Psychology Oct 1st 2013
Sensation Vs. Perception
• Sensory Receptors
• Transduction - results of info in environment, and transferred into action potentials
• Interpretation of sensory information based, in part, on previous experiences. (i.e.
listening to someone speak a foreign language. You can hear the sound, but it
does not register as words)
• Discriminate Among The Senses
• sensory receptors are specialized to absorb a particular type of energy.
• sensory receptors have different neural pathways
• loss of sensory channel often results in enhanced sensory skills in another area
•blind people are more accurate at locating a sound source and are more
sensitive to touch.
• Brain automatically perceives the information it receives from the sense organs
• bottom-up processing vs. top-down processing.
•bottom-up: sensory processing
link between physical properties of stimuli and a person’s experience of stimuli
(sensation -> perception)
• sensation begins with a detectable stimulus
• Gustave Fechner: the concept of the threshold
•Absolute Threshold - lower limit for detecting presence of stimulus
•Absolute Thresholds aren’t really absolute
•The probability of detecting a stimulus increase gradually with stimulus
intensity, as shown in red; an “absolute” threshold is defined as the intensity
level at which the probability of detection is 50%.
• Candle flame at 30 miles on a dark clear night
• Hearing a ticking watch at 20 feet under quiet conditions Psychology Oct 1st 2013
•Smell one drop of perfume diffused through-out three rooms
•Taste a teaspoon of sugar in 2 gallons of water
•Touch the wing of a fly falling on your cheek from a distance of one
• Environment is seldom ideal
•Noise (Any extra stimulus) is an irrelevant and competing stimulus
• Individuals have different absolute thresholds
• Individuals can detect information that is below the lebel of conscious awareness
• Fowler et al. (1981)
• presented words subliminally (e.g. lodge)
• asked which of two words was most like subliminal word (e.g. hotel or book)
• results: usually picked correct word.
• There is no evidence subliminal perception affects conscious thoughts and
• Difference Thresholds
• Just Noticeable Difference (JND)
• smallest difference in stimulation required to discriminate one stimulus from
another 50% of the time
• Weber’s Law
Two stimuli must differ by a constant proportion for the difference to be
detected. (e.g. 100lbs weight compared to another weight must be 10lbs or up
and constant to get accurate detection)
•proportion varies with type of stimulus
• Signal Detection Theory
• Detection of a stimulus depends on a variety of factors besides the physical
intensity of the stimulus and the sensory abilities of the observer
• fatigue, expectancy and urgency affect detection.
• Light = Electromagnetic Radiation
• wavelength: perception of colour
• amplitude: perception of bri