Thanks to a survival mechanism devised by the brain, we can recognise a person irrespective of any turn of the face or angle of viewing.
This is also the reason why we miss out on identifying Johnny Depp's stunt double even as we pick our child from a crowd, according to a UCBerkeley study.
Study participants were asked to search for an exact match to a "target" face on a computer screen.
Each six seconds, a "target face" flashed on the computer screen for less than a second, followed by a series of faces that morphed with each click to the next face. Participants kept clicking till they found the best match.
They consistently identified a face that was not the target face, but a composite of the faces they had seen over the past few seconds.
In fact, they felt the composite to be more similar to the target face than it really was.
"Regardless of whether study participants cycled through many faces until they found a match or quickly named which face they saw, perception of a face was always pulled towards face identities they saw within the last 10 seconds," Alina Liberman, a doctoral student in neuroscience at UC Berkeley and lead author of the study said.
"Importantly, if the faces that participants recently saw all looked very distinct, the visual system did not merge these identities together, indicating that this perceptual pull does depend on the similarity of recently seen faces."
Earlier studies on the persistence of vision concept familiar from school, had established the existence of a 'Continuity Field' in which we visually merge similar objects seen within a 15-second time frame.
This is the reason why we may overlook an actor wearing two different shirts in two consequent shots.
The present study looked at how the Continuity Field applies to our observation and recognition of faces.
While changes in viewpoint, noise, blur, and lighting changes commonly cause faces to appear very different from moment to moment, the study results suggest that the visual system is thankfully biased against such wavering perception in favour of continuity.