Frequently Asked Questions

Popular questions about hardware and software, answered. Includes a general troubleshooting guide for common problems encountered during setup and testing..

Overview

This guide is a list of frequently asked questions related to our products, and answers to these questions. The sections below are divided into general topics: Sales, Hardware, Software and General Troubleshooting. The Hardware section include a few subcategories for device-specific questions.

To navigate this page, use the table of contents in the side bar to navigate to a section, and then click on the question to toggle open the answer.

Some of the answers below contain links to third-party products like adapters and switches. None of these links are affiliate links; they are simply products we have tested and verify work with our devices. 

If you have specific questions related to your system, feel free to reach out to our support staff at support@vpixx.com

Sales and Ordering Information

Where is VPixx located? Do you have distribution facilities in my country?

Our offices and manufacturing facilities are located just outside of Montreal, Canada. All orders are shipped from Canada.

If you are based in China, Taiwan, Korea, Japan or India, we work with distributors in these countries to facilitate import of our products. Please contact us at sales@vpixx.com and we will put you in touch with the distributor for your region.

Do you ship to my country?

We ship worldwide, including to the Americas, Europe, Australia and the Middle East. For sanctioned countries listed on the Global Affairs Canada website, please contact us at sales@vpixx.com to determine your eligibility.

If you are based in China, Taiwan, Korea, Japan or India, we work with distributors in these countries to facilitate import of our products. Please contact us at sales@vpixx.com and we will put you in touch with our distributors.

How do I place an order?

If you are interested in our products, you can contact our team via our contact portal (https://vpixx.com/contact/ ) or sales@vpixx.com to obtain an official quote. If you’re not sure what specific tools you need, our team of experienced staff scientists will be happy to provide you with a tailored consultation, either by video/phone call or email. These quotes are valid for 90 days from issue and include the cost of shipment to your institution.

If you would like to place an order, your institution will need to submit a purchase order referencing your quote. Once the purchase order is received, we will provide a Sales Order Acknowledgment for you to approve (see: https://vpixx-support.atlassian.net/wiki/spaces/support/pages/edit-v2/41124043#What-is-a-SOA-and-why-do-I-have-to-sign-it?). We will then manufacture your products.

When your order ships, our team will contact you with tracking information and the invoice.

Please contact us at sales@vpixx.com for enquiries related to payment methods and payment terms.

When will my order be delivered?

Our official lead time is 45 days from when the purchase order is received, to when the item ships. Please allow for some additional time for shipping. Unfortunately, we cannot guarantee a specific delivery date.

Can you deliver by XX date?

We will ship your order within 45 days of receipt of the purchase order. However, once the order leaves our facility, we cannot predict or prevent delays due to shipping agents or customs.

If you have a specific deadline by which you need our products, please notify a VPixx associate as soon as possible. We will do our best to accommodate your deadline. If you have an extremely strict deadline (e.g., expiring funding), we recommend placing orders as early as feasible.

Do you charge taxes/VAT?

If you are based in Canada, we will charge taxes that apply to your province or territory. These taxes will be included in your quote.

If you are outside of Canada we cannot directly charge taxes on our products. The taxes on shipped goods will be determined by a customs agent, and charged by the shipping agent. VPixx cannot pay these charges on behalf of the customer. If your university or institution has tax-exempt status, we ask that you provide us with the required documents to be included in the shipment. Please speak with your institution’s purchasing office to find out the specific documents required for your region.

What is a SOA and why do I have to sign it?

SOA stands for “Sales Order Acknowledgment.” The SOA is a document created by VPixx which summarizes the order information. It includes the following details:

• A shipping address

• A billing address

• A contact at the university for financial inquiries and invoicing

• A contact at the university who can respond to inquiries from our shipping agent (Fedex)

• A summary of the ordered items

• A copy of our payment terms

The SOA provides an opportunity to verify the terms of the sale and should be reviewed by a representative of the university for correctness. The SOA does not supersede the purchase order, although it may contain information (such as the shipping contact) that does not appear on the official order.

