A strategy to improve arithmetical performance in four day-old domestic chicks (Gallus gallus)

Abstract

A large body of literature shows that non-human animals master numerical discriminations, but a limit has been reported in a variety of species in the comparison 3vs.4. Little is known regarding the possibility of using “cognitive strategies” to enable this discrimination. The aims of this study were to investigate: whether domestic chicks discriminated 3vs.4, and if changes in stimuli presentation could improve chicks’ numerical performance. Newly hatched chicks were reared with seven identical objects. On day 4, they underwent 20 consecutive testing trials to assess their capability to discriminate 3vs.4. The objects were presented, one-by-one, to the chicks and hidden behind one of two identical panels. As expected, the chicks did not discriminate (Experiment 1). When objects were presented and hidden in groups comprising one or two objects (2 + 1)vs.(2 + 2), the chicks succeeded (Experiment 2). The grouping strategy did not help in the case of a harder discrimination of (3 + 1)vs.(3 + 2) (Experiment 3), unless chicks were allowed to rest for two hours between testing sessions (Experiment 4). Our results suggest that in some cases, the limits reported for numerical performance in animals do not depend on cognitive limitations but on attentional or motivational factors, which can be overcome employing simple procedural adjustments.

Individually distinctive features facilitate numerical discrimination of sets of objects in domestic chicks

“…In the absence of such features (i.e. when all objects were identical), the chicks failed the 3 vs 4 discrimination (Experiment 1), which is consistent with previous results 21 . Experience with a set of heterogeneous objects in which each stimulus www.nature.com/scientificreports/ presents individually distinctive features might reduce the cognitive load involved in creating representations of the stimulus sets, facilitating the comparison between the groups.…”

“…In Experiment 1, we used all identical objects (red squares, Fig. 1a), and we expected the chicks to be unable to discriminate between them, consistent with previous evidence 21 . In Experiment 2, each square differed from the others in terms of the relative orientation of two black segments (Fig.…”

“…The chicks' performance did not differ from chance when considering only the first five trials: M = 0.387; ES = 0.066; V = 37, p = 0.195, r = − 0.341. Hence, their overall performance did not seem to depend on a progressive decrease in motivation or attention, which might have occurred during testing 21 . The chicks seemed unable to discriminate between 3 and 4 identical objects when these were presented and hidden in spatiotemporal discontinuity.…”

“…Day-old domestic chicks reared with identical objects, when presented with sets of 2 vs 3, 1 vs 4, 1 vs 5 and 2 vs 4 objects that disappear one-by-one behind separate panels spontaneously inspect the panel occluding the larger set 18,19 . Chicks discriminate between large numerousnesses, such as 6 vs 9 and 5 vs 10 20 but fail with 3 vs 4 21 . This is consistent with findings on infants that report an upper limit of 3 in tracking and representing multiple occluded objects [22][23][24] .…”

“…Failure could occur because the ratio is difficult (too small) to discern using the AMS or because the number of elements exceeds the OFS limit. Interestingly, the use of cognitive strategies, such as grouping, improves numerical discrimination (probably by increasing object storage in the working memory) in infants [25][26][27] and chicks 21,28 . Grouping strategies in particular may be crucial in the absence of linguistic labels or when stimuli only allow for category-level processing, such as when objects are identical and cannot be distinguished at the individual level.…”