Table 2.
Individual performance in the test phase (different length control, outward arrows control, inward arrows control and overall length control, summed controls: frequency of choices for the longerline; presence of arrowhead control: frequency of choices for the line with the outward arrowheads; illusory trials: frequency of choices for the line with the inward arrowheads)
| Subject | Different length control | Outward arrows control | Inward arrows control | Summed controls | Müller–Lyer illusion | Overall length control | Presence of arrowhead control |
|---|---|---|---|---|---|---|---|
| 1 | 12/20 | 14/20 | 16/20 | 42/60 | 10/20 | 15/20 | 11/20 |
| P = 0.504 | P = 0.115 | P < 0.05* | P < 0.05* | P = 1.000 | P < 0.05* | P = 0.824 | |
| 2 | 12/20 | 14/20 | 13/20 | 39/60 | 12/20 | 11/20 | 11/20 |
| P = 0.504 | P = 0.115 | P = 0.263 | P < 0.05* | P = 0.504 | P = 0.824 | P = 0.824 | |
| 3 | 11/20 | 15/20 | 13/20 | 39/60 | 16/20 | 12/20 | 10/20 |
| P = 0.824 | P < 0.05* | P = 0.263 | P < 0.05* | P < 0.05* | P = 0.504 | P = 1.000 | |
| 4 | 14/20 | 12/20 | 17/20 | 43/60 | 13/20 | 12/20 | 14/20 |
| P = 0.115 | P = 0.504 | P < 0.05* | P < 0.05* | P = 0.263 | P = 0.504 | P = 0.115 | |
| 5 | 14/20 | 11/20 | 15/20 | 40/60 | 15/20 | 15/20 | 11/20 |
| P = 0.115 | P = 0.824 | P < 0.05* | P < 0.05* | P < 0.05* | P < 0.05* | P = 0.824 | |
| 6 | 15/20 | 15/20 | 14/20 | 44/60 | 17/20 | 17/20 | 8/20 |
| P < 0.05* | P < 0.05* | P = 0.115 | P < 0.05* | P < 0.05* | P < 0.05* | P = 0.504 | |
| 7 | 13/20 | 14/20 | 11/20 | 38/60 | 15/20 | 15/20 | 10/20 |
| P = 0.263 | P = 0.115 | P = 0.824 | P = 0.052 | P < 0.05* | P < 0.05* | P = 1.000 | |
| 8 | 11/20 | 13/20 | 13/20 | 37/60 | 15/20 | 11/20 | 12/20 |
| P = 0.824 | P = 0.263 | P = 0.263 | P = 0.092 | P < 0.05* | P = 0.824 | P = 0.504 | |
| 9 | 12/20 | 11/20 | 16/20 | 39/60 | 13/20 | 12/20 | 7/20 |
| P = 0.504 | P = 0.824 | P < 0.05* | P < 0.05* | P = 0.263 | P = 0.504 | P = 0.263 | |
| 10 | 15/20 | 15/20 | 13/20 | 43/60 | 13/20 | 15/20 | 12/20 |
| P < 0.05* | P < 0.05* | P = 0.263 | P < 0.05* | P = 0.263 | P < 0.05* | P = 0.504 | |
| 11 | 14/20 | 13/20 | 16/20 | 43/60 | 14/20 | 12/20 | 17/20 |
| P = 0.115 | P = 0.263 | P < 0.05* | P < 0.05* | P = 0.115 | P = 0.504 | P < 0.05* | |
| 12 | 11/20 | 15/20 | 16/20 | 42/60 | 13/20 | 8/20 | 12/20 |
| P = 0.824 | P < 0.05* | P < 0.05* | P < 0.05* | P = 0.263 | P = 0.504 | P = 0.504 | |
| Mean proportion | 0.642 | 0.675 | 0.721 | 0.679 | 0.692 | 0.646 | 0.563 |
| 95% confidence interval | 0.593, 0.690 | 0.627, 0.723 | 0.663, 0.779 | 0.654, 0.704 | 0.631, 0.752 | 0.566, 0.725 | 0.480, 0.645 |
If guppies perceived the Müller–Lyer illusion as Redtail splitfins and humans, they were expected to select more than chance the stimulus with inward-pointing arrowheads “><.” Asterisks (*) denote a significant departure from chance level (0.5) at binomial tests.