiments, the SDS is derived from the observer vibration (or combinations of observer vibration and viewed object vibration)

SIM stroboscopic image modulation—a SIM control system causes a SIM device to operate in an alternating on/off temporal pattern according to a SIM drive signal to reduce the visual blur of the image of an object being viewed by an observer experiencing vibration.

SIM ds SIM display shutter—SIM object shutter wherein the object being viewed is a display

SIM disp SIM display—SIM device comprising a display controlled by a SIM control system

SIM os SIM object shutter—SIM device comprising a shutter interposed between the observer and an object being viewed by the observer

SIM il SIM illuminator—SIM device comprising an illuminator that illuminates the object being viewed

SIM ls SIM light shutter—SIM device comprising a shutter interposed between a non-SIM illuminator (illuminating the viewed object) and the viewed object

SP sim SIM synchronizing parameter—parameter synchronizing the start of a SIM control system's “on” pulse with the observer's vibration, expressed as a SIM temporal delay

SPI SDS parameter information—information for SDS parameters (characterizing the SDS) determined from VFI for a given vibration (observer or viewed object), wherein the SDS parameters are selected from the group consisting of: frequency, duty cycle, SIM synchronizing parameter, “on” time duration, SIM onset trigger mechanism, SIM shutoff trigger mechanism, “on” pulse time duration, SIM temporal delay, and combinations of the foregoing;

SSP Strobe synchronization processing

STM sim SIM shutoff trigger mechanism—the trigger mechanism that terminates an individual SDS “on” pulse

T on “On” time duration—value of time from which the SIM duty cycle is calculated DC sim =T on *F sds for embodiments where the SDS is deterministic with frequency, F sds

T p “On” pulse time duration—width (duration of time) for a given SDS “on” pulse. For a periodic SIM drive signal, T p is constant. For a periodic SIM drive signal with frequency, F sds , T p is equivalent to T on . For other SIM drive signals, T p may be variable.

TD sim SIM temporal delay—time interval between the trigger point in the observer vibration signal and a SIM device's “on” pulse (measured from the beginning, center, or end of the pulse).

VFI vibration feature information—information for vibration features extracted from VQI for a given vibration (observer or viewed object), wherein the vibration features include, but are not limited to: frequency, amplitude, phase, zero-crossings, local extrema (local minima or maxima), and combinations of the foregoing

VQI vibration quantifier information—information for vibration quantifiers for a given vibration (observer or viewed object), wherein the vibration quantifiers include: acceleration, velocity, displacement, EMG, EOG, and combinations of the foregoing,

Aspects of the present invention disclose reducing the visual blur of an object being viewed (particularly the elements of a display) for an observer experiencing vibration (“observer vibration”) while viewing the object. In various embodiments of the present invention, the visual image of an object viewed by the observer is stroboscopically modulated to reduce the visual blur of the viewed object. Stroboscopic image modulation serves to reduce visual blur by “freezing” (or reducing to a slow drift) the viewed object's visual image. This SIM manner of operation comprises operating a device (“SIM device”) in an alternating “on/off” temporal pattern (on/off states) according to a SIM drive signal (SDS) generated by a SIM control system. In various embodiments, the SDS is derived from the observer vibration. In various embodiments, the SDS is derived from a combination of the observer vibration and viewed object vibration. In various embodiments, the SDS comprises a pulsed signal with two-state logic (on/off). Since the SIM control system operates a SIM device in an alternating on/off temporal pattern by an SDS on/off pulse(s), a SIM device “on” pulse is to be understood as having equivalent meaning as the SDS “on” pulse, as well as a SIM device “cycle” having equivalent meaning as an SDS “cycle”. Similarly, a SIM control system's “on” pulse and cycle are to be understood as having equivalent meanings as the SDS “on” pulse and cycle. In various embodiments, an SDS derived from the observer vibration comprises an SDS generated from one or more SDS parameters that have been determined from information about the observer vibration (e.g., vibration quantifier information [VQI] and vibration feature information [VFI]). In various embodiments, an SDS derived from the observer vibration comprises an SDS generated from one or more SDS parameters that have been determined from observer VQI/VFI and viewed object VQI/VFI.

In various embodiments, the SIM control system, causes a device (“SIM device”), for example, such as illuminator(s), shutter(s), display control system(s), and combinations of the foregoing (including the use of multiple illuminators, shutters, and display control systems), to operate in the SIM manner. In various embodiments, the SIM control system is separate from the SIM device it is controlling. In various embodiments, the SIM control system is incorporated into the SIM device. In various embodiments, the SDS (generated by the SIM control system) causes a SIM device to operate in alternating “on/off” states. In various embodiments, a SIM illuminator (SIM il ), operating according to an SDS, provides light to the viewed object when in the “on” state and no light in the “off” state. In various embodiments, a SIM object shutter (SIM os ), operating according to an SDS, is interposed between the observer and the object being viewed. In the “on” state, the SIM os allows the observer to view the object, and prevents the observer from viewing the object in the “off” state. In various embodiments, the viewed object is a display, and the SIM object shutter comprises a SIM display shutter (SIM ds ). In various embodiments, a SIM light shutter (SIM ls ), operating according to an SDS, is interposed between the viewed object and a non-SIM illuminator (i.e., an illuminator that is “continuously on” and not under the control of the SIM) providing light to the viewed object. In the “on” state, the SIM light shutter allows light from the non-SIM illuminator to illuminate the viewed object, and prevents light from the non-SIM illuminator from illuminating the viewed object in the “off” state. In various embodiments, a SIM display control system (SIM dcs ), controlling a display to operate according to an SDS, directs at least a portion of the display to display an image when in the “on” state, and directs that portion of the display to a uniform blank image when in the “off” state. In various embodiments, in the “off” state, the uniform blank image is matched to various aspects of the “on” display image (e.g., background, average luminance, etc.).

