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Psychology

<OpenstaxParagraph>
	We do not see the world in black and white; neither do we see it as two-dimensional (2-D) or flat (just height and width, no depth). Let’s look at how color vision works and how we perceive three dimensions (height, width, and depth).
</OpenstaxParagraph>
<OpenstaxH3>Color Vision</OpenstaxH3>
<OpenstaxParagraph>
	Normal-sighted individuals have three different types of cones that mediate <OpenstaxTerm>color vision</OpenstaxTerm>. Each of these cone types is maximally sensitive to a slightly different wavelength of light. According to the <OpenstaxTerm>trichromatic theory of color vision</OpenstaxTerm>, shown in <a href="#Figure_05_03_Trichrom">Figure 5.14</a>, all colors in the spectrum can be produced by combining red, green, and blue. The three types of cones are each receptive to one of the colors.
</OpenstaxParagraph>
<OpenstaxFigure id="Figure_05_03_Trichrom" src="https://openstax.org/apps/archive/20240226.174525/resources/a64eff29d4c7d338b9a588b7e5e195747c9e2c4b" alt="A graph is shown with “sensitivity” plotted on the y-axis and “Wavelength” in nanometers plotted along the x-axis with measurements of 400, 500, 600, and 700. Three lines in different colors move from the base to the peak of the y axis, and back to the base. The blue line begins at 400 nm and hits its peak of sensitivity around 455 nanometers, before the sensitivity drops off at roughly the same rate at which it increased, returning to the lowest sensitivity around 530 nm . The green line begins at 400 nm and reaches its peak of sensitivity around 535 nanometers. Its sensitivity then decreases at roughly the same rate at which it increased, returning to the lowest sensitivity around 650 nm. The red line follows the same pattern as the first two, beginning at 400 nm, increasing and decreasing at the same rate, and it hits its height of sensitivity around 580 nanometers. Below this graph is a horizontal bar showing the colors of the visible spectrum." mediaType="image/jpg" width="649" height="452" />
<OpenstaxFigureText width="649">
	Figure 5.14 This figure illustrates the different sensitivities for the three cone types found in a normal-sighted individual. (credit: modification of work by Vanessa Ezekowitz)
</OpenstaxFigureText>
<OpenstaxNote>
	<OpenstaxNoteTitle> Connect the Concepts </OpenstaxNoteTitle> <OpenstaxH3> Colorblindness: A Personal Story </OpenstaxH3>
	<OpenstaxParagraph>
		Several years ago, I dressed to go to a public function and walked into the kitchen where my 7-year-old daughter sat. She looked up at me, and in her most stern voice, said, “You can’t wear that.” I asked, "Why not?" and she informed me the colors of my clothes did not match. She had complained frequently that I was bad at matching my shirts, pants, and ties, but this time, she sounded especially alarmed. As a single father with no one else to ask at home, I drove us to the nearest convenience store and asked the store clerk if my clothes matched. She said my pants were a bright green color, my shirt was a reddish orange, and my tie was brown. She looked at my quizzically and said, "No way do your clothes match." Over the next few days, I started asking my coworkers and friends if my clothes matched. After several days of being told that my coworkers just thought I had "a really unique style," I made an appointment with an eye doctor and was tested (<a href="#Figure_05_03_Ishihara">Figure 5.15</a>). It was then that I found out that I was colorblind. I cannot differentiate between most greens, browns, and reds. Fortunately, other than unknowingly being badly dressed, my colorblindness rarely harms my day-to-day life.
	</OpenstaxParagraph><OpenstaxFigure id="Figure_05_03_Ishihara" src="https://openstax.org/apps/archive/20240226.174525/resources/21632351cd15e26896aa4e56c6f36100c9b380d4" alt="The figure includes three large circles that are made up of smaller circles of varying shades and sizes. Inside each large circle is a number that is made visible only by its different color. The first circle has an orange number 12 in a background of green. The second color has a green number 74 in a background of orange. The third circle has a red and brown number 42 in a background of black and gray." mediaType="image/jpg" width="731" height="210" />
