SAN JOSE, CA: Technology giant Apple has acquired an artificial intelligence (AI) start-up that uses facial recognition technology to analyse people's emotions.

San Diego-based Emotient has developed patented software that is said to be able to interpret people's emotions and the technology has been used by advertisers to help analyse reaction to their ads.

According to the company, retailers have also used it to monitor shoppers' reactions in-store while doctors have used the technology to help interpret signs of pain among patients.

Apple confirmed to the Wall Street Journal that it had bought Emotient, although it did not give further details, stating only that it "buys smaller technology companies from time to time, and we generally do not discuss our purpose or plans".

While it may not be immediately clear why Apple has acquired Emotient, the development is the latest indication of its growing interest in the field of artificial intelligence.

In October 2015, Apple acquired another AI start-up, VocalIQ, which specialises in speech recognition, while other purchases have included Faceshift, Perceptio and Metaio.

Swiss-based Faceshift, which was acquired last November, uses motion capture technology that also captures people's facial expressions, while Perceptio uses AI to classify photos on smartphones.

German start-up Metaio, an augmented reality firm that was acquired by Apple in May 2015, uses technology that overlays images of the real world onto a smart device screen.

With its purchase of Emotient, Apple takes a further step towards catching up with Facebook and Alphabet, the parent company of Google, which have been investing heavily in AI techniques.

As the advertising industry gets to grips with such rapid technological developments, a recent Warc Trends report explored what artificial intelligence means for brands.

The paper concluded that one of the probable benefits of AI is achieving personalisation at scale, allowing for fewer but more specific – and, therefore, more influential – targeted ads.

But a key challenge for brands is about striking the right balance between man and machine in order to avoid alienating customers who may be unsettled by increasingly smart technology.

Data sourced from Wall Street Journal, TechCrunch; additional content by Warc staff