Rats have “double view” of world

world-science.net

May 28, 2013
Courtesy of Max-Planck-Gesellschaft
and World Science staff

If you’ve ev­er ex­pe­ri­enced how hard it is to sneak up on a fuzzy but un­wanted lit­tle ro­dent, here may be your ex­plana­t­ion.

Rats see the world very dif­fer­ently from us, re­search­ers say, be­cause they’re able to keep the world above them in per­ma­nent view—but ap­par­ently can’t merge the views from both eyes in­to one im­age.

With hawks and the like trail­ing ro­dents at ev­ery op­por­tun­ity, na­ture seems to have just de­cid­ed the first abil­ity is im­por­tant enough to sac­ri­fice the sec­ond, said the sci­en­tists.


De­scribing them­selves as to­tally sur­prised by the discovery, they found that the ro­dents move their eyes in op­po­site di­rec­tions, not to­geth­er like us, when run­ning around. Their pre­cise eye move­ment, which de­pends on the change in the head po­si­tion, pre­vents a “fu­sion” of both vis­u­al fields, the re­search­ers added.

With peo­ple, “both our eyes move to­geth­er and al­ways fol­low the same ob­jec­t,” while coun­ter­act­ing head move­ments, said neuro­bi­ol­o­gist Ja­son Kerr of the Max Planck In­sti­tute for Bi­o­log­i­cal Cy­ber­net­ics in Tü­bin­gen, Ger­ma­ny, one of the re­search­ers.

“In rats, on the oth­er hand, the eyes gen­er­ally move in op­po­site di­rec­tions.”

Kerr and col­leagues not­ed that de­spite the dif­fer­ent ways of look­ing, the im­ages from the rats’ eyes are fed in­to pret­ty much the same brain path­ways as hu­mans.

Like many mam­mals, rats have their eyes on the sides of their heads. This gives them a very wide vis­u­al field, good for de­tect­ing preda­tors. But three-di­men­sion­al vi­sion re­quires over­lap of the two vis­u­al fields. So the rats’ vis­u­al sys­tem must meet two con­flict­ing de­mands: max­i­mum sur­veil­lance, and de­tailed bin­oc­u­lar vi­sion.

The sci­en­tists fit­ted ti­ny cam­er­as to the an­i­mals’ heads, which could rec­ord the lightning-fast eye move­ments. They al­so used anoth­er new meth­od to meas­ure the head’s po­si­tion and di­rec­tion of the head, so they could re­con­struct the rats’ ex­act line of view mo­ment by mo­ment.

“When the head points down­ward, the eyes move back, away from the tip of the nose,” Kerr said. “When the rat lifts its head, the eyes look for­ward: cross-eyed, so to speak. If the an­i­mal puts its head on one side, the eye on the low­er side moves up and the oth­er eye moves down.”

This system en­sures that the ar­ea above the an­i­mal is al­ways in both eyes’ view sim­ul­ta­ne­ously, they added.

In peo­ple, the eyes’ gaze di­rec­tion must be pre­cisely aligned; even a one-degree de­via­t­ion can cause dou­ble vi­sion. In rats, the op­pos­ing eye move­ments mean that the line of vi­sion varies by as much as 40 de­grees in the hor­i­zon­tal plane and up to 60 de­grees in the ver­ti­cal plane, Kerr and col­leagues said.

The find­ings were pub­lished on­line May 26 in the jour­nal Na­ture.
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台灣醒報作者： 莊瑞萌 | 台灣醒報 – 2013年5月29日 下午2:52


    快速跑動的老鼠，兩眼可以同時看不同方向物體。德國科學家利用高速攝影機觀察跑動中的老鼠眼部運動，發現老鼠兩顆眼睛可同時看不同方向事物，也就是說，當老鼠在跑動時，不僅可以偵測上方動靜，還可以注意前方一舉一動。科學家認為，老鼠獨特的眼睛移動方式，就是為了觀察上方鳥類的動靜，避免遭到攻擊。




【台灣醒報記者莊瑞萌綜合報導】快速跑動的老鼠，兩眼可以同時

看不同方向物體。德國科學家利用高速攝影機觀察跑動中的老鼠眼

部運動，發現老鼠兩顆眼睛可同時看不同方向事物，也就是說，當

老鼠在跑動時，不僅可以偵測上方動靜，還可以注意前方一舉一動

。科學家認為，老鼠獨特的眼睛移動方式，就是為了觀察上方鳥類

的動靜，避免遭到攻擊。

德國「馬克斯普朗克生物模控學研究所」科學家將小型高速攝影機

裝在老鼠頭
上，觀察老鼠眼睛移動，另一部攝影機則觀察老鼠頭部移動，藉此

觀察老鼠是如何觀察身旁一切動靜。事後科學家重建老鼠之前所看

的景象發現，老鼠跟人類看東西方式截然不同，因為牠們是將2個獨

立畫面，一起傳給大腦處理，而且不會混淆。

研究者寇爾表示，「人類利用眼睛觀看前方事物，兩眼通常同一時

間定焦在同一物體上，但老鼠的兩顆眼睛，卻可以同時觀看相反方

向的移動物體，」而且人類2顆眼睛的對角角度，必須超過1度以上

，才能看清物體，否則會產生雙重影像，但是老鼠視線則不受限，

其兩眼距離水平面可以超過40度，垂直面可超過60度以上。

老鼠除了看事物的方式與人類不同，其嗅覺更是有特殊作用，因為

根據美國凱斯西儲大學研究發現，老鼠們彼此溝通是靠嗅覺來決定

地位，一般而言，地位較高的老鼠，可以多聞對方，但若是較年輕

的老鼠多聞幾下，就會導致被其他老鼠攻擊的命運。

本次研究結果已刊登在《自然》期刊。

圖說：德國研究發現，老鼠觀看事物的方式與人類不同，其2眼可以

觀察不同方向的事物，其原因可能是避免被天空的掠食者攻擊，而

逐漸演化成這項功能。