Visual acuity is a description of how acute, or “sharp,” an animal’s vision is. Animals which rely on vision to navigate their world typically have higher visual acuity, whereas animals with lower visual acuity will rely on other senses. In some animals, certain environmental variables have an impact on visual acuity. These can include light, shape, color, and movement. This article will describe specifically how movement impacts visual acuity.
Most animals that are capable of vision are also capable of motion perception, the process by which the speed and trajectory of objects in their field of vision are estimated. In many animals, including humans, an object in motion is far easier to detect than a stationary object, especially if the object is camouflaged in some way. Static objects tend to be harder to distinguish against static backgrounds, even if they are within the viewer’s range of vision.
Some species of animals exhibit this effect to a greater degree than others. Frogs, for example, are terribly nearsighted, but are attuned to moving objects even if they are farther away. Since many frogs are insectivorous, this does not hinder their ability to capture prey. Insects themselves are also attuned to movement rather than stationary details, a consequence of their compound eyes. Fish and some mammals such as dogs, cattle, and deer are more likely to react to objects in motion, and may not perceive a stationary object right away.
In de-extinct animals
Movement-based visual acuity is seen in Tyrannosaurus rex due to the hybridization needed to bring this species back from extinction. Using casts of the animal’s brain case, paleontologist Dr. John Roxton had proposed sometime before the 1980s that tyrannosaurs were neurologically similar to amphibians and were therefore unable to distinguish stationary objects from a stationary background. Because this theory was already established in the paleontological field, International Genetic Technologies likely did not realize that hybridization with Rana temporaria DNA was the cause of this attribute. This was also observed in other dinosaurs cloned by InGen in C/N canon.
Unlike frogs, the tyrannosaur may sometimes be hindered by this trait, as its prey can remain still to try and avoid detection. This was tested and demonstrated by Dr. Alan Grant, though subsequent attempts to evade tyrannosaurs by standing still failed. Such a failed attempt led to the death of Dr. George Baselton, a paleontologist hired by BioSyn. It was proposed that the tyrannosaurs could, in fact, see stationary objects despite clear signs during the previous incident that they were unable to. Alternatively, since the tyrannosaur has a highly-developed sense of smell, it may use other senses to detect nearby animals when its vision fails it.
Movement-based visual acuity in Tyrannosaurus rex was introduced in C/N canon and explained as an unintended result of Rana temporaria genes used to complete the genome. This attribute has carried over into other franchise canons, particularly S/F.
Along with many other technical scientific aspects of the story, the visual acuity being the result of an amphibian gene donor was not discussed in the film version; instead, it is presented only as a paleontological theory endorsed explicitly by Dr. Alan Grant. The theory was put to the test during the 1993 incident, and it succeeded, saving the lives of Dr. Grant and Lex Murphy. As a result, the theory of movement-based vision in tyrannosaurs was popularized as supposed scientific fact. However, the journal of InGen‘s Dr. Laura Sorkin discusses the possibility that the theory is wrong, suggesting instead that InGen’s Tyrannosaurus exhibit this trait due to donor genes from modern frogs being used to complete the tyrannosaur genome.
Regardless of the cause, vision based on movement has allowed humans to escape hunting tyrannosaurs on several occasions. This attribute was taken advantage of extensively during the 1993 Isla Nublar incident, and was used on at least one occasion by Eric Kirby while he was marooned on Isla Sorna in 2001. Attempts to use this strategy during the 1997 Isla Sorna incident by Dr. Ian Malcolm were unsuccessful as his colleagues did not comply with his directions.
The standstill method does not always work, and tyrannosaurs are not always encumbered by this trait when hunting. During the 1997 and 2001 incidents, tyrannosaurs encountered humans on several occasions and were able to perceive them even when standing relatively still. This is because the Tyrannosaurus has a superior olfactory sense, as well as a strong auditory sense. It can smell or hear nearby animals even if they are not moving. This is an intelligent animal with object permanence capabilities, so if an animal seems to vanish, the tyrannosaur may still attempt to flush it out of hiding. This was observed directly during the 2001 incident; a group of plane-crash survivors led by Dr. Alan Grant stumbled upon a tyrannosaur feeding ground and the animal itself, but froze still before it had spotted them. The presence of a large partially-eaten carcass would have overwhelmed the tyrannosaur’s sense of smell, so the humans were protected in this way. Despite this, they had been running through the forest and speaking to each other, so the animal was aware of their presence. Using a startlingly loud roar, it was able to frighten them into motion so that it could see them.
In actuality, there is no evidence of any specific dinosaur having vision so heavily reliant upon motion. Tyrannosaurids in particular had binocular vision and are believed to have had superb eyesight. Among all of the theropods, only modern-day birds of prey such as eagles have comparably good vision. While other theropods did not have vision as acute as tyrannosaurs, none are thought to have vision based largely on the movement of objects against the background.