If no modification request is submitted within 5 business days, the provided information will be considered verified and the order confirmed. 

Can I change the shipping address after the purchase order has been issued by my institution?

You can change the shipping address by sending us a revised purchase order. We can accept this revision up until the product is packed and labelled for shipping.

Can I use my university’s shipping agent or broker?

Yes, you can. Please inform the VPixx associate who is managing your quote if you wish to use your own shipping arrangements.

We will need to know if you plan to arrange your own pick up, which carrier you intend to use, and we will need contact information for your shipping agent. If you are planning to use a University Fedex account, we will manage the shipping and provide Fedex with your account number for invoicing.

Do you provide on-site installation and training?

We are currently reviewing in-person installation requests on a case-by-case basis. If you are interested in having your equipment installed by our team, please contact sales@vpixx.com with your location and approximate timeline for the installation.  

Our technical support staff are always happy to provide live remote installation support. Please contact support@vpixx.com for assistance.

Hardware

General

What are the system requirements for VPixx hardware?

The short answer: our hardware is compatible with all recent major operating systems. To see what versions of each operating system we currently support, see https://vpixx-support.atlassian.net/wiki/spaces/support/pages/41123939 .

The long answer: it depends on what you are trying to do. While our hardware supports all major operating systems, some of them are better suited to research. On the one hand, for timing-sensitive experiments and low-level control, open-source advocates like the makers of Psychtoolbox strongly recommend Linux-based operating systems. On the other hand, some major high-level experiment software tools like Presentation and E-Prime are only supported on Windows. 

If you need an out-of-the box solution that works, the dual boot Linux/Windows machine service is thoroughly tested and tweaked. It is the only complete system guaranteed to work with our devices and is backed by a 3-year manufacturer’s warranty.

What kind of graphics card do I need?

We have a whole page dedicated to this.

What is the difference between a “Lite” and a “Full” data acquisition system?

Can I upgrade my “Lite” data acquisition system to a “Full” system?

Can I drive VPixx hardware from multiple PCs?

Yes, you can. The easiest way to do this is to use a KVM switch. These switches allow you to toggle between different PC inputs to the same display hardware. We recommend the following models:

Can I use a video adapter if my graphics card does not have dual-link DVI output?

Our VIEWPixx CRT replacement monitors use Dual-link DVI, and now come with a DisplayPort to Dual-Link DVI adapter. Our other systems use DisplayPort. Below are some general recommendations for older systems and systems without our adapter.

Can I use multiple screens at the same time?

Best practice during data collection is to disable all secondary displays and only run the stimulus display. This reduces load on your graphics card and minimizes the risk of frame dropping and other latency issues associated with overtaxing your graphics processor.

Of course, in some labs this impossible, or at least very inconvenient. Your main display may be in another room, or you may be required to monitor specific trial metadata in an experimenter view. 

There are two general solutions for running multiple displays during an experiment. First, you can connect a monitor to the secondary video port on the side of your VPixx device (available on all screens and I/O hubs except for the VIEWPixx /EEG). The hardware will generate a copy of the experiment display and show it on this secondary “console” display. You can then use the console to keep track of participant progress.

Because the console duplicates the video to the main display, it does not add any load to your graphics card; however, by default it can only mirror the main display. Some of our special video modes such as M16 allow for an overlay on the console, which allows you to show some trial metadata specifically in the experimenter view. The console output for the TRACKPixx3 2 kHz eye tracker can also show a live camera feed, in addition to the participant’s view. 

Please note that not all monitors will work well as a console display. We maintain a list of third party screens we have tested and verified work well with our devices. For an up-to-date list, please contact scientist@vpixx.com.

The second option for driving a secondary display is to drive it directly from a second port on the graphics card. The effect this will have on the performance of the main display will vary from system to system. A powerful graphics card may be able to manage both displays without significant frame dropping. If you decide on this route, it is a VERY good idea to run some synchronization tests prior to data collection, to ensure you have a tolerable rate of frame dropping and you are not compromising your stimulus presentation.

