PSYA01H3 Chapter 4: Psychology Textbook Chapter 4
Chapter 4:
4.1 Sensation and Perception at a Glance
Sensation: is the process of detecting external events by sense organs and turning those
events into neural signals.
Perception: involves attending to, organizing, and interpreting stimuli that we sense.
Transduction: is the process in which physical or chemical stimulation is converted into a nerve
impulse that is relayed to the brain.
• When patterns of light reach receptors at the back of the eye, they are converted into
nerve impulses that travel to numerous brain centers where color and motion are
perceived, and objects are identified.
• The transduction of sound takes place in the cochlea, where what we hear is converted
into messages that travel to the hearing centers of the brain.
Sensory adaptation: is the reduction of activity in sensory receptors with repeated exposure to
a stimulus.
• Sensations tend to become less intense even if the stimuli remain the same. For
example, when you exit a dark movie theater, the sound and light you encounter
initially seem intense, however you gradually adapt to it.
Stimulus Thresholds:
• Psychophysics: the field of study that explores how physical energy such as light and
sound and their intensity relate to psychological experience.
• Absolute threshold: the minimum amount of energy or quantity of a stimulus required
for it to be reliably detected at least 50% of the time it is presented.
• Difference threshold: is the smallest detectable difference between stimuli.
Signal detection theory: states that whether a stimulus is perceived depends on both sensory
experience and judgment made by the subject.
• The theory requires us to examine two processes: a sensory process and a decision
process. Whether you are able to detect a weak stimulus depends on your expectations,
arousal level, and motivation.
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Gestalt psychology is a approah to pereptio that ephasizes, The hole is greater tha
the su of its parts. I other ords, the idiidual parts of a iage ay hae little eaig
on their own, but when combined the whole takes on a significant, perceived form.
• Oe asi Gestalt priiple is that ojets or figures i our eiroet ted to stad
out against a background, the figure-ground principle.
• Another set of gestalt principles include proximity and similarity. We tend to treat two
or more objects that are in close proximity to each other as a group. For example, we
see a dozen eggs in a carton as two rows of six eggs rather than six rows of two.
Similarity can be experienced by viewing the intermixing of sports fans from opposing
teams which typically yields distinct patches of crowd wearing similar clothing. Thus
objects are grouped based on similarity of properties such as coloration, shape, and
orientation.
• Continuity, or good otiuatio, refers to the pereptual rule that lies ad other
objects tend to be continuous, rather than abruptly changing direction. A related
principle, called closure, refers to the tendency to fill in gaps to complete a whole
object.
Top-down processing: occurs when prior knowledge and expectations guide what is perceived.
Bottom-up processing: is the construction of a whole stimulus or concept from bits of raw
sensory information.
• The way we perceive the world is a combination of both top-down and bottom-up
processing.
• Parallel processing refers to the simultaneous use of top-down and bottom-up
processing as we perceive and interpret the world. It is what allows us to attend to
multiple features of what we sense. Perceiving the world, whether done form a bottom-
up, top-down, or combined direction, requires attending to relevant features.
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Attention and Perception
• Selective attention involves focusing on one particular event or task.
• Divided attention involves paying attention to several stimuli or tasks at once.
Inattentional blindness is a failure to notice clearly visible events or objects because attention
is directed elsewhere.
• For example, the dancing gorilla film. The audience is focused on watching what the
studets i the ideo are doig that they do’t otice a gorilla walk in and dance.
• Inattentional blindness accounts for many common phenomena. For example, those
who witness auto accidents or criminal behavior may offer faulty or incomplete
testimony. This is not necessarily because they failed to remember, but because they
did not even notice critical events.
1.3 The Visual System
How the Eye Gathers Light;
• Light refers to radiation that occupies a relatively narrow band of the
electromagnetic spectrum. It travels in waves
• that vary in terms of two different properties:
1. length
2. amplitude
Wavelength: refers to the distance between peaks of a wave
• Differences in wavelength correspond to different colors on the electromagnetic
spectrum.
• Long wavelengths correspond with the reddish colors
• short wavelengths correspond with the bluish colors
• The amplitude (or height) of the peaks of a wave gives different experiences.
• Low-amplitude waves correspond with dim colors, and high-amplitude waves with
bright colors
• We do not typically see pure coloration, rather, what we see is based on a mixture of
wavelengths that vary by hue (colors of the spectrum), intensity (brightness), and
saturation (colorfulness, or density).
The Structure of the Eye:
• The sclera is the white, outer surface of the eye
• The cornea is the clear layer that covers the front portion of the eye and also
contributes to the eye’s aility to fous
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Document Summary
Sensation: is the process of detecting external events by sense organs and turning those events into neural signals. Perception: involves attending to, organizing, and interpreting stimuli that we sense. Sensory adaptation: is the reduction of activity in sensory receptors with repeated exposure to a stimulus: sensations tend to become less intense even if the stimuli remain the same. For example, when you exit a dark movie theater, the sound and light you encounter initially seem intense, however you gradually adapt to it. Signal detection theory: states that whether a stimulus is perceived depends on both sensory experience and judgment made by the subject: the theory requires us to examine two processes: a sensory process and a decision process. Whether you are able to detect a weak stimulus depends on your expectations, arousal level, and motivation. We tend to treat two or more objects that are in close proximity to each other as a group.