	<OpenstaxFigureText width="731">
		Figure 5.15 The Ishihara test evaluates color perception by assessing whether individuals can discern numbers that appear in a circle of dots of varying colors and sizes.
	</OpenstaxFigureText>
	<OpenstaxParagraph>
		Some forms of color deficiency are rare. Seeing in grayscale (only shades of black and white) is extremely rare, and people who do so only have rods, which means they have very low visual acuity and cannot see very well. The most common X-linked inherited abnormality is red-green color blindness (Birch, 2012). Approximately 8% of males with White European descent, 5% of Asian males, 4% of African males, and less than 2% of Indigenous American males, Australian males, and Polynesian males have red-green color deficiency (Birch, 2012). Comparatively, only about 0.4% in females from White European descent have red-green color deficiency (Birch, 2012).
	</OpenstaxParagraph>
</OpenstaxNote>
<OpenstaxParagraph>
	The trichromatic theory of color vision is not the only theory—another major theory of color vision is known as the <OpenstaxTerm>opponent-process theory</OpenstaxTerm>. According to this theory, color is coded in opponent pairs: black-white, yellow-blue, and green-red. The basic idea is that some cells of the visual system are excited by one of the opponent colors and inhibited by the other. So, a cell that was excited by wavelengths associated with green would be inhibited by wavelengths associated with red, and vice versa. One of the implications of opponent processing is that we do not experience greenish-reds or yellowish-blues as colors. Another implication is that this leads to the experience of negative afterimages. An <OpenstaxTerm>afterimage</OpenstaxTerm> describes the continuation of a visual sensation after removal of the stimulus. For example, when you stare briefly at the sun and then look away from it, you may still perceive a spot of light although the stimulus (the sun) has been removed. When color is involved in the stimulus, the color pairings identified in the opponent-process theory lead to a negative afterimage. You can test this concept using the flag in <a href="#Figure_05_03_Afterimage">Figure 5.16</a>.
</OpenstaxParagraph>
<OpenstaxFigure id="Figure_05_03_Afterimage" src="https://openstax.org/apps/archive/20240226.174525/resources/5e8fc0c62762dd4aa31174013a2b04dfee33db8b" alt="An illustration shows a green flag with a thick, black-bordered yellow lines meeting slightly to the left of the center. A small white dot sits within the yellow space in the exact center of the flag." mediaType="image/jpg" width="487" height="352" />
<OpenstaxFigureText width="487">
	Figure 5.16 Stare at the white dot for 30–60 seconds and then move your eyes to a blank piece of white paper. What do you see? This is known as a negative afterimage, and it provides empirical support for the opponent-process theory of color vision.
</OpenstaxFigureText>
<OpenstaxParagraph>
	But these two theories—the trichromatic theory of color vision and the opponent-process theory—are not mutually exclusive. Research has shown that they just apply to different levels of the nervous system. For visual processing on the retina, trichromatic theory applies: the cones are responsive to three different wavelengths that represent red, blue, and green. But once the signal moves past the retina on its way to the brain, the cells respond in a way consistent with opponent-process theory (Land, 1959; Kaiser, 1997).
</OpenstaxParagraph>
<OpenstaxNote>
	<OpenstaxNoteTitle> Link to Learning </OpenstaxNoteTitle> 
	<OpenstaxParagraph>
		Watch this <a href="http://openstax.org/l/colorvision"> video about color perception</a> to learn more.
	</OpenstaxParagraph>
</OpenstaxNote>
<OpenstaxH3>Depth Perception</OpenstaxH3>
<OpenstaxParagraph>
	Our ability to perceive spatial relationships in three-dimensional (3-D) space is known as <OpenstaxTerm>depth perception</OpenstaxTerm>. With depth perception, we can describe things as being in front, behind, above, below, or to the side of other things.
</OpenstaxParagraph>
<OpenstaxParagraph>
