In just five hours, an average farm pig can learn how to interpret an image in the mirror and use it to find hidden food.

    Scientists consider the ability to use a mirror a sign of complex cognitive processing and an indication of a certain level of awareness. In addition to humans and some primates, dolphins, elephants, magpies and a famous African grey parrot named Alex have all been known to retrieve objects or remove marks on their body using a mirror. Now it looks like pigs should be added to the list of clever critters that can master a mirror: After spending five hours with a mirror in their pen, seven out of eight pigs could use the reflection to find a hidden bowl of grub.

    "This is the first demonstration of the ability of pigs to use mirrors," animal behavior expert Donald Broom of the University of Cambridge wrote in an e-mail. "Finding sophisticated learning and awareness in animals can alter the way that people think about the species and may result in better welfare in the long run." Broom co-authored the paper published this month in Animal Behaviour.

    Like most animals, the pigs were immediately curious when researchers placed the shiny, reflective object in their pen. They approached the mirror until they bumped into it with their snout, and then checked to see what was behind the mirror. The pigs spent an average of 20 minutes gazing at their reflection, often turning in different directions to inspect themselves from several angles.

    "These kind of movements suggest that the pigs were correlating the movements of their body with the visual stimulus they were receiving from the mirror, and so learning the contingency between the two," biologist Louise Barrett of the University of Liverpool wrote in a commentary about the paper, also published this month in Animal Behaviour.

    After five hours with a mirror, the pigs were placed in a new test area that contained a food bowl hidden behind a barrier. Although the pigs could see the reflection of the bowl in the mirror, they couldn't see the food directly. A fan above the bowl circulated the scent of food around the room, prohibiting the pigs from smelling their way to the treat.

    Seven out of eight of the pigs with previous mirror experience spotted the reflection of the food bowl and correctly interpreted its location: Instead of searching for the food in its apparent position behind the mirror, the pigs headed around the barrier and straight for the true location of the bowl. When the researchers tested pigs with no prior mirror exposure, however, nine out of 11 of them became confused, searching behind the mirror for the food.

    "These results suggest not only that pigs learn the contingency between their own movements and their image in the mirror," Barrett wrote, "but that their knowledge incorporates the layout of the environment as well, so that they can locate objects in space."

    The researchers say their experiment is more than a nifty trick: The fact that pigs can learn to use a mirror means they are capable of a type of awareness called assessment awareness, which means they can understand the significance of a situation in relation to themselves, over a short period of time. In this case, the pigs remembered how their own movements appeared in the mirror, and were able to apply that knowledge to a separate situation involving a hidden food bowl.

    "Having a sense of self and using it is a form of assessment awareness," Broom wrote. Although the mirror experiment doesn't directly prove that pigs have a sense of self, the researchers suggest that given how quickly the pigs learn to recognize their own movements in a mirror, they may have some degree of self-awareness. "We have no conclusive evidence of a sense of self," Broom wrote, "but you might well conclude that it is likely from our results."

    Other mirror tests have been used to more directly examine an animal's sense of self - if researchers apply a yellow mark to the black feathers of a magpie, for instance, the bird will use a mirror to clean itself off. Unfortunately, Broom says the mark experiments just don't work on pigs: Pigs are so accustomed to being streaked with mud, they don't much care if researchers apply extra marks on their bodies. "We have put marks on pigs," Broom wrote. "They take little notice of them."

    Combined with a host of other research studies demonstrating the keen intelligence of pigs, the researchers hope their study will lead to better treatment of the farm animals. "If an animal is clever," Broom wrote, "it is less likely to be treated as if it is an object or a machine to produce food, and more likely to be considered as an individual of value in itself."

    一只尋常的家養(yǎng)豬可以用五小時(shí)學(xué)會(huì)如何看懂鏡子里的圖像并用它找到隱藏的食物。

    科學(xué)家認(rèn)為使用鏡子是一種復(fù)雜的認(rèn)知過(guò)程，這是一定觀察認(rèn)知水平的象征。除了人類(lèi)和一些靈長(zhǎng)類(lèi)動(dòng)物，海豚，大象，喜鵲和一只叫Alex的著名的非洲灰鸚鵡也都能夠通過(guò)使用鏡子找到目標(biāo)物或者除去它們身上的記號(hào)�？雌饋�(lái)豬也是一種會(huì)使用鏡子的生物，因?yàn)樵谖逍�時(shí)時(shí)間中，八只被研究的豬中有七只可以通過(guò)鏡子反射找到隱藏的裝有食物的碗。

