Psych Chapter 4
•Psychophysics: Basic Concepts and Issues
oThresholds: Looking for Limits
oWeighing the Differences: The JND
oPerception without Awareness
•Our Sense of Sigh: The Visual System
oThe Stimulus: Light
oThe Eye: A Living Optical Instrument
oThe Retina: The Brain’s Envoy in the Eye
oVision and the Brain
oViewing the World in Colour
oPerceiving Forms, Patterns, and Objects
oPerceiving Depth or Distance
oPerceptual Constancies in Vision
oThe Power of Misleading Cues: Optical Illusions
oVision for Perception and Vision for Actions
•Our Sense of Hearing: The Auditory System
oThe Stimulus: Sound
oHuman Hearing Capacities
oSensory Processing in the Ear.
oAuditory Perception: Theories of Hearing
oAuditory Localization: Perceiving Sources of Sound
oMusic and Its Effects
•Our Chemical Senses: Taste and Smell
oTaste: The Gustatory System
oSmell: The Olfactory System
•Our Sense of Touch: Sensory Systems in the Skin
•Our Other Senses:
oThe Kinaesthetic System
oThe Vestibular System
Psychophysics – Study of how physical stimuli are translated into
Sensation is the stimulation of sense organs.
Perception is the selection, organization, and interpretation of sensory
Thresholds: Looking for Limits
•Sensation begins with stimulus (Any detectable input).
•Threshold: Dividing point between energy levels that do and do not have a detectable
oAbsolute Threshold: Minimum amount of stimulation that an organism can
•As stimulus intensity increases, subjects’ probability of responding to stimuli
•Absolute threshold as the stimulus intensity detected 50% of the time.
Weighing the Differences: The JND
•Just Noticeable Difference (JND) –The smallest difference in the amount of
stimulation that a specific sense can detect.
•JND closely related to absolute threshold. Absolute Threshold is simply the JND
•Weber’s Law: States that the size of JND is a constant proportion of the size of the
initial stimulus. The constant proportion is called the Weber Fraction.
•Weber Fraction for weights: 1/30. This means you can only tell the difference
between 300 grams and 310 grams, not 300 grams and 305 grams.
•Scale – Judging the increase in sensory input.
•Fechner’s Law – The magnitude of a sensory experience is proportion to the number
of JNDs that the stimulus causing the experience is above the absolute threshold.
oEx: Being in a darkroom, and turning on one light bulb. Second light bulb you
notice a small difference. Third one you hardly notice anything different.
•Perception can’t be measured on absolute scales.
•Signal-detection theory – The detection of stimuli involves decision processes as well
as sensory processes, which are both influenced by a variety of factors besides
•Hits – Detecting signals when present. Misses – Failing to detect signals when
present. False Alarms – Detecting signals when not present. Correct Rejections
– Not detecting signals when they are absent.
•Noise – Irrelevant stimuli that interferes with your ability to pick up weak signals.
Perception without Awareness
•Subliminal Perception – Registration of sensory input without conscious awareness.
(Limen = Threshold, sub = below. Therefore Subliminal = Below Threshold.
•Sensory Adaption – Gradual decline in sensitivity due to prolonged stimulation.
The Visual System
The Stimulus Light
Psychophysics study of how physical stimuli are translated into psychological experience. Perception is the selection, organization, and interpretation of sensory input. Just noticeable difference (jnd) the smallest difference in the amount of stimulation that a specific sense can detect. Absolute threshold is simply the jnd from nothing: weber"s law: states that the size of jnd is a constant proportion of the size of the initial stimulus. The constant proportion is called the weber fraction: weber fraction for weights: 1/30. This means you can only tell the difference between 300 grams and 310 grams, not 300 grams and 305 grams. Second light bulb you notice a small difference. Third one you hardly notice anything different: perception can"t be measured on absolute scales. Signal-detection theory: signal-detection theory the detection of stimuli involves decision processes as well as sensory processes, which are both influenced by a variety of factors besides stimulus intensity, hits detecting signals when present.