ArticlePDF Available

Quantity discrimination in felines: A preliminary investigation of the domestic cat (Felis silvestris catus)

Authors:

Abstract and Figures

A large body of studies has investigated the capacity of non-human primates, dogs, birds and lower vertebrates to estimate different quantities of objects or events. Little attention, however, has been devoted to felines, and no study has specifically concentrated on cats’ numerical cognition. The present study aims to investigate the capacity of domestic cats to distinguish between two and three dots in order to obtain food; results showed that cats can be trained to discriminate between the two quantities. Furthermore our research suggests that cats do not spontaneously use numerical information, but rather seem to make use of visual cues that co-vary with numerosity in order to solve the task.
Content may be subject to copyright.
SHORT COMMUNICATION
Quantity discrimination in felines: a preliminary investigation
of the domestic cat (Felis silvestris catus)
Paola Etel Pisa ÆChristian Agrillo
Received: 21 July 2008 / Accepted: 8 September 2008 / Published online: 2 October 2008
ÓJapan Ethological Society and Springer 2008
Abstract A large body of studies has investigated the
capacity of non-human primates, dogs, birds and lower
vertebrates to estimate different quantities of objects or
events. Little attention, however, has been devoted to
felines, and no study has specifically concentrated on cats’
numerical cognition. The present study aims to investigate
the capacity of domestic cats to distinguish between two
and three dots in order to obtain food; results showed that
cats can be trained to discriminate between the two quan-
tities. Furthermore our research suggests that cats do not
spontaneously use numerical information, but rather seem
to make use of visual cues that co-vary with numerosity in
order to solve the task.
Keywords Cat Numerical competence
Quantity discrimination Counting Animal cognition
Introduction
Numerical skills appear to be fairly widespread among
species: a large number of experiments conducted in the
laboratory and in the field have provided compelling evi-
dence that numerical abilities are not uniquely human
(Hauser et al. 2000). Lyon (2003), for instance, reported a
spontaneous use of numerical information in a natural
context as a strategy to reduce the costs of conspecific
brood parasitism in American coots. Previously, Wilson
et al. (2001) demonstrated how, in wild chimpanzees, the
decision to enter an intergroup contest depends on
favourable numerical asymmetries between the groups
rather than range location or other factors known to affect
response in other territorial species.
The ability to count seems to involve complex cognitive
skills, as outlined by Gelman and Gallistel (1978).
According to the authors, a robust definition of counting
should include five different principles: ‘one-to-one cor-
respondence’ (each component of a counted set must
correspond to one single numeron), ‘stable order’ (nume-
rons must be ordered in a sequence that is reproducible
every time), ‘cardinality’ (the last numeron in a sequence
also represents the total numerosity of the set), ‘abstrac-
tion’ (counting applies to homogeneous and heterogeneous
groups of objects of both physical and mental construction)
and lastly ‘order irrelevance’ (the number in which the
numerons correspond to each item is not important in the
counting process).
If, however, counting can be considered the highest
level of mathematical process, the simplest form of
numerical knowledge may be represented by a discrimi-
nation between two quantities, usually called ‘judgement of
relative numerosity’ (Anderson et al. 2005) or ‘quantity
discrimination’ (Agrillo et al. 2007; Stevens et al. 2007).
The ability to distinguish among different quantities may
have evolved to enhance survival of organisms in different
ecological contexts, such as foraging, group conflicts,
parental care and predator avoidance (Lyon 2003;
McComb et al. 1994; Wilson et al. 2001). It is possible that
quantity information may be more relevant in nature: for
example, in foraging situations animals often attempt to
maximise the amount of food acquired per unit time spent
foraging (Stephens and Krebs 1986). According to this,
P. E. Pisa
Psychology Department, Goethe-Universita
¨t,
Frankfurt am Main, Germany
C. Agrillo (&)
Department of General Psychology, University of Padova,
via Venezia 8, 35131 Padova, Italy
e-mail: christian.agrillo@unipd.it
123
J Ethol (2009) 27:289–293
DOI 10.1007/s10164-008-0121-0
even though number often predicts total amount, some-
times this is not the case, in particular when the size of food
items differs greatly (e.g. four very small grapes can be less
advantageous than three larger ones for a monkey). Ani-
mals may therefore use non-numerical quantitative
variables such as surface area as the basis for discrimina-
tion, especially when the goal is to maximise amount (and
not number), and it has been well demonstrated that the
overall area of the stimulus is one of the main non-
numerical cues used in quantity discrimination tasks when
visual stimuli are presented (Agrillo et al. 2008; Davis and
Perusse 1988; Feigenson et al. 2002).
To date, little attention has been focused on quantity
discrimination in felines. McComb et al. (1994) reported a
rare example of the use of quantity information in nature.
In playback experiments, recordings of single female lions
roaring and groups of three females roaring together were
played back, in order to simulate the presence of unfamiliar
intruders in the Serengeti National Park. Results showed
that defending adult females were less likely to approach
playbacks of three intruders than a single intruder; fur-
thermore, when the subjects approached three intruders,
they did so more cautiously. However, the exact nature of
such a skill is still unclear: since several features of the
stimuli tend to co-vary with numerosity, control experi-
ments are necessary to confirm whether felines can count
or, conversely, use other visual or auditory information to
compare two quantities. It is worth noting that, surpris-
ingly, we must record a lack of further studies in felines,
with the exception of a subsequent study on African lions
(Heinsohn 1997) in which, using a playback technique that
followed that of McComb et al. (1994), it was confirmed
that lionesses can distinguish among different quantities of
conspecifics roaring.
