Getting answers

HUJ offers a series of "Why?" lectures on topics from economics to literature, religious thought and veterinary medicine.

Zebra and man 521 (photo credit: Courtesy)
Zebra and man 521
(photo credit: Courtesy)
Why doesn’t your dog (or for that matter, your cat) watch TV? Who has better vision – the dog, the cat or the horse? Are animals colorblind? The answers to these and other fascinating questions concerning vision in the animal kingdom were the subject of a lecture by Prof. Ron Ofri of the Hebrew University’s Koret School of Veterinary Medicine that was delivered earlier this month as part of the weekly “Why?” series presented by the University’s Center for Partnership and Outreach of the Authority for Community and Youth.
Speaking in Hebrew to an audience of some 400 Jerusalemites at the University’s Edmond J. Safra – Givat Ram campus, Ofri gave a lecture that, at one and the same time, provided enough meat to be of interest to those with medical backgrounds as well as being comprehensible to the layman.
This kind of lecture – one with depth but still for a general audience – typifies the “Why?” series.
Presented by leading university researchers, the weekly lectures cover a wide range of topics including medicine, economics, rationalism, genetics, physics, literature, religious thought, nutrition and health.
The 29 lectures in this year’s series “aim to bring science and research from the university to the community,” says Osnat Dolinsky of the Center for Partnership and Outreach. “The community supports the university and we want to give the community an idea of what we are doing.”
In addition to the “Why?” series, the center offers free theater performances, seminars, festivals and events to the general public.
Lectures in the “Why?” series open with a short musical interlude featuring young Jerusalem musicians.
Ofri’s lecture was preceded by a presentation by pianist Sofia Mazar and soprano Iri Shmuel.
“I am a veterinary eye doctor,” began Ofri, who is both an internationally recognized researcher and a practicing veterinary ophthalmologist. “Most people don’t even know that there is such a profession. But veterinary medicine has advanced greatly in the last 20 years. Today, there are both general practitioners and specialists for animals.”
He proceeded to give a brief overview of the sense of sight, explaining how light-sensitive tissue lining the retina of the eye captures the image of the visual world, much like film in a camera. The retina contains light-sensitive photoreceptors – cells made up of rods and cones. Rods specialize in perception in dim light, detecting motion and registering shapes. Cones support daytime vision and color perception.
After this short introduction, it was on to the pressing questions of the day. Firstly – why aren’t dogs and cats interested in TV? “Television is made up of flickering signals,” Ofri noted. “The frequency of flickering pictures broadcast on TV is higher than the ability of the cones in the human retina to detect. Therefore, we see the pictures as continuous.” The frequency at which intermittent light appears to be steady, known as the flicker fusion frequency (FFF) happens at different frequencies in different species. People start to see continuous light at between 35 and 40 hertz; dogs and cats at around 70 to 80 hertz. Television broadcasting is generally at around 50 hertz.
“Because the cones in most animals can detect higher flashes than we can, they see the flickering pictures as individual units instead of one continuous picture,” Ofri continued. “Think of it as looking at a flickering fluorescent light. This is not something you want to look at.”
Are animals color-blind? “Rich color vision is made possible by three types of cones that give us the three basic colors – red, green and blue,” he explained.
“Dogs and cats are not totally colorblind. They do not see in black and white. They have two out of the three cones – red and blue – and therefore see colors on a more limited basis.” Different colors have different wavelengths and the ability of the cones to absorb these wavelengths is what determines which basic colors are seen.
“Most animals are dichromatic in that they see two out of the three colors,” said Ofri. “Very few animals are totally color-blind, seeing only black and white.
These include deepwater fish and one type of lizard.
Night animals and marine animals are monochromatic, seeing only red. Primates and reptiles see all three colors, while fish and birds are tetra-chromatic – they see all three colors plus ultraviolet light.”
As for who sees better – the horse wins over both the dog and the cat. “Visual acuity or resolution is characterized by the cones,” stated Ofri. “All these animals have less visual acuity than humans because they have fewer cones than humans. Cats have more rods than cones, which gives them better night vision. But if a cat stands six meters from an object, it sees what a human standing at 45 meters away would see; a dog what a human at 22 meters would see; and a horse what a human at 10 meters would see.”
Often asked if it is possible to improve animal acuity with glasses, Ofri said, “No. This is not an optical problem but rather an anatomical one.”
Among those attending Ofri’s lecture was Elzara Vikhanski, a retired Jerusalem doctor. She has been attending the series for some time. “I come for different lectures on various subjects. Some are on medical subjects but some are not. I find them all to be very interesting.”
Hava Nathan, another Jerusalemite, also attends the series from time to time. “Last year, I came to a lot of lectures – mainly those on scientific subjects. This year, I have not been able to come very often. The lectures are very stimulating and I learn a lot. I came to this particular lecture because my daughter-in-law is a veterinarian.”
• Lectures are at 5 p.m. Sundays at the Wise Auditorium on Givat Ram. The next lecture is December 16.
For more information see:\