Approach direction and accuracy, but not response times, show spatial-numerical association in chicks

Abstract

Chicks 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.

Hybro chicks outperform Ross308 in a numerical-ordinal task. Cognitive and behavioral comparisons between 2 broiler strains of newborn domestic chicks (Gallus gallus)

“…Food rewards following correct responses were administered only in pre-established trials (i.e., trial 4, 5, 7, 10, 13, 14, 16, and 19). In all testing trials (rewarded and unrewarded), the chicks kept searching for food because all items looked identical and this task was associated with food during training ( Rugani et al, 2011 , 2016b ; Rugani and Regolin, 2020 , 2021 ). This variable reward schedule has been designed to maintain motivation for food throughout the test, preventing response extinction over multiple unrewarded trials ( Rugani et al, 2016b ; Rugani and Regolin, 2020 ).…”

“…Regardless of changes in the location of the series, the position of the containers, and the distance between them from trial to trial, day-old chicks succeeded ( Rugani et al, 2007 , 2011 , 2016b ; Rugani and Regolin, 2020 , 2021 ). The secondary role of the spatial cue in performing an ordinal task has also been proved when ordinal and spatial cues were pulled apart.…”

“…Chicks consistently selected the container that was associated with food during training, but they may have relied on either numerical or spatial information. To rule out the possibility that chicks relied on cues other than ordinal, in subsequent studies birds were trained and tested for their ability to select the 4th container ( Rugani et al, 2011 ; 2016b ; Rugani and Regolin, 2020 , 2021 ).…”

“…Given their symmetrical distribution on the left and right space, the 4th left and right containers should have been selected equally often. Instead, only the left one was selected above chance ( Rugani et al, 2010a , 2011 ; Rugani and Regolin, 2021 ). The result implies that the search for an ordinal position from left to right exists without immersion in a culture that reads and writes from left to right, which has long been a major explanation of the human spatialization of numbers ( Shaki et al, 2009 ), as in the Mental Number Line where small numbers are typically on the left and larger ones on the right ( Galton, 1880 ; Dehaene et al, 1993 ; Dehaene, 2011 ).…”

“…Despite their scientific relevance regarding the identification of the precocious ability of avian species to encode and use ordinal cues, these studies imply methods that have been focused on a group-level analysis of performance. Moreover, the subjects could advance to test after they have reached an arbitrary and preestablished learning criterion of at least 8 correct responses across 20 valid trials ( Rugani et al, 2007 , 2010a , 2011 , 2016b ; Rugani and Regolin, 2020 , 2021 ). Thus, each bird may have received a different amount of training before testing, canceling individual differences in the acquisition.…”