I need to connect my VPixx hardware to another system via the I/O ports. Where do I start?

This response is focused on setting up hardware. For tips on how to set up triggers in software, please see our software demos. Pin assignment information can be found in your device user manual.

VPixx hardware has several ports dedicated to input and output. Each port consists of a series of pins that are numbered according to an industry standard. Our I/O ports use a DB-25 connector, and so have 25 pins labelled 0-24.

Other common I/O port formats include BNC/coaxial (common in MRI/MEG systems) and other multi-pin D-sub connectors like DE-9. It is possible to have a cable with different types of connectors on each end, or a cable with one end that splits into multiple connectors or even exposed wires that can be slotted into other electronics.

In all cases, each pin on an I/O device has a specific role, or assignment. Pin assignments vary from system to system. Pin 1 on system “A” might listen for incoming digital signals, while pin 1 on system “B” acts as a ground. 

In order to connect two I/O devices, you must know the specific pin assignments of both ends, and make sure your cable is wired to connect the appropriate pins to one another. Do not assume any cable with the correct number of pins is wired to work with your particular configuration. Connecting pins with incompatible assignments can do physical damage to your ports.

Pin assignment details for specific ports are typically provided by the manufacturer. Pin assignments for all VPixx I/O ports are listed in the specific device user manual. The exception to this is a PC Parallel Port, which has a specific industry standard pin assignment.

Our team is familiar with many neuroimaging, eye tracking, and neurophysiological solutions and can provide advice on how best to connect hardware based on your specific synchronization needs. We manufacture a variety of trigger cables, custom cables and adapters in order to connect different systems safely. If you’re not sure how best to configure your system, we are happy to help.

For more details, please contact our team of trained vision scientists at scientist@vpixx.com. 

How do I (re)calibrate my display? How often should I recalibrate?

Instructions for running our automated calibration routines for the VIEWPixx and VIEWPixx /3D CRT replacement monitors, and the PROPixx DLP projector, can be found on page 115 of our Product Application Guide [pdf].

Our displays use LED light sources that have a very long lifespan. They are are factory calibrated prior to shipment according to the following specifications:

• VIEWPixx /EEG

  • Luminance with scanning backlight: 100 cd/m^2

  • Luminance without scanning backlight: 250 cd/m^2

• VIEWPixx /3D

  • Luminance with scanning backlight: 100 cd/m^2

  • Luminance without scanning backlight: 250 cd/m^2

  • White point: D65

• VIEWPixx:

  • Luminance with scanning backlight: 100 cd/m^2

  • Luminance without scanning backlight: 250 cd/m^2

  • White point: D65

• PROPixx:

  • Luminance: Depends on projection screen size, type  and distance

  • White point: D65

We have found that our displays maintain luminance and chromaticity characteristics consistently for a long time. Your displays should not require re-calibration for about 5-10 years, depending on how heavily they are used. After 5 years you may wish to take occasional measurements to verify your displays are still within an acceptable range of luminance/white point.  

Is VPixx hardware rated for medical applications?

VPixx Technologies develops and manufactures research tools, which are not regulated for use as diagnostic or medical equipment. 

To be rated as a medical diagnostic device, research equipment must go through comprehensive regulatory testing specific to each country (e.g., FDA, MHRA). This certification process takes many years, and may or may not be recognized by other countries and governing bodies.

VPixx Technologies’ goal has always been to enable researchers to push the boundaries of what can be studied in vision research. Our products and tools are often developed by request, and in response to specific, pressing research questions. We have chosen to dedicate our efforts to this fast-paced development, rather than attempting to acquire medical ratings for our devices. 

How do I clean my VPixx devices and displays?

Cleaning recommendations for specific devices can be found in the documentation for that device

PROPixx

Does VPixx manufacture projection screens?

Yes! We manufacture a variety of screen sizes and shapes for tabletop, standalone and in-bore use.

