Why missing out on subtle visual changes keeps us sane

If you have ever failed to notice how Harry Potter's T-shirt abruptly changes from a crewneck to a henley shirt in 'The Order of the Phoenix,' or how in 'Pretty Woman,' Julia Roberts' croissant inexplicably morphs into a pancake, don't worry.

Vision scientists at the University of California, Berkeley, and the Massachusetts Institute of Technology have discovered an upside to the brain mechanism that can blind us to subtle changes in movies and in the real world.

They've discovered a "continuity field" in which the brain visually merges similar objects seen within a 15-second time frame, hence the previously mentioned jump from crewneck to henley goes largely unnoticed.

Unlike in the movies, objects in the real world don't spontaneously change from, say, a croissant to a pancake in a matter of seconds, so the continuity field stabilizes what we see over time.

"The continuity field smoothes what would otherwise be a jittery perception of object features over time," David Whitney, associate professor of psychology at UC Berkeley and senior author of the study, said.

"Essentially, it pulls together physically but not radically different objects to appear more similar to each other. This is surprising because it means the visual system sacrifices accuracy for the sake of the continuous, stable perception of objects," Whitney added.

Conversely, without a continuity field, we may be hypersensitive to every visual fluctuation triggered by shadows, movement and myriad other factors. For example, faces and objects would appear to morph from moment to moment in an effect similar to being on hallucinogenic drugs, researchers said.

"The brain has learned that the real world usually doesn't change suddenly, and it applies that knowledge to make our visual experience more consistent from one moment to the next," Jason Fischer, a postdoctoral fellow at MIT and lead author of the study, which he conducted while he was a Ph.D. student in Whitney's lab at UC Berkeley said.

The research is published online in the journal Nature Neuroscience.