Sensation and Perception All is not as it appears!!

Sensation and Perception

All is not as it appears!!


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


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


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


Dark Adaptation– Photopigment molecules are regenerated,

increasing receptor sensitivity

– Cones reach maximum sensitivity in 5 minutes; rods take 1/2 hour


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


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


Sound localization

– Sounds arrive first at the ear closest to the sound

– Judgments of sound intensity also affect localization


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

Humans have about 40 million olfactory 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


Stimulus factors in attention

– !!!Intensity!!!

– Novelty– Movement

–Contrast– Repetition Repetition

Personal factors in attention

– Motives

– Interests

Gestalt Principles of Perceptual Organization

Gestalt Principles of Perceptual Organization

Figure-Ground Relations


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


Illusions are false perceptions

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

Psychology and Pain

Can psychology help people

suffering from pain?

http://www.crha-health.ab.ca/clin/adultpsy/features/chronic.htm

Sensation and Perception All is not as it appears!!

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