All of our screens use a solid plastic frame with a thin, flexible screen material that minimizes internal reflections. We have different materials optimized for front- or rear-projection, and 2D or 3D stimuli. Our screens use aluminum bases and are safe for use in MRI, MEG  and other ferromagnetically sensitive environments. 

We do not offer hard acrylic screens or roll-up screens.

What is the difference between a 2D and a 3D projection screen?

Screen material optimized for 3D projection has a silver/grey coating that preserves the clockwise and anticlockwise polarization of light for left- and right-eye images. This coating has a high peak luminance gain that drops off rapidly with increasing viewing angles. In comparison, screen material optimized for 2D projection has moderate luminance gain and a more uniform luminance profile. In practice, when viewed directly, screens optimized for 3D will appear brighter but less uniform than screens optimized for 2D. However, when used with a 3D polarizer and passive filter glasses, the perceived brightness of images projected on a screen optimized for 3D is reduced significantly compared to a 2D screen due to the relatively low transmittance of the polarizer and the on-off nature of alternate frame sequencing.

For front projection, we stock a ‘5D’ screen material, a good all-in-one compromise between 2D- and 3D-optimized screen materials. 

For rear projection, researchers must choose between 2D and 3D optimized screen materials. Showing 2D images on a 3D screen is possible, especially on smaller screens. However, 2D material will scatter 3D polarization and is incompatible with 3D stimulus presentation with a polarizer.

Can I use a SHIELDPixx with a third-party projector?

The SHIELDPixx MRI shielding enclosure is designed specifically for in-room installations with the PROPixx MRI-safe projector. It is not sold as an independent unit and cannot be used with third-party projection systems. 

What is the gamma of the PROPixx?

The PROPixx uses DLP technology, which has an inherently linear gamma of 1.

My current PROPixx lens doesn’t work with my new research space. Can I change lenses?

Yes! If you are moving labs, or changing your testing layout, and your current lens does not support the distance/size requirements of the new space, you can purchase a new lens and install it on your current projector. Along with the new lens, we will provide you with instructions on how to swap your lenses out. The process takes less than 15 minutes.

Please note, we do not accept used or returned lenses.

Not sure what lens you need? You can check out our guide to , or contact our scientist team at scientist@vpixx.com.

What is the lifespan of the PROPixx light source? Is it possible to replace it?

The PROPixx uses RGB LED light sources with a lifetime of approximately 60,000 hours. Even with heavy use, this light source should last decades. 

In the event the light source exceeds its lifetime and must be replaced, the unit can be shipped to VPixx Technologies for disassembly, LED chip replacement, and full factory calibration. If you require this service, please contact our technical support team (support@vpixx.com) for more details and a quote for the LED replacement costs.

I’d like to mount the PROPixx on a ceiling or wall bracket. Do you have recommendations?

We do not have specific recommendations for mounting brackets for the PROPixx. The PROPixx has three M4 mounting holes with a 0.7 mm pitch on the base for bolting the device to a ceiling or wall plate. Please see page 13 of the PROPixx user manual for spacing (measurements are in inches).

The PROPixx weighs roughly 15 kg (33 lbs). Please ensure your mounting solution is capable of supporting this weight before installing your PROPixx.

Once mounted, the PROPixx can be set to “ceiling mount” in PyPixx to invert the display.

RESPONSEPixx

Can I connect a RESPONSEPixx button box directly to my PC?

The RESPONSEPixx button boxes use a digital TTL triggering system and terminates in a DB-25 connector. These boxes are designed to work with the digital input port on our data acquisition systems, including the DATAPixx video I/O hubs, the VIEWPixx /3D and VIEWPixx CRT replacement monitors, and the PROPixx Controller. When paired with these systems, the RESPONSEPixx provides microsecond-precise measurements of button press/release times.

It is possible to connect a RESPONSEPixx to the parallel port on your PC with a cable manufactured by VPixx. You can then use the button boxes in conjunction with experiment software that samples parallel port input. 