The present study aims to fill this gap. Four domestic
cats were initially trained to discriminate between groups
composed of two and three dots. Then, subjects were
observed in a control test, where the overall areas of the
stimuli were exactly matched within each pair of stimuli
presented, in order to see whether cats have previously
learned the task by counting the elements or, in contrast, by
comparing the amount of area (or other non-numerical cues
that co-vary with area and numerosity) between the two
groups.
Materials and methods
Subjects and stimuli
Four domestic pet cats (Felis silvestris catus) were used for
this experiment. Subjects were mature females (Nerina,
Wieso, Wilde and Suesse) between the ages of 4 and
5 years (mean age: 4.25). They were fed with meat and dry
cat food before and after the experiment. During the
training and test phases, however, no food was provided
outside the experimental session. The whole experiment
was set up inside a comfortable room in the private house
of the first author and videorecorded by a camera placed
behind the subjects and opposite the experimental setting.
Two green plastic bowls (11 cm diameter) were placed
40 cm apart, adjacent to a white wall. In the middle, an
opaque barrier (50 950 cm) divided the two bowls in
order to force the cats to choose between the two alterna-
tives soon after being released by the experimenter, thereby
reducing the potential influence of olfactory cues on the
cats’ choices. The cats were released 145 cm from the wall
where the two bowls were presented (Fig. 1). A sheet of A4
paper (21 929.7 cm) on which the stimuli were presented
was placed 10 cm above each bowl. The stimuli consisted
of a group of three black dots or a group of two black dots;
during the training phase all dots were the same size
(diameter: 3.07 cm). A total of 30 different pairs of stimuli
were used during the training; the position of the elements
was changed to avoid the cats learning how to distinguish
on the basis of the overall configuration of the stimuli
rather than on the quantity/numerosity of the sets.
In the test phase, the stimuli were figures that differed in
numerosity (three elements and two) but that were matched
for the overall area, i.e. elements in the two-dot groups
were enlarged and/or the elements in the three-dot groups
were reduced. Thirty different pairs (with different object
Fig. 1 Experimental setting used. Two bowls were placed the same
distance from the cat, and the bowl chosen by the subject was
recorded after each trial
290 J Ethol (2009) 27:289–293
123
sizes and positions) were used in the test phase. Also
during the test phase, the position of the elements was
varied.
Procedure
During the training phase, cats were individually observed
in a binary choice between two bowls: only the one asso-
ciated with the reinforced numerosity presented food
(commercial wet cat-food as normally eaten by the subjects
before the experiment). The empty bowl was scented at the
beginning and in the middle of each session with food to
prevent olfactory cues being used to find the reward. Fur-
thermore, a small amount of food was provided them
during each trial in order to reduce any olfactory cue and to
motivate cats to reach the bowls for the whole session. Two
cats (Suesse and Wieso) were reinforced toward the
smaller quantity (2), whereas the two other subjects
(Nerina and Wilde) were reinforced toward the larger
quantity (3).
Two 10-trial sessions were performed daily, one in the
morning and the second one in the afternoon, for 5 days,
and for a total of 100 trials. The location of food (and hence
the position of the two numerosities) was swapped in half
of the tests during each session: half of the trials presented
the reinforced numerosity on the left and the second half
presented it on the right. The position of the reinforced
quantity was randomly distributed within each session.
When cats found the reinforced bowl, they were allowed to
feed for a maximum of 10 s; a total of 10 s was also
allowed for the time between when they selected the empty
bowl and started the new trial. Only one experimenter was
inside the testing room during each trial. The experimenter
released the cat and stayed 80 cm behind the starting point
of the test. After the cat selected one bowl, the experi-
menter returned her to the starting point, while the other
experimenter entered the room and changed the stimuli.
However, the subject could not see any manipulation of the
stimuli since an opaque barrier was placed in front of her
by the experimenter who was near the cat.
In the test phase, we adopted an extinction procedure
used in other species with cognitive tasks that require a
training phase (Chiandetti and Vallortigara 2008; Sovrano
et al. 2007): neither bowl held food and no further rein-
forcement was therefore provided. Such a procedure was
similar to the previous training, except that a new set of
stimuli (with paired areas) was used. A total of 60 trials had
been planned (six overall sessions, two per day, ten trials
per session). However, since the cats’ motivation to select a
bowl in the absence of reinforcement was likely to decrease
with an increasing number of trials, a criterion was agreed
upon whereby the trials in which subjects spent longer than
5 min reaching any bowl should be discarded. The number
of trials that fell within this category differed for each cat
(17 Nerina, 4 Wilde, 24 Wieso, and 27 Suesse).
The cats’ ability to discriminate between the two
quantities was initially analysed by v
2
tests on the
frequency of choices between the groups; subsequently,
one-sample ttests on the proportion of accuracy were
performed to see whether cats were globally able to solve
both training and test phases. Statistical tests were carried
out with SPSS 15.0.
Results
Training: can cats learn how to distinguish between two
quantities?
Subjects easily learned to associate food and stimuli
(Fig. 2), preferentially selecting the bowl placed below the
reinforced quantity (Nerina, v
(1)
=17.640, P\0.001;
Wilde, v
(1)
=33.640, P\0.001; Wieso, v
(1)
=27.040,
P\0.001; Suesse, v
(1)
=19.160, P\0.001). Thereby,
we observed an overall ability to distinguish between the
two quantities when the proportion of correct choices was
analysed (mean ±SD: 0.758 ±0.034; one sample ttest,
t
(3)
=15.132, P\0.001). A subsequent analysis showed
that the overall proportion of correct choices in the first half
of the training (1–5 sessions) statistically differed from the
proportion of correct choices in the following trials (6–10
sessions; paired ttest, t
(3)
=-6.794, P=0.007).
Test: do cats use non-numerical cues to solve the task?
