The numerical ordination of quantities would intuitively be thought to be just a unique humanly ability. However, the numerical capacity of perceiving number has been evident in non-human animals too, including dolphins, birds, chimps, ants, and bees.
It is thought that the ability to recognise numbers is an innate ability that is not driven by conscious operation. This process of subitizing refers to the immediate apprehension and perceptual enumeration of small quantities, without recourse to any previously learned mathematical ability. It leads to the effortless visualization of a small number of objects. For instance, if one were to roll a die, one would be able to make an absolute and accurate judgement on the arising number of dots without having to count them, given that the numerosities are limited (<6).
It is a point of contention 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. However, in diametric opposition is the notion that counting competencies do arise prior to the process of subitizing. Indeed, children have shown a basic ability to subitize limited numerosities, without being able to count them. In addition, 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, the reaction times steepen in a markedly rapid fashion as six items are surpassed. However, other propositions have argued that subitizing is in itself a form of counting. This proposition adopts the notion that subitizing involves a form of very rapid, albeit non-instantaneous counting. In this view, there is significant overlap between both processes since subitizing, like counting, also involves some sort of individualistic representation and organizing of the numerical sets. This is suggested by the notion that if the numerical sets are superimposed and not positioned in a discretely separate manner, the subject employs counting rather than subitizing.
Such 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 the 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 able to count. A landowner had been quite bothered by the crow since it had chosen to nest in his watch-house. He had planned to shoot it. The bird 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 it, the landowner had two people enter the watch-house and one leave. The crow was not deceived by this malicious plan, even when three men entered and two 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 shows 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 could be argued that subitizing involves some sort of empirical abstraction. For instance, to get back to the die example, one can subitize a perceptual pattern and associate it with a word, the case of which would not require the concept of a number. A frequently recurring perceptual stimulus is elicited to match information form 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).
This innate numerical capacity of subitizing is a process that is prevalent among non-human species and the range of which is also possessed by humans. Human adults, human infants, and nonhuman species can 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.