The disadvantage to this strategy is that you are then constrained by the sampling rate of the port and your experiment software. Just as there is a limit to how quickly your PC can check for keyboard presses and mouse clicks, there is a maximum sampling rate with which you can read input from the parallel port. 

The precise sampling rate will depend on your particular experiment program and what is happening in your checking loop. It will absolutely be slower than the sampling rate of a digital input log running on separate, dedicated hardware. Depending on your experiment this may not be an issue, but it is certainly something to keep in mind when designing timing-sensitive research paradigms.

Can I get custom button colours, or a custom layout?

We can create custom button layouts according to your specifications. Please contact scientist@vpixx.com with your desired layout (including spacing and number of buttons) or colour requests.  

Do you have a joystick or gamepad option available?

We do not. However, our data acquisition systems are capable of receiving analog signals from third party devices, such as joysticks.

VIEWPixx /EEG, VIEWPixx and VIEWPixx /3D

What is a “CRT replacement monitor?”

Our VIEWPixx series of monitors are LCD displays that use modern-day technology, but have custom hardware to mimic the highly desirable temporal properties of old-fashioned CRT displays. To find out more, see .

What is the difference between the three VIEWPixx monitors?

There’s an entire VOCAL guide that explains this in detail: . You can jump to the end for a summary table that provides a side-by-side comparison.

What is the gamma of your VIEWPixx displays?

The exact number varies slightly from unit to unit. A good rule of thumb for most LCD monitors, including our VIEWPixx displays, is a gamma of 2.2.

If your experiment requires extremely precise gamma correction, the best method to determine your display-specific gamma is to measure it directly with a spectrophotometer or colorimeter. See .

I want to mount my monitor on a wall bracket or rolling stand. What are your recommendations?

All three of our VIEWPixx monitors use the following mounting standards:

• VESA MIS-D/E, MIS-F

• Hole pattern: 100 x 100 mm & 75 x 75 mm

This size is an industry standard, and mounting bracket manufacturers should specify if they are compatible. Please note, our monitor casing is metal and is fairly heavy (around 13.6 kg /30 lbs including the removable stand). Any mounting solution must be rated to support this weight. 

At the office, we mount our test displays on mobile relay racks like these, along with a fixed TV wall mount bracket similar to these. This wall mount is large enough to be fixed on the rack and has adjustable brackets that can be used to attach the monitor. This solution works well for a mobile display.

Can I run my display at 60 Hz during an experiment? Why is there a flashing red square in the corner?

The VIEWPixx series of monitors are designed to run at 100 Hz or 120 Hz. When the video signal drops below 100 Hz, the display automatically implements an internal frame buffer and begins resampling the video signal to maintain a screen refresh rate of 120 Hz. A flashing red square will appear in the top left corner of the screen whenever your display is in resampling mode. 

This resampling mode can cause problems for timing-sensitive experiment tools. For this reason, we do not recommend using 60 Hz in experiments where timing is critical for stimulus presentation or data collection. 

Do the VIEWPixx and VIEWPixx /3D run at high bit depth by default? How do I enable these modes?

The VIEWPixx can display up to 12 bits per colour (bpc), and the VIEWPixx /3D can display up to 10 bpc. By default, both displays will show 8 bpc, high definition full-colour video at 120 Hz. This is the maximum possible bandwidth supported by a dual-link DVI protocol.

In order to show video at higher bit depths, it is necessary to make a tradeoff to free up bandwidth for the additional bits. There is a guide to our high bit depth modes here: .

Software

Where can I find the most recent software release information?

You can find all details and documentation related to our releases in our release log: .

How can I find out my current software/firmware revision?

In PyPixx, navigate to System > About us. You will see a list of software and firmware revisions below the information about our company.

Don’t see this content? You may be using an older version of our tools. You can also get this information in the VPutil command-line software using ‘rev’.

How do I check for software and firmware updates?

