PSY 1101 Chapter Notes - Chapter 6: Absolute Threshold, Detection Theory, Subliminal Stimuli
21 Jun 2018
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CHAPTER 6: SENSATION AND PERCEPTION
6.1 → BASIC CONCEPTS OF SENSATION AND PERCEPTION
Sensation: the process by which our sensory receptors and nervous system receive
and represent stimulus energies from our environment
Perception: the process of organizing and interpreting sensory information, enabling us
to recognize meaningful objects and events
Bottom-up processing: analysis that begins with the sensory receptors and works up
to the brain’s integration of sensory information
Top-down processing: information processing guided by higher-level mental
processes; such as when we construct perceptions drawing on our experience and
expectation
TRANSDUCTION
Transduction: conversion of one form of energy into another
oIn sensation, the transformation of stimulus energies such as sight, sounds, and
smells, into neural impulses our brain can interpret
Our senses:
o Receive sensory stimulation, often using specialized receptor cells
oTransform that stimulation into neural impulses
oDeliver the neural information to our brian
Psychophysics: the study of the relationship between the physical characteristics of
stimuli, such as their intensity, and our psychological experience of them
THRESHOLDS
ABSOLUTE THRESHOLDS
Absolute threshold: the minimum stimulus energy needed to detect a particular
stimulus 50% of the time
Signal detection theory: a theory predicting how and when we detect the presence of a
faint stimulus (signal) amid background stimulation (noise)
oAssumes there is no single absolute threshold and that detection depends partly
on a person’s experience, expectations, motivation, and alertness
o“Hits” or “false alarms”
Subliminal: below one’s absolute threshold for conscious awareness
Priming: the activation, often unconscious, of certain associations, thus predisposing
one’s perception, memory, or response
A brief stimulus can trigger a weak response that can be detected by brain scanning
The stimulus may reach consciousness only when it triggers synchronized activity in
multiple brain area
Much of our information processing occurs automatically
DIFFERENCE THRESHOLD
Difference threshold: the minimum difference between two stimuli required for
detection 50% of the time
oWe experience the difference threshold as a just noticeable difference (or jnd)
oDifference threshold increases with the size of the stimuli
If we listen to our music at 40 decibels, we might detect an added 5
decibel
But if we increase the volume to 110 decibels, we probably won’t detect a
5 decibel difference, but we would be able to detect a larger decibel
difference
Subliminally presented stimuli can subtly influence people
oExperiments discount attempts at subliminal advertising or self-improvement
We can perceive the benefits we expect (placebo)
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Weber’s Law: the principle that, to be perceived as different, two stimuli must differ by a
constant minimum percentage (rather than a constant amount)
SENSORY ADAPTATION
Sensory adaptation: diminished sensitivity as a consequence of constant stimulation
oOur nerve cells fire less frequently
Sensory adaptation allows freedom to focus on informative changes in our environment
We perceive the world not exactly as it is, but as it is useful for us to perceive it
Visual system adapts to a static facial expression by becoming less responsive to it
PERCEPTUAL SET
Perceptual set: a mental predisposition to perceive one thing and not another
Through experience we form concepts, or schemas, that organize and interpret
unfamiliar information
Some differences, it seems, exist merely in the eye of their beholders
CONTEXT EFFECTS
The brain can work backward in time to allow a later stimulus to determine how we
perceive an earlier one
The context creates an expectation that, top-down, influences our perception
MOTIVATION AND EMOTION
To believe is to see
After listening to sad songs individuals may hear:
oDie instead of dye
oMourning instead of morning
Walking destinations look farther to those who have been fatigued by prior exercise
A target seems farther away to those throwing a heavy rather than a light object
Desired objects seems closer
oPerceptual bias energizes our going for it
6.2 → VISION: SENSORY AND PERCEPTUAL PROCESSING
LIGHT ENERGY AND EYE STRUCTURES
THE STIMULUS INPUT: LIGHT ENERGY
The stimuli striking your eyes art not particles of colours but pulses of electromagnetic
energy
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Wavelength: the distance from the peak of one light or sound wave to the peak of the
next
oElectromagnetic wavelengths vary from the short blips of cosmic rays to the long
pulses of radio transmission
oFrequency: the number of complete wavelengths that can pass a point in a given
time (depends on wavelength)
The shorter the wavelength, the higher the frequency
Hue: the dimension of colour that is determined by wavelength of light
Intensity: the amount of energy in a light wave or sound wave, which influences what
we perceive as brightness or loudness
oIntensity is determined by the wave’s amplitude (height)
THE EYE
Light enters the eye through the cornea
oBends light to help provide focus
Pupil: the adjustable opening in the center of the eye through which light enters
Iris: a ring of muscle tissue that forms the coloured portion of the eye around the pupil
and controls the size of the pupil opening in response to light intensity
oAlso responds to our cognitive and emotional states
When you feel disgust or about to answer No to a question, your pupils
constrict
Rays from the top of an lit object (such as a candle) hit the bottom of the retina, and
those from the left side hit the right side of the retina
oImage in the eye appears upside down and reversed
Lens: the transparent structure behind the pupil that changes shape to help focus
images on the retina
Retina: the light-sensitive inner surface of the eye, containing the receptor rods and
cones plus layers of neurons that begin the processing of visual information
Accommodation: the process by which the eye’s lens changes shapes to focus near or
far objects on the retina
The retina doesn’t “see” a whole image
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Document Summary
6. 1 basic concepts of sensation and perception. Sensation: the process by which our sensory receptors and nervous system receive and represent stimulus energies from our environment. Perception: the process of organizing and interpreting sensory information, enabling us to recognize meaningful objects and events. Bottom-up processing: analysis that begins with the sensory receptors and works up to the brain"s integration of sensory information. Top-down processing: information processing guided by higher-level mental processes; such as when we construct perceptions drawing on our experience and expectation. Transduction: conversion of one form of energy into another o. In sensation, the transformation of stimulus energies such as sight, sounds, and smells, into neural impulses our brain can interpret. Receive sensory stimulation, often using specialized receptor cells o: transform that stimulation into neural impulses, deliver the neural information to our brian. Psychophysics: the study of the relationship between the physical characteristics of stimuli, such as their intensity, and our psychological experience of them.