Two cats successfully discriminated the reinforced quantity
when the overall area between the two stimulus sets was
equated (Nerina, v
(1)
=10.256, P\0.001; Suesse,
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1
1
Nerina
Wilde
Wieso
Suesse
Training Sessions
Proportion of choices toward the reinforced quantity
2345678910
Fig. 2 Proportion of correct choices of the four subjects during the
10 training sessions
J Ethol (2009) 27:289–293 291
123
v
(1)
=9.308, P=0.002) whereas no significant choice
was found for the other two subjects (Wilde, v
(1)
=0.286,
P=0.593; Wieso, v
(1)
=1.778, P=0.182, Table 1). An
overall analysis indicated that the cats did not correctly
choose the reinforced quantity when the area was con-
trolled for (0.633 ±0.126; t
(3)
=2.111, P=0.125).
A subsequent analysis on the proportion of correct
choices of the first session (10 trials) revealed that subjects’
performance at the beginning of the extinction procedure
(Nerina, 71% correct choices, v
(1)
=1.286, P=0.257;
Wilde, 50% correct choices, v
(1)
=0.000, P=1.000;
Suesse, 70% correct choices, v
(1)
=1.600, P=0.206;
Wieso, 60% correct choices, v
(1)
=0.400, P=0.527) was
positively correlated with the proportion of correct choices
of the following trials (r=0.994, P=0.006).
Discussion
The present work is intended to be a preliminary study of
cats’ numerical competence. We demonstrated that cats
can easily discriminate between different quantities of dots.
The ability to select the largest quantity may be used in
different ecological contexts, and feeding behaviour, in
which animals try to maximise the amount of food, rep-
resents one of the most important situations. To date, apart
from the McComb et al. study (1994) and a subsequent
investigation on African lions (Heinsohn 1997), this work
represents the only experimental evidence on rudimentary
quantity discrimination abilities in felines.
Results of the training phase clearly showed that cats
can learn how to distinguish between two groups of ele-
ments differing in numerosity. The fact that cats’
performance was more accurate in the second half of the
training phase demonstrates how quantity discrimination in
this task was learned over the trials and was not sponta-
neously achieved by the subjects, as has instead been found
in other species (Hauser et al. 2000; Uller et al. 2003).
On the other hand, results of the test phase provided
evidence that subjects did not strictly use numerical
information but rather seemed to analyse the quantity of
area of the dots, as has also been observed in non-human
primates (Tomonaga 2008). The fact that cats’ performance
during the first trials of the test was very similar to what
was exhibited in the following trials strongly supports the
idea that the reduced motivation resulting from the
extinction procedure cannot be the basis for the minor
accuracy of subjects’ response when the area was con-
trolled for.
It is not possible at present to exclude the possibility that
cats can use other non-numerical variables (such as the sum
of their contours and the density of the elements) that
cannot be fully matched when we control for the area.
Regardless of the exact perceptual cue involved, non-
numerical information seems to be spontaneously preferred
to numbers in a quantity discrimination task, as previously
observed in other vertebrates such as human infants
(Feigenson et al. 2002), apes (Beran et al. 2008), monkeys
(Stevens et al. 2007) and fish (Agrillo et al. 2008).
The trend exhibited by the subjects during the training
demonstrates that our procedure may be successfully
used in further studies on cats’ cognition, particularly to
extend research into felines’ numerical competence. For
instance, the next step of the project will involve a
training procedure where the range of the possible non-
numerical cues (such as area, contour, brightness and
density of the elements) will be fully investigated. Once
we understand the exact mechanism employed by cats to
distinguish between two quantities, continuous variables
will be matched from the start of the initial training
phase. Further research employing the methodology
presented here will therefore address whether or not cats
possess the ability to discriminate between two quantities
by counting each element.
However, we have now provided clear evidence on
quantity discrimination in felines. The literature on the
capacity for discriminating among sets containing different
numbers of objects, previously reported in human babies,
several non-human mammals, birds and fish is therefore
extended to include the domestic cat as well.
Acknowledgments The authors would like to thank the two anon-
ymous referees for their comments and useful suggestions. The
reported experiments comply with all laws of the country (Italy) in
which they were performed.
References
Agrillo C, Dadda M, Bisazza A (2007) Quantity discrimination in
female mosquitofish. Anim Cogn 10:63–70
Agrillo C, Dadda M, Serena G, Bisazza A (2008) Do fish count?
Spontaneous discrimination of quantity in female mosquitofish.
Anim Cogn 11(3):495–503
Anderson US, Stoinski TS, Bloomsmith MA, Marr MJ, Smith AD,
Maple TL (2005) Relative numerousness judgment and summa-
tion in young and old western lowland gorillas. J Comp Psychol
119(3):285–295
Table 1 Overall percentage of correct choices during training and
test phase for each cat
Subject Reinforced toward Percentage of correct choices during
Training (%) Test (%)
Nerina 3 71 74
Wilde 3 79 46
Suesse 2 77 82
Wieso 2 76 61
292 J Ethol (2009) 27:289–293
123
Beran MJ, Evans TA, Harris EH (2008) Perception of food amounts
by chimpanzees based on the number, size, contour length and
visibility of items. Anim Behav 75:1793–1802
Chiandetti C, Vallortigara G (2008) Is there an innate geometric
module? Effects of experience with angular geometric cues on
spatial re-orientation based on the shape of the environment.
Anim Cogn 11:139–146
Davis H, Perusse R (1988) Numerical competence in animals:
definitional issues, current evidence and a new research agenda.
Behav Brain Sci 11:561–579
Feigenson L, Carey S, Spelke ES (2002) Infants’ discrimination of
number vs. continuous extent. Cogn Psychol 44:33–66
Gelman R, Gallistel CR (1978) The child’s understanding of numbers.
