How ambush predators focus when catching prey
For ambush predators with vertical-slit pupils, the authors noted the importance of accurately gauging the distance animals would need to pounce on their prey. Researchers identified three cues generally used to gauge distance: stereopsis, or binocular disparity; motion parallax, in which closer objects move farther and faster across our field of vision; and blur, in which objects at different distances are out of focus.
The researchers ruled out motion parallax as a factor since using that cue would require head movement that could reveal the predator's position. The remaining two cues, binocular disparity and blur, work together with vertically elongated pupils and front-facing eyes, the researchers said.
Binocular vision works better at judging differences when contours are vertical and objects are at a distance, while blur comes into play for horizontal contours and near-field targets. Vertical-slit pupils maximize both cues, the researchers said.
Vertical pupils are not equally distributed among ambush predators, however.
"A surprising thing we noticed from this study is that the slit pupils were linked to predators that were close to the ground," said William Sprague, a postdoctoral researcher in Banks' lab. "So domestic cats have vertical slits, but bigger cats, like tigers and lions, don't. Their pupils are round, like humans and dogs."
How ambush predators focus when catching preyFor ambush predators with vertical-slit pupils, the authors noted the importance of accurately gauging the distance animals would need to pounce on their prey. Researchers identified three cues generally used to gauge distance: stereopsis, or binocular disparity; motion parallax, in which closer objects move farther and faster across our field of vision; and blur, in which objects at different distances are out of focus.The researchers ruled out motion parallax as a factor since using that cue would require head movement that could reveal the predator's position. The remaining two cues, binocular disparity and blur, work together with vertically elongated pupils and front-facing eyes, the researchers said.Binocular vision works better at judging differences when contours are vertical and objects are at a distance, while blur comes into play for horizontal contours and near-field targets. Vertical-slit pupils maximize both cues, the researchers said.Vertical pupils are not equally distributed among ambush predators, however."A surprising thing we noticed from this study is that the slit pupils were linked to predators that were close to the ground," said William Sprague, a postdoctoral researcher in Banks' lab. "So domestic cats have vertical slits, but bigger cats, like tigers and lions, don't. Their pupils are round, like humans and dogs."
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