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At the root of number competence Meta-analysis of the literature on different animal species and an experimental contribution to the understanding of rudimental numerical abilities in an animal model, the young domestic chick (Gallus gallus)
No full textLa capacità di rappresentarsi esattamente i numeri e di risolvere problemi aritmetici è stata per lungo tempo considerata una prerogativa degli esseri umani. Tuttavia nell’ultimo decennio si è rinnovato l’interesse per lo studio delle abilità numeriche in soggetti non-verbali, allo scopo di capire il ruolo del linguaggio in questo tipo di compiti (rassegne in Gallistel e Gelman, 1992; Dehaene, 1997; Hauser e Spelke, 2004). La possibilità di impiegare test comportamentali, per lo studio di questi soggetti, fornisce un’opportunità unica nella comprensione dello sviluppo ontogenetico e filogenetico di queste abilità.
Il presente lavoro si compone di tre differenti serie di esperimenti volti ad indagare le abilità numeriche di base, impiegando tre differenti paradigmi sperimentali, in un modello animale: Il pulcino di pollo domestico (Gallus gallus).
Dai dati relativi alla prima serie di esperimenti, dove le abilità discriminative venivano testate mediante l’impiego di una scelta spontanea tra differenti numerosità in seguito all’imprinting filiale, è emerso come pulcini di tre giorni età siano in grado di discriminare spontaneamente (ovvero senza necessità di addestramento) set di oggetti anche quando le variabili continue vengono sperimentalmente controllate.
In un seconda serie di esperimenti, è stato indagato il sistema alla base delle abilità discriminative. In questo caso le variabili continue sono state controllate sia mediante l’impiego di stimoli di diversa grandezza che mediante l’impiego di stimoli parzialmente occlusi. Il successo nella discriminazione di 1 vs. 2 e di 2 vs. 3 oggetti unito al fallimento nella discriminazione di 4 vs. 6 e 3 vs. 4 ha portato a concludere che il sistema alla base delle abilità numeriche dei soggetti sia l’Object File System (che si fa carico della discriminazione di piccole numerosità con un limite situato intorno ai 2 vs.3 e 3 vs. 4) con un limite di 2 vs. 3 elementi.
In un’ultima serie si esperimenti sono state prese in considerazione le abilità numeriche ordinali. In seguito ad addestramento pulcini di cinque giorni di vita sono in grado di identificare un elemento unicamente sulla base della sua posizione in una serie di elementi identici quando le variabili spaziali, oggettuali e olfattive sono state tenute sotto controllo.
Complessivamente il valore innovativo di questi esperimenti consiste nell’aver indagato due differenti tipologie di abilità numeriche in soggetti animali giovani. Fatta eccezione per la specie umana, infatti, le abilità numeriche erano state indagate solo su animali adulti. Per la prima volta inoltre la capacità a discriminare tra differenti numerosità è stata verificata, in un test di scelta spontanea, quando le variabili continue sono state sperimentalmente controllate. La discriminazione di piccole numerosità può quindi essere effettuata utilizzando il solo indizio numerico: e’ quindi possibile affermare che il giudizio avvenga su base numerica e non solo protonumerica. E’ stato inoltre dimostrato che l’Object File System sia alla base delle abilità discriminative di questi soggetti. Per quanto concerne invece l’ordinalità, i pulcini a soli cinque giorni di età riescono ad utilizzare questo tipo di indizio per identificare una posizione target. L’asimmetria, in fase di generalizzazione, sbilanciata a sinistra sembra inoltre far pensare ad una dominanza emisferica destra nella risoluzione di questo tipo di compito
Left- right brain asymmetries in number space processing. An experimental investigation in the domestic chick (Gallus gallus).
No full textAt the root of number competence. Meta-analysis of literature on different animal species and an experimental contribution to the understanding of rudimental numerical abilities in an animal model, the young domestic chick (gallus gallus).
