Apple Inc. has acquired the Emotient Inc., a San Diego startup working on artificial intelligence technology that analyzes facial expressions to detect emotions.

An Apple spokeswoman confirmed the purchase, stating that Apple buys smaller technology companies from time to time, and usually, they do not discuss their purpose or plans. However, it is not yet clear why Apple bought Emotient, which mostly sold its software to advertisers, but the company has made some other recent acquisitions that are likely complementary, according to Wired. 

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In addition, the Cupertino-based tech giant has bought two companies: Faceshift, a motion capture startup focused on facial analysis, and Perceptio, a company with deep-learning image recognition technology designed for mobile processors.

Emotient uses artificial intelligence to scan a person's face and read their emotions in a fraction of a second. It is a technology that is particularly designed and useful to advertisers and salespeople. One of its first wearable applications was a Google Glass add-on that the company hoped salespeople could use to judge whether a person really loves a product or not. Facial recognition is an area in which several major tech companies have interest.

Andrew Moore, the dean of computer science at Carnegie Mellon, said that such technology can be used for everything from security to accessing mental health. The startup said that doctors have also used the technology to determine patient pain, and retailers have used it to track how shoppers react to products in stores.

One of the keys to Emotient's technology is being able to scan a person's face for emotions, but not store any personally identifiable information about them in the process. The use of face-scanning technology has been a privacy concern for many startups, Business Insider reported. 

Improving image recognition is a hot topic in Silicon Valley. Companies such as Alphabet Inc.’s Google and others are investing heavily in artificial-intelligence techniques.

Before Apple, Facebook, Microsoft and Google have all played around with facial recognition technology to some extent over the past few years. Microsoft’s Kinect sensor for the Xbox One features facial recognition technology and Facebook’s facial recognition tech is so good that it can correctly identify your face 97 percent of the time.