In various embodiments, the object being viewed by the observer includes (but not limited to): a) printed material; b) text/graphics/markings on or near instruments, switches, controls, dials, signs, and placards; c) displays; and d) combinations of the foregoing. In various embodiments, the display (or portion thereof) may comprise: mechanical displays (including but not limited to mechanical gauges and dials); electromechanical displays (including but not limited to electromechanical gauges and dials); electronic displays (including but not limited to LCD displays, LED displays, OLED displays, plasma displays, CRT displays, electroluminescent displays, electronic paper displays); or combinations of the foregoing. In various embodiments, the “front” of the viewed object (of which a display may comprise a subset or the entirety) is the surface of the viewed object that faces the observer, and the “back” of the viewed object is the surface of the viewed object that faces away from observer (i.e., the surface opposite from the “front” surface).

In various embodiments, information for one or more observer vibration quantifiers is determined, wherein said observer vibration quantifier(s) include: acceleration, velocity, displacement, Electromyography (EMG), Electrooculography (EOG), and combinations of the foregoing. Vibration quantifier information (VQI) include: i) previously determined VQI; ii) currently determined VQI; and iii) combinations of the foregoing. In various embodiments, previously determined VQI include, for example: a) previous VQI measurements, for an environment similar to the one being experienced or expected to be experienced by said observer; b) previous VQI from estimation algorithms, for an environment similar to the one being experienced or expected to be experienced by said observer; c) combinations of the foregoing. In various embodiments, currently determined VQI includes: a) VQI from estimation algorithms during observer vibration; b) VQI measured in real-time by transducer(s) during observer vibration; and c) combinations of the foregoing. Previously determined VQI may be available in various forms including but not limited to: a) printed hardcopy; b) stored on computer or electronic medium; c) personal knowledge of the observer or a third party; or d) combinations of the foregoing. In various embodiments, VQI from estimation algorithms comprises output from analyses using engineering models and existing data. In various embodiments, estimation algorithms are implemented on computer hardware/software. In various embodiments, EOG measurements are used to quantify observer eye movements responding to experienced observer vibration. In various embodiments, EMG measurements are used to quantify observer muscle contractions responding to experienced observer vibration. In various embodiments, model(s) of individual observer vibration sensitivity to vibration provide(s) features or parameters for strobe synchronization processing. Such a model would predict retinal image motion (or perceived blur) for the individual observer that would result from the measured whole-body vibration input. The model would include the biological elements governing oculomotor response such as eye-head-neck biodynamics and vestibulo-ocular reflex gain factors. The strobe's frequency, duty cycle, and phasing would be set to levels that the model predicts will minimize retinal image motion (or perceived blur). In various embodiments, when the viewed object is also experiencing vibration, viewed object VQI (for quantifiers: acceleration, velocity, displacement) may be determined in the same manner as described earlier in this paragraph for observer VQI (for quantifiers: acceleration, velocity, displacement).

In various embodiments, information is determined for one or more vibration feature(s) including: frequency, amplitude, phase, zero-crossings, local extrema (local minima or maxima), and combinations of the foregoing. Vibration features may be extracted e.g., by: 1) comparators [analog or digital], implemented in electronic circuit(s), Field Programmable Gate Array(s) (FPGAs), microcontroller(s), digital signal processor(s) [DSPs], computer hardware/software, or combination of the foregoing; 2) signal analysis methods such as (but not limited to) Fourier analysis, wavelet analysis, etc., via microcontrollers, DSPs, computer hardware/software or combinations of the foregoing suitable for signal analysis; or 3) combinations of the foregoing. In various embodiments, Fourier analysis is utilized for vibration feature extraction. Fast Fourier Transforms (FFTs) are computed repeatedly on continuously updated vibration quantifier(s) measurement(s) as provided by an accelerometer (or other transducer). Each FFT reveals amplitude of the dominant sinusoidal component for complex (deterministic or random) waveforms over the frequency range of interest. In addition to the amplitude of each sinusoidal component, the FFT also provide phase angle information (i.e., baseline delay) associated with each sinusoidal component. The total delay (either in terms of time or phase angle) for the dominant sinusoidal component may be increased by adding to the baseline phase. Since the FFT reveals the vibration's dominant frequency, the duration of “on” pulses can be controlled in terms of duty cycle (i.e., the fraction or percentage of SIM drive signal cycle period, 1/F sds ) or directly as a time duration. In various embodiments, observer VFI is determined from VFI that include: i) previously determined VFI (VFI extracted from previously determined VQI; ii) currently determined VFI (VFI extracted from currently determined VQI); and iii) combinations of the foregoing. Previously determined VFI may be available in various forms including but not limited to: a) printed hardcopy; b) stored on computer or electronic medium; c) personal knowledge of the observer or a third party; or d) combinations of the foregoing. In various embodiments, VFI for the viewed object (when the viewed object is experiencing vibration) may be determined in the same manner as described earlier in this paragraph for observer VFI.