Full text linkDavis and Pérusse (1988) argued that, although animals can be trained to make numerical discriminations, they do so only as a last-resort strategy, when extensive training is provided and all other cues are eliminated. In spite of this criticism, in the last decade various types of numerical competences have been demonstrated in nonverbal creatures - namely pre-verbal infants and non-human species - that demonstrated the presence of number competence in the absence of language (reviews in Gallistel and Gelman, 1992; Dehaene, 1997; Hauser and Spelke, 2004).
In the present study three separate sets of experiments were carried out to investigate respectively: Spontaneous numerical discrimination following imprinting, number discrimination using a conditioning procedure and ordinal numerical competence.
In the first set of experiments, by employing a spontaneous choice paradigm, the ability to discriminate small sets of objects was confirmed in 3-day-old-chicks even when the continuous variables were controlled for. These data showed, for the first time, that spontaneous number discrimination can be based on numerical cues only.
In the second set of experiment, chicks' ability to discriminate between small sets of object (up to 3) was confirmed by employing operant conditioning procedures. What is interesting is that although training was done with only one specific set of stimuli, in which number co-varied with several continuous physical variables, the chicks seemed to encode number rather than physical variables. These data also provided the first evidence of numerical discrimination of partly occluded objects. Furthermore, discrimination of small numerosities in young chicks seems to be carried out using an Object File System, with a set-size limit of around 4 elements.
In the third set of experiments investigating ordinal abilities show that 5-day-old-chicks can successfully learn to identify a target on the exclusive basis of its serial position in a series of 10. A peculiar finding, in Experiment 4.3, was that whenever position had to be identified on a left/right oriented series, in the generalization test, chicks would more often find the correct position by starting from the left end of the series rather than from the right end. In the absence of environmental asymmetries a possible explanation would be that there is a right hemispheric dominance (left visual hemifield) for this sort of task. It would be interesting for future experiments to establish the limit of such ordinal ability, using a different apparatus with more positions as well as trying to understand the hemispheric asymmetry raised in this experiment.
All these data demonstrated the presence of rudimentary numerical competence even in a species so distant and so different from humans. These results support the hypothesis that numerical competences are not only a prerogative of adult humans but that such abilities should have an evolutionary precursor in animals
Number-space associations without language. Behavioral evidence from an animal model: the domestic chick (Gallus gallus).
No full textApproach direction and accuracy, but not response times, show spatial-numerical association in chicks
Full text linkChicks trained to identify a target item in a sagittally-oriented series of identical items show a
higher accuracy for the target on the left, rather than that on the right, at test when the series
was rotated by 90 ̊. Such bias seems to be due to a right hemispheric dominance in visuospatial tasks. Up to now, the bias was highlighted by looking at accuracy, the measure
mostly used in non-human studies to detect spatial numerical association, SNA. In the present study, processing by each hemisphere was assessed by scoring three variables: accuracy, response times and direction of approach. Domestic chicks were tested under
monocular vision conditions, as in the avian brain input to each eye is mostly processed by
the contralateral hemisphere. Four-day-old chicks learnt to peck at the 4th element in a sagittal series of 10 identical elements. At test, when facing a series oriented fronto-parallel,
birds confined their responses to the visible hemifield, with high accuracy for the 4th element.
