Computer
scientists at the University of California, San Diego, have combined
sophisticated computer vision algorithms and a BCI to find mines in sonar
images of the ocean floor. The study shows that the new method speeds detection
up considerably, when compared to existing methods--mainly visual inspection by
a mine detection expert. Researchers worked with the U.S. Navy's Space and
Naval Warfare Systems Center Pacific to collect a dataset of 450 sonar images
containing 150 inert, bright-orange mines placed in test fields in San Diego
Bay. An image dataset was collected with an underwater vehicle equipped with
sonar. In addition, researchers trained their computer vision algorithms on a
data set of 975 images of mine-like objects. They first showed six subjects a
complete dataset, before it had been screened by computer vision algorithms.
Then they ran the image dataset through mine-detection computer vision
algorithms they developed, which flagged images that most likely included
mines. They then showed the results to subjects outfitted with an EEG system,
programmed to detect brain activity that showed subjects reacted to an image
because it contained a salient feature. Subjects detected mines much faster
when the images had already been processed by the algorithms.
The algorithms
are what's known as a series of classifiers, working in succession to improve
speed and accuracy. The classifiers are designed to capture changes in pixel
intensity between neighboring regions of an image. The system's goal is to
detect 99.5 percent of true positives and only generate 50 percent of false
positives during each pass through a classifier. As a result, true positives
remain high, while false positives decrease with each pass. Researchers took
several versions of the dataset generated by the classifier and ran it by six
subjects outfitted with the EEG gear, which had been first calibrated for each
subject. It turns out that subjects performed best on the data set containing
the most conservative results generated by the computer vision algorithms. They
sifted through a total of 3,400 image chips sized at 100 by 50 pixels. Each
chip was shown to the subject for only 1/5 of a second (0.2 seconds) --just
enough for the EEG-related algorithms to determine whether subject's brain
signals showed that they saw anything of interest. All subjects performed
better than when shown the full set of images without the benefit of pre-screening
by computer vision algorithms. Some subjects also performed better than the
computer vision algorithms on their own.
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