Harvard University Press, Cambridge
Hauser MD, Carey S, Hauser LB (2000) Spontaneous number
representation in semi-free-ranging rhesus monkeys. Proc R Soc
Lond B Biol Sci 267:829–833
Heinsohn R (1997) Group territoriality in two populations of African
lions. Anim Behav 53:1143–1147
Lyon BE (2003) Egg recognition and counting reduce costs of avian
conspecific brood parasitism. Nature 422:495–499
McComb K, Packer C, Pusey A (1994) Roaring and numerical
assessment in the contests between groups of female lions,
Panther leo. Anim Behav 47:379–387
Sovrano VA, Bisazza A, Vallortigara G (2007) How fish do geometry
in large and in small spaces. Anim Cogn 10:47–54
Stephens DW, Krebs JR (1986) Foraging theory. Princeton University
Press, Princeton
Stevens JR, Wood JN, Hauser MD (2007) When quantity trumps
number: discrimination experiments in cotton-top tamarins
(Saguinus oedipus) and common marmosets (Callithrix jacchus).
Anim Cogn 10:429–437
Tomonaga M (2008) Relative numerosity discrimination by chim-
panzees (Pan troglodytes): evidence for approximate numerical
representations. Anim Cogn 11(1):43–57
Uller C, Jaeger R, Guidry G, Martin C (2003) Salamanders
(Plethodon cinereus) go for more: rudiments of number in a
species of basal vertebrate. Anim Cogn 6:105–112
Wilson ML, Hauser MD, Wrangham RW (2001) Does participation in
intergroup conflict depend on numerical assessment, range
location, or rank for wild chimpanzees? Anim Behav 61:1203–
1216
J Ethol (2009) 27:289–293 293
123
... As with discriminating natural categories, discriminating between objects that vary in mass or quantity may be relatively primordial and shared broadly in the animal kingdom because of the adaptive value of being able to discriminate larger and smaller amounts of food, prey, mating opportunities, and the like. Quantity discrimination is also one of the more heavily researched topics in comparative cognition; as such, there are data from several carnivore species, such as dogs (Ward & Smuts, 2007), cats (Bánszegi, et al., 2016;McComb, Packer, & Pusey, 1994;Pisa & Agrillo, 2009), raccoons (Davis, 1984) and bears (Vonk & Beran, 2012). Most of the work with carnivores has used actual food items as stimuli (Bánszegi et al., 2016;Ward & Smuts, 2007), although McComb et al. (1994) assessed the ability of lions (Panthera leo) to detect how many lions were vocalizing using auditory stimuli. ...
... Cats have also been trained to choose between two and three dots (Pisa & Agrillo, 2009), but some have argued that trained, versus spontaneous, discriminations may be less informative in revealing the underlying strategies used by a species as a response to contingencies found in nature (Agrillo & Bisazza, 2014). That is, an animal's ability in a given context reflects the contingencies of the current task demands, and not necessarily innate abilities. ...
Article
Full-text available
Although categorization abilities may serve as the foundation for most other complex cognitive processes, this topic has been grossly understudied in the order Carnivora. However, there are a growing number of studies examining the abilities of bears, felines, and canines to discriminate among stimuli that could represent conceptual categories. These studies are few in number compared to the extensive work conducted on non-human primates, but, thus far, results suggest that carnivores show comparable abilities to, for example; form natural categories, discriminate quantities, recognize cues of human emotion, and to discriminate kin. There is little existing work exploring concepts of sameness and relational reasoning in carnivores, and work on social concepts, such as representations of mental states, exist only in canines. Future studies are necessary to better understand the mechanisms underlying carnivores’ categorization abilities and conceptual representations. Furthermore, future work should focus on differences in conceptual ability as a function of social lifestyle and dietary preferences within carnivores. Such studies will be helpful in understanding the evolutionary pressures responsible for conceptual processes in a variety of species, including humans.
... 16 and non-human animals e.g. 17,18 . Convex hull-the area of a shape that includes all the items of an array-represents another perceptual cue often used to estimate the quantity of items in a set e.g. ...
Article
Full-text available
In humans, numerical estimation is affected by perceptual biases, such as those originating from the spatial arrangement of elements. Different animal species can also make relative quantity judgements. This includes dogs, who have been proposed as a good model for comparative neuroscience. However, dogs do not show the same perceptual biases observed in humans. Thus, the exact perceptual/cognitive mechanisms underlying quantity estimations in dogs and their degree of similarity with humans are still a matter of debate. Here we explored whether dogs are susceptible to the connectedness illusion, an illusion based on the tendency to underestimate the quantity of interconnected items. Dogs were first trained to choose the larger of two food arrays. Then, they were presented with two arrays containing the same quantity of food, of which one had items interconnected by lines. Dogs significantly selected the array with unconnected items, suggesting that, like in humans, connectedness determines underestimation biases, possibly disrupting the perceptual system’s ability to segment the display into discrete objects. The similarity in dogs’ and humans’ susceptibility to the connectedness, but not to other numerical illusions, suggests that different mechanisms are involved in the estimation of quantity of stimuli with different characteristics.
... It has been found that adult domestic cats (Felis silvestris catus) are able to discriminate between quantities differing in both number and size in a manner similar to humans Pisa & Agrillo, 2009) and that they are also susceptible to the Delboeuf illusion when presented with two same-size food stimuli but on different-size plates (Szenczi et al., 2019). The latter study, however, drew attention to a potentially interesting phenomenon: the lack of correlation between individual performance in size discrimination and susceptibility to the Delboeuf illusion. ...