In various embodiments, information is determined for one or more SDS parameters from observer VFI (or observer VFI and viewed object VFI). SDS parameters include: frequency; duty cycle; SIM synchronizing parameter; “on” time duration; SIM onset trigger mechanism; SIM shutoff trigger mechanism; “on” pulse time duration; SIM temporal delay; and combinations of the foregoing. In various embodiments, determination of SDS parameter information (SPI) comprises: a) strobe synchronization processing of VFI with apparatus including electronic circuits, microcontrollers, DSPs, computer hardware/software, and combination of the foregoing; b) manual entry of SPI by the observer (or a third party); c) utilization of previously determined SPI, and d) combinations of the foregoing. Enabling manual entry (prior to vibration, during vibration, or both) of SPI by the observer (or a third party) allows for the perceived image quality to be optimized as desired. Manual entry apparatus may include but are not limited to: manual controls, voice controls, and combinations of the foregoing. Computer hardware/software may be utilized to analyze VFI in order to determine SDS parameter(s) as desired. In various embodiments, when the viewed object is also experiencing vibration, strobe synchronization processing uses a combination of observer VFI and viewed object VFI. SPI is used in the generation of an SDS by a strobe signal generator. In various embodiments, SPI may include: i) previously determined SPI (using previously determined VFI); ii) currently determined SPI (using currently determined VFI); and iii) combinations of the foregoing. Previously determined SPI may be available in various forms including but not limited to: a) printed hardcopy; b) stored on computer or electronic medium; c) personal knowledge of the observer or a third party; or d) combinations of the foregoing. In various embodiments, computer hardware/software may be utilized to coordinate the various types of SPI (e.g., previously determined SPI that would need to be retrieved from storage [computer media, electronic media], SPI determined from VFI, SPI entered by the observer [or third party]).

In various embodiments, real-time measurement(s) of one or more observer vibration quantifier(s) is (are) taken by transducer(s) at a location (or locations) include, but are not limited to: the observer's head; at or near the observer's eye(s); other location(s) on the observer's person, a structure supporting the observer (e.g., a chair on which the observer is sitting or structure on which the observer is standing); and combinations of the foregoing. In various embodiments, real-time measurement(s) of one or more viewed object vibration quantifier(s) is (are) taken by transducer(s) at or near the viewed object location. In various embodiments, vibration (observer, viewed object) quantifier(s) include amplitude, velocity, displacement, and combinations of the foregoing, is measured in up to six spatial (three rectilinear and three rotational) degrees-of-freedom. In various' embodiments, real-time EMG measurement(s) is (are) taken by transducer(s) at locations on the observer's head, neck, or torso. In various embodiments, real-time EOG measurement(s) is (are) taken.

In various embodiments, the observer vibration is deterministic and characterized by a single sinusoid with frequency, F ovs , wherein observer vibration frequency F ov =F ovs . In various embodiments, the observer vibration is deterministic and characterized by a composite of multiple sinusoids, wherein F ov is set equal to the frequency, F ovd , of the dominant sinusoidal component (e.g., sinusoidal component with the largest amplitude), in the frequency range of interest. In various embodiments, F ov is a vibration feature extracted from the observer vibration quantifier information.

In various embodiments, the viewed object vibration is deterministic, and characterized by a single sinusoid with frequency, F objvs , wherein the viewed object vibration frequency F objv =F objvs . In various embodiments, the viewed object vibration is deterministic and characterized by a composite of multiple sinusoids, wherein F objv is set equal to the frequency, F objvd , of the dominant sinusoidal component (e.g., sinusoidal component with the largest amplitude), in the frequency range of interest. In various embodiments, F objv is a vibration feature extracted from the viewed object vibration quantifier information.

In various embodiments, the observer vibration is deterministic and the SDS is characterized by SIM frequency F sds derived from F ov . In various embodiments, F sds is set equal to F ov . In various embodiments, F sds is determined by setting F sds =F ov /n, where n is an integer factor (divisor) of F ov . In various embodiments, where F ov =F ovd , then F sds is set to a frequency within ±X Hz of F ov , with X typically less than 3 Hz. Where the observer vibration is deterministic and F ov =F ovd , then setting F sds to be a frequency within ±X Hz of F ov may not “freeze” the image (as would be the case if F sds =F ov =F ovs ), but would result in the viewed object's visual image perceived by the observer to “drift” slowly enough such that the image can be visually tracked, thereby still reducing blur of the visual image perceived by the observer. In various embodiments, one or more parameters including F sds , integer factor n, and X are under the control of the observer (or a third party) who can adjust the parameter(s) to optimize the perceived image quality of the viewed object as desired.

In various embodiments, F sds is determined by setting F sds to the greatest (or other) common factor of F ov and F objv . For example, if F ov is 12 Hz and F objv is 16 Hz, then F sds would be set to 4 Hz. Where there is no exact common integer factor of F ov and F objv , F sds is set to a frequency such as F ov , F objv , and a frequency within ±X Hz of either F ov or F objv . The range ±X provides a frequency range that results in acceptably slow “drift” of the viewed object's image providing reduced blur of the visual image perceived by the observer. The value of X may be specified ahead of time (prior to vibration onset) or manually controlled by the observer (such as during vibration to allow finer tuning). In various embodiments, X is less than 3 Hz. In various embodiments, one or more parameters including F sds , greatest (or other) common factor of F ov and F objv , and X, are under the control of the observer (or a third party) who can adjust the parameter(s) to optimize the perceived image quality of the viewed object as desired.

In various embodiments where the SDS is characterized by SDS frequency F sds , SDS is further characterized by a parameter including such as: a) SIM duty cycle DC sim ; b) SIM synchronizing parameter SP sim ; c) SIM “on” time duration T on ; d) SIM temporal delay TD sim ; and e) combinations of the foregoing. In various embodiments, the observer (or a third party) may adjust one or more SDS parameter(s) to optimize the perceived image quality of the viewed object as desired, wherein the SDS parameter includes F sds , DC sim , SP sim , T on , TD sim , and combinations of the foregoing.

In various embodiments where the SDS is characterized by SDS frequency, F sds , SIM duty cycle DC sim is the percentage of time (e.g., 35% of an SDS cycle) during each period of the SDS cycle (period=1/F sds ) that the SIM device is “on”, i.e., when a SIM illuminator is providing light, a SIM light shutter or SIM object shutter is open, or a display is displaying a visual image according to a SIM display control system. Since the duty cycle affects the perceived brightness of the visual image (thereby also affecting legibility), in various embodiments, the observer (or a third party) can manually vary DC sim (or increase the brightness for embodiments where the SIM device is a SIM illuminator or a SIM display). In various embodiments, DC sim is pre-set to a specific value before onset of vibration. In various embodiments, DC sim is specified by the observer (or a third party) either prior to onset of vibration or during vibration. In various embodiments, a specific duration of time, T on , is specified (e.g., 40 milliseconds) that the SIM device is “on” during each SDS cycle. The duty cycle DC sim may be calculated as DC sim =T on *F sds .