If you have a recent copy of our software tools, you can check for software and firmware updates in the PyPixx program by navigating to:

System > Check Software Update
System > Firmware Update (requires hardware to be connected and powered on)

Don’t see these options? You are running an older version of our software tools. You can update to the newest version manually by installing our software tools: . Once installation is complete, you can use PyPixx to check for firmware updates.

How do I install VPixx Software Tools?

Your VPixx purchase should include a USB stick containing a copy of VPixx Software Tools. This includes all programs and software packages needed to run our devices. There is one set of Software Tools that covers all VPixx hardware.

Misplaced your USB? No problem! You can download a copy of our software tools from our website: .

In Windows, open the USB contents/Downloads folder and launch setup.exe, and follow the instructions in the installation wizard.

In Linux, download or copy the .deb file to your machine and then run the following to install all tools and dependencies:

Note, if you get an error installing on Ubuntu 18.04 because of missing dependencies, these can be fixed with the following commands:

In Mac, mount the DMG by double clicking on it, then double click the VPixx Software Tools.pkg to launch the installation wizard and follow the instructions.

What is PyPixx?

PyPixx is a standalone software utility included in our VPixx Software Tools. It is officially deprecated as of release 1.6.1.

What is VPutil?

VPutil is a command-line tool that is included with our VPixx Software Tools. It allows you to change basic settings on your VPixx device, install firmware updates, manually read the device register for diagnostic purposes, and run several demos to test hardware performance.

Do you support MATLAB/Octave?

Our free software tools include an API specifically designed to work with MATLAB/Octave and Psychtoolbox. 

For more details on installing our MATLAB/Octave tools, and for some example code, check out our

Please note we no longer support 32-bit versions of MATLAB.

Do you support PsychoPy?

See our VOCAL:

Do you support Python IDEs (PyCharm, Spyder, etc?)

Absolutely. Our Python API comes in two flavours. Pypixxlib uses an object-oriented approach, while the libdpx wrapper permits more sequential programming. Which strategy you opt for is a matter of personal preference. Throughout several VOCAL guides we provide examples of both types of Python code.

For more details on how to install our Python tools, see our .

Do you support Presentation?

We do not currently provide software support for NeuroBehavioral Systems’ Presentation software. However, it is possible to configure our hardware to communicate with the Presentation PC via the parallel port and our DB25 digital output. 

With this method, you can log button presses from our response boxes, capture automated frame-locked TTL triggers from our hardware via Pixel Mode and synchronize your experiment code with eye tracking data from either of our eye tracking systems. For more details on how to set up this connection, please contact scientist@vpixx.com.

Presentation does have MATLAB extension that allows users to run MATLAB scripts. As of April 2021, this extension only supports 32-bit MATLAB (r2015 and earlier). As soon as the extension supports 64-bit MATLAB, in theory it will be possible to use our full MATLAB API in Presentation.

Do you support E-Prime?

It is possible to use our MATLAB/Psychtoolbox tools in E-Prime by running a MATLAB server. You will need a copy of MATLAB and administrator privileges to do this.

Full instructions for how to use our devices in E-Prime can be found on page 128 of the VPixx Application Guide [pdf].

Do you support __________?

In a lot of cases, if a piece of software has some kind of extension or tool for running MATLAB or Python code, there is a chance our API can be integrated into it. 

Even if your software does not support these APIs, there is still the possibility to run the systems in parallel and use TTL triggers to synchronize events. Alternatively, you can take advantage of our data acquisition system to stream data (like eye position coordinates) onto our devices and log them on the same clock as your visual events. 

Not sure whether integration might be possible with your existing experiment pipeline? Reach out to our technical support team at support@vpixx.com and we will help you investigate.