Article
To date, no studies have examined the ontogeny of susceptibility to visual illusions in nonhuman mammals. Our previous study on the perception of the Delboeuf illusion by adult cats suggested they perceive this illusion, and that the visual processing involved in size judgment differs in the presence or absence of a misleading surround. We therefore asked whether weanling kittens are susceptible to the Delboeuf visual illusion, as adult cats are. Like the adults, kittens were presented with a series of 2-way food choice tasks where same- or different-size food portions were presented on same- or different-size plates. In control trials, the kittens significantly discriminated between 2 different amounts of food on same-size plates and, like adults, they chose the larger amount; when the difference between the food amounts was greater, the kittens chose the larger amount more reliably. Olfactory control trials confirmed that kittens, like adults, used visual cues when comparing quantities in this setting. In contrast to adults, however, in the illusion trials with same-size food portions on different-size plates, the kittens did not choose either of the 2 different-size plates significantly above chance and so did not appear to perceive the illusion. This suggests heterochronicity in the development of the cat visual system in which the ability to discriminate sizes develops before susceptibility to an illusion using these stimuli. Remaining questions include at what age susceptibility to visual illusions emerges and whether this depends on continued maturation of the brain, on experience of the visual world, or both. (PsycInfo Database Record (c) 2021 APA, all rights reserved).
... Quantity assessments do not rely solely on the overall quantity of the stimulus set. For instance, cumulative surface area -the overall area covered by elements of a visual array -is often used as a proxy for the estimation of numerosity in human e.g., 16 and non-human animals e.g., 17,18 . Convex hull -the area of a shape that includes all the items of an array -represents another perceptual cue often used to estimate the quantity of items in a set e.g., 19,20 . ...
Preprint
Full-text available
In humans, numerical estimation is affected by perceptual biases, such as those originating from the spatial arrangement of elements. Different animal species can also make relative quantity judgements. This includes dogs, who have been proposed as a good model for comparative neuroscience. However, dogs do not show the same perceptual biases observed in humans. Thus, the exact perceptual/cognitive mechanisms underlying quantity estimations in dogs and their degree of similarity with humans are still a matter of debate. Here we explored whether dogs are susceptible to the connectedness illusion, an illusion based on the tendency to underestimate the quantity of interconnected items. Dogs were first trained to choose the larger of two food arrays. Then, they were presented with two arrays containing the same quantity of food, of which one had items interconnected by lines. Dogs significantly selected the array with unconnected items, suggesting that, like in humans, connectedness determines underestimation biases, possibly disrupting the perceptual system’s ability to segment the display into discrete objects. The similarity in dogs’ and humans’ susceptibility to the connectedness, but not to other numerical illusions, suggests that different mechanisms are involved in the estimation of quantity of stimuli with different characteristics.
... Cats can also differentiate between the quantities of two and three and may use visual cues associated with quantity (Pisa & Agrillo, 2009). Lastly, cats possess the required neural mechanisms for color vision and can discriminate between some colors, such as blue from gray or green, if the stimuli has a large visual angle and stimulates a large retinal area (Loop, Bruce & Petuchowski, 1979). ...
Thesis
http://deepblue.lib.umich.edu/bitstream/2027.42/79456/1/kerei.pdf
... The strong reliance of cleaners on numerical cues contrasts with results from various other studies in which species use the cumulative surface area as a cue to discriminate between continuous quantities, such as other fish , cats (Pisa and Agrillo 2009), and humans (Feigenson et al. 2002). On the other hand, previous research on fish numbering skills employed a multitude of different quantities used in the tests, from a few to hundreds of elements (see review by Agrillo et al. 2017). ...
Thesis
Full-text available
There is substantial variation in either absolute or relative brain size between vertebrates. Comparing vertebrate species is the most commonly used method when exploring the link between brain size variation and ecological conditions. Nevertheless, there is an ongoing debate about whether the main selective factors on the evolution of brain complexity are driven by social or environmental challenges. Furthermore, the measures of brain complexity that correlate best with cognitive performance remain contested. It has thus been proposed that a “bottom-up” approach, by studying individual variation, may yield important complementary insights on the links between ecological conditions, cognitive performance and brain complexity. This PhD thesis aimed to use the bottom-up approach in a study on the cleaner fish Labroides dimidiatus. Cleaner fish engage in mutualistic cleaning interactions, by removing ectoparasites from a variety of “client” coral reef fishes. Previous research has documented a strong behavioural divergence within the same population in this species. Cleaners differed in their strategic sophistication in laboratory experiments that feature key aspects of cleaner-client interactions: 1) reputation management, wherein the adjustment of service quality in the presence of bystanders; and 2) cleaning service priority to clients with partner choice option. From this, the main question was which ecological factors can explain this behavioural variation. In Chapter I, the succession of environmental perturbations at the study site in Lizard Island, Great Barrier Reef, Australia, provided natural conditions for my experiment as the perturbations significantly altered ecological variables on the reef. The study consisted of collecting fish censuses and behavioural recordings at various reef sites around the island, as well as testing cleaners from these sites in the two laboratory-based cognitive tasks. I found that formerly socially complex sites with high fish densities, and cleaners with high strategic sophistication, recorded very low fish densities after the perturbations with cleaners showing low strategic sophistication in the tasks. This study suggests that individuals adjusted their strategic sophistication to the new ecological conditions from before to after the perturbations. In Chapter II, an analysis of fish censuses, behavioural recordings and cleaners’ performance in laboratory tasks over several years revealed that the reduction in cleaner density (i.e., a reduced supply in the cleaning biological market), was the primary driver of low strategic sophistication. Also, cleaner density was strongly correlated with large client density, suggesting that the results cannot be well explained by changes in the supply-to-demand ratio. Based on the results of Chapters I and II, I employed cleaner density as a proxy of both the intra- and interspecific social complexity in Chapter III and IV. The aim of Chapters III and IV were thus to investigate potential correlations between social complexity, strategic sophistication and brain complexity. In Chapter III, the magnetic resonance imagery (MRI) method was used to estimate with high precision the volumes of the five main brain major areas (i.e., telencephalon, diencephalon, mesencephalon, cerebellum, and brain stem). I found that cleaner density correlated positively with relative forebrain size (i.e., telencephalon and diencephalon together form the forebrain). Indeed, the forebrain harbours the “social decision-making network”; a network of brain nuclei involved in decision-making within a social context. These findings were mirrored in the outcomes of Chapter IV where I found a positive correlation between social complexity and the number of brain cells and neurons. Interestingly, strategic sophistication did not predict brain complexity. Instead, cleaners demonstrated social competence by displaying strategies that were optimal at their reef site of capture (i.e., low sophistication at low cleaner density, and high sophistication at high cleaner density). These cleaners also had relatively larger forebrains with more cells/neurons. The effect of size was strong, where there was a ~ 40 % difference in relative forebrain neuron count between low and high social complexity. In conclusion, this thesis provides unique insights on the links between ecology, cognition and brain features within a species. The results support the idea that the bottom-up approach may provide important insights into the selective pressures on brain complexity. Importantly, most of the documented variation is likely due to ontogenetic effects, as the egg and larval stages are pelagic in the cleaner fish species. This implies that laboratory experiments that manipulate key ecological factors during development can be used to test for potential effects on brain structure. According to the results, social complexity is a key factor driving forebrain size and cell/neuron number adjustments. Finally, the social competence analysis suggests that, in the case of cleaner fish, part of the selection on increased forebrain complexity is due to intraspecific social complexity.