In various embodiments the SDS is characterized by SDS frequency, F sds . In various embodiments where the SIM device comprises a SIM illuminator, the SIM illuminator can be increased in brightness to compensate for the reduced average luminance resulting from the period of time during an SDS cycle when the SIM device is not providing light. In various embodiments where the SIM device comprises a SIM light shutter, the non-SIM illuminator may be increased in brightness to compensate for the reduced average luminance resulting from the period of time during an SDS cycle when the SIM light shutter is blocking light from the non-SIM illuminator. In various embodiments where the SIM device comprises a SIM object shutter and the viewed object comprises a display, the display's image may be increased in brightness to compensate for the reduced average luminance resulting from the period of time during an SDS cycle when the SIM object shutter is blocking viewing of the display. In various embodiments where the SIM device comprises a SIM display, the display's image may be increased in brightness to compensate for the reduced average luminance resulting from the period of time during an SDS cycle when the display is not displaying an image.

SIM synchronizing parameter SP sim comprises how the start of the SIM control system's “on” pulse is synchronized with the observer vibration. In various embodiments, SP sim comprises a temporal delay TD sim (time interval between onset of an observer vibration pulse and the SIM control system's “on” pulse). For deterministic observer vibration, TD sim can be represented by a phase angle difference between the observer vibration and the SIM device (driven according to the SDS). TD sim may be set or measured (as desired) relative to the start, middle, or end of the SIM's “on” pulse. In various embodiments, TD sim is set (manually or automatically) prior to onset of observer vibration, during observer vibration, or both.

In various embodiments, the SIM control system operates a SIM device with a SIM onset trigger mechanism, OTM sim , that initiates an individual SDS “on” pulse. In various embodiments, the OTM sim includes: a) the absolute value or root mean square (rms) of the amplitude of an observer vibration quantifier being greater than a specified threshold, wherein the quantifier includes: a) acceleration, velocity, displacement, EMG, EOG, and combinations of the foregoing; b) occurrence of zero-crossing(s) in an observer vibration quantifier (as determined, for example, by a threshold crossing carried out by a digital algorithm or comparator threshold crossing by an analog circuit), wherein the quantifier includes displacement, velocity, acceleration, EOG, EMG, and combinations of the foregoing; c) occurrence of local extrema (local minima or maxima) in an observer vibration quantifier as determined, for example, by sign changes in the first derivative with respect to time of the quantifier, wherein the quantifier is includes displacement, velocity, acceleration, EOG, EMG, and combinations of the foregoing; and d) combinations of the foregoing. In various embodiments, OTM sim further comprises a lockout mechanism to prevent spurious re-triggering of SIM device initiation during an SDS period due to noisy measurements (of observer vibration quantifiers). In various embodiments, the lockout mechanism comprises a low-pass filter. In further embodiments, the lockout mechanism comprises a non-retriggerable flip-flop logic element that prevents the OTM sim from reset for a fixed-time duration (such as during an SDS “on” pulse period). In various embodiments, OTM sim is under the control of the observer (or a third party) who can adjust the OTM sim to optimize the perceived image quality of the viewed object as desired.

In various embodiments, the SIM is operated with a SIM shutoff trigger mechanism STM sim , wherein STM sim comprises the trigger mechanism that terminates an individual SIM “on” pulse. In various embodiments, the STM sim comprises the absolute value or root mean square (rms) of the amplitude of an observer vibration quantifier being less than a specified threshold, wherein the quantifier includes: acceleration, velocity, displacement, EOG, EMG, and combinations of the foregoing. In various embodiments, an “on” pulse time duration T p is specified. In various embodiments, T p is determined by an action including: a) assignment of a value of T p that is known empirically to reduce visual image blur for the observer vibration (expected or actual); b) calculation of the maximum rate of change of an observer vibration quantifier (including displacement, velocity, acceleration, EOG, EMG, and combinations of the foregoing), which, when divided by a specified amount of change of said vibration quantifier, yields a value of T p ; and c) combinations of the foregoing. In various embodiments, STM sim (and/or T p ) is under the control of the observer (or a third party) who can adjust the STM sim (and/or T p ) to optimize the perceived image quality of the viewed object as desired.

In various embodiments, the SIM control system (through appropriate computer hardware/software, electronic components, or combination of the foregoing) controls the SDS signal in order to operate a SIM device in various “enabled” operating modes (ENAB sim ) include: a) constant firing mode (SDS characterized by F sds ); b) episodic firing mode; and c) automatic mode (ability to switch between constant firing and episodic firing modes). In various embodiments, in the SIM device “disabled” mode, the SIM device is not operating in an “enabled” mode (i.e., no stroboscopic image modulation). In various embodiments, a SIM device in disabled mode including: a) a SIM illuminator that is always on or always off; b) a SIM light shutter that is always open (allowing light from a non-SIM illuminator to reach the viewed object); c) a SIM object shutter that is always open (allowing the observer to view the viewed object); and d) a SIM display where the SIM control system does not stroboscopically modulate the display image. In various embodiments, the observer (or a third party) can switch between the enabled and disabled modes as desired.

In the constant firing mode (SDS characterized by F sds for deterministic, periodic observer vibration), the SIM device operates in a continuous alternating on/off temporal pattern until the SIM is switched to the SIM disabled mode by action including: manual operation; by timer; STM sim threshold reached; and combinations of the foregoing. In various embodiments, the constant firing mode is initiated by action including: manual operation; by timer; OTM sim ; and combinations of the foregoing.

