PSYC 110 Lecture 5: Chapter 5_ Sensation and Perception
Chapter 5: Sensation and Perception
Two Sides of the Coin
●Sensation is the detection of physical energy by our sense organs, which send that
information to the brain.
●Perception is the brain’s interpretation of raw sensory data.
●When the way we perceived a stimulus does not match reality, that's an illusion
Sensation
●Despite their differences, all of our senses rely on a handful of principles.
●The external stimulus is converted by a sense receptor into neural activity via
transduction.
●Activation is the highest when stimulus is first detected, then sensory adaptation occurs.
Psychophysics
●Study of how we perceive sensory stimuli based on their physical characteristics.
●Absolute threshold is the lowest level of a stimulus we can detect 50% of the time.
○A single candle 30 miles away
○50 odorant molecules
●Subliminal Messages
○When sensory information is received below the absolute threshold- we receive
the information but are not consciously aware of it.
●The just noticeable difference is the smallest amount of stimulus change we can detect.
●Follow Weber’s law- the stronger the stimulus, the greater change needed to detect.
Signal Detection Theory
●Theory regarding how stimuli are detected under different conditions.
●Like when there’s a lot of background noise.
Cell Specialization
●Doctrine of Specific Nerve Energies
○States that even though there are distinct stimulus energies, the sensation we
experience is determined by the nature of the sense receptor, not the stimulus.
●Phosphenes is an example (pressing on eyes and seeing light)
Cross-Modal Senses
●The rubber-hand illusion and the McGurk effect (bar/far) demonstrates sensory-cross
modality.
●This may help to explain synesthesia- hearing sounds when one sees colors or tasting
colors.
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When Senses Meet the Brain
●After being transduced, our brains then organize the sensory data into meaningful
concepts=> perception
●Our brains piece together
○a.) what’s in our sensory field
○b.) what was there a moment ago
○c.) what we remember from our past
Sensation => Perception
Environment + Energy + Sense Organs + Sense Receptors + Sensory Nerves + Brain
The Multitasking Brain
●We attend to multiple senses at once, called parallel processing.
●Bottom-up processing:
○Starts with a raw sensory data/stimuli
○Construct a whole stimulus from its parts
○
Top-down processing:
○Starts with our beliefs and perceptions
○Which we impose raw sensory stimuli we perceive
Perceptual Hypotheses
●Perceptual sets occur when our expectation influence our perceptions.
●Perceptual constancy allows us to perceive stimuli consistently across conditions.
●We don't see the size, shape, or color of an object changing despite the objective fact that
they do.
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●Color perception in particular derives from its context.
The Role of Attention
●Selective attention allows us to choose which sensory inputs to focus and which to “turn
down”
●The other “channels” are still being processed at some level, through, even when we’re
not aware of it
○Someone says your name at a party.
●We’re poor at detecting stimuli in plain sight if our attention is focused elsewhere.
●Inattentional blindness (failure to detect stimuli in plain sight when our attention is
focused elsewhere) and change blindness (failure to detect changes in one environment)
SIMILAR PHENOMENA
Waves and Wavelengths
●Visual and auditory stimuli both occur is the form of waves
○Vision => light
○Audition => vibration
●Amplitude of wave = height of the wave from highest point to lowest point
●Wavelength = length of wave from one peak to next
●Frequency of wave = number of waves that pass through a given point in a given time
period.
○Often expressed in Hertz (Hz) or cycles per second
○Longer wavelengths have lower frequencies, shorter wavelengths, have higher
frequencies.
The Visual System
●Light is the form of sensory energy that the visual system responds to.
●When light reaches an object, part of that light gets reflected by the object and part gets
absorbed.
●Light wavelength is associated with perception of color (hue)
○Red = longer wavelengths
○Green = intermediate wavelengths
○Blue = shorter wavelengths
●Amplitude of light waves is associated with brightness or intensity of color
○Larger amplitudes appear brighter
Structure of Eye
●Sclera- white portion of the eye
●Iris- colored portion and controls how much light enters the eye
●Pupil- hole where light enters the eye
●Cornea- contains transparent cells that focus light on the back of the eye
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Document Summary
Sensation is the detection of physical energy by our sense organs, which send that information to the brain. Perception is the brain"s interpretation of raw sensory data. When the way we perceived a stimulus does not match reality, that"s an illusion. Despite their differences, all of our senses rely on a handful of principles. The external stimulus is converted by a sense receptor into neural activity via transduction. Activation is the highest when stimulus is first detected, then sensory adaptation occurs. Study of how we perceive sensory stimuli based on their physical characteristics. Absolute threshold is the lowest level of a stimulus we can detect 50% of the time. When sensory information is received below the absolute threshold- we receive the information but are not consciously aware of it. The just noticeable difference is the smallest amount of stimulus change we can detect. Follow weber"s law- the stronger the stimulus, the greater change needed to detect.