	Our world is three-dimensional, so it makes sense that our mental representation of the world has three-dimensional properties. We use a variety of cues in a visual scene to establish our sense of depth. Some of these are <OpenstaxTerm>binocular</OpenstaxTerm> <OpenstaxTerm>cues</OpenstaxTerm>, which means that they rely on the use of both eyes. One example of a binocular depth cue is <OpenstaxTerm>binocular disparity</OpenstaxTerm>, the slightly different view of the world that each of our eyes receives. To experience this slightly different view, do this simple exercise: extend your arm fully and extend one of your fingers and focus on that finger. Now, close your left eye without moving your head, then open your left eye and close your right eye without moving your head. You will notice that your finger seems to shift as you alternate between the two eyes because of the slightly different view each eye has of your finger.
</OpenstaxParagraph>
<OpenstaxParagraph>
	A 3-D movie works on the same principle: the special glasses you wear allow the two slightly different images projected onto the screen to be seen separately by your left and your right eye. As your brain processes these images, you have the illusion that the leaping animal or running person is coming right toward you.
</OpenstaxParagraph>
<OpenstaxParagraph>
	Although we rely on binocular cues to experience depth in our 3-D world, we can also perceive depth in 2-D arrays. Think about all the paintings and photographs you have seen. Generally, you pick up on depth in these images even though the visual stimulus is 2-D. When we do this, we are relying on a number of <OpenstaxTerm>monocular cues</OpenstaxTerm>, or cues that require only one eye. If you think you can’t see depth with one eye, note that you don’t bump into things when using only one eye while walking—and, in fact, we have more monocular cues than binocular cues.
</OpenstaxParagraph>
<OpenstaxParagraph>
	An example of a monocular cue would be what is known as linear perspective. <OpenstaxTerm>Linear perspective</OpenstaxTerm> refers to the fact that we perceive depth when we see two parallel lines that seem to converge in an image (<a href="#Figure_05_03_LinPerspec">Figure 5.17</a>). Some other monocular depth cues are interposition, the partial overlap of objects, and the relative size and closeness of images to the horizon.
</OpenstaxParagraph>
<OpenstaxFigure id="Figure_05_03_LinPerspec" src="https://openstax.org/apps/archive/20240226.174525/resources/a2f5de5ca9ad047dfd4f0d2b3994b3504a04fb79" alt="A photograph shows an empty road that continues toward the horizon." mediaType="image/jpg" width="649" height="390" />
<OpenstaxFigureText width="649">
	Figure 5.17 We perceive depth in a two-dimensional figure like this one through the use of monocular cues like linear perspective, like the parallel lines converging as the road narrows in the distance. (credit: Marc Dalmulder)
</OpenstaxFigureText>
<OpenstaxNote>
	<OpenstaxNoteTitle> Dig Deeper </OpenstaxNoteTitle> <OpenstaxH3> Stereoblindness </OpenstaxH3>
	<OpenstaxParagraph>
		Bruce Bridgeman was born with an extreme case of lazy eye that resulted in him being stereoblind, or unable to respond to binocular cues of depth. He relied heavily on monocular depth cues, but he never had a true appreciation of the 3-D nature of the world around him. This all changed one night in 2012 while Bruce was seeing a movie with his wife.
	</OpenstaxParagraph>
	<OpenstaxParagraph>
		The movie the couple was going to see was shot in 3-D, and even though he thought it was a waste of money, Bruce paid for the 3-D glasses when he purchased his ticket. As soon as the film began, Bruce put on the glasses and experienced something completely new. For the first time in his life he appreciated the true depth of the world around him. Remarkably, his ability to perceive depth persisted outside of the movie theater.
	</OpenstaxParagraph>
	<OpenstaxParagraph>
		There are cells in the nervous system that respond to binocular depth cues. Normally, these cells require activation during early development in order to persist, so experts familiar with Bruce’s case (and others like his) assume that at some point in his development, Bruce must have experienced at least a fleeting moment of binocular vision. It was enough to ensure the survival of the cells in the visual system tuned to binocular cues. The mystery now is why it took Bruce nearly 70 years to have these cells activated (Peck, 2012).
	</OpenstaxParagraph>
</OpenstaxNote>