In the episodic firing mode, SDS “on” pulses are generated according to OTM sim and STM sim (or T p ) thresholds being met based on features from measured observer vibration information. In various embodiments, the episodic firing mode is initiated by action including: manual operation; by timer; and combinations of the foregoing. In the episodic firing mode, the general assumption is that the observer vibration is random. However, operation of a SIM in the episodic firing mode with a deterministic observer vibration would result in similar behavior as in the constant firing mode (albeit the SIM constantly needing to measure observer vibration, and perform signal analysis to derive appropriate “on” pulse information). The episodic firing mode is terminated (switched to SIM disabled mode) by action including: manual operation, by timer, automatic operation based on detection of observer vibration below a threshold, and combinations of the foregoing.

In the automatic firing mode, the SIM device begins operation in either the constant firing or episodic firing mode. Computations based on the observer vibration may be used to automatically switch the SIM device operating mode. For example, with the SIM device initially operating in constant firing mode (deterministic observer vibration), if it is detected that the observer vibration is random rather than deterministic (e.g., initial assumption of deterministic vibration is in error, or vibration behavior changes) then the SIM control system automatically switches the SIM device to episodic firing mode. Similarly, with the SIM device initially operating in episodic firing mode, if it detected that the observer vibration is deterministic then the SIM control system automatically switches the SIM device to constant firing mode. Automatic switching between SIM device operating modes may be implemented via the SIM control system changing the SDS signal (changing the SPI provided to the strobe signal generator depending on the observer vibration exhibiting random or deterministic behavior). The automatic firing mode is terminated (switched to SIM device disabled mode) by action including: manual operation, by timer, automatic operation based on detection of observer vibration below a threshold, and combinations of the foregoing.

In various embodiments, observer vibration is experienced by a person in space flight (including but not limited to launch or entry, planetary/lunar orbit departure). In various embodiments, observer vibration is one experienced by a person onboard an aircraft (military or commercial, including but not limited to fixed-wing and rotorcraft). In various embodiments, the observer vibration is one experienced by a person in a land vehicle (including but not limited to off-road vehicles, or vehicles moving at high speed such as emergency vehicles or racing vehicles). In various embodiments, observer vibration is experienced by a person onboard a water-borne vehicle, particularly those experiencing high vibration due to high speed, (including but not limited to amphibious landing craft). In various embodiments, observer vibration is experienced by a person on military, industrial or agricultural machinery. In various embodiments, observer vibration is experienced by a person utilizing handheld/portable computing and/or communication devices (e.g., smartphones, laptops/netbooks, iPads and other tablets, e-book readers).

In various embodiments, the SIM control system is a stand-alone apparatus (separate from the illuminator(s); shutter(s), display(s) it is controlling). In various embodiments, the SIM control system is incorporated into the device (“SIM device”) it is controlling (e.g., illuminator(s), shutter(s), display(s)). The SIM control system comprises a system of one or more components including mechanical, electric, electronic, electro-mechanical, software components, and combinations of the foregoing configured to direct a SIM device (illuminator(s), shutter(s), display(s), combinations of the foregoing) to operate in an alternating on/off temporal pattern according to the SDS. In various embodiments, the SIM control system incorporates the strobe signal generator that generates the SIM drive signal using SDS parameter information (SPI). In various embodiments, the SIM control system incorporates the transducer(s) that measure(s) vibration quantifier information (VQI). In various embodiments, the transducer(s) is (are) separate from the SIM control system. In various embodiments, the SIM control system incorporates the apparatus (hardware, software, combination of the foregoing) for extracting vibration feature information (VFI) from the vibration (observer, observer and viewed object). In various embodiments the VFI extraction apparatus is separate from the SIM control system. In various embodiments, the SIM control system incorporates the strobe synchronization processing (SSP) apparatus (hardware, software, combination of the foregoing) that determines SPI from VFI. In various embodiments the strobe synchronization processing apparatus is separate from the SIM control system. In various embodiments, the SIM control system incorporates storage media (including computer medium, electronic medium, printed hardcopy, and combinations of the foregoing), to store SPI, VFI, VQI, and combinations of the foregoing. In various embodiments where the SIM control system is not incorporated with the SIM device it is controlling, the SIM control system incorporates the appropriate interface apparatus (hardware, software, combinations of the foregoing) for communication of the SDS between the SIM control system and the SIM device. In various embodiments, the SDS is transmitted from the SIM control system to the SIM device by a wired connection. In various embodiments, the SDS is transmitted from the SIM control system to the SIM device by a wireless connection.

In various embodiments, the viewed object is a display, and a SIM illuminator (SIM il ) provides light to a surface of the display. In various embodiments, where the SIM il provides light to the front of the display, the display including: mechanical displays (including but not limited to mechanical gauges/dials); printed text/graphics displays (including but not limited to panel labels, control markings or labels); electromechanical displays (including but not limited to electromechanical gauges/dials); electronic paper displays; and combinations of the foregoing. In various embodiments, the SIM il is an apparatus separate from the display. In various embodiments, the SIM il is incorporated into the display.

In various embodiments, the viewed object is a display, and a SIM illuminator provides light to a surface of the display. In various embodiments, where the SIM il provides light to the back of the display, the display including: mechanical gauges/dials; LCD displays; and combinations of the foregoing. In various embodiments, the SIM il is an apparatus separate from the display. In various embodiments, the SIM il is incorporated into the display.