... Among mammals, primates have been the main focus of research on comparative numerical cognition and not only different species demonstrated to possess this ability (Thomas and Chase, 1980;Brannon and Terrace, 1998;Anderson et al., 2005;Beran et al., 2008) but also they showed patterns of behavior very similar to those of humans Merten and Nieder, 2009). Numerical competences have been reported in rats (Davis and Albert, 1986), dogs (Ward and Smuts, 2007), cats (Pisa andAgrillo, 2009), lions (McComb et al., 1994), elephants (Perdue et al., 2012), and several other mammals. The main feature reported by these behavioral experiments is the animals' capacity to perceive the numerosity of sensory stimuli in an analog and noisy way, relying on an isomorphism between the physical quantity and its internal representation. ...
Article
Full-text available
The ability to represent, discriminate, and perform arithmetic operations on discrete quantities (numerosities) has been documented in a variety of species of different taxonomic groups, both vertebrates and invertebrates. We do not know, however, to what extent similarity in behavioral data corresponds to basic similarity in underlying neural mechanisms. Here, we review evidence for magnitude representation, both discrete (countable) and continuous, following the sensory input path from primary sensory systems to associative pallial territories in the vertebrate brains. We also speculate on possible underlying mechanisms in invertebrate brains and on the role played by modeling with artificial neural networks. This may provide a general overview on the nervous system involvement in approximating quantity in different animal species, and a general theoretical framework to future comparative studies on the neurobiology of number cognition.
... Animals that can judge relative quantities may be able to assess whether a location has more or less food, competitors, mates, or refuge for rearing young, and so quantity judgment has important implications for survival and reproduction. Previous studies have found that individuals from a wide variety of species (e.g., Gorillas, Gorilla gorilla gorilla: Anderson et al. 2005; Orangutans, Pongo pygmaeus abelii and Pongo pygmaeus pygmaeus: Anderson et al. 2007; Chimpanzees, Pan troglodytes: Beran et al. 2005; Rhesus monkeys, Macaca mulatta: Beran 2007a, b; Lions, Panthera leo: McComb et al. 1994; Spotted hyenas, Crocuta crocuta: Benson-Amram et al. 2011; Domestic dogs, Canis lupus familiaris: Bonanni et al. 2011;Miletto Petrazzini et al. 2020; Domestic cats, Felis silvestris catus: Pisa and Agrillo 2009;Chacha et al. 2020; Sea lions, Otaria flavescens: Abramson et al. 2011; Asian elephants, Elephas maximus: Irie-Sugimoto et al. 2009;Plotnik et al. 2019; Domestic horses, Equus caballus: Uller and Lewis 2009; African grey parrots, Psittacus erithactts: Pepperberg 1987Pepperberg , 2006Pepperberg , 2012 North island robins, Petroica longipes: Garland et al. 2012; Oriental fire-bellied toads, Bombina orientalis: Stancher et al. 2015; Red-backed salamanders, Plethodon cinereus: Uller et al. 2003; Eastern mosquito fish, Gambusia holbrooki: Agrillo et al. 2007Agrillo et al. , 2008; Mealworm beetles, Tenebrio molitor: Carazo et al. 2009) are able to discriminate whether one quantity is larger or smaller than another. There is still debate, however, about the mechanisms underlying relative quantity judgment and whether these mechanisms differ among species. ...
Article
Full-text available
Using an object-choice task, we measured the relative quantity discrimination ability of Asian elephants. Two zoo-housed elephants were given auditory cues of food being dropped into two containers (Nonvisible condition), and in one condition they could also see the food on top of the containers (Visible condition). Elephants received sets of varying ratios and magnitudes. We found that the elephants chose the greater quantity of food significantly above chance in both the Visible and Nonvisible conditions. Additionally, we found the elephants’ ability to discriminate between quantities decreased as the ratio, and not the absolute difference, between the quantities increased, which is predicted by the accumulator model. We also compare our findings to those from a study using the same methods with African savanna elephants and found that the two species performed at similar levels, but given our small sample size it is difficult to make strong species-level conclusions. In discussing our results, we consider differences between the two species’ wild environments as well as the types of sensory cues provided in human care, and we provide recommendations for extensions of this work.
