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Sensation and Perception
Sensation
– The process by which our sense organs respond to and translate stimuli into nerve impulses sent to the brain
Perception
– Organizing the stimulus input and giving it meaning
Sensation and Perception
Stages of sensation and perception– Stimuli activate sensory receptors– Sensory receptors translate information into
nerve impulses– Specialized neurons analyze stimuli features– Stimulus pieces are reconstructed and
compared to stimuli in memory– Perception is then consciously experienced
Psychophysics: Studies of Sensitivity to Stimuli
Absolute limits of sensitivity
– Dimmest light in which we can see objects
– Softest sound we can hear
Recognizing differences between stimuli– Smallest difference in
brightness detectable
– Recognizing differences between tones
The Absolute Threshold
– The lowest intensity at which a stimulus can be detected 50% of the time
Stimulus Detection
Signal Detection Theory
Decision criterion: A personal standard of certainty before a person will say that they detect a stimulus
– Affected by:• Conservativeness or boldness
• Increasing rewards for hits or costs for misses
Subliminal Perception
A subliminal stimulus cannot be perceived consciously but do register in the nervous system
– “subliminal perception”
Subliminal Perception: Research Results
Stimuli above threshold influence behavior much more than subliminal stimuli
Subliminal stimuli have stronger effects on attitudes
Effects may be due to placebo effects
The Difference Threshold
The difference threshold (just noticeable difference or JND) is the smallest difference between two stimuli that people can perceive 50% of the time
– Weber’s Law: the JND is directly proportional to the magnitude of the stimulus with which the comparison is made (e.g 1/50 for weight)
Sensory Adaptation (Habituation)
Sensory neurons respond to a constant stimulus by decreasing their activity
The Sensory Systems: Vision
Lens:– Becomes thinner to
focus on distant objects and thicker to focus on closer ones
Rods: Black and white receptors
Cones: Color receptors
The Sensory Systems: Vision
Transduction
– Absorption of light by photopigments produces a chemical reaction changing the rate of neurotransmitter release at the receptor’s synapse
– The greater the change in release, the stronger the signal passed into the optic nerve
The Sensory Systems: Vision
Dark Adaptation– Photopigment molecules are regenerated,
increasing receptor sensitivity
– Cones reach maximum sensitivity in 5 minutes; rods take 1/2 hour
The Sensory Systems: Vision
Young-Helmholtz trichromatic theory– Individual cones are
most sensitive to wavelengths corresponding to:
• Blue• Green• Red
Opponent Process Theory (Hering, 1870)– Three cone types
respond to two different wavelengths
Red/Green
Blue/Yellow
Black/White
The Sensory Systems: Vision
Dual-Process Theory
– Trichromatic theory confirmed
– Opponent processes occur in the ganglion cells of the retina rather than the cones
The Sensory Systems:Color Blindness
Dichromat
– Blind in Red - Green or Yellow - Blue systems or both
Monochromat
– Sensitive only to the Black - White system
The Sensory Systems: Audition
Characteristics of sound waves
– Frequency: the number of sound waves, or cycles, per second (measured in Hz)
– Amplitude: the vertical size of the sound waves (measured in dB)
The Sensory Systems: Auditory Transduction
1. Sound waves strike eardrum, setting cochlear fluid into motion
2. Fluid waves vibrate the basilar membrane, bending the hair cells in the organ of Corti
3. Neurotransmitters are released into the synapse, resulting in a nerve impulse
Frequency Theory
– Nerve impulses sent to the brain match the frequency of the sound wave
Place Theory
– There is a specific point in the cochlea where the fluid wave peaks and most strongly bends the hair cells
Audition: Theories of Pitch
The Sensory Systems: Audition
Sound localization
– Sounds arrive first at the ear closest to the sound
– Judgments of sound intensity also affect localization
The Sensory Systems: Audition
Types of Deafness– Conduction
• Caused by problems transmitting sound waves to cochlea
– Nerve deafness• Caused by damaged receptors in inner ear or damaged
auditory nerve
The Sensory Systems: Gustation
A “taste” results from complex patterns of neural activity produced by the four types of taste receptors
The Sensory Systems: Olfaction
Menstrual Synchrony
– The tendency of women who live together or are close friends to become similar in their menstrual cycles
– May be due to pheromones (Preti et al., 1986), but synchrony was not found in cohabiting lesbian couples (Weller & Weller, 1997, 1998)
The Sensory Systems: The Tactile Sensations
Humans are sensitive to:– Pressure (touch)
– Pain
– Warmth
– Cold
The Sensory Systems: The Body Senses
Kinesthesis
– Provides us with feedback about our muscles and joints’ positions and movements
Perception: The Creation of Experience
Bottom-up processing– Taking individual
elements of a stimulus and combining them into a perception
Top-down processing– Using existing
knowledge in perception
Attention:– Focusing on certain
stimuli
– Filtering out other information
Perception: The Creation of Experience
Stimulus factors in attention
– !!!Intensity!!!
– Novelty– Movement
–Contrast– Repetition Repetition
Personal factors in attention
– Motives
– Interests
Perception: The Creation of Experience
Perceptual schemata: allow us to classify sensory input in a top-down fashion
Perceptual set: A readiness to perceive stimuli in a particular way
Perceptual constancies: Allow us to recognize familiar stimuli under varying conditions
Depth Perception
Monocular cues– Light and shadow– Linear perspective– Interposition– Height in the
horizontal plane– Texture– Clarity– Relative size– Motion parallax
Binocular cues
– Binocular disparity
– Convergence
Understanding Pain
Endorphins: Natural opiates inhibit the release of neurotransmitters involved in pain perception
Stress-induced analgesia: A reduction in perceived pain that occurs under stressful conditions– Adaptive for functioning so that a person can
deal with the stressful stimulus