Troubleshooting

General

VPixx hardware is plugged in and powered on, but is not detected by software

If you recently crashed out of an experiment program, your VPixx Device Server may have frozen. You can restart it via the following methods:

• Windows:

  • Search for the “services” application in the menu, and open it (should have a gear icon)

  • Scroll down the list of services to “VPixx Device Server”, right click this and select “restart”

• Mac:

  • Open a terminal and enter:

sudo launchctl stop com.vpixx.deviceserver
sudo launchctl start com.vpixx.deviceserver

• Linux:

  • Open a terminal and enter

sudo systemctl restart vpixx-device-server

If this does not resolve the issue, please contact technical support (support@vpixx.com)

Console display (video out 2) shows an “Out of Range” error

If the console monitor is a make and model recommended by the VPixx team, or if it was purchased directly from us, this error is normal and should disappear on its own after about a minute. After this your screen will work normally.

If the message persists for several minutes, or is accompanied by other screen artefacts (like tearing or flickering), your monitor may not be suitable for use as a console. Please ensure it is set to 1920 x 1080 @ 120 Hz. If this does not resolve the issue, you may need to use a different monitor.

VPixx hardware is detected, but video is not showing or is showing poor quality video

You may be sending video at an unsupported resolution or refresh rate. Check your graphics card and display settings and make sure they are set to one of our specified resolutions and refresh rates. Please also ensure your video cable is dual-link DVI, not single-link.

In some cases you may also need to specify your display EDID. The EDID is a setting on your display hardware that indicates to the graphics card the preferred resolution and refresh rate of the display.

If your desired resolution does not appear in your display settings, you can specify the display EDID in PyPixx in the Configuration widget. There are two ‘slots’ available, which you can set to two of your preferred settings. You may need to restart your VPixx device for the new EDIDs to take effect.

PROPixx image is flickering

This is typically a sign that your video signal is being attenuated. This is common with longer cables. If you have a booster (small box connected to the video cable, located near the projector), you can try adjusting the dial on the side until you achieve a stable image. If you do NOT have a booster, you may want to try a different, shorter video cable.

VIEWPixx monitor has a flashing red square in the top corner

The flashing red square in the top corner of the display indicates that your video frame rate has dropped below 100 Hz (usually to 60 Hz). When this happens, the VIEWPixx goes into “resampling” mode and repeats incoming video frames in order to continue displaying images at a rate of 120 Hz.

Resampling mode can cause problems for timing-sensitive experiments; the red square is a warning that is a bad idea to collect data while the display is behaving this way.

You can resolve the issue by changing your display settings such that the VIEWPixx is showing full HD (1920 x 1080) at 120 Hz. You can usually change this in your display settings.

If you don’t see an option for 1920 x 1080 @ 120 Hz, it may be that you are using a single-link DVI cable, not dual-link. In that case you may need to swap cables and restart the monitor to be able to change the display settings.

 MATLAB/Psychtoolbox

Invalid MEX-file or Datapixx(‘Open’) fail in MATLAB

This error is usually caused by an outdated MATLAB executable (.mex file) in your Psychtoolbox folder. This file must be manually updated each time you update VPixx Software Tools. Please follow the steps on this page:

MATLAB -1010 error or MATLAB script freezes and crashes

There are many possible reasons for this error, but common culprits are the following commands:

RegWrVideoSync
RegWrPixelSync

Both of these commands instruct your VPixx hardware to perform a register write when a specific event is detected in the video signal. They are non-blocking commands, so the rest of your MATLAB code will continue to run. However, your device is now in a “busy” state while it waits for the event, and any further attempts to perform a write or write-read to the device register will be queued until the event is detected and the write can execute.

Queuing many attempts to write to or read from the device register while it is “busy” can throw errors and crash your program. If this is happening to you, most likely your VideoSync or PixelSync commands are waiting for a very long time for their triggering event (or the event just doesn’t happen) and this is causing subsequent attempts to communicate with the device to stack up and crash the program.

If you are not using either of these commands in your code, you may want to check and see if one of your PsychDataPixx commands might be using them “under the hood.” PsychDataPixx commands that reference timing are almost certainly using these sync functions.