In various embodiments, the SIM device comprises a SIM object shutter (SIM os ) interposed between the observer and the object being viewed by the observer. In various embodiments, the SIM os including mechanical shutters, chemical shutters (e.g., photochromic), electro-optical shutters (e.g., electrochromic), liquid crystal display (LCD) based shutters, mirror-based shutters, polarizers, and combinations of the foregoing. In various embodiments, the SIM os is an apparatus separate from the viewed object. In various embodiments, the SIM os is incorporated into the viewed object. In various embodiments, the SIM os is incorporated into apparatus (including but not limited to goggles, spectacles, headset) worn by the observer. In various embodiments, the SIM comprises a SIM display shutter (SIM os ) and the viewed object comprises a display including, for example: electromechanical displays; electronic displays (including but not limited to LCD displays, LED displays [including OLED displays], plasma displays, CRT displays, electroluminescent displays, electronic paper displays); and combinations of the foregoing.

In various embodiments, the SIM device comprises a SIM light shutter (SIM ls ) interposed between the object being viewed and a non-SIM illuminator (one that is not operating in a SIM manner, i.e., constantly “on”) illuminating the viewed object. In various embodiments, the SIM ls including mechanical shutters, chemical shutters (e.g., photochromic), electro-optical shutters (e.g., electrochromic), liquid crystal display (LCD) based shutters, mirror-based shutters, polarizers, and combinations of the foregoing. In various embodiments, the viewed object comprises a display, and said non-SIM illuminator provides light to a surface of said display. In various embodiments wherein the non-SIM illuminator is providing light to the front of the display, the display including displays such as: mechanical displays (including but not limited to mechanical gauges/dials); printed text/graphics displays (including but not limited to panel labels, control markings or labels); electromechanical displays (including but not limited to electromechanical gauges/dials); electronic paper displays; and combinations of the foregoing. In various embodiments where the non-SIM illuminator is providing light to the back of the display, the display including displays such as: mechanical gauges/dials; LCD displays; and combinations of the foregoing. In various embodiments, the SIM ls is an apparatus separate from the non-SIM illuminator. In various embodiments, the SIM light shutter is incorporated into the non-SIM illuminator. In various embodiments, the SIM ls is incorporated into apparatus (including but not limited to goggles, spectacles or a headset) worn by the observer.

In various embodiments, the viewed object comprises a display (SIM disp ) controlled by a SIM control system. The display includes: electromechanical displays; electronic displays (including but not limited to LCD displays, LED displays [including OLED displays], plasma displays, CRT displays, electroluminescent displays, electronic paper displays); and combinations of the foregoing. In various embodiments, the SIM control system stroboscopically modulates only a portion of the display (i.e., only selected parts of the display are redrawn) during an SDS “on/off” pulse. In various embodiments, the entire display is stroboscopically modulated during an SDS “on/off” pulse. In various embodiments, the SIM control system is separate from the SIM disp . In various embodiments, the SIM control system is incorporated into the SIM disp .

In various embodiments, the light (visible spectrum) from the SIM illuminator includes: a) laser light; b) non-laser light); c) polarized light; d) non-polarized light; and e) lens-focused light.

In various embodiments, one or more SIM devices (illuminator, shutter, or combinations of the foregoing) are incorporated into displays. In various embodiments, one or more SIM devices (illuminator to illuminate an object being viewed, shutter, or combinations of the foregoing) are incorporated into gear (e.g., spectacles, goggles, headset), worn by the observer. In various embodiments, one or more SIM devices (illuminator, shutter, or combinations of the foregoing), are incorporated into head-mounted displays (HMDs).

Various aspects of exemplary SIM control system embodiments are described hereunder with reference to FIG. 1A . Referring to FIG. 1A , an internal controller clock (in some embodiments, under the high-level control of the observer 1 ) provides a timing signal 5 which is used by strobe signal generator 15 for generating a SIM drive signal (SDS). Use of a timing signal 5 would be for embodiments where SDS parameter(s) (e.g., F ov ) are already known and not determined from real-time measurements of vibration quantifiers. In various embodiments where a timing signal is used, the SDS parameter(s) may be known from previous experience, determined from estimation algorithms for the vibration environments expected to be experienced by the observer, or combinations of the foregoing.

Various aspects of exemplary SIM control system embodiments are described hereunder with reference to FIG. 1B . Referring to FIG. 1B , various embodiments are illustrated where the observer vibration 2 is deterministic and the SDS is derived from real-time measurements of one or more observer vibration quantifier(s). In various embodiments, transducers are used for measurement of observer vibration quantifier(s). One or more vibration features are extracted 8 [e.g., by: 1) analog or digital comparators implemented in electronic circuit(s), FPGAs, microcontroller(s), DSPs, computer hardware/software, or combination of the foregoing; 2) signal analysis methods such as (but not limited to) Fourier analysis, wavelet analysis, etc., implemented via microcontrollers, DSPs, or computer hardware/software; or 3) combinations of the foregoing] from the measured vibration quantifier information. Such vibration feature(s) may include but are not limited to vibration frequency, amplitude, phase, zero-crossings, and local extrema (local minima or maxima). Extracted vibration feature(s) provide(s) information for one or more SDS parameters to be determined through strobe synchronization processing 12 (e.g., by electronic circuits, microcontrollers, DSPs, computer hardware/software, or combination of the foregoing). Using the SPI, strobe signal generator 15 generates a SIM drive signal.

