PSYC 1001 Chapter Notes - Chapter 4: Gustav Fechner, Detection Theory, Absolute Threshold
16 Jun 2018
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Psychology Chapter 4 Notes
- Synesthesia: a condition in which perceptual or cognitive activities trigger exceptional
experiences
- Emotional synesthesia: a condition in which specific stimuli are consistently and involuntarily
associated with emotional responses
- Sensation: the stimulation of sense organs
- Perception: the selection, organization, and interpretation of sensory input
Sensation vs Perception
Sensation
Perception
Passive process
Active process
Detect physical energy from environment
Actively organizes sensation
Transmitted to brain
Interpreted by brain
Bottom up
Top down
Psychophysics
- Psychophysics: the study of how physical stimuli are translated into psychological experience
- Gustav Fechner
- 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 and organism can detect
o Difference between not perceiving & just being able to perceive a stimulus.
o Minimum sensory stimulation that can be detected 50% of time.
- Just noticeable difference (JND): the smallest difference in the amount of stimulation that a
specific sense can detect; a percentage of total value of stimulus.
o Difference threshold: “allest irease or derease i stiulus for just otieale
differee JND detetale 50% of tie.
- Weber’s law: states that the size of a just noticeable difference is a constant proportion of the
size of the initial stimulus
- This constant proportion is called Weer’s fraction
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 besides stimulus intensity
o Detection of stimulus depends on more than physical intensity of stimulus & sensory
abilities of observer.
o Fatigue, expectancy, urgency.
o Decision making about stimuli in presence of uncertainty depends on criterion.
- Performance depends on the criterion you set for how sure you must feel before you react and
o the leel of oise i the system (noise comes from all the irrelevant stimuli in the
environment)
- The more noise the harder it is to pick up a weak signal
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- Detectability is measured in terms of probability and depends on decision making processes as
well as sensory processes
Perception without awareness
- Subliminal perception: the registration of sensory input without conscious awareness
- Subliminal stimuli generally produce weak effects
Transduction
- Process by which sensory receptors convert stimulation into neural impulses
- Sensory receptors detect and respond to various stimuli
Sensory adaptation
- Sensory adaption: is a gradual decline in sensitivity due to prolonged stimulation
- Built in process that keeps people tuned in to the changes rather than the constants in their
sensory input
- Probably an adaption that has been sculpted from natural selection
- Process of becoming less sensitive to an unchanging sensory stimulus over time
The visual system
- The stimulus is light
- Light waves vary in amplitude and in wavelength
- Amplitude affects the perception of brightness
- Wavelength affects the perception of color
- Light can also vary in purity
- Purity influences perception of the saturation, richness of colors
The eye
- The eyes serve two main purposes: channel light to the neural tissue that receives it (i.e. the
retina) and they house that tissue
- Cornea: light enters through here and form an upside-down image of objects on the retina
- Lens: the transparent eye structure that focuses the light rays falling on the retina
- Accommodation: occurs when the curvature of the lens adjusts to alter visual focus
- Near sightedness: close objects are seen clearly but distant objects appear blurry
o Near sightedness is due to the focus of lights from distant objects falls a little short of the
retina and occurs when the cornea or lens bends the light too much, or when the eyeball
is too long
- Farsightedness: distant objects are seen clearly but close objects appear blurry
Nothing There
Something really there
othig there
Correct rejection
Miss
soethig reall there
False alarm
HIT
REALITY
DECISION
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o Due to the fact that the focus of light from close objects falls behind the retina, typically
occurs when the eyeball s 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
- When the pupil constricts less light into the eye and the image is sharpened
- Dilates: more light into the eye and the image is less sharp (occurs in dim light)
- Saccades: eye movements where the eyes scan the visual environment and make brief fixations
at various parts of the stimuli
- retina: the neural tissue lining the inside back surface of the eye; it absorbs light, processes
images, and sends visual information to the brain
- Optic disk: a hole in the retina where the optic nerve fibers exit the eye (blind spot)
How the eye works
- Light reflects off objects, passes thru cornea, pupil, lens & focus on retina & fovea.
- Ciliary muscles alter shape of lens.
- Receptors (rods & cones), convert (transduce) light into neural signals.
- Cones (6 million) provide colour & detail.
- Rods (120 million) provide night vision, better in dim light.
- Detailed vision best at fovea, where cones most common
retina
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Document Summary
Synesthesia: a condition in which perceptual or cognitive activities trigger exceptional experiences. Emotional synesthesia: a condition in which specific stimuli are consistently and involuntarily associated with emotional responses. Perception: the selection, organization, and interpretation of sensory input. Psychophysics: the study of how physical stimuli are translated into psychological experience. Absolute threshold: for a specific type of sensory input is the minimum amount of stimulation. Weber"s law: states that the size of a just noticeable difference is a constant proportion of the size of the initial stimulus. Performance depends on the criterion you set for how sure you must feel before you react and o(cid:374) the le(cid:448)el of (cid:862)(cid:374)oise(cid:863) i(cid:374) the system (noise comes from all the irrelevant stimuli in the environment) The more noise the harder it is to pick up a weak signal. Detectability is measured in terms of probability and depends on decision making processes as well as sensory processes.
