September 7, 2004 | David F. Coppedge

Archer Fish Learns the Laws of Optics

Imagine you’re a kid in a swimming pool, underwater with a squirt gun.  Lurking under the surface, you detect the wavy, distorted image of your big brother standing on the deck.  You sneak up, fire from below– and miss, because you didn’t know how to correct for refraction and distance through the air-water interface.  There’s a fish that would put you to shame; it squirts jets of water precisely at its prey, bugs crawling above water on leaves and stems.  Scientists have been intrigued for many years at the accuracy of the aptly named “archer fish”  (see 09/30/2002 headline, an article by Taylor Reeves on Apologetics Press and footage of the fish in action in the film Wonders of God’s Creation).
    A new paper about the aquatic sharpshooters has been published in the Sept. 7 issue of Current Biology.1  The title says it all:  “Archer fish learn to compensate for complex optical distortions to determine the absolute size of their aerial prey.”  Researchers gave the fish target practice with colored disks.  A summary in EurekAlert explains the result: “Although naïve fish often selected disks that would be too large to be swallowed, all could eventually learn to judge absolute size with great precision; in doing so, they perfectly accounted for the complex optical situation posed by their underwater viewpoint” (emphasis added in all quotes).  What’s even more amazing, EurekAlert continues, is that this was not just a conditioned response.  The fish learned physics:

In a series of experiments, the researchers showed that the fish do not learn this by remembering which combinations of spatial configurations and the corresponding images were rewarding in the past.  Rather, the fish extracted the underlying law that connects spatial configuration and apparent size.  This remarkable cognitive ability allows the fish to readily judge a target’s objective size from underwater views they have never encountered before.

—and all this “in a world of distortion” caused by refraction and a moving surface.  The researchers, Schuster et al. in Germany, seemed pretty amazed, because “the deviations between real and apparent horizontal size are substantial” due to distortion.  But the fish took this all in stride:

Moreover, the strong viewpoint dependency can even cause changes in the size relations among the disks.  For instance, if the fish makes its selection while close to a large disk, the apparent size of a more-distant small disk can be larger than that of the close large disk.  In principle, the fish could overcome these problems by scanning the targets and taking a view of each target from the same horizontal distance.  However, this is clearly not what the fish did; as soon as the objects were shown, the fish swam straight to their shooting position and fired.

The original paper describes some of the clever experiments the researchers devised to test whether the fish were actually learning optical principles.  They wanted to know if the fish could learn to adjust for optical distortion, so they trained four fish to shoot at 6mm disks at various horizontal and vertical distances.  Successful target shooting within 10 seconds was rewarded with a fly.  After 4-8 weeks of training, the winners in the school of fish archery all passed: “All four fish mastered the task and selected the correct size at any height.”  This was a hard task for any fish, but the archer fish achieved “impressive precision,” able to hit a 1mm bull’s-eye from 800mm.
    Additional experiments led the researchers to conclude that the fish did not just memorize the shots that worked.  They actually had to learn how to correct for distortion.  Think about all that is involved in this skill:

In learning the objective size of their targets, the archer fish thus had not simply learned combinations that were rewarded in the past but went beyond to acquire a concept of objective size that they later could readily apply to the novel views.  This ability is remarkable in several respects.  First, the optical effects require rather precise knowledge of spatial configuration….  The question of how the fish’s visual system is able to provide this information is presently wide open.  When fish aim their shots, for which precise distance information is also required, monocular cues suffice and binocular distance cues are not required.  Whether stereo vision is also unnecessary for size constant vision cannot, however, be said at present.  Second, the fish apparently is able to combine such spatial knowledge in a yet-unknown way with apparent size (or apparent locomotion-induced image transformations) to deduce a concept of objective size.  Whatever sensory representation it uses, the fish evidently is able to form a concept of size that is tailored to the complex optics at the water-air interface.  Because this situation poses particularly rigorous requirements on the relation the animal must make between target localization and the apparent image, the fish is an attractive model to explore how animals learn to form concepts to bring order into their sensory experiences.

Kind of makes you hope the little champs don’t get targeted by the optical targeting apparatus of a diving cormorant (see 05/24/2004 headline).


1Schuster et al., “Archer Fish Learn to Compensate for Complex Optical Distortions to Determine the Absolute Size of Their Aerial Prey,” Current Biology, Volume 14, Issue 17, 7 September 2004, Pages 1565-1568, doi:10.1016/j.cub.2004.08.050.

Stories like this are such wonderful relief from the incessant storytelling of Darwinists.  There was no mention of evolution in this article, and if there had been, it wouldn’t be worth a spit.  Here evolutionists cannot even find a clear beneficial mutation (see next headline), and they want us to believe this and thousands of other wonders of creation are the result of accidents?  Shoot.

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Categories: Amazing Facts

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