Number sense in animals
[3] At the beginning of the 20th century, Wilhelm von Osten famously, but prematurely, claimed human-like counting abilities in animals on the example of his horse named Hans.
His claim is widely rejected today, as it is attributed to a methodological fallacy, which received the name Clever Hans phenomenon after this case.
Today, the arithmetic abilities of Clever Hans are commonly rejected and the case serves as a reminder to the scientific community about the necessity of rigorous control for experimenter expectation in experiments.
[4] In one of his studies[5] he showed that a raven named Jacob could reliably distinguish the number 5 across different tasks.
The experimental setup for the study of numerical cognition in animals was further enriched by the work of Francis[6] and Platt and Johnson.
If the animal prefers a bigger number of pieces also in this condition, the alternative explanation is rejected, and the claim of numerical ability supported.
[9] The approximate number system (ANS) is fairly imprecise and relies heavily on cognitive estimation and comparison.
This system does not give numbers individual value, but compares quantities based on their relative size.
The efficiency of this ANS depends on Weber’s law, which states that the ability to distinguish between quantities is dictated by the ratio between two numbers, not the absolute difference between them.
The tendency of macaques to categorize and equate groups of items by number is extremely suggestive of a functioning ANS in primates.
[9] This social numerical superiority concept exists across many primate species and displays the understanding of power in numbers, at least in a comparative way.
[13] The number skill most thoroughly supported in primates is ordinality – the ability to recognize sequential symbols or quantities.
[17] Rather than merely determining if a value is greater or less than another like the ANS, ordinality requires a more nuanced recognition of the specific order of numbers or items in a set.
[20] Without being provided with visual representation of the quantity that the number represented, this task signified a more advanced cognitive ability— differentiating symbols based on how they relate to each other in a series.
This is because it requires the understanding that each number is a symbolic representation of a unique quantity that can be manipulated mathematically in a distinct way.
[11] The PIS unlike the ANS, is therefore independent of the need for comparison, allowing each number to exist on its own with a value defined by arithmetic.
[15] For example, the "chimp challenge" only displayed primates' understanding that three exists before four and after two, not that three can act on its own and independently hold a consistent value.
Once a primate has been trained on a task long enough to display the PIS, the results are usually attributed to mere associative learning rather than exact number comprehension.
Essentially, it can give one a number sense without needing to understand the numerical system at low quantities.
For example, preference for a bigger social group in mosquitofish was exploited to test the ability of the fish to discriminate numerosity.
A raven named Jacob was able to distinguish the number 5 across different tasks in the experiments by Otto Koehler.
[28][29] In highly social species such as red wood ants scouting individuals can transfer to foragers the information about the number of branches of a special “counting maze” they had to go to in order to obtain syrup.
Similar to some archaic human languages, the length of the code of a given number in ants’ communication is proportional to its value.