Various aspects of exemplary SIM control system embodiments are described hereunder with reference to FIG. 1C . Referring to FIG. 1C , various embodiments are illustrated where the observer vibration 2 comprises a random vibration and the SDS is derived from real-time measurements of observer vibration quantifier(s). In various embodiments, transducers are used for measurement of observer vibration quantifiers. One or more vibration features are extracted 8 [e.g., by: 1) analog or digital comparators implemented in electronic circuit(s), FPGAs, microcontroller(s), DSPs, computer hardware/software, or combination of the foregoing); 2) signal analysis methods such as (but not limited to) Fourier analysis, wavelet analysis, etc., implemented via microcontrollers, DSPs, or computer hardware/software; or 3) combinations of the foregoing] from the measured vibration quantifier information. Such vibration feature(s) may include but are not limited to vibration frequency, amplitude, phase, zero-crossings, and local extrema (local minima or maxima). Extracted vibration feature(s) enable one or more SDS parameters to be determined through strobe synchronization processing 12 (e.g., by electronic circuits, microcontrollers, DSP, computer hardware/software, or combination of the foregoing) of vibration feature information. Using the SPI, strobe signal generator 15 generates a SIM drive signal.

Referring to FIG. 1D , various exemplary embodiments are illustrated with respect to vibration feature(s) extraction. In various embodiments, a measured vibration signal (“vibration quantifier info”) from an accelerometer (not shown) is provided to comparator 9 . The comparator 9 issues a transition (low-to-high, or vice versa) whenever the measured vibration signal crosses a pre-set threshold (e.g., zero acceleration). In various embodiments, the comparator 9 (such as a 323 high-speed analog comparator IC) indicates a zero-crossing (or other amplitude crossing) of the analog accelerometer output signal. In various embodiments, the comparator 9 (comprising a digital comparator) indicates a zero-crossing (or other amplitude crossing) of the accelerometer output signal that has been converted from analog to digital. Exemplary digital comparators may be (but not limited to): a software programmable filter on FPGA, microcontroller, DSP, or software code on a computer.

Referring to FIG. 1D , various exemplary embodiments are illustrated with respect to vibration feature extraction. In various embodiments, the signal (“vibration quantifier info”) provided to comparator 9 is the first derivative with respect to time (“first derivative signal”) of the accelerometer output signal. The first derivative signal may be provided by (but not limited to) an analog amplifier differentiation circuit. The first derivative signal may be implemented via (but not limited to) digital filtering of analog-to-digital converted accelerometer output signal. Implementations of the digital filter may include (but not limited to): a) a multi-tap digital circuit; b) a software programmable filter on FPGA, microcontroller, or DSP, or c) software code on a computer. In various embodiments, comparator 9 issues a transition (low-to-high, or vice versa) whenever the first derivative signal crosses zero level. The zero-crossings of the first derivative signal detected by comparator 9 correspond to extrema of the accelerometer output signal. In various embodiments, comparator 9 may be (but not limited to) implemented as an analog comparator circuit. In various embodiments, comparator 9 may be (but not limited to) implemented as a digital comparator acting on a first derivative signal (as provided by (for example): a) output from an analog amplifier differentiation circuit which is then converted from analog to digital, and b) output from digital filtering of analog-to-digital converted accelerometer output signal. Implementations of the digital comparator 9 may include (but not limited to) a software programmable filter on FPGA, microcontroller, or DSP, or software code on a computer.

Referring to FIG. 1D , various exemplary embodiments are illustrated with respect to strobe synchronization processing. In various embodiments, strobe synchronization processing 12 receives high-to-low or low-to-high pulse transition (i.e., step) (digital or analog). Phase shift adjustment 11 may be implemented in a variety of ways, wherein a few exemplary embodiments are herewith disclosed. In various embodiments, the transition (low-to-high or high-to-low) on each cycle of the analog signal pulse can be used to produce a time-delayed pulse using a timer integrated circuit (e.g., a 555, or one-half of a 556 IC) set up in monostable mode. In various embodiments, the amount of time delay is tuned manually by a variable resistor and/or capacitor. In various embodiments, the amount of time delay is obtained with integrated logic circuits (e.g., a 74LS122 IC). In various embodiments, the time delay function is carried out via a programmable delay on an FPGA, microcontroller, DSP, or software code on a computer. In various embodiments, time delay is manipulated up or down in digital implementations via toggle switches. Duty-cycle adjustment 13 may be implemented in a variety of ways, wherein a few exemplary embodiments are herewith disclosed. In various embodiments, the time-delayed pulse from phase shift adjustment 11 drives a second monostable timer integrated circuit (e.g., 555, one-half of 556) that could lengthen or shorten the “on” portion of each cycle. In various embodiments, the “on” duration is set for a fixed “on” time or for a duty cycle percentage of each cycle time (e.g., 74LS123). In various embodiments, duty-cycle adjustment is carried out via a programmable delay on an FPGA, microcontroller, DSP, or software code on a computer. In various embodiments, time delay is manipulated up or down in digital implementations via toggle switches.

Various aspects of the SIM drive signal and observer vibration are described hereunder with reference to FIGS. 2A-2E . Referring to FIG. 2A , the observer vibration is one in which a dominant primary frequency may be determined. Although the peak amplitudes are shown in the figure as unchanging, it is to be understood that over time the individual cycle amplitudes may increase, decrease, or remain constant. Referring to FIG. 2B , the SIM drive signal constitutes a pulsed signal with two-state logic (on/off), having a duty cycle (amount of time that the signal is on relative to the total cycle period), periodicity, and phase angle (advance/delay) of the SIM drive signal with respect to the observer vibration. In various embodiments, the SIM is not activated unless the absolute value or root mean square (rms) of the amplitude of an observer vibration quantifier is greater than a threshold, the quantifier includes items such as: acceleration, velocity, displacement, and combinations of the foregoing. Referring to FIG. 2C , the observer vibration frequency comprises a complex waveform. In various embodiments, signal processing of the complex (deterministic or random) waveform is used to create the SIM drive signal. Referring to FIG. 2D , a SIM drive signal is characterized by a waveform where the trigger timing of the “on” pulses varies. Referring to FIG. 2E , a SIM drive signal is characterized by a waveform where the time duration of the “on” pulse varies. In various embodiments, the SIM drive signal is characterized by one or more parameters including: a) periodicity (based on frequency derived from the observer vibration); b) variable “on” pulse trigger timing; c) variable “on” pulse time duration, T p ; d) periodicity and variable “on” pulse time duration; and e) variable “on” pulse triggering and variable “on” pulse time duration. In various embodiments, the observer vibration is random, and the SIM drive signal is characterized by one or more parameters including: a) variable “on” pulse trigger timing; b) variable “on” pulse time duration T p ; and c) variable “on” pulse triggering and variable “on” pulse time duration.

