1. Introductory Psychology Concepts
Sensation
Instructor name
Class Title, Term/Semester, Year
Institution
© The McGraw-Hill Companies, Inc.

2. Sensation: The activation of the sense organs by a source of physical energy.
Human sensory capabilities go well beyond the basic five senses (sight, sound, taste, smell, touch).
We are sensitive not merely to touch but to a considerably wider set of stimuli—pain, pressure, temperature, vibration.
Vision has two subsystems—relating to day and night vision.
The ear is responsive to information that allows us not only to hear but also to keep our balance.

3. Sensory Receptors: Specialized neurons activated by stimuli.
Ganglion cells
Amacrine cells
Bipolar cells
Horizontal cells
Cone
Rod
Back of eye
Light
Optic nerve fibers (to brain)
Blind spot (optic disk)
Ganglion cell layer
Bipolar cell layer
Photoreceptor layer
Photoreceptors in the retina, the rods and cones, synapse with bipolar cells, which in turn synapse with ganglion cells whose axons form the optic nerve.

4. Thresholds Absolute Threshold
Defined as the lowest intensity at which a stimulus can be detected 50 percent of the time.
The lower the absolute threshold, the greater the sensitivity.
Approximate Absolute Thresholds for Humans
Sensory Modality Absolute Threshold
Vision Candle flame seen at 30 miles on a clear, dark night
Hearing Tick of a watch under quiet conditions at 20 feet
Taste 1 teaspoon of sugar in 20 gallons of water
Smell 1 drop of perfume diffused into the entire volume of a large apartment
Touch Wing of a fly or bee falling on a person’s cheek from a distance of 1 centimeter
Source: Based on Galanter, 1962.

5. Thresholds Just Noticeable Difference (JND)
The smallest difference between two stimuli that people can perceive 50 percent of the time.
Weber’s law states that the difference threshold, or JND, is directly proportional to the magnitude of the stimulus with which the comparison is being made and can be expressed as a Weber fraction.
Weber’s law breaks down at extremely high and low intensities of stimulation, but holds up reasonably well within the most frequently encountered range.

6. Thresholds Signal Detection Theory
Concerned with the factors that influence sensory judgments.
There is no single point on the intensity scale that separates stimulus detection from nondetection.
People set their own decision criterion, a standard of how certain they must be that a stimulus is present before they will say they detect it.
Decision criterion can change, depending on such factors as fatigue, expectation, and the potential significance of the stimulus.

7. Thresholds Subliminal Stimuli
A subliminal stimulus is one that is so weak or brief that although it is received by the senses, it cannot be perceived consciously.
Research suggests that subliminal stimuli may affect subtle phenomena, such as perceptions and attitudes. (Greenwald & Banaji, 1995)
In one study, college students who were exposed to subliminal presentations of aggressively toned words like “hit” and “attack” later judged ambiguous behaviors of others as more aggressive.
They were also more likely to behave aggressively than were participants who had been exposed to subliminal nonaggressive words. (Todorov & Bargh, 2002)