U2.4 SENSATION & PERCEPTION

Color blindness is typically an inherited genetic disorder. It is most commonly inherited from mutations on the X chromosome.

Two of the most common inherited forms of color blindness are protanomaly (and, more rarely, protanopia—the two together often known as "protans") and deuteranomaly (or, more rarely, deuteranopia—the two together often referred to as "deutans"). 

Both "protans" and "deutans" (of which the deutans are by far the most common) are known as "red–green color-blind". They comprise about 8% of human males and 0.6% of females of Northern European ancestry. 

The Ishihara test is a color perception test for red-green color deficiencies, the first in a class of successful color vision tests called pseudo-isochromatic plates ("PIP"). It was named after its designer, Shinobu Ishihara, a professor at the University of Tokyo, who first published his tests in 1917.

The D-15 Test is intended for the detection of color vision defects such as red-green and blue-yellow deficiencies as opposed to color acuity. The test consists of a reference cap and 15 removable chips of incremental hue variation.

The Farnsworth–Munsell 100 Hue Color Vision test is a test of the human visual system often used to test for color blindness. The system was developed by Dean Farnsworth in the 1940s and it tests the ability to isolate and arrange minute differences in various color targets with constant value and chroma that cover all the visual hues described by the Munsell color system.

The anomaloscope is the most accurate tool to classify your color blindness. Since it was developed by a German ophthalmologist just over 100 years ago it is used all over the world to check the severity of ones color vision deficiency and its specific subtype.

Students will review the commercially available Ishihara 38 Plate Color Vision Deficiency Test book.

[Square A is exactly the same shade of grey as Square B.] (See Checker shadow illusion.) 

An illusion is a distortion of the senses, which can reveal how the human brain normally organizes and interprets sensory stimulation. Though illusions distort our perception of reality, they are generally shared by most people.

Illusions may occur with any of the human senses, but visual illusions (optical illusions) are the best-known and understood. The emphasis on visual illusions occurs because vision often dominates the other senses. For example, individuals watching a ventriloquist will perceive the voice is coming from the dummy since they are able to see the dummy mouth the words.

Some illusions are based on general assumptions the brain makes during perception. These assumptions are made using organizational principles (e.g., Gestalt theory), an individual's capacity for depth perception and motion perception, and perceptual constancy. Other illusions occur because of biological sensory structures within the human body or conditions outside the body within one's physical environment.

The pair of organs on either side of your nose is one of your top tools for receiving information from the world around you. 

Often, our eyes tell us just about everything we need to know. But there are certain situations when the eyes don't have it. Sometimes our eyes can deceive us -- and we're better off keeping them closed. 

Top-down processing, refers to perception that is driven by cognition. Your brain applies what it knows and what it expects to perceive and fills in the blanks, so to speak. 

First, let us look at a visual example: Look at the shape in the box above. Seen alone, your brain engages in bottom-up processing. There are two thick vertical lines and three thin horizontal lines. There is no context to give it a specific meaning, so there is no top-down processing involved.  

The combination of these simple features allow us to recognize more complex patters. Say you were presented with a word, in bottom up processing you would first look at the feature of the word (lines, slants, etc.), then you would look at the letters of each word, and finally the word in its entirety. So you are working your way from the bottom up. 

Now, look at the same shape in two different contexts.

Surrounded by sequential letters, your brain expects the shape to be a letter and to complete the sequence. In that context, you perceive the lines to form the shape of the letter “B.” 

Surrounded by numbers, the same shape now looks like the number “13.” 

When given a context, your perception is driven by your cognitive expectations. Now you are processing the shape in a top-down fashion.  

Bottom-up refers to the processing of a stimulus in which information form a physical stimulus rather than from a general context. Stimulus information arrives from the sensory receptors (the bottom level of processing).  

The combination of these simple features allow us to recognize more complex patters. Say you were presented with a word, in bottom up processing you would first look at the feature of the word (lines, slants, etc.), then you would look at the letters of each word, and finally the word in its entirety. So you are working your way from the bottom up.