Eye Spy

With the power back on, we continued to explore the senses.  We compared the sensory abilities of several animals and looked at how different animals are able to detect forms of energy that humans cannot.  For example, butterflies can detect ultraviolet light and sharks have receptors sensitive to electrical fields.  We moved on to the structure of the eye and focused on how the lens inverts the visual field on the retina.  We also discussed how the cornea and lens help focus light on the photoreceptors in the retina.  Groups of monks received magnifying glasses that modeled the lens of the eye.  They were instructed to focus incoming light on a piece of paper and to trace this image.  The monks could easily see for themselves that light that passed through the lens was turned upside down and that right and left were inverted.

The discussion then turned to color vision and cone receptors. The previous day, the monks had already done an experiment to illustrate how rod receptors were located primarily in the periphery of the retina and cones were found in the central part of the retina.  Now they learned about the three different types of cones and how they responded to different wavelengths of light to provide information about color.  The monks were very interested in what would happen if one type of cone receptor was missing, so we looked at images the test for colorblindness.

The optic nerve must leave the eye as it travels to the brain.  The blind spot on the retina is where all of the axons from the retina gather; this area does not have any photoreceptors.  Strips of paper with a happy and sad face were used to demonstrate the blind spot.

We ended our discussion with two activities:  visual illusions and a depth perception competition.  We looked at several illusions including afterimages of the US and Tibetan flags.  The advantages of two eyes were demonstrated with a depth perception game where the monks were divided into teams who tried to toss plastic washers into cup using one or two eyes.