What your baby sees…and you don’t

Infants may not speak but they are able to see, sometimes better than adults. New research, conducted by Japanese researchers from Chuo University in Tokyo and published May 17 in the PNAS, suggests that babies younger than 7 months can perceive objects that neither older children nor adults can see. An astonishing result which can be explained by the phenomenon of “visual masking behind”.

Interference with feedback processing

Visual backward masking is a phenomenon used in science to study how visual perception is processed in the brain. This consists of briefly presenting an image immediately after a brief “target” visual stimulus for a very short time. This normally results in an inability to consciously perceive the first image. Interestingly, this phenomenon occurs even if the second object does not spatially overlap the first object, the Japanese researchers note. This technique is used in particular in psychophysiological studies of fear and phobias which study unconscious reactions to fear-related stimuli.

The inability to perceive the first image is thought to be due to an interruption in “feedback processing”. When we see something, visual information is serially processed from the lower visual areas to the upper areas of the brain in an upward fashion. However, downward feedback processing, in which visual signals are returned from higher areas to lower areas, also plays a critical role in visual perception. Visual backward masking is thought to occur due to interference with feedback processing.

Immature feedback processing

The researchers conducted experiments to test whether backward masking occurs in infants. “We applied backward masking to infants aged 3-8 months to examine the development of feedback processingcontinues Yusuke Nakashima, lead author of the study. Recent studies in vision science have revealed the importance of feedback processing in visual perception, but its development is poorly understood..” For this, the scientists presented images of faces on a computer screen and measured the time the infants spent looking at them. Since infants tend to look at faces longer, researchers can test whether infants perceive faces by measuring their gaze time. Two types of experiments were performed: in the first, a face was followed by a mask image so that infants would not see the face if back masking occurred; in the second, nothing appeared after the face, so infants could see the face.

The results revealed that infants aged 7-8 months did not perceive mask-tracked faces, indicating that backward masking occurred, as in adults. In contrast, those younger than 7 months managed to see faces even when the faces were followed by the mask image, indicating that there was no masking and that younger infants could see faces than older infants cannot see. “These results suggest that feedback processing is immature in infants younger than 7 months.assures Yusuke Nakashima. That is, younger infants do not have feedback processing and therefore, masking is ineffective for them..”

Seemingly counter-intuitive results

These observations reveal that the mechanisms of visual perception change radically after the first 6 months of life. The results also showed that objects that can be perceived in early childhood become imperceptible during development. “It may seem counter-intuitivesays Masami Yamaguchi, professor at Chuo University and also author of the study. Important visual abilities would be acquired by the maturation of feedback processing.”

Feedback processing is essential to robustly perceive ambiguous visual images, such as occluded objects. “Younger infants with immature feedback processing may perceive the outside world ambiguouslyconcludes Masami Yamaguchi. In exchange for susceptibility to visual masking, we gain the ability to robustly perceive ambiguous visual scenes..”