Prenatal light exposure affects number sense and the mental number line in young domestic chicks
- Department of General Psychology, University of Padua, Italy
- Department of Psychology, The Ohio State University, United States
Figures
Figure 1
Illustration of the experimental apparatus and of the three conditions of vision.
(A) Array configuration used at training and sagittal test. (B) Array configuration used for the fronto-parallel tests. S.P. indicates the chick’s starting position. (C) Binocular condition of vision: both eyes, thus both hemispheres (left in red and right in blue), in use. (D) Right monocular condition with the right eye and the left hemisphere in use, in red. (E) Left monocular condition with the left eye and the right hemisphere in use, in blue. In monocular conditions, the eye not receiving light and its contralateral hemisphere are depicted in gray.
Figure 2
Results of Experiment 1.
The average percentage of chicks' choices (y-axis) as a function of item positions (x-axis), light exposure modulating brain lateralization, and tests. Error bars indicate ± standard error. Di chicks: n = 24, Li chicks: n = 24 (consistent across all tests). The gray dashed line indicates chance level (10%). Significant deviations from chance level were assessed through Wilcoxon one-sample signed-rank tests with Bonferroni correction (P < 0.001, P < 0.01, P < 0.05). (A) Results of the Sagittal test. (B) Results of the Fronto-Parallel Binocular test. (C) Results of the Fronto-Parallel Monocular Left test. (D) Results of the Fronto-Parallel Monocular Right test.
Figure 3
Results of Experiment 2.
The average percentage of chicks' choices (y-axis) as a function of item positions (x-axis), light exposure modulating brain lateralization, and tests. Error bars indicate ± standard error. Di chicks: n = 26, Li chicks: n = 26 (consistent across all tests). The gray dashed line indicates chance level (10%). Significant deviations from chance level were assessed through Wilcoxon one-sample signed-rank tests with Bonferroni correction (P < 0.001, P < 0.01, P < 0.05). (A) Results of the Sagittal test. (B) Results of the Fronto-Parallel Binocular test. (C) Results of the Fronto-Parallel Monocular Left test. (D) Results of the Fronto-Parallel Monocular Right test.
Figure 4
Time schedule of the experiments.
During the last 3 days of incubation, eggs were incubated either in darkness (weakly lateralized chicks) or under light exposure (strongly lateralized chicks). When chicks were 3 days of age, the shaping procedure started, followed by pre-training and training. In the following days, chicks were re-trained and then underwent all four tests.
Videos
Video 1
Visual summary of research outcomes: illustrative video of the experimental procedure and main results.
Tables
Table 1
Models and hypotheses explaining spatial-numerical association (SNA).
For each of the three main models, a brief explanation of the hypotheses regarding SNA mechanisms and the predicted outcomes for experiments 1 and 2 is reported.
| Model | Hypothesis | Predictions for experiment 1 | Predictions for experiment 2 |
|---|---|---|---|
| Right hemisphere dominance | Right hemisphere dominance in visuospatial attention. | Right hemisphere dominance leads to left-to-right scanning. The left bias should be more pronounced in light-incubated chicks. | Absence of spatial cues results in diminished involvement of the right hemisphere, and the left bias is predicted to be less pronounced. |
| Emotional valence | Left hemisphere dominance in processing positive emotions; right hemisphere dominance in processing negative emotions. | Left hemisphere processing of positive rewards (e.g. food) leads to a rightward bias. This should be more pronounced in light-incubated chicks. | Lack of spatial cues is not expected to cause differences compared to the predictions of Experiment 1. |
| Brain asymmetric frequency tuning (BAFT) | Left hemisphere dominance in high-frequency processing; right hemisphere dominance in low-frequency processing. | No bias is expected due to the symmetrical array configuration. No difference is expected between light- and dark-incubated chicks. | Lack of spatial cues is expected to have no significant impact on the predicted outcomes of experiment 1. |
Table 2
Descriptive statistics.
