Visual cliff

Sixteen infants born at term and sixteen born preterm were encouraged to crawl to their caregivers on a modified visual cliff. Successful trials, crossing time, duration of visual attention, duration of tactile exploration, motor strategies, and avoidance behaviors were analyzed. A significant surface effect was found, with longer crossing times and longer durations of visual attention and tactile exploration in the condition with the visual appearance of a deep cliff. Although the two groups of infants did not differ on any of the timed measurements, infants born at term demonstrated a larger number of motor strategies and avoidance behaviors by simple tally. This study indicates that infants born at term and those born preterm can perceive a visual cliff and change their responses accordingly.[2]

Another study measured the cardiac responses of human infants younger than crawling age on the visual cliff.[6] This study found that the infants exhibited distress less frequently when they were placed on the shallow side of the apparatus in contrast to when they were placed on the deep side. This means that prelocomotor infants can discriminate between the two sides of the cliff.[7]

James F Sorce et al. tested [8] to see how maternal emotional signaling affected the behaviors of one-year-olds on the visual cliff. To do this they placed the infants on the shallow side of the visual cliff apparatus and had their mothers on the other side of the visual cliff eliciting different emotional facial expressions. When the mothers posed joy or interest most of the babies crossed the deep side but if the mothers posed fear or anger, most of the babies did not cross the apparatus.

In contrast, when the visual cliff effect was absent, most of the babies crossed regardless of the mother's facial expressions. This suggests that babies look to their mother's emotional expressions for advice most often when they are uncertain about the situation.[9] Joseph J. Campos research focuses on facial expressions between the caregiver and infant. Specifically his research shows that the infants will not crawl if the caregiver expresses a signal of distress. If the caregiver gives the infant a positive facial expression the child is more likely to crawl across the visual cliff.

Rats do not depend upon visual cues like some of the other species tested. Their nocturnal habits lead them to seek food largely by smell. When moving about in the dark, they respond to tactual cues from their stiff whiskers (vibrissae) located on the snout. Hooded rats tested on the visual cliff show little preference for either side of the visual cliff apparatus as long as they could feel the glass with their vibrissae. When placed upon the glass over the deep side, they move about as if there was no cliff.[11]

Cats, like rats, are nocturnal animals, sensitive to tactual cues from their vibrissae. But the cat, as a predator, must rely more on its sight. Kittens were observed to have excellent depth-discrimination. At four weeks, the earliest age that a kitten can skillfully move about, they preferred the shallow side of the cliff. When placed on the glass over the deep side, they either freeze or circle backward until they reach the shallow side of the cliff.[11]

The late Robert M. Yerkes of Harvard University found in 1904 that aquatic turtles have somewhat worse depth-discrimination than land turtles. On the visual cliff one might expect an aquatic turtle to respond to the reflections from the glass as it might to water and prefer the deep side for this reason. They showed no such preference; 76% of the aquatic turtles crawled onto the shallow side. The large percentage that choose the deep side suggests either that this turtle has worse depth-discrimination than other animals, or that its natural habitat gives it less occasions to "fear" a fall.[11]

The ability for cows to perceive a visual cliff was tested by NA Arnold et al. Twelve dairy heifers were exposed to a visual cliff in the form of a milking pit while walking through a milking facility. Over this five-day experiment the heifers’ heart rates were measured along with the number of times they stopped throughout the milking facility. Dairy heifers in the experimental group were exposed to a visual cliff while dairy heifers in the control group were not. The experimental group was found to have significantly higher heart rates and stop more frequently than the heifers in the control group. Depth exposure did not have any effect on cortisol levels or the ease of handling of the animals. These findings provide evidence of both depth perception and acute fear of heights in cows. This may lead to a reorganization of the way milking factories function.[12]