Various SIM device embodiments are described hereunder with reference to FIG. 3 . SIM control system 20 sends a SIM drive signal (SDS) to operate one or more SIM illuminator(s) 25 (shown as a separate apparatus from SIM control system 20 ) in an alternating on/off temporal pattern according to the SDS. In various embodiments, where SIM control system 20 is incorporated into SIM illuminator 25 , SIM control system 20 also can control brightness and/or wavelength. Display 30 may receive light from SIM illuminator(s) 25 from the front, back, or combinations of the foregoing.

Various SIM device embodiments are described hereunder with reference to FIG. 4 . In various embodiments, SIM control system 20 sends a SIM drive signal to operate one or more SIM display(s) 30 (shown as a separate apparatus from SIM control system 20 ) in an alternating on/off temporal pattern according to the SDS. In various embodiments, where SIM control system 20 is incorporated into SIM display 30 , SIM control system 20 can also control brightness and/or color of the image displayed.

Various SIM embodiments are described hereunder with reference to FIG. 5 . In various embodiments, SIM control system 20 sends a SIM drive signal (SDS) to operate one or more SIM shutter devices in an alternating on/off temporal pattern according to the SDS. In various embodiments, SIM shutter control system 20 sends a SIM drive signal to one or more SIM display shutter(s) 55 interposed between display 30 (receiving light from non-SIM illuminator 65 ) and the observer 3 . In various embodiments, SIM control system 20 sends a SDS drive signal to one or more SIM light shutter(s) 60 interposed between display 30 and non-SIM illuminator 50 . In various embodiments, display 30 may receive light from one or more non-SIM illuminator(s) from the front, back, or combinations of the foregoing. As explained above, in various embodiments, observer VFI 70 is determined from VFI that include: i) previously determined VFI (VFI extracted from previously determined VQI; ii) currently determined VFI (VFI extracted from currently determined VQI); and iii) combinations of the foregoing. Previously determined VFI may be available in various forms including but not limited to: a) printed hardcopy; b) stored on computer or electronic medium; c) personal knowledge of the observer or a third party; or d) combinations of the foregoing. In various embodiments, VFI for the viewed object 30 (when the viewed object is experiencing vibration) may be determined in the same manner as described earlier in this paragraph for observer VFI.

With an observer 3 seated in a vibrating chair, the efficacy of stroboscopically image modulating the observer's visual image of a display can be determined. The display is a flat-panel 15-inch-diagonal LCD (1600×1200 pixels, 0.19 mm per pixel resolution) with single edge-mounted LED backlight and full screen diffuser. The display is positioned approximately 51 cm from the observer's eyes, subtending approximately 33 by 25 degree (vertical-by-horizontal) field of view. Strobe circuitry switches the backlight between its full-luminance “on” and completely “off” states according to the duty cycle and phase settings specified. With the backlight in the “on” state, the display has a maximum brightness of 140 cd/m 2 . The strobe circuitry receives synchronizing trigger inputs from an accelerometer mounted on the vibrating chair. The display is not vibrated, while the observer is. The observer views a display image comprising a six-by-six array of white-frame boxes interconnected by a variety of paths. Each box contains three rows of three digit numbers (10-point font size). One of the boxes is highlighted at random, and the observer is asked to respond “yes” if the digits in the middle row digits of the highlighted box formed a monotonically increasing or decreasing sequence and “no” if it did not. The response accuracy and the reaction time (from the appearance of each new number array) is recorded. A 12-Hz vibration in the x-axis (sternum-to-spine) at a constant 0.7 g amplitude (zero-to-peak), which produces observer head “surge” translation as well as “pitch” rotation, is used. Measurements are taken for conditions of vibration/no-vibration, and strobed/constantly “on” (no strobe) display backlight conditions. The constantly “on” display backlight condition is achieved by strobing the backlight at 100-Hz (a frequency above human detection thresholds for display flicker). Strobe duty cycles (percentage of time that the backlight is illuminated during each vibration cycle) of 5% and 25% are used. Phase angles of 0, 45, 90 and 135 degrees are used. Phase angle is defined as the time from positive-going zero-crossing of the vibration waveform until the center of the strobe's “on” pulse, expressed as a portion of the full 360 degrees of a single vibration cycle. In data collected from 11 observers, error rates for the non-strobed condition increased more than fourfold from 3.5% under no vibration to 16.4% under the 12 Hz vibration. In the non-strobed condition, average response times increased under vibration by 325 ms (from 1.833 seconds under no vibration to 2.159 seconds under vibration). In the non-strobed condition, changing the backlight brightness from 40.5 cd/m 2 to 9 cd/m 2 slowed response time by 133 ms independent of vibration level. For the non-vibrating condition, strobing the display slowed response time by 103 ms. In the non-vibrating condition, response time was slowed by an additional 83 ms when the display's equivalent luminance was dimmed from 40.5 cd/m 2 to 9 cd/m 2 . For the 12-Hz vibration condition, strobing reduced error rates to 6% for both duty-cycles and all four phase conditions, a level that was statistically indistinguishable from the non-vibrating non-strobed condition. For the 12-Hz vibration condition, response time was 240 ms faster under strobing than for the non-strobed condition. Compared to the non-vibrating non-strobed baseline, strobing (under 12-Hz vibration) slowed response time by 190 ms.