The ability to numerically ordinate quantities or perceive number is intuitively thought to be a unique human capacity. Such an ability, however, has been demonstrated in non-human animals all the same, including but not limited to dolphins, birds, chimps, ants, and bees.
It is thought that the ability to perceive number is an innate ability that is not driven by conscious operation. This is known as subitizing and it refers to an immediate apprehension and perceptual enumeration of small quantities, without recourse to antecedent learned ability. It leads to an effortless visualization of a small number of objects. If one were to roll a die, one would be able, given limited numerosities (<6), to make an absolute and accurate judgement regarding the arising number of dots without having to count them. One is said to have subitized the dots.
It is contentious where the process of counting in humans develops in relation to the process of subitizing. It is thought that subitizing is an inner process out of which counting is then evolved. In opposition is the notion that counting competencies do arise prior to the process of subitizing. Children, however, show a basic ability to subitize limited numerosities, without being able to count them. Further, data from studies show that reaction time increases, as the number of items in a numerical set increases, lending credence to the former proposition. Indeed, reaction times steepen in a markedly rapid fashion as six items are surpassed. The idea that subitizing is in itself a form of counting has also been advanced. This adopts the notion that subitizing involves a form of very rapid, albeit non-instantaneous counting. In this proposition, there is significant overlap between both processes since subitizing, like counting, also involves some sort of individualistic representation and organizing of numerical sets. This is reinforced by the notion that when numerical sets are superimposed rather than positioned in a discretely separate manner, a subject employs counting rather than subitizing.
Accurate numerosity judgements and immediate perception of numeracy, as explicated by the process of subitizing, is thought to be employed by animals such as dolphins, rats, ravens, birds, chimpanzees, and bees. Rambaugh et al. 1987 showed that chimps would choose trays with food wells containing the larger number of chocolate chips. The chimpanzees merely recognize the number but do not count. Similarly, a raven is immediately able to visually perceive a pattern of dots.
Sir John Lubbock in his book, On the Senses, Instincts, and Intelligence of Animals, speaks of his “bird-nesting recollections”. He noted that if two eggs are removed from a nest containing four eggs, it is consequently deserted by the bird. He also recounts an observational recollection of a crow that was shown to have employed to ability to count. In this example, a landowner had been quite bothered by a crow that had chosen to nest in his watch-house. He had planned to shoot it. The bird, however, would fly away and wait until the landowner had left to return to its nest inside the watch-house, given that no-one would be inside to shoot it. In order to deceive the bird, the landowner had two people enter the watch-house and one leave. The crow, however, was not deceived by the plot, even when three men had entered and two had left. It wasn’t until five men had entered the tower and four had left that the bird did eventually fly back inside the watch-house. The crow thus showed a certain numerical ability to count up until four but not five.
It can be argued that when animals subitize, they are not counting. Counting involves the attentional reciting of an invariant sequence for the items presented and the assigning of a numerical label for each item. Subitizing, however, does not involve any sequential counting. It may even involve some sort of empirical abstraction. For instance, in the die example, one can subitize a perceptual pattern and associate it with a word, the case of which would not require any concept of a number. A frequently recurring perceptual stimulus is elicited to match information from an initial short-term stimulus, hence the short numerosity range of 4 associated with subitizing (Simon, 1997). Subitizing animals can accordingly take a numerical snapshot of a stimulus and compare it with a test pattern (Rambaugh and Washburn, 1993).
The innate capacity of subitizing is a process that is inherent in non-human species as well as humans. Human adults, human infants, and nonhuman species can all immediately apprehend and subitize small numerosities in their visual field, without thinking about them.
Rambaugh DM, Savage-Rambaugh ES, Hegel M (1987) Summation in a chimpanzee (Pan troglodytes). J Exp Psychol. 13: 107 – 115.
Simon, TJ (1997) Reconceptualizing the origins of number knowledge: A “non-numerical” account. Cognitive Development. 12: 349 – 372.
Rambaugh DM and Washburn, DA (1993) Counting by chimpanzees and ordinality judgements by macaques in video-formatted tasks. In ST Boysen and EJ Capaldi (Eds.), The Development of Numerical Competence: Animal and Human Models. Hillsdale, NJ: Erlbaum.