Member

At the time of posting this 3 people had posted an answer and only one did not get it right.

Arunn was the first, he got his answer in within 2 hours. He should learn to trust his first impressions.

I saw the optical illusion / perceptual puzzle in the January 2003 issue of Academic Radiology, in a short article by Calvin F. Nodine, PhD.

The original article is no longer available free on the net. So I have reproduced the relevant explanatory text. The emphases are mine.

The perceptual puzzle depicts a cow — or more accurately, a frontal view of the head and forequarters of a cow. Even knowing this, some observers have failed to recognize the cow in the picture. They have reported seeing an abstract fish, a bird, and even a fragment from a fresco in the Sistine Chapel. Once again the Gestalt laws of perceptual organization are at work, and they again reveal that the perceptual whole is more than the sum of its parts. But holistic perception does not come easily when viewing this illustration. Perhaps it is because most observers (except radiologists?) typically infer that the dark areas are the figure and the light areas are background. Try reversing this expectation, and look for the figure in the white spaces. Radiologists are practiced at switching their attention back and forth between dark and light structures in interpreting objects in medical images.

The reactions of observers to this perceptual puzzle have been very interesting. In his early perceptual experiments using this image, psychologist Karl M. Dallenbach tried to help observers perceive the cow by giving them clues such as “Try to find the familiar animal,” “Look for the cow’s head,” and “Look for the cow’s head front view.” None of these instructions seemed to aid their perception, so Dallenbach concluded that the observers were not “set” (prepared) to see this unique partial view of the cow. In later experiments, a colleague and I presented the cow puzzle to observers for short intervals while recording their eye fixations. After each presentation, we asked the observers to draw what they saw. Most used the dark areas as building blocks in their drawings. Very few perceived the cow on the first trial. Eye fixations were typically scattered over the dark areas, as if the observers were trying to make sense of them. After a few trials, some of our observers saw the cow and drew their rendition of it. Correspondingly, their eye fixations tended to focus on the large white structure that is the center of the cow’s head, in the upper left-hand quadrant of the picture. Thus, we had both pictorial and eye-fixation records of the perceptual process of recognizing the cow. But what went on behind the eyes that led to this perception still remains a mystery. Perhaps this is why we who study visual perception or use it in our trade find such perceptual puzzles both intriguing and challenging. The human perceptual process of recognizing the cow is like scientific problem solving in which the observer is forced to reject his or her initial intuitive hypothesis in favor of one that is perceptually counterintuitive but that fits the visual data. The best payment for this problem-solving effort is that once you’ve seen the cow, it is impossible not to see it.