... Carnivorans have been shown to discriminate quantity spontaneously in forced choice tests both in the wild and after training in the laboratory. The species that have been tested include dogs, cats, bears, lions, hyenas, sea lions and raccoons (West and Young, 2002;Pisa and Agrillo, 2009;Chacha et al., 2020;Vonk and Beran, 2012;McComb et al., 1994;Benson-Amram et al., 2011;Abramson et al., 2011;Davis, 1984). ...
Article
Full-text available
Many species from diverse and often distantly related animal groups (e.g. monkeys, crows, fish and bees) have a sense of number. This means that they can assess the number of items in a set – its ‘numerosity’. The brains of these phylogenetically distant species are markedly diverse. This Review examines the fundamentally different types of brains and neural mechanisms that give rise to numerical competence across the animal tree of life. Neural correlates of the number sense so far exist only for specific vertebrate species: the richest data concerning explicit and abstract number representations have been collected from the cerebral cortex of mammals, most notably human and nonhuman primates, but also from the pallium of corvid songbirds, which evolved independently of the mammalian cortex. In contrast, the neural data relating to implicit and reflexive numerical representations in amphibians and fish is limited. The neural basis of a number sense has not been explored in any protostome so far. However, promising candidate regions in the brains of insects, spiders and cephalopods – all of which are known to have number skills – are identified in this Review. A comparative neuroscientific approach will be indispensable for identifying evolutionarily stable neuronal circuits and deciphering codes that give rise to a sense of number across phylogeny.
Article
Full-text available
Background: Age-related dementia has been documented in domestic cats; however, its interaction with naturally occurring feline immunodeficiency virus (FIV) infection has been investigated minimally. Methods: Visuospatial working memory (VSWM) and problem-solving (PS) ability were evaluated in FIV-infected (n = 37) and control cats (n = 39) using two cognitive tasks tested serially, which assessed the ability of cats to remember the location of a baited container after a set delay, then evaluated the capability of the cats to manipulate the container to obtain the food within a time limit. Cats were categorized using 7 years of age as a cut-off to determine age-related differences. The relationship between cognitive performance and FIV viral load was investigated using real-time PCR cycle threshold (Ct ) values. Results: Age significantly affected VSWM and PS ability. Younger cats had better VSWM performance and PS ability compared to older cats with the same FIV status. There was no difference between younger FIV-positive and negative cats in either part of the task. While older FIV-positive cats had significantly worse VSWM than older FIV-negative cats, no differences were found in PS ability. Additionally, Ct values predicted VSWM but not PS ability. Conclusion: Age-related cognitive impairments and FIV infection appear synergetic, causing greater cognitive deficits in older FIV-infected cats.
Article
Full-text available
Numerical competence is one of the many aspects of animal cognition that have enjoyed a resurgence of interest during the past decade. Evidence for numerical abilities in animals has followed a tortuous path to respectability, however, from Clever Hans, the counting horse, to modern experimental studies. Recent surveys of the literaturereveal theoretical as well as definitional confusion arising from inconsistent terminology for numerical processes and procedures. The term “counting” has been applied to situations having little to do with its meaning in the human literature. We propose a consistent vocabulary and theoretical framework for evaluating numerical competence. Relative numerousness judgments, subitizing, counting, and estimation may be the essential processes by which animals perform numerical discriminations. Ordinality, cardinality, and transitivity also play an important role in these processes. Our schema is applied to a variety of recent experimental situations. Some evidence of transfer is essential in demonstrating higher-order ability such as counting or “sense of number.” Those instances of numerical competence in which all viable alternatives to counting (e.g., subitizing) have been precluded, but no evidence of transfer has been demonstrated might be described as “protocounting.” To show that animals are capable of “true” counting future research will have to demonstrate generality across situations.
Article
Full-text available
Seven studies explored the empirical basis for claims that infants represent cardinal values of small sets of objects. Many studies investigating numerical ability did not properly control for continuous stimulus properties such as surface area, volume, contour length, or dimensions that correlate with these properties. Experiment 1 extended the standard habituation/dishabituation paradigm to a 1 vs 2 comparison with three-dimensional objects and confirmed that when number and total front surface area are confounded, infants discriminate the arrays. Experiment 2 revealed that infants dishabituated to a change in front surface area but not to a change in number when the two variables were pitted against each other. Experiments 3 through 5 revealed no sensitivity to number when front surface area was controlled, and Experiments 6 and 7 extended this pattern of findings to the Wynn (1992) transformation task. Infants' lack of a response to number, combined with their demonstrated sensitivity to one or more dimensions of continuous extent, supports the hypothesis that the representations subserving object-based attention, rather than those subserving enumeration, underlie performance in the above tasks.
Article
Male chimpanzees, Pan troglodytes, engage in cooperative territorial defence and sometimes kill members of neighbouring communities. Observations of intergroup interactions suggest that escalation of aggression depends on numerical assessment, with lethal attacks occurring when numerical advantage reduces the costs of attacking. To gain a better understanding of the factors guiding participation in intergroup conflict, we conducted a series of playback experiments with the Kanyawara chimpanzee community of the Kibale National Park, Uganda. We tested whether the response to the playback of the 'pant-hoot' call of a single extragroup male depended on the number of adult males in the listening party, the location of the speaker relative to the territory edge, and each male's agonistic rank. These playbacks elicited cooperative responses, with the nature of the response depending on the number of adult males in the party. Parties with three or more males consistently joined in a chorus of loud vocalizations and approached the speaker together. Parties with fewer adult males usually stayed silent, approached the speaker less often, and travelled more slowly if they did approach. In contrast to many territorial species, the location of the simulated intruder did not affect the response. Although high-ranking males might be expected to benefit more from repelling outside males, both high-and low-ranking males showed a similar pattern of response. Each male responded as if he benefited from repelling intruders, but only if he had strength in numbers. This pattern of response is consistent with cooperation based on mutualism.