5.3.2 Color and Depth Perception

1 Introduction to Psychology

1.1 What Is Psychology?

1.1.1 Why Study Psychology?

1.2 History of Psychology

1.2.1 Wundt and Structuralism

1.2.2 Functionalism

1.2.3 Freud and Psychoanalytic Theory

1.2.4 Wertheimer, Koffka, Köhler, and Gestalt Psychology

1.2.5 Pavlov, Watson, Skinner, and Behaviorism

1.2.6 Maslow, Rogers, and Humanism

1.2.7 The Cognitive Revolution

1.2.8 Multicultural And Cross-Cultural Psychology

1.2.9 Women in Psychology

1.3 Contemporary Psychology

1.3.1 Biopsychology and Evolutionary Psychology

1.3.2 Sensation and Perception

1.3.3 Cognitive Psychology

1.3.4 Developmental Psychology

1.3.5 Personality Psychology

1.3.6 Social Psychology

1.3.7 Industrial-Organizational Psychology

1.3.8 Health Psychology

1.3.9 Sport and Exercise Psychology

1.3.10 Clinical Psychology

1.3.11 Forensic Psychology

1.4 Careers in Psychology

1.4.1 Other Careers in Academic Settings

1.4.2 Career Options Outside of Academic Settings

2 Psychological Research

2.1 Why Is Research Important?

2.1.1 Use of Research Information

2.1.2 NOTABLE RESEARCHERS

2.1.3 The Process of Scientific Research

2.2 Approaches to Research

2.2.1 Clinical or Case Studies

2.2.2 Naturalistic Observation

2.2.3 Surveys

2.2.4 Archival Research

2.2.5 Longitudinal and Cross-Sectional Research

2.3 Analyzing Findings

2.3.1 Correlational Research

2.3.2 Causality: Conducting Experiments and Using the Data

2.3.3 Reliability and Validity

2.4 Ethics

2.4.1 Research Involving Human Participants

2.4.2 Research Involving Animal Subjects

3 Biopsychology

3.1 Human Genetics

3.1.1 Genetic Variation

3.1.2 Gene-Environment Interactions

3.2 Cells of the Nervous System

3.2.1 Neuron Structure

3.2.2 Neuronal Communication

3.2.3 Neurotransmitters and Drugs

3.3 Parts of the Nervous System

3.3.1 Peripheral Nervous System

3.4 The Brain and Spinal Cord

3.4.1 The Spinal Cord

3.4.2 The Two Hemispheres

3.4.3 Forebrain Structures

3.4.4 Midbrain and Hindbrain Structures

3.4.5 Brain Imaging

3.5 The Endocrine System

3.5.1 Major Glands

4 States of Consciousness

4.1 What Is Consciousness?

4.1.1 Biological Rhythms

4.1.2 Problems With Circadian Rhythms

4.2 Sleep and Why We Sleep

4.2.1 What is Sleep?

4.2.2 Why Do We Sleep?

4.3 Stages of Sleep

4.3.1 NREM Stages of Sleep

4.3.2 REM Sleep

4.4 Sleep Problems and Disorders

4.4.1 Insomnia

4.4.2 Parasomnias

4.4.3 Sleep Apnea

4.4.4 Narcolepsy

4.5 Substance Use and Abuse

4.5.1 Substance Use Disorders

4.5.2 Drug Categories

4.6 Other States of Consciousness

4.6.1 Hypnosis

4.6.2 Meditation

5 Sensation and Perception

5.1 Sensation versus Perception

5.1.1 Sensation

5.1.2 Perception

5.2 Waves and Wavelengths

5.2.1 Amplitude and Wavelength

5.2.2 Light Waves

5.2.3 Sound Waves

5.3 Vision

5.3.1 Anatomy of the Visual System

5.4 Hearing

5.4.1 Anatomy of the Auditory System

5.4.2 Pitch Perception

5.4.3 Sound Localization

Question	Answer
continuation of a visual sensation after removal of the stimulus	afterimage
slightly different view of the world that each eye receives	binocular disparity
ability to perceive depth	depth perception
perceive depth in an image when two parallel lines seem to converge	linear perspective