Here we are! reminder for OCTOBER: DATE = Oct 2nd VENUE CHANGE FOR PAINTING EXERCISE
you will all recieve an email confirming either here at the equestrian centre or over at Dingo lane...also, please remember: CONDITION SCORING SHEETS AND PHOTOS, and
BEFORE AND AFTER TRIM SHOTS, INCLUDING SIDE SHOT OF HORSE!
Superficial muscle system...
will upload and pictures monday 13th Sept..
Eyesight…
Horses can see colour. Their experience is a little different than ours…they could be likened to the colourblind in humans but this is not quite correct. Acuity is a little less too. However, they are better attuned to movement and they see better than us in the dark. Adjusting from one to the other though (light-dark) takes longer.
Depth is difficult for a horse to assess, and have a bit of difficulty judging how far things are from their body.
We know they have a blind spot in front of them…and behind, generally the horse has around 130 degres of sight in each eye, so has a field of 260 degrees vision. Of course given a slight head movement they have almost 360 for maintaining a watch for predators.
A horse with a broader forehead has a longer blind spot.
The horse has both
binocular and monocular vision…ie he can see independently out of each eye and
also focus on one thing. Switching from one to the other causes disortion and
may explain sudden spooking here and there. The horse cannot do both at one
time!
Like us, the colour of the eye has no impact on eyesight, it is simply pigmentation.
His
extravagantly big eyeball (largest of any land mammal's!) magnifies everything
fifty percent larger than we perceive it.
That enables him to see distant objects in clearer detail than we can (an
advantage for a prey animal needing to spot predators far away).
Nigra (pronounced NYE-grah) bodies--those round shapes in each pupil--seem to serve as a built-in visor, shielding interior eye structures from excess glare.
The third eyelid is a lightning-fast flap that zips across from the inner corner to seal the eye shut against threat even before the lids can close. It's also the source of lubricating tears.
Retinas are lined with two types of light-sensing cells, called rods and cones. This is why colours are barely, if at all, distinguishable to us in low light, as the cones are not sensitive enough in these conditions.Rods look after vision in low light, and cones handle colour
Rods, the light-sensitive cells that are responsive in dim light, outnumber the colour-sensitive cones by about 9:1.
Eyes are believed to have started evolving some 540 million years ago. They have evolved in different ways to meet specialist needs throughout the animal kingdom.
In insects, for example, we find compound eyes. Horses and humans have what could best be called a camera-type eye.
Light passes through the lens and focuses the image on the retina at the back of the eye - much like a camera lens throwing an image on to a piece of film. The eye also has a reflective layer, the Tapetum Lucidum, which reflects light back through the retina increasing the light available to the light responsive cells..
The eye's curved retina is linked to the
optic nerve, which transmits information about the visual environment to the
brain.
Not all cones are created equal. In humans there are three types of cone cells - each one is most sensitive to a different wavelength (colour) of light. Inside each cone is a photopigment, and it is this pigment that gives a particular cone its characteristic sensitivity.
Horses - in common with pigs, goats, cows, sheep and deer - have only two different cone types on their retina, providing them with what scientists call dichromatic vision. trichromatic vision is what we and primates have.
So, the way that humans and other primates see is fairly unique in the world of mammals. However, 1993 research revealed that birds go one better, having four cone types (tetrachromacy), as well as ultra violet (UV) sensitivity.
People, with their trichromic vision, see
four basic unique colours: red, green, blue, and yellow, as well as a range of
intermediate hues.
The research showed that horses, with their dichromatic vision, cannot distinguish red.
...It's not that they don't 'see' red. "They just can't discriminate in the red/green region of the spectrum. They are also slightly less sensitive to red light.
One of the most dramatic differences believed to differentiate the visual world of the dichromat from the trichromat is that, for dichromats, there are no intermediate hues.
A 1992 study showed that
horse vision is not as sharp as human sight. If good human vision is 20/20, a
horse rates as 20/60. This means that details a person with 20/20 vision can
see at 60m are only visible to a horse at 20m. The findings were obtained by
measuring brain activity when horses saw different sets of lines on a television
screen. 
Research into horse vision has also been conducted in New Zealand. Tania Blackmore, when a graduate student in the Department of Psychology at the University of Waikato, designed a research study for her Masters thesis.
Her test was behavioural-based, involving four horses who were incentivised to distinguish between a colour and grey. They had to achieve an 85% success or better for a pass.
Her study found that horses could
definitely see the difference between blue and grey, between yellow and grey
and between green and grey. They could tell red from grey to some extent but
they found this much more difficult, as would be expected when considered in
tandem with other findings.
Blue vs Grey
All horses learned this task reasonably quickly and soon had five consecutive sessions above 85% correct, even when it was the first condition they experienced.
Red vs Grey
This was not so easy. None of the horses managed five consecutive session above 85% correct. Candy and Ginger got close, showing they could do the task to some extent, but that they could not make this discrimination as easily as they had blue vs grey. Red (the pony) had more than one go at this colour and although better than chance he never managed a high per cent correct. George is currently working on this condition but it doesn't look like he'll be any different, he is still performing at around 50% (chance level responding).
Yellow vs Grey
Candy, Ginger and George were all able to discriminate yellow from grey and learned the task quite quickly. Red was not as good on the task but performing above chance levels and almost made the criterion!
Green vs Grey
This one is interesting it gave us results that appear to depend on the previous experience. Candy, Ginger and George all reached criterion, Red did not.
The graphs show that when a horses was changed from one colour to another their accuracy would normally drop to chance levels for a day or two. This did not happen when the change was from green vs grey to yellow vs grey or vice versa and the horse had been successful on the first of these to be presented. This can be seen clearly for Ginger who, after taking 28 days to complete green vs grey, moved on to yellow without dropping in accuracy - staying at around 90% correct.
It is also interesting to note that, while Red did not reach criterion with green vs grey on either of his two attempts, his performance on green vs grey improved after he had been exposed to yellow vs grey.
The conclusion
So what is the answer to the question Tania was asking - Do horses see colour?
The answer is yes.
- They can definitely see the difference between blue and grey, between yellow and grey and between green and grey.
- It appears that yellow and the green we used look similar, although we need to study this further.
- They can tell red from grey to some extent but they find this much more difficult than the other discriminations.