Article
Theoretical and experimental studies of assessment in animal contests have, until now, focused on disputes between single individuals. However, whereas single competitors usually avoid fights with opponents that are larger or stronger than themselves, in contests between social groups competitors might be expected to adjust their agonistic behaviour according to the number of individuals in their own and the opposing group. This hypothesis was tested using playback experiments to generate controlled artificial contests between groups of female lions. Recordings of single females roaring and groups of three females roaring in chorus were played back to simulate the presence of unfamiliar intruders within the territories of 21 different lion prides in Serengeti National Park, Tanzania. Defending adult females were less likely to approach playbacks of three intruders than of a single intruder and on occasions when they did approach three intruders they made their approach more cautiously. Defenders also carefully adjusted their decision to approach according to the size and composition of their own group, and attempted to recruit extra companions to the contest by roaring when some were absent at the time of playback. A strong selective advantage to avoiding the costs of fighting with larger groups could have led to the widespread evolution of numerical assessment skills in social species.
Article
Male chimpanzees, Pan troglodytes, engage in cooperative territorial defence and sometimes kill members of neighbouring communities. Observations of intergroup interactions suggest that escalation of aggression depends on numerical assessment, with lethal attacks occurring when numerical advantage reduces the costs of attacking. To gain a better understanding of the factors guiding participation in intergroup conflict, we conducted a series of playback experiments with the Kanyawara chimpanzee community of the Kibale National Park, Uganda. We tested whether the response to the playback of the ‘pant-hoot’ call of a single extragroup male depended on the number of adult males in the listening party, the location of the speaker relative to the territory edge, and each male's agonistic rank. These playbacks elicited cooperative responses, with the nature of the response depending on the number of adult males in the party. Parties with three or more males consistently joined in a chorus of loud vocalizations and approached the speaker together. Parties with fewer adult males usually stayed silent, approached the speaker less often, and travelled more slowly if they did approach. In contrast to many territorial species, the location of the simulated intruder did not affect the response. Although high-ranking males might be expected to benefit more from repelling outside males, both high- and low-ranking males showed a similar pattern of response. Each male responded as if he benefited from repelling intruders, but only if he had strength in numbers. This pattern of response is consistent with cooperation based on mutualism.
Article
Nonhuman animals reliably select the largest of two or more sets of discrete items, particularly if those items are food items. However, many studies of these numerousness judgments fail to control for confounds between amount of food e.g., mass or volume) and number of food items. Stimulus dimensions other than number of items also may play a role in how animals perceive sets and make choices. Four chimpanzees (Pan troglodytes) completed a variety of tasks that involved comparisons of food items (graham crackers) that varied in terms of their number, size, and orientation. In Experiment 1, chimpanzees chose between two alternative sets of visible cracker pieces. In Experiment 2, the experimenters presented one set of crackers in a vertical orientation (stacked) and the other in a horizontal orientation. In Experiment 3, the experimenters presented all food items one-at-a-time by dropping them into opaque containers. Chimpanzees succeeded overall in choosing the largest amount of food. They did not rely on number or contour length as cues when making these judgments but instead primarily responded to the total amount of food in the sets. However, some errors reflected choices of the set with the smaller total amount of food but the individually largest single food item. Thus, responses were not optimal because of biases that were not related to the total amount of food in the sets.
Article
Lionesses, Panthera leoin the Serengeti ecosystem, Tanzania, assess the odds of winning group-territorial contests by counting the number of opponents they hear roaring. They will approach intruders aggressively only if they outnumber them. Here the lionesses in the Serengeti are compared with another population living nearby but in strikingly different ecological circumstances. The lions of Ngorongoro Crater live at much higher densities owing to year-round availability of non-migratory prey species, but also suffer higher mortality from fighting. Playback experiments showed that lionesses in the crater differ from those in the Serengeti by approaching 'intruders' more quickly when the odds of winning are low. This increased aggression is interpreted in terms of the greater difficulty of holding a territory at high population density.
Article
Previous research has shown that animals possess considerable numerical abilities. However, this work was based on experiments involving extensive training, a small number of captive subjects and relatively artificial testing procedures. We present the results of experiments on over 200 semi-free-ranging rhesus monkeys using a task which involves no training and mimics a natural foraging problem. The subjects observed two experimenters place pieces of apple, one at a time, into each of two opaque containers. The experimenters then walked away so that the subjects could approach. The monkeys chose the container with the greater number of apple slices when the comparisons were one versus two, two versus three, three versus four and three versus five slices. They failed at four versus five, four versus six, four versus eight and three versus eight slices. Controls established that it was the representation of number which underlay their successful choices rather than the amount of time spent placing apple pieces into the box or the volume of apple placed in the box. The failures at values greater than three slices stand in striking contrast to other animal studies where training was involved and in which far superior numerical abilities were demonstrated. The range of success achieved by rhesus monkeys in this spontaneous-number task matches the range achieved by human infants and corresponds to the range encoded in the syntax of natural languages.
Article
Birds parasitized by interspecific brood parasites often adopt defences based on egg recognition but such behaviours are puzzlingly rare in species parasitized by members of the same species. Here I show that conspecific egg recognition is frequent, accurate and used in three defences that reduce the high costs of conspecific brood parasitism in American coots. Hosts recognized and rejected many parasitic eggs, reducing the fitness costs of parasitism by half. Recognition without rejection also occurred and some hosts banished parasitic eggs to inferior outer incubation positions. Clutch size comparisons revealed that females combine egg recognition and counting to make clutch size decisions--by counting their own eggs, while ignoring distinctive parasitic eggs, females avoid a maladaptive clutch size reduction. This is clear evidence that female birds use visual rather than tactile cues to regulate their clutch sizes, and provides a rare example of the ecological and evolutionary context of counting in animals.