    "這是第一次對(duì)于豬使用鏡子能力的展現(xiàn)，"來(lái)自哥倫比亞大學(xué)的動(dòng)物行為專(zhuān)家Donald Broom在一封電子郵件中寫(xiě)道："對(duì)于動(dòng)物具有復(fù)雜的學(xué)習(xí)和認(rèn)知能力這一認(rèn)識(shí)可能會(huì)改變?nèi)祟?lèi)看待物種的態(tài)度，并可能會(huì)帶來(lái)長(zhǎng)期的福利。"Broom合著了一篇這個(gè)月在《動(dòng)物行為》發(fā)表的論文。

    和大部分別的動(dòng)物一樣，豬也馬上對(duì)研究人員放在豬圈里面發(fā)光的、會(huì)反射的東西表現(xiàn)出好奇心。它們慢慢靠近鏡子直到鼻子碰到了鏡面，然后查看鏡子后面到底是什么。它們平均花了差不多20分鐘注視鏡中的自己，一直換不同的方向角度來(lái)觀察。

    "這種移動(dòng)表明豬把自己身體的動(dòng)作和鏡中的影像聯(lián)系在一起，然后學(xué)會(huì)這兩者間的關(guān)聯(lián)性。"來(lái)自利物浦大學(xué)的生物學(xué)家Louise Barrett 在一篇也是這個(gè)月發(fā)表在《動(dòng)物行為》中的論文的評(píng)論中寫(xiě)道。

    五小時(shí)過(guò)后，這些豬被安置在一個(gè)新的測(cè)試環(huán)境中，而一個(gè)裝著食物的碗被藏在障礙物后面。豬不能直接看到碗，只可以通過(guò)鏡子反射看到。碗上方的風(fēng)扇使食物的香味在房間里流通，避免豬通過(guò)味道找到食物。

    八只有觀察鏡子經(jīng)驗(yàn)的豬中有七只看到了反射的碗并準(zhǔn)確的找到了它的位置。它們并沒(méi)有直接在鏡子后面尋找，它們穿過(guò)了障礙物并準(zhǔn)確直接的走到了放碗的位置。當(dāng)研究者測(cè)試沒(méi)有觀察鏡子經(jīng)驗(yàn)的豬時(shí)，11只中有九只被鏡子迷惑，在鏡子后面尋找食物。

    "這些結(jié)果表明豬不僅僅學(xué)會(huì)了它們自己的動(dòng)作和鏡中影像動(dòng)作之間的關(guān)聯(lián)，"Barrett寫(xiě)道，"它們也會(huì)把周?chē)�環(huán)境布局考慮在內(nèi)，因而他們可以在一個(gè)空間中確認(rèn)目標(biāo)物的位置。"

    研究人員說(shuō)他們的實(shí)驗(yàn)不僅僅是一個(gè)俏皮的手法。豬會(huì)使用鏡子的事實(shí)說(shuō)明他們有一種評(píng)估認(rèn)知，也就是說(shuō)他們可以在短時(shí)間內(nèi)理解環(huán)境和他們自身的關(guān)系。在這個(gè)實(shí)驗(yàn)中，豬記住了它們的行為是如何在鏡子中呈現(xiàn)的，并能把這個(gè)經(jīng)驗(yàn)應(yīng)用到涉及隱藏的裝有食物的碗這一獨(dú)立事件中去。

    "擁有自我意識(shí)并能應(yīng)用是有評(píng)估認(rèn)知的一種形式。"Broom寫(xiě)道。雖然鏡子實(shí)驗(yàn)不能直接證明豬有自我意識(shí)，研究人員指出豬對(duì)于鏡中它們自己身體移動(dòng)認(rèn)知的速度表明它們有一定的自我認(rèn)知程度。"我們沒(méi)有決定性的證據(jù)證明自我意識(shí)，"Broom寫(xiě)道，"但是你應(yīng)該還是可以通過(guò)我們的結(jié)論推斷這是可能的。"

    其它鏡子實(shí)驗(yàn)被用來(lái)更直接的檢驗(yàn)動(dòng)物的自我意識(shí)。比如，研究人員在一只黑色羽毛的喜鵲上涂上黃色記號(hào)，它能通過(guò)照鏡子來(lái)擦掉記號(hào)。然而，Broom說(shuō)記號(hào)實(shí)驗(yàn)不適用于豬：豬太習(xí)慣于身體涂上泥巴，它們并不太在意研究人員是否在它們身上涂上了多余的記號(hào)。"我們?cè)�在豬身上涂記號(hào)，"Broom寫(xiě)道，"它們并不怎么在意這些記號(hào)。"

    結(jié)合豬有智慧這些研究結(jié)果，研究人員希望他們的研究可以使得農(nóng)場(chǎng)里的動(dòng)物得到較好的對(duì)待。"如果一只動(dòng)物是聰明的，"Broom寫(xiě)道，"它就不大會(huì)被看成一個(gè)東西或者制造食物的機(jī)器，它更會(huì)被看成有自我價(jià)值的獨(dú)立個(gè)體。"