The first element in the series was also highly selected, suggesting an anchoring strategy to
start the proto-counting at one end of the series. In the left monocular condition, chicks
approached the series starting from the left, and in the right monocular condition, they
started from the right. Both hemispheres appear to exploit the same strategy, scanning the
series from the most lateral element in the clear hemifield. Remarkably, there was no effect
in the response times: equal latency was scored for correct or incorrect and for left vs. right
responses. Overall, these data indicate that the measures implying a direction of choice,
accuracy and direction of approach, and not velocity, i.e., response times, can highlight
SNA in this paradigm. We discuss the relevance of the selected measures to unveil SNA
The use of proportion by young domestic chicks (Gallus gallus)
No full textWe investigated whether 4-day-old domestic
chicks can discriminate proportions. Chicks were trained to
respond, via food reinforcement, to one of the two stimuli,
each characterized by different proportions of red and
green areas ( vs. ). In Experiment 1, chicks approached
the proportion associated with food, even if at test the
spatial dispositions of the two areas were novel. In
Experiment 2, chicks responded on the basis of proportion
even when the testing stimuli were of enlarged dimensions,
creating a conflict between the absolute positive area
experienced during training and the relative proportion of
the two areas. However, chicks could have responded on
the basis of the overall colour (red or green) of the figures
rather than proportion per se. To control for this objection,
in Experiment 3, we used new pairs of testing stimuli, each
depicting a different number of small squares on a white
background (i.e. 1 green and 3 red vs. 3 green and 1 red or
5 green and 15 red vs. 5 red and 15 green). Chicks were
again able to respond to the correct proportion, showing
they discriminated on the basis of proportion of continuous
quantities and not on the basis of the prevalent colour or on
the absolute amount of it. Data indicate that chicks can
track continuous quantities through various manipulations,
suggesting that proportions are information that can be
processed by very young animals
Imprinted numbers
No full textA scientific interest in animal non-linguistic-numerical competence has been documented for almost 100 years (Rilling 1993). Although it has been argued that animals represent number as a last resource strategy and only following an extensive training (Davis and Pèrusse, 1988), a growing body of data suggests that different animal species can resolve different kinds of numerical problems spontaneously (o in absence of any training) (Wynn, 1992; Anderson 2003; Lyon, 2003). Nevertheless, it has become apparent that when the number of stimulus elements is contrasted with their overall area or contour length infants sometimes preferentially relied on the continuous physical extent (Xu, 2003; Clearfield and Mix, 1999; Feigenson, Carey and Hauser, 2002).
In the present work we focused of these two claims, investigating numerical spontaneous discrimination of social companions when all the continuous physical variables were controlled for.
Chicks were imprinted for three days with different numerosities of imprinting balls, because of the imprinting process, such objects were treated by chicks as social companions. At their 3rd day of life, each chick took part at a spontaneous preference test, where they were required to choose between a familiar numerosities of ball and a new one. We found that when the objects were similar, chicks faced with choices between 1 vs. 2 or 2 vs. 3 objects chose the set of objects of larger numerosity, irrespective of the number of objects they had been reared with. Moreover, when volume and area were controlled for using sets of 1 vs. 4 or 1 vs. 6 objects, chicks resorted to choosing the larger object, rather than the familiar numerosity. When, however, chicks were reared with objects differing in their aspect (colour, size, and shape) and then tested with completely novel objects (of different colour and shape but controlled for continuous extent), they chose to associate with the set of objects comprising the same number of elements they had been reared with during imprinting. These results suggest that identification of objects as different and separate individuals is crucial for the use of number rather than continuous extent in numerical representation of small numerosities and provide a striking parallel with results obtained in human infants. Early availability of small numerosity discrimination by chicks strongly suggests that these abilities are in place at birth
Rudimental numerical competence in 5-day-old domestic chicks (Gallus gallus): Identification of ordinal position
Full text linkNumerical competencies were investigated for the 1st time in very young nonhuman animals. Chicks (Gallus gallus) learned to identify the 3rd, 4th, or 6th positions in a series of 10 identical positions (Experiment 1). Use of spatial information (i.e., distances) was ruled out in Experiment 2 (chicks generalized the reinforced response to an array of stimuli rotated by 90 as compared with training) and Experiment 3 (chicks generalized their response to a series in which distances between the single positions had been manipulated). Chicks found the correct position even when both identity and distance of each position changed from trial to trial (Experiment 4). Overall, young chicks seemed to use ordinality when required to identify a target by its numerical serial position
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