Photosensor data

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Joined: Mon Sep 16, 2019 5:24 pm

Photosensor data

Post by ciara123 »


I am using the BioSemi photosensor for the first time and am not sure if we are using it correctly. I have attached one example of data output from the sensor where I have tested it with black/white/gray screen colour changes every 2s. We seem to have very noisy data. The photosensor is attached to the bottom right corner of the monitor.

We want to specifically use it for a visual paradigm to correct for any delay in stimulus triggers and presentation. For the task will use black screen and flash a white box in the corner where the sensor is located every time a stimulus is presented).

I was also wondering if you could provide instructions on the best way to set up and mount the photosensor for testing - in case we are not using the most efficient set up.

I look forward to hearing from you.

Kind regards,

photosensor_testing.png (148.98 KiB) Viewed 1530 times

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Re: Photosensor data

Post by Coen »

The "noise" may be 50 Hz by room lightning. Test with the room lightning on and off (view the waveform in ActiView, switch the ERGO low-pass display filter off).

It may also be due to modulation of the backlight of the monitor (test sensor with an on/off flashlight). In this case, only another monitor would help. Nevertheless, the present data should be good enough to determine the timing of the edges.

The ERGO data seems low-pass filtered. Did you apply an off-line filter ?

Sent a picture of the sensor tip and the delivery date of the photo sensor to (we want to determine the exact sensor version that you have).

Best regards, Coen (BioSemi)

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