To fix these errors, please ensure the following:

• Video is running through your VPixx hardware to the display 

• Your script calls VideoSync and PixelSync commands (or the PsychDataPixx functions invoking them) right before the screen flip which should trigger them, so there will be little delay

• For PixelSync: You are not applying blending, anti-aliasing or other display changes which could alter your PixelSync trigger after you have set it

• For PixelSync: Your graphics card is not dithering. Check out our guide to diagnosing and disabling dithering to learn more.

If these sync functions are not relevant or you want to get around them for debugging purposes, both functions have a timeout argument that can be set to 1-2 frames to cause them to execute right away and prevent queuing subsequent commands. Doing this renders their sync function useless and will definitely mess up any timing or synchronization that depends on them. We do not recommend doing this during data collection.

 Python

“Module not found” / code unable to find pypixxlib

As a first step, please follow the instructions here: and install your pypixxlib file in the appropriate Python folder. This is usually something like:

C:UsersuserAppDataLocalProgramsPythonPython37Libsite-packages

If you have done so already and the error persists, check for multiple instances of Python on your computer. Applications like PsychoPy and Anaconda have their own dedicated Libsite-packages folders and you may need to install or copy pypixxlib into these folders to ensure your program sees it.

Depending on your software, you may also need to explicitly add site-packages to your path. Some Python IDEs have a PYTHONPATH manager that allows you to do this, usually in the “Tools” section of the menu

If you are using the PsychoPy builder, you can add locations to your path by navigating to File-> Preferences -> General and clicking on the little square with the ‘…’ from the row labelled “paths”. 

Pixel Mode triggers not working properly (in PsychoPy)

Pixel mode is a method of sending automated TTL triggers, with timing locked to the onset of your visual stimuli. This is an easy and efficient method for sending triggers to external systems to synchronize them with display behaviour.

Pixel Mode can be used with any of our displays, or the DATAPixx series I/O hubs paired with a third party screen. For an in-depth discussion of the timing and principles of Pixel Mode, please see our VOCAL guide on the subject: .

While your system is in Pixel Mode, TTL signals are sent automatically based on the colour of the top left pixel on your display, as it is detected by the video signal. If, for some reason, the pixel you define is altered by either your experiment software or your GPU, this can lead your trigger to be altered.

If you are using PsychoPy to draw your top left pixel on your target video frame, there are a few known PsychoPy elements that can impact your pixel output. Below is a list of things you can try to achieve a 1-1 mapping between pixel assignment and output.

By the way, if you want to check your digital TTL output without turning on your receiver, you can see the current states of the digital output ports in our PyPixx utility, under Demo > Digital I/O Demo.

1. Make sure Pixel Mode is enabled. On some of our systems it is not on by default. The easiest way to turn this setting on is to navigate to our PyPixx software utility and go to Configuration > Output Mode. If this is a shared testing station, make sure to disable it after using.

2. If you are using the Builder, consider drawing your pixel in the Coder rather than using a drag and drop item. This will give you full control over the parameters which may be hidden in the Builder view. Some example code is given below.

3. Use the rgb255 colour space. This avoids rounding issues in colour assignment.

4. Draw your pixel as a line, not a shape. PsychoPy shape classes have both a line and a fill colour parameter, which do not seem to be fully compatible with the rgb255 colour space. Lines seem to be much more reliable.

5. Turn off interpolation. In PsychoPy pixel interpolation is on by default, and this can alter pixel values. Set this parameter to false for your specific line serving as your Pixel Mode pixel.

6. Account for any gamma correction applied by the monitor center. If you are applying blanket gamma corrections to your pixel values, this will surely alter your pixel as it is drawn in your code. This is not a problem as long as you account for this and draw a pixel that, when gamma corrected, produces the desired output.

7. Turn off the GUI feature. This feature adds a narrow interactive border to the window that can overwrite your pixel.

8. Check for dithering. The issue may not be specific to PsychoPy, especially if it is intermittent. See our guide: for more details.

Below is a snippet of code demonstrating how to draw a pixel with PsychoPy visual elements: