Author Archives: Eligio Paul Zaragoza

Monocular Depth Cues

For this assignment, we were asked to take a concept or theory and explain how it applied to an experience in our life.  The experience that stands out most to me occurred when I was a senior in high school. During my senior year, I had the privilege of attending an art history class that looked at numerous paintings, drawings, pictures, and sculptures by various artists; however, there was one artist’s work that really caught my eye. The artist was none other than Maurits Cornelis (M.C.) Escher. Escher constructed many drawings that were not only abstract in nature but perceptively complex.  Escher had a keen understanding of how the human eye perceived space and as a result was able to expand this knowledge into his drawings in which objects were perceived as three dimensional.

This ability of inferring three dimensional objects from a two dimensional drawing, is mainly due to the concept of monocular depth cues. In class, we learned that monocular cues allow us to perceive depth which creates the representation of three dimensional (3-D) space (Wolfe, 2012). There are several monocular depth cues that allow this perception of 3-D to occur: occlusion (infers relative position in depth: front of/behind), relative size (comparison of size of objects without knowing their absolute size), relative height (comparison that objects at different distances on the ground plane will form different heights: objects lower in the plane will seem closer), texture gradient (a combination of relative size and height that the texture (geometric shapes) of an object gets smaller when farther away), familiar size (based on knowledge of an objects size), aerial perspective (distant objects appear fainter, bluer and less recognizable), and linear perspective (parallel lines converge to a vanishing point) (Wolfe, 2012).

To better illustrate the correlation of monocular depth cues to Escher’s artwork, we will look at his famous drawing (Hand with a Reflecting Sphere: Figure 1). In the drawing, we can see that Escher uses linear perspective to reflect depth when drawing the walls. As you can see, the walls get closer (converge) as they move towards the window at the back which causes are visual system to perceive that this depth signifies farthest away.  Additionally, relative height is being applied to the drawing (compare the size of the stools at the front and back of the room: they get smaller farther back), relative size (the books get smaller as they move away/towards the window), texture gradient (the texture/geometric shape of the pictures becomes smaller and less recognizable), and occlusion (the depiction of the hand with the fingers around the sphere give depth; fingers and hand positioned before/front of the sphere).

The summation of these cues causes are visual system to take the various depth perspectives and construct a three dimensional representation of space within the art work. Therefore, the keen understanding of how our visual system works has proved to be instrumental to Escher’s success. Without this understanding of how are monocular depth cues constructs our perspective; the inference of three dimensional objects would not be possible.

 

References

upload.wikimedia.org/wikipedia/en/6/66/Hand_with_Reflecting_Sphere.jpg

Wolfe, J. M. (2012). Sensation & perception (3rd ed.). Sunderland, Mass.: Sinauer

Associates.

Hand_with_Reflecting_Sphere_Escher

Figure 1: Hand_with_Reflecting_Sphere_Escher

Visual and Auditory Senses

For this assignment, we were asked to take a concept or theory and explain how it applied to an experience in our life.  The experience that stands out the most to me and is applicable to the principles of sensation and perception occurred when I was in the process of joining the military. Prior to be sent to basic military training, each individual is screened to ensure they are medically clear to pursue the endeavors encompassed in serving our nation. As a result, there are several tests an individual must take to determine their physical ability to include those pertaining to visual and auditory senses.

The first test, I recall taking is the visual test. The test was taken in a medium sized room that had separated cubicles, each with a chair and a computer. The medical technician instructed me that I was to sit in front of the computer and tell her the numbers that I saw within an image. There were several images presented, however they differed in color in the context of the numbers and surrounding (Example 1). After I took the test, the medical technician informed me that I did very well and was visually cleared.  When I asked the technician what the test was looking for, she informed me the test was looking for color blindness. This test relates closely to the concept of retinal information processing. Although, there are five neuron sections within the retina that effect processing; the primary focus is the photoreceptors. There are two primary types of photoreceptors within the retina, which are rods and cones. Cones are specialized for color vision and contain three types of photopigment: short wavelength-sensitive cones (S-cones), medium wavelength-sensitive cones (M-cones), and long wavelength-sensitive cones (L-cones) (Wolfe, 2012). Thus, the absence of any of the cone photopigments would result in color blindness (Wolfe, 2012). Therefore, the test is seeking to find the status/health of the cones within the retina. After taking the visual test, I was then directed to take a test that examined my auditory senses.

Like the visual test, an auditory test was administered by a medical technician in a medium sized room. However, the within the room was a single enclosed cubicle that was well-insulated. The test required that I wear headphones and hold an electronic remote. The technician administering the test explained the procedures to me that compromised of the following:  1) Listen for a beep tone 2) Press the button on the electronic remote once you hear the tone. At first it seemed like the tone started off faint before becoming louder but as the test went on I realized that the tone was in random order. This auditory test, relates strongly to Gustav Fechner’s concept of psychophysical methods.

Fechner’s psychophysical methods revolve around the consensus that there must be a threshold or minimum amount of stimulation needed to detect a stimulus (Wolfe, 2012). In order to measure this threshold, Fechner created the psychophysical methods: 1) method of constant stimuli 2) method of limits 3) method of adjustment (Wolfe, 2012).  Since I was presented the beeping tone (stimulus) multiple times, in random order, one at a time; the auditory test correlates strongly to the method of constant stimuli. The purpose of the auditory test was to detect my hearing ability and as such the medical technician had to find where my threshold was through the tones loudness (measured in decibels). As a result of my responses, the medical technician was able to determine not only my threshold but whether I had good hearing or not.

 

References

http://en.wikipedia.org/wiki/File:Ishihara_11.PNG

Wolfe, J. M. (2012). Sensation & perception (3rd ed.). Sunderland, Mass.: Sinauer

Associates.

Example 1