SAN JOSE, Calif. -  A witness for Apple Inc. (Nasdaq: AAPL) testified Friday that a “substantial portion” of consumers confuse Samsung Electronics Co.’s tablet computers and smartphones with Apple products.

In the sixth day of the companies’ intellectual property trial in federal court in San Jose, California, Apple used the testimony of Kent Van Liere, an expert in market research, to try to show a likelihood of confusion among consumers, a requirement to demonstrate that Samsung infringes the trademarked look of Apple’s devices.

Van Liere said he concluded from his surveys that 37 to 38 percent of consumers confused the Samsung Fascinate and Galaxy SII Epic 4G smartphones with Apple’s iPhone. He said a “net rate” of 12 percent of consumers confused Samsung’s tablets with Apple’s iPad.

There are a “substantial portion of consumers who are likely to be confused when they see” Samsung’s products, who will think that “they are actually seeing an Apple product,” Van Liere told the court.

Apple and Samsung are the world’s largest makers of the high-end handheld devices that blend the functionality of a phone and a computer. The trial is the first before a U.S. jury in a battle being waged on four continents for dominance in a smartphone market valued by Bloomberg Industries at $219.1 billion. Each company is trying to convince jurors that its rival infringed patents covering designs and technology.

In addition to patent infringement, Apple contends that Samsung’s copying of the look of the iPhone and iPad has diluted the values of its iconic brands.

A paid expert witness called by Apple, industrial designer Peter Bressler, told the jury Aug. 6 about data in a report showing that the most common reason some Best Buy Co. customers return Samsung’s Galaxy Tab 10.1 tablet computer is because they thought they had bought the iPad 2.

Samsung, based in Suwon, South Korea, countersued and will present claims that Apple is infringing its patents.

The case is Apple Inc. v. Samsung Electronics Co. Ltd., 11- cv-01846, U.S. District Court, Northern District of California (San Jose).