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Chapter 4

textbook notes chapter 4

Course Code
Dax Urbszat

of 12
Nov/1/2003 CHANAPS
Notes From Reading
Chapter 4
Sensation and Perception
Visual agnosia- an inability to recognized objects through sight
Sensation- the stimulation of sense organs
Perception- the selection, organization, and interpretation of sensory input
Psychophysics: Basic concepts and Issues
-Psychophysics is the study of how physical stimuli are translated into
psychological experience.
-Gustav Fechner was an important contributor to psychophysics in 1860
Threshold: Looking For Limits
-For any given sense what is the weakest detectable stimulus? (what is the minimal
amount of light needed to detect that there is light)
-Threshold is a dividing point between energy levels that do and do not have a
detectable effect.
-An absolute threshold for a specific type of sensory input is the minimum amount
of stimulation that an organism can detect.
Weighing the Differences: The JND
-A just noticeable difference (JND) is the smallest difference in the amount
of stimulation that a specific sense can detect.
-Weber’s law states that the size of a just noticeable difference is a constant
proportion of the size in the initial stimulus.
-As stimuli increases in magnitude JND becomes larger.
Psychophysical Scaling
-Fechner’s law, which states that the magnitude of a sensory experience is
proportional to the number of JNDs that the stimulus causing the
experience is above absolute threshold.
-Three equal increases in stimulus intensity produce progressively smaller
differences in the magnitude of sensation.
-People’s inner “measurements of sensory experiences are not a simple
linear function of the physical intensity of the stimuli
Signal-Detection Theory
Nov/1/2003 CHANAPS
Notes From Reading
-Signal detection theory proposes that the detection of stimuli involves
decision processes as well as sensory processes, which are both influenced
by a variety of factors besides stimulus intensity.
-Hits are detecting signals when they are present
-Misses are failing to detect signals when they are present
-False Alarms are detecting signals when they are not present
-Correct rejections are not detecting signals when they are absent
-Performance will depend on the level of noise in the system
-The more noise in the system, the harder it will be for you to pick up a
weak signal
Perception Without Awareness
-Subliminal perception is the registration of sensory input without
conscious awareness
-Sexual words and drawings are embedded subliminally in magazine
advertisements to elicit favorable unconscious reactions from consumers
-Perception without awareness can take place
-No evidence that subliminal stimuli can lead people to buy specific
products, abandon their sexual inhibitions, become Satan worshippers, or
improve themselves
-Research has not bolstered the idea that persuasive efforts operating
beneath the surface of conscious awareness are especially powerful.
Sensory Adaptation
-Sensory adaptation is a gradual decline in sensitivity to prolonged
-Sensory adaptation is an automatic, built-in process that keeps people
tuned into the changes rather than the constants in their sensory input
-Example would be, Smelling Garbage in the kitchen once you first enter it,
after a while the smell is still stable but with continued exposure, your
sensitivity to it decreases
-Sensory adaptation is probably behavioral adaptation that has been
sculpted by natural selection
-People’s experience of the world depends on both the physical stimuli
they encounter and their active processing of stimulus inputs.
Our Sense of Sight: The Visual System
The Stimulus: Light
-Light is a form of electromagnetic radiation that travels as a wave, moving
naturally enough, at the speed of light.
Nov/1/2003 CHANAPS
Notes From Reading
-Light waves vary in amplitude (height) and in wavelength (the distance
between peaks).
-Amplitude affects mainly the perception of brightness, while wavelength
affects mainly the perception of color.
-Purity influences perception of the saturation, or richness, of colors.
-Although the sense of sight depends on light waves, for people to see,
incoming visual input must be converted into neural impulses that are sent
to the brain.
The Eye: A Living Optical Instrument
-Two main purposes: Channel light to the neutral tissue that receives it,
called retina, and they house that tissue
-Light enters the eye through a transparent window at the front called the
-Cornea and the crystalline lens which are behind it form an upside down
images of objects on the retina
-The lens is the transparent eye structure that focuses the light rays falling
on the retina
-Accommodation occurs when the curvature of the lends adjust to alter
visual focus
-Visual deficiencies caused by the lens: Nearsightedness is when close
objects are seen clearly but distant objects appear blurry
-Farsightedness is when distant objects are seen clearly but close objects
appear blurry
-Iris is the colored ring of muscle surrounding the pupil
-The pupil is the opening in the center of the iris that helps regulate the
amount of light passing onto the rear chamber of the eye
The Retina: The Brain’s Envoy in the Eye
-The retina is the neural tissue lining the inside back surface of the eye; it
absorbs light, processes images, and sends visual information to the brain.
-Retina is a piece of the central nervous system and it is the brains envoy in
the eye
-Axons that run from the retina to the brain converge at the optic disk: a
hole in the retina where the optic nerve fibers exit the eye
Visual Receptors: Rods and Cones
-only about 10% of the light arriving at the cornea reaches these receptors
-Retina contains two types of receptors: rods and cones