FAQ


How does Aurora's sleep staging algorithm work and how accurate is it?

Aurora is able to classify human sleep stages by analyzing EEG, EOG, and movement measured by the device during sleep. Aurora's embedded algorithm achieves near real-time classification by analyzing a 2-second window of time. Before feeding into Aurora's classification algorithm (described below), data is first checked for muscle-artifacts (head jerks and overt body movement). If the data is clean enough, it is decomposed into an array of custom descriptors including time and frequency-based features. The feature arrays are then normalized and fed into the classification algorithm. (Aurora's feature set has been developed over years to maximize accuracy while minimizing battery drain.)

Feedfoward Neural Network

Aurora's classification algorithm includes a shallow feedforward artificial neural network (ANN) architecture. The net was designed in MATLAB. Performance surface evalutions were utilized to choose the optmial training update rule, hidden network size and training parameters.

Training

The initial algorithm was trained with the help of a professional sleep clinic using a library of 100+ sessions collected from over 40 subjects wearing medical-grade PSG equipment in tandem with the Aurora. The Levenbergue-Marquadt gradient descent update rule was employed to train Aurora's initial ANN. Training/test/validation data segemntation is 70/15/15 respectively.

Accuracy

Training performance on the 4-way classification (wake, light, deep, REM) surpassed 90% on the user-submitted database, with cross-validated test data trailing by just a few % points.


How do I download RAW data collected by Aurora?

First you need to make sure the data streams you are interested in collecting are configured for file output. Aurora Desktop provides an easy way to do this in its profile section's "Advanced Options". The default profile already has some of the most popular data streams configured for file output, so this step is only necessary if you want to modify the streams that are saved to files or had previously disabled file output.

With file output enabled, the next time a new session is started stream data will be saved to the SD card. When a sync is performed with Aurora Desktop, any stream data saved to the SD card will be synced with your session. However, when syncing with Aurora Mobile, only basic sleep data is synced since bluetooth data transfer of such a large amount of data would take too long. You can still sync with Aurora Desktop at a later time to sync the raw stream data as long as you haven't reformatted your SD card or upgraded your firmware (which erases the SD card). Once a session has been synced with Aurora Desktop, downloading the session within the app will include any synced stream data in the archive.

As an alternative to syncing with Aurora Desktop, you can manually pull your data off using Storage Mode. It should be noted that in this case, it might be more convenient to save stream data as CSV files instead of raw binary (Aurora Desktop performs this conversion step for you automatically). See Stream Outputs for more information.


Help! Aurora no longer turns on!

If Aurora is no longer turning on (and you've tried a hardware reset), it's possible the battery has been fully discharged. When this happens, it can take longer than usual for Aurora to reach a usable charge level. If the unit still doesn't turn on after charging for 4-5 hours there is a chance your USB cable is not making a good connection with the Aurora USB connector, preventing your battery from charging properly. Try an alternative cable if you have one handy. In rare circumstances the USB connector can become damaged if excessive force was applied when inserting/removing the cable. In these cases your Aurora will likely need to be replaced. Contact support for assistance.


Why are REM stimulations happening when I'm awake?

Aurora only presents REM stimulations when it thinks you are experiencing REM sleep, however differentiating between REM sleep and a meditative awake state can sometimes be tricky. For this reason, we recommend using the REM stim delay option to prevent REM stimulations for the first few hours. Furthermore, its quite common for the first REM stimulation to gently arouse you so that when the stimulation is repeated a short time later, you find yourself already awake. Quickly pressing the power button once when this happens will prevent REM stimulations for 5 minutes to allow you to fall back asleep.


I've turned on REM stimulations but they don't seem to be working. How can I tell?

The default REM light settings are set at half brightness. Depending on ambient light conditions, this may not be bright enough to come through in your dream or wake you up. One way to tell if REM stimulations are being triggered properly is to use Aurora Desktop to view your session timeline. REM stimulations are represented by a small "light bulb" icon. If there is a number underneath this icon it means there were several REM stimulations within a short period.


Why won't Aurora connect to Aurora Mobile?

Aurora Mobile requires a Bluetooth LE capable smart phone. You also need to make sure that Bluetooth is enabled on your phone. You might need to restart the app if bluetooth was previously not enabled. Then with the app open and bluetooth enabled, turn Aurora on. Aurora will advertise itself agressively for the first 2 minutes. If after two minutes your Aurora doesn't connect, something else could be going wrong. Use Aurora Desktop to check your BLE firmware version (under the top menu Aurora -> Firmware Info) and contact support for further assistance.


Why won't Aurora connect to Aurora Desktop?

If you are having difficulty connecting to Aurora Desktop over USB, first make sure your USB cable is making a good connection and is capable of transmitting data. Trying any other cables and/or USB ports on your computer can also help. Windows users (especially Windows 7) might require a driver installation if Aurora is showing up with an exclamation point within Device Manager or not showing up at all. Try installing this standard driver. For help installing an INF file, refer to the first section of this guide. If the connection to Aurora Desktop is finicky (i.e. moving the unit ever so slightly causes a disconnect/reconnect) your USB cable may not be making a good connection with Aurora. In this case, try swapping out the cable with another one.


Why is Aurora turning off in the middle of the night?

If you wake up in the morning and find Aurora off, this could be for one of two reasons. The first is that the Aurora battery level became so low that the system had to shut itself down. An automatic shutdown can also happen when Aurora loses an EEG signal for an extended period (2 hours). If you are positive the Aurora battery is fully charged and that the headband is making good contact with your forehead during the entire night, there is a chance your sensor band is not functioning properly.

To test if your sensor band is functioning properly, disconnect the Aurora from USB and close any running Aurora Mobile apps. Then while holding the unit in your hands without touching the sensors, power Aurora on. Pink LEDs should turn on after the Aurora boots up. Wait 10 seconds to make sure these LEDs remain on. Then touch and hold the two outside sensors with your fingers. The pink LEDs should go off within a few seconds. While continuing to touch the sensors, wait another 10 seconds to make sure the LEDs remain off. Alternate between touching and releasing the sensors to make sure the signal detection is functioning properly. If it is not, unsnap the headband from the plastic unit and repeat the above test, only instead of touching the sensors, place your fingers on the female snap sockets on the case. If signal detection works without the headband, your sensor headband is likely to blame and will need to be replaced. If both tests fail, it's possible your unit is defective and will need to be replaced. In both cases, please contact support for assistance.

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