Psychology
Twelfth Edition
Chapter 6
Sensation and Perception
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Copyright © 2017, 2014, 2011 Pearson Education, Inc. All Rights Reserved
Our Sensational Senses
LO 6.1.A Distinguish between the basic processes of sensation and perception, explain how the doctrine of specific nerve energies applies to perception, and discuss how synesthesia contributes to our understanding of sensory modalities.
LO 6.1.B Differentiate between absolute thresholds, difference thresholds, and signal detection.
LO 6.1.C Discuss why the principle of sensory adaptation helps us understand how the human perceptual system works.
LO 6.1.D Describe how selective attention and inattentional blindness are related.
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The Riddle of Separate Sensations (1 of 5)
Sensation is the detection of physical energy emitted or reflected by physical objects.
The cells that do the detecting are located in the sense organs:
eyes
ears
tongue
nose
skin
internal body tissues
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The Riddle of Separate Sensations (2 of 5)
Perception is the process by which sensory impulses are organized and interpreted.
Sensation begins with the sense receptors, cells located in the sense organs.
Receptors for smell, pressure, pain, and temperature are extensions (dendrites) of sensory neurons.
The receptors convert the energy of a stimulus into electrical impulses that travel along nerves to the brain.
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The Riddle of Separate Sensations (3 of 5)
Separate sensations in the nervous system can be accounted for by:
anatomical codes (as set forth by the doctrine of specific nerve energies)
Müller
functional codes
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The Riddle of Separate Sensations (4 of 5)
Sensory crossover from one modality to another can sometimes occur.
In synesthesia, sensation in one modality consistently evokes a sensation in another.
A person with synesthesia may say things like:
the color purple smells like a rose
the aroma of cinnamon feels like velvet
the sound of a note on a clarinet tastes like cherries
The neurological basis of synesthesia is uncertain.
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The Riddle of Separate Sensations (5 of 5) Figure 6.1 The General Process of Sensation
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Although the Individual senses respond to different kinds of energy in the world, the overall process of sensation is the same.
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Measuring the Senses (1 of 3)
Psychological scientists specializing in psychophysics have studied sensory sensitivity by measuring absolute and difference thresholds.
Absolute threshold: The smallest quantity of physical energy that can be reliably detected by an observer.
Difference threshold: The smallest difference in stimulation that can be reliably detected by an observer when two stimuli are compared; also called just noticeable difference (jnd).
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Measuring the Senses (2 of 3)
Signal-detection theory, however, holds that responses in a detection task depend on both:
a sensory process, and
a decision process
Responses will vary with the person’s:
motivation
alertness
expectations
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Measuring the Senses (3 of 3) Figure 6.2 The Visible Spectrum of Electromagnetic Energy
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Our visual system detects only a small fraction of the electromagnetic energy around us.
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Sensory Adaptation
Our senses are designed to respond to change and contrast in the environment.
When stimulation is unchanging, sensory adaptation occurs.
sensation fades or disappears
Too little stimulation can cause sensory deprivation.
The human brain requires a minimum amount of sensory stimulation to function normally.
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Sensing without Perceiving
Selective attention prevents us from being overwhelmed by the countless stimuli impinging on our senses.
It allows us to focus on what is important.
It also deprives us of sensory information we may need, as in inattentional blindness.
Example: failing to consciously register objects that we are looking straight at
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Vision (1 of 2)
LO 6.2.A Describe the three psychological dimensions of vision, and relate them to the three physical properties of light that produce them.
LO 6.2.B Locate the structures and cells of the human eye, tracing the path that light follows all the way from the cornea to the optic nerve.
LO 6.2.C Summarize the evidence indicating that the visual system is not simply a “camera.”
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Vision (2 of 2)
LO 6.2.D Compare the strengths and weaknesses of the trichromatic and opponent-process theories of color vision.
LO 6.2.E Summarize the principles and processes that guide form perception, depth and distance perception, visual constancies, and visual illusions.
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What We See (1 of 2)
The stimulus for vision is light, which is a form of electromagnetic radiation.
Vision is affected by the wavelength, intensity, and complexity of light.
These produce the psychological dimensions of visual experience:
hue
brightness
saturation
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What We See (2 of 2) Figure 6.3 Psychological Dimensions of the Visual World
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Variations in brightness, hue, and saturation represent psychological dimensions of vision that correspond to the intensity, wavelength, and complexity of wavelengths of light.
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An Eye on the World (1 of 7)
The visual receptors are located in the retina of the eye.
rods
cones
They send signals (via other cells) to the ganglion cells and ultimately to the optic nerve.
The optic nerve carries visual information to the brain.
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An Eye on the World (2 of 7)
Rods are responsible for vision in dim light.
Cones are responsible for color vision.
The process of dark adaptation involves chemical changes in the rods and cones.
Example: It takes time for our eyes to adjust fully to dim illumination.
Rods and cones are connected by synapses to bipolar cells, which in turn communicate with neurons called ganglion cells.
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An Eye on the World (3 of 7)
The axons of the ganglion cells converge to form the optic nerve.
The optic nerve carries information out through the back of the eye and on to the brain.
Where the optic nerve leaves the eye, at the optic disk, there are no rods or cones.
The absence of receptors produces a blind spot in the field of vision.
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An Eye on the World (4 of 7) Figure 6.4 Major Structures of the Eye
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Light passes through the pupil and lens and is focused on the retina at the back of the eye. The point of sharpest vision is at the fovea.
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An Eye on the World (5 of 7) Figure 6.5 The Retinal Image
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When we look at an object, the light pattern on the retina is upside down. René Descartes was probably the first person to demonstrate this fact. He cut a piece from the back of an ox’s eye and replaced the piece with paper. When he held the eye up to the light, he saw an upside-down image of the room on the paper. You could take any ordinary lens and get the same result.