For each test in the two experiments, the accuracy of selecting the 4th item in the sagittal test and the 4L or 4R items in the fronto-parallel (FP) tests is reported.
| Experiment 1: Ordinal and spatial cue | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Test | Hatch condition | Choice | mean | SD | SE | n | r | p | BF |
| Sagittal | Di-chicks | 4 | 28.436 | 9.374 | 1.913 | 24 | 0.878 | <0.001 | >10,000 |
| Li-chicks | 4 | 36.382 | 8.164 | 1.666 | 24 | 0.88 | <0.001 | >10,000 | |
| FP binocular | Di-chicks | 4L | 18.958 | 10.527 | 2.149 | 24 | 0.727 | 0.005 | 169 |
| 4R | 19.792 | 11.371 | 2.321 | 24 | 0.724 | 0.003 | 188 | ||
| Li-chicks | 4L | 28.851 | 12.598 | 2.572 | 24 | 0.859 | <0.001 | >10,000 | |
| 4R | 11.894 | 7.503 | 1.532 | 24 | 0.337 | 0.798 | 0.741 | ||
| FP monocular left | Di-chicks | 4L | 12.780 | 8.309 | 1.696 | 24 | 0.376 | 0.532 | 1.287 |
| 4R | 3.990 | 6.154 | 1.256 | 24 | –0.708 | 1.000 | 0.05 | ||
| Li-chicks | 4L | 22.595 | 8.736 | 1.783 | 24 | 0.876 | <0.001 | >10,000 | |
| 4R | 6.297 | 6.747 | 1.377 | 24 | –0.465 | 1.000 | 0.068 | ||
| FP monocular right | Di-chicks | 4L | 3.746 | 3.668 | 0.749 | 24 | –0.798 | 1.000 | 0.013 |
| 4R | 13.417 | 8.781 | 1.792 | 24 | 0.406 | 0.398 | 1.936 | ||
| Li-chicks | 4L | 5.219 | 6.356 | 1.297 | 24 | –0.594 | 1.000 | 0.057 | |
| 4R | 21.484 | 10.734 | 2.191 | 24 | 0.807 | 0.001 | 1843 | ||
| Experiment 2: Ordinal cue only | |||||||||
| Test | Hatch condition | Choice | mean | SD | SE | n | r | p | BF |
| Sagittal | Di-chicks | 4 | 31.487 | 15.337 | 3.008 | 26 | 0.863 | <0.001 | >10,000 |
| Li-chicks | 4 | 32.275 | 11.232 | 2.203 | 26 | 0.876 | <0.001 | >10,000 | |
| FP binocular | Di-chicks | 4L | 18.725 | 9.246 | 1.813 | 26 | 0.74 | 0.001 | 836.246 |
| 4R | 19.666 | 10.024 | 1.966 | 26 | 0.786 | 0.002 | 1070.73 | ||
| Li-chicks | 4L | 21.771 | 9.888 | 1.939 | 26 | 0.819 | <0.001 | >10,000 | |
| 4R | 15.800 | 9.239 | 1.812 | 26 | 0.603 | 0.024 | 21.919 | ||
| FP monocular left | Di-chicks | 4L | 14.835 | 9.878 | 1.937 | 26 | 0.473 | 0.122 | 5.337 |
| 4R | 8.333 | 6.912 | 1.356 | 26 | –0.316 | 1.000 | 0.102 | ||
| Li-chicks | 4L | 15.011 | 9.344 | 1.832 | 26 | 0.518 | 0.050 | 8.449 | |
| 4R | 7.939 | 6.082 | 1.193 | 26 | –0.302 | 1.000 | 0.084 | ||
| FP monocular right | Di-chicks | 4L | 8.290 | 7.659 | 1.502 | 26 | –0.269 | 1.000 | 0.102 |
| 4R | 12.457 | 9.255 | 1.815 | 26 | 0.29 | 0.850 | 0.839 | ||
| Li-chicks | 4L | 6.288 | 6.151 | 1.206 | 26 | –0.515 | 1.000 | 0.06 | |
| 4R | 17.984 | 9.634 | 1.889 | 26 | 0.78 | 0.001 | 214 | ||
Additional files
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Supplementary file 1
Descriptive statistic—experiment 1.
Descriptive statistics of the accuracy in selecting each of the 10 items in the sagittal test, and in selecting the 5 items on the left (L) and the 5 items on the right (R) in the fronto-parallel (FP) tests of experiment 1.
- https://cdn.elifesciences.org/articles/106356/elife-106356-supp1-v1.docx
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Supplementary file 2
Descriptive statistic—experiment 2.
Descriptive statistics of the accuracy in selecting each of the 10 items in the sagittal test, and in selecting the 5 items on the left (L) and the 5 items on the right (R) in the fronto-parallel (FP) tests of experiment 2.
- https://cdn.elifesciences.org/articles/106356/elife-106356-supp2-v1.docx
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MDAR checklist
- https://cdn.elifesciences.org/articles/106356/elife-106356-mdarchecklist1-v1.docx
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Prenatal light exposure affects number sense and the mental number line in young domestic chicks
eLife 14:RP106356.
https://doi.org/10.7554/eLife.106356.3
