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Chapter 4

PSYC 1200 Chapter Notes - Chapter 4: Occipital Lobe, Opponent Process, Ames Room


Department
Psychology
Course Code
PSYC 1200
Professor
Jason Leboe- Mcgowan
Chapter
4

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Ian Howard is known internationally as a pioneer in sensation/perception research
People can rely on 3 types of cues to determine which way is up - visual, gravity, and body
direction
Sensation: the stimulation of sense organs
Perception: the selection, organization, and interpretation of sensory input
Psychophysics: the study of how physical stimuli and translated into psychological
experience
Thresholds: Looking for Limits
Stimulus: any detectable input from the environment
o Sensation begins with a stimulus
Threshold: a dividing point between energy levels that do and do not have a detectable
effect
Absolute threshold: for a specific type of sensory input is the minimum amount of
stimulation that an organism can detect
Weighing the Differences
Just noticeable difference (JND): the smallest difference in the amount of stimulation that a
specific sense can detect
Weber's law: states that the size of a JND is a constant proportion of the size of the initial
stimulus
o As the stimulus increases in magnitude, the JND becomes larger
Psychophysical Scaling
Fechner's law: states that the magnitude of a sensory experience is proportional to the
number of JNDs that the stimulus causing the experience is above the threshold
Signal Detection Theory
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 other than
stimulus intensity
o The more 'noise' in a system, the harder it will be for you to pick up a weak signal
Subliminal Perception
Subliminal perception: the registration of sensory input without conscious awareness
('limen' is another term for threshold, so 'subliminal' means below threshold)
o Subliminal messaging controversy began in 1957 - with James Vicary hiding 'eat
popcorn' on the screen at a film showing
o Cooper and Cooper demonstrated subliminal presentations of Coca-Cola cans and the
word 'thirsty', in 2002
Sensory Adaptation
Sensory adaptation: a gradual decline in sensitivity due to prolonged stimulation
The Stimulus: Light
Light is a form of electromagnetic radiation that travels as a wave, moving, naturally
enough, at the speed of light
Light waves vary in amplitude (height) and in wavelengths (the distance between peaks)
o Amplitude affects the perception of brightness
o Wavelength affects the perception of color
Light can also vary in its purity (how varied the mix is)
Purity influences perception of the saturation, or richness, of colors
The Eye: A Living Optical Instrument
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The eye serves two main purposes
o Channels light into neural tissue that receives it - retina
o Houses that tissue
Light enters the eye through the cornea
o The cornea and the crystalline lens located behind it form an upside down image of
objects on the retina
Lens: the transparent eye structure that focuses the light rays falling on the retina
Nearsightedness: close objects are seen clearly but distant objects appear blurry
o Occurs when cornea bends light too much - light falls short of retina - or eyeball is
too long
Farsightedness: distant objects are clear, but close objects are blurry
o Focus of light from close objects falls behind the retina
o Typically occurs when eyeball is too short
Pupil: the opening in the center of the iris that helps regulate the amount of light passing
into the rear chamber of the eye
Saccades: when looking at something, eyes make brief fixations at various parts of the
stimuli
The Retina: the Brain's Envoy in the Eye
Retina: neural tissue lining the inside back surface of the eye
o Absorbs light, processes images, and sends visual information to the brain
o Contains two types of receptors - rods and cones
Cones: specialized visual receptors that play a key role in daylight vision and color vision
o Provide better visual acuity - sharpness and precise detail - then rods
Fovea: a tiny spot in the center of the retina that contains only cones
o Visual acuity is greatest at this spot
Rods: specialized visual receptors that play a key role in night vision and peripheral vision
Optic disk: a hole in the retina where the optic nerve fibers exit the eye
Dark adaptation: the process in which eyes become more sensitive to light in high
illumination
The receptive field of a visual cell: the retinal area that, when stimulated, affects the firing
of that cell
Lateral antagonism: occurs when neural activity in a cell opposes activity in surrounding
cells
Vision and the Brain
Optic chiasm: the point at which the optic nerves from the inside half of each eye cross
over and then project to the opposite half of the brain
Optic nerve divides into 2 paths
o The main path projects into the thalamus, the brains major rely station
Here, about 90% of the axons from the retinas synapse in the lateral geniculate
nucleus (LGN)
Subdivided into 2 more pathways - magnocellular and parvocellular
These channels engage in parallel processing: involves simultaneously
extracting different kinds of info from the same input
o The second path braches off into an area in the midbrain called the superior colliculus
Principle function appears to be the coordination of visual input with other
sensory input
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