GENERAL PSYCHOLOGY
Chapter 4
Sensation and Perception
Chapter Introduction: What is Reality?
Sensory input +
Sense organ functioning ability +
World view based on life experiences = REALITY
Sensory Input
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With few exceptions, a sensory-perceptual experience starts with some form of environmental stimuli
Changes in properties of stimuli
If the change in the stimulus is above a threshold, detection is possible
Sense Organ Functioning
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Sense organs detect changes or variants in environmental stimuli
Information is forwarded to the brain
World View Based on Life Experiences
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When detected changes get to the brain, the brain begins to recognize them, and assign meanings to
the changes
The recognition of and meanings given to stimuli are based largely on personal experiences
Familial upbringing, peers, culture, race, religion, economic status, political affiliation, personality
factors, and intelligence all influence how stimuli are perceived
Question: How can two people experience the same stimulus and have a different reality?
Defining Sensation and Perception
Sensation: The process of receiving information from the outside world and sending it to the brain.
Sensation involves the use of the 5 senses including the visual, auditory, olfactory, tactile and gustatory
senses. Sensation is more of a physiological process of the body as it principally involves the use of the
sense organs.
Perception: The process of organizing, interpreting and assigning meaning to the sensory information
receive from the outside world through the sense organs. Perception involves taking fundamentally
meaningless sensory information and interpreting it’s meaning to the individual. Perception is more of a
cognitive process since it involves what we ‘think’ and feel about the information received from the 5
senses. Our perceptions are notably influenced by our life experiences and our beliefs and values.
Therefore, perceptions of a certain sensory stimulus may differ greatly from one individual to another.
Selecting Sensory Information for Processing
The things in our environment that cause us to have sensations and subsequent perceptions are know as
stimuli or ‘sensory stimuli.’ A sensory stimulus is any aspect of the outside world that directly influences
our behavior or our conscious experience.
Theory of Selective Attention: The theory of selective attention contends that, in order to cope with the
infinite number of sensory stimuli bombarding us at any given second, we will ‘selectively attend to’
certain kinds of stimuli based on several properties. These principles are noted below.
Meaning: Stimuli that are personally relevant to an individual will attract the attention of the
individual.
Intensity: Stimuli that are especially strong in their magnitude will attract the focus of our
attention.
Novelty: Stimuli that are in some way new, different or unique will attract the focus of our
attention
Change: Any change in the presence, frequency or intensity of a stimulus will attract the focus of
our attention.
Sensory Limits
The concept of sensory limits focuses upon these two questions. How much of a stimulus is needed for it
to be detected and become a part of our consciousness? How much of a change in an existing (currently
detected stimulus of which a person is aware) is needed before the change can be detected.
Absolute Threshold: The smallest magnitude (or amount) of a stimulus that can be detected.
Difference Threshold: The smallest amount of change in an existing (currently detected) stimulus that
can be detected. Also known as the ‘JND’ or ‘just noticeable difference.
Visual Perceptual Organization
Although perceptual processes for each of the five senses have been studies for years, perhaps the most
researched and therefore best understood is visual perception. While our visual perceptual processes
are, like all perceptions, affected by our personal biases and past experiences, there are several definite
patterns and tendencies that humans use in the process of organizing and assigning meaning to visual
sensory stimuli. Some of these principles of visual perceptual organization are listed below.
Figure-Ground: Perhaps the most fundamental of all principles of perceptional organization, the figureground principle asserts that when we look at a visual stimulus, we actually arrange our visual field into
two dimensions – the figure, or the focus of our attention, and the background, or that which is not
distinct to us at that very moment. In short, we always use the background as a context in which to
interpret the figure.
Similarity: The similarity principle contends that objects that are similar in their appearance will generally
be perceived as belonging together.
Proximity: The proximity principle asserts that objects that are physically closer together will generally
be perceived as belonging together.
Continuity: The tendency to perceive a series of points or lines as having unity or a continuous
connection as a part of a set or series.
Closure: The closure principle is a basic concept of the ‘Gestalt’ principles of visual perceptual
organization. The closure principle asserts that we have a tendency to perceive incomplete figures or
patterns as being whole or compete figures. Apparently, when our brains sense an incomplete visual
stimulus, we have an overwhelming tendency to see this incomplete figure as being whole or complete –
a tendency to ‘fill in the gaps’ and enclose the ambiguous stimuli to make some kind of complete pattern.
When our brains do organize and make sense out of an incomplete figure, we are said to have made a
‘gestalt’ – to have a kind of perceptual epiphany as a light bulb is turned out and we think ‘ah…aha, now
I’ve got it.’
Context Effects: Objects and figures surrounding a visual stimulus influence how the stimulus is
perceived.