Call of Duty: Ghosts' "juddering" PS4 frame rate is actually a visual phenomenon caused by the game rendering faster than 60FPS, it's been revealed.

According to a Digital Foundry study, the PS4 version of Ghosts "actually runs at higher frame-rates than 60fps on a fairly frequent basis", which, owing to the console's 60Hz video output restriction, results in a "judder and perceived frame-rate loss".

Because of the technical inconsistencies, the user actually sees "skipped and incomplete frames" appearing on screen - an effect, Digital Foundry says is "arguably far more noticeable than a few prolonged drops down to 50fps or so seen the 360 version of the game."

The day one patch for Ghosts (which also increases the campaign's resolution to native 1080p) is said to reduce the effect, but not completely.

"The good news is that the issue of skipped frames is reduced to a noticeable degree, particularly in some of the opening moments of the game," reports the site, "although the problem hasn't been completely eliminated. There is still noticeable judder present throughout the patched campaign that appear on a regular basis, which is often distracting when trying to line up a quick succession of precise shots in the heat of battle."

Digital Foundry also states that the higher resolution of the PS4 version can lead to some frame drops, falling to 40FPS when under heavy stress, but mostly sticking between 50 and 60FPS.

"Thankfully, the effects of these normal frame-rate drops are less obviously visible than the judder caused by the renderer exceeding the 60Hz refresh," the report continues, "although even with the 1080p patch enabled things don't appear as smooth as the Xbox 360 version of the game."

Some reviewers criticised Ghosts for its perceived lower frame rate, with Joystiq claiming that the game sometimes slows "to a crawl, particularly during set-piece moments with multiple effects".

The PS4 version launched alongside the Xbox 360, PlayStation 3, PC and Wii U versions earlier this month, with the console due to go on sale next Friday, November 29.