The research on the visual cliff describes a developmental shift in emotion, but does not explain that shift. Why do infants become afraid of heights? Is it because they suffer a hard fall and become conditioned to heights as a source of potential pain? Possibly, but some infants do not have falls and still show the developmental shift toward wariness of heights. Is it that the mother or other important person in the baby’s life communicates emotion when the infant is near a dropoff, and the infant learns to link the dropoff to the emotional communication (e.g., “NO. JOHNNY, YOU CAN FALL!!!!”)? Possibly, but the cognitive skills required for this type of learning seem to develop somewhat later than the afe of the developmental shift involving fear of falling.


Our current research centers on a very subtle process that involves the emotion that takes place when there is a discrepancy in perception across different sensory modalities. Consider one discrepancy—between touch and vision. There is a well-known science museum demonstration where a person is attracted to reach for a ball. It happens to be a virtual ball, not a real one, but it looks very real. When people try to grasp the virtual ball, they show quite a surprise when they fail to grasp it! We believe that a similar perceptual discrepancy takes place to account for the development of the fear of heights.


Just as vision and touch can both specify that a ball is graspable, so different sensory modalities are involved in one’s sense of self-motion. One source comes from sensors in the inner ear (that provide so-called “vestibular” stimulation). Another is the visual system, the periphery of which seems particularly suited to specify that one is moving. This visual information is called “visual proprioception.” The vestibular system functions quite well in the newborn; to some minimal extent, visual proprioception is also present in the newborn. However, with locomotor experience, there is a vast improvement in the use of visual proprioception by the infant.


This demonstration shows an investigation into visual proprioception. It shows the so-called “moving room,” which is a box-like apparatus in which the ceiling and two sides can move while the front wall does not, thus providing peripheral visual proprioception, or ceiling, sides, and front move together in what is called “global optic flow.” In the study you are to see, the floor does not move in any condition.


If you were to be inside the moving room, and the moving room moved from front to back, you would feel yourself moving in the direction opposite to the movement of the room. In addition, you would compensate for your apparent forward body movement by moving your body in the opposite direction, to keep your body upright. Older infants, capable of standing, show this postural compensation by actually falling down in the direction of room movement. Younger infants, not capable of standing, must be tested while seated in a special chair designed to capture their leaning forward or backward.


The results of this series of studies reveals that:


1.    Prelocomotor infants show minimal postural compensation to movement in the periphery of the visual field; on the other hand, infants who can crawl, or prelocomotor infants who have had experience moving about “artificially” by using a walker device, do show postural compensation.


2.    Both prelocomotor and locomotor infants show postural compensation when the whole room (minus the floor) is moved. So, the findings in point 1 above cannot be due to prelocomotor infants lacking the capacity to show postural compensation. The effects of locomotor experience seem to focus on the periphery of the visual field.


3.    Locomotor and pre-locomotor infants with walker experience show emotional reactions to the movement of the sides of the visual cliff;  prelocomotor infants with no locomotor experience do not typically show emotional reactions.



INFANT ONE:  Observe the dramatic change in posture.


INFANT TWO:  Here we see a very strong emotional reaction.