Learning Targets:

Describe the vision process, including the specific nature of energy transduction, relevant anatomical structures, and specialized pathways in the brain for each of the senses.
Explain common sensory conditions.

AP psychology course and exam description, effective fall 2020. (n.d.). https://apcentral.collegeboard.org/media/pdf/ap-psychology-course-and-exam-description.pdf

Vision

EM Spectrum

Vision is our most dominating sense and one that many know little about. The organ for the sense of vision is our eyes, and they are what we use to process the physical energy of light. Look at the image of the color spectrum. This illustrates all the various kinds of electromagnetic energy waves, however, as you will notice, humans are only able to see a tiny portion of the entire spectrum.

A light wave has three properties: hue, saturation, and brightness. The waves that we do see are called visible light. The electromagnetic energy from these waves is transduced into neural impulses. Before we talk about transduction, let's discuss what makes up a light wave.

A light wave has three properties: hue, saturation, and brightness. The hue varies with the wavelength of light from violet to red. Saturation describes the purity of the wavelength. The wavelength is the distance from the peak of one light wave to the peak of the next. The longer the distance, the closer the color is to the red end of the spectrum. Brightness is the intensity or amplitude of the light wave. The higher the wave of light, the brighter the perception of color.

Color vision is an additive process, meaning it is determined by the wavelength of light an object reflects. When we view something that is white, it reflects all visible wavelengths with the absorption of none. Black on the other hand absorbs all wavelengths of visible light and reflects none. If you are wearing a green t-shirt, the cloth reflects only the wavelengths of light that correspond to that portion of the spectrum, while absorbing all others.

Anatomy of the Eye and Transduction

Before we discuss transduction, let's look at the structure of the eye and the role each part plays.

Learn more about the anatomy of the eye in the activity below.

Once light reaches the retina, transduction begins to take place. The retina is the back of the eye and is the most important structure. The retina is made up of several layers of cells, all of which must be passed for transduction to take place.

The first layer that is activated by light is called rods and cones. Rods are long and thin with blunt ends and outnumber cones about 20 to 1. They are more sensitive to light and provide us with night vision. They adapt slowly to changes in light, taking as long as thirty minutes. Cones are short and fat in shape with tapered ends. They are sensitive to the wavelengths that show color and adapt quickly to changes. Cones are in the fovea (or focal point of the retina).

Once the rods and cones fire, the information is then sent to the second layer of cells, called bipolar cells. Bipolar cells pass the information on to the ganglion cells. The axons of the ganglion cells make up our optic nerve. This is how information is sent to the brain. The optic nerve carries the messages to the thalamus which will then send them to the occipital lobes.

Once the information reaches the occipital lobe in the visual cortex, we then process the image. Our visual cortex contains many specialized neurons that allow us to distinguish lines, angles, edges, and movement. The concept of specific nerve cells in the brain responding to unique features of stimuli is called feature detectors. It is here that the brain also processes several aspects of a problem simultaneously through parallel processing.

Test your knowledge of the anatomy of the eye below.

Please take a moment to view this video on Feature Detection and Parallel Processing.

Vision Problems

Image showing myopia and hyperopia If your lens is abnormally shaped it may not focus light onto your retina properly. When this happens, the retina is unable to read images as a whole. Instead, the images are converted into neural impulses which are constructed in the brain. This affects our acuity or ability to distinguish the sharpness of an image.

Myopia is a condition in which the light from rays from distant objects is focused in front of the retina. This causes objects that appear up close to be clear, but those far away to be fuzzy. Hyperopia is when light rays reach the retina before they have produced a focused image. This condition causes us to not be able to focus well up close and often overstrain our eyes. Wearing glasses, Lasik surgery, and contacts can all reshape the cornea to change how light enters the eye, and where it hits, and thus correct many vision problems.

Video Credit: Video from https://www.khanacademy.org/science/health-and-medicine/nervous-system-and-sensory-infor/sight-2014-03-27T18:45:34.237Z/v/feature-detection-and-parallel-processing

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