Transcript PSY 2012 General Psychology Chapter 5: Sensation and Perception Samuel R. Mathews, Ph.D. Associate Professor The Department of Psychology The University of West Florida.

PSY 2012 General Psychology
Chapter 5: Sensation and Perception
Samuel R. Mathews, Ph.D.
Associate Professor
The Department of Psychology
The University of West Florida
Sensation
Environmental
Stimuli
Stimuli must exceed the threshold necessary
to trigger the sense receptors in the sense organs
Sensory Organs
Sense organs change the physical
stimuli into electrochemical energy
that travels across the neural pathways
in a process termed transduction
The brain converts the neural impulses to the
experiences we report of sight, sound, touch,
smell, taste, etc.
Brain
Key Concepts in Sensation
• Transduction: the process of converting physical energy
(e.g., light, sound waves, pressure) to electrochemical
energy in the cells of the sense organs
• Sensory Adaptation: the process of our sense organs
becoming habituated to levels of stimulation in our
environment (e.g. losing sensitivity to the experience)
Key Concepts in Sensation
• Thresholds: Sensitivity of the sense organ
– Absolute threshold: lowest level of physical energy
a sense organ can detect
– Difference threshold: the minimal difference
between two levels of a given stimulus for which a
difference can be detected.
Did you see that?
Or
Signal Detection Theory
• Sense organs’ abilities to detect the
presence or change in a stimulus is based
on:
– Signal strength and quality
– Background noise
– Expectations or mental set
– Prior experience with the stimulus
– Fitness/health of the organ itself
The Human Eye
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Visual Sensation
Light Energy
Light energy varies in wave length (within the electromechanical
spectrum) which produces color and intensity or amplitude
which produces brightness
Transduction occurs in the retina
of the eye in specialized cells (rod &
cone cells) that detect color and intensity
Eyes
The optic nerve via the bipolar cells and ganglion cells
transmits the signals from the retina to the brain. These signals
feed primarily to the parietal lobe and visual cortex of the
occipital lobe.
Parietal and
Occipital Lobes
Color Sensation
• Cone cells, concentrated in the fovea of the eye are sensitive to
color but require relatively high levels of light to “fire”
• Initial process of color sensation is the stimulation of 3 types of cone
cells (each type senses either red, blue, or green) in the retina of the
eye—the trichromatic process
• The second phase of color sensation is in the bipolar cells and
operates within the opponent-process theory
– Cone cells transmit nerve signal to the bipolar cells
– Opposing colors cancel each other out (red and green are opponent
colors and yellow and blue are opponent colors)
– The results of this process are transmitted to the brain via the optic
nerve.
Opponent Process Theory
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Seeing in the dark
or
The Perception of Brightness
• Rod cells
– Sensitive to lower levels of light;
– Located around the periphery of the fovea;
– Responsible for so-called night vision
• Note: Night vision can be enhanced by looking slightly away
from the object in darker situations. Rod cells are more
densely concentrated outside the fovea of the eye.
Did you hear that?
or
Auditory Sensation
Auditory Sensation
Sound Waves
Sound waves vary in frequency (Hz or CPS) that relates to pitch
and amplitude (peak-to-peak within a cycle) that relates to volume
Ears
Transduction occurs in the ear as the
sound waves impact the tympanic membrane
which sets up vibrations impacting bones
(hammer, anvil, & stirrup) which pass vibrations
to the cochlea stimulating the basilar membrane which
converts the energy to neural signals
The auditory nerve transmits the signals from the inner ear
to the brain. These signals feed primarily to the auditory cortex
of the temporal lobe
Temporal
Lobe
Qualities of Sensation of Sound
• Pitch:
– Based on the frequency of the sound waves;
– 20Hz to 20,000Hz is the normal range for humans with healthy
hearing sense
– Location on basilar membrane that receives the greatest
stimulation represents one system of picking up pitch above
1000Hz (place theory);
– Basilar membrane neurons rate of firing based on frequency is
related to sounds below 5000Hz (frequency theory).
– Between 1000Hz and 5000Hz is the range of typical human
speech—hence redundancy.
Qualities of Sensation of Sound
• Loudness
– Based on amplitude of the sound waves
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1 Cycle
Frequency=number of cycles/second
Qualities of Sensation of Sound
• Timbre:
– Characteristic sound of a particular event (e.g.
dog barking, door slamming, heavy metal
guitar rip)
• Attack and decay: the onset and duration of a
sound coupled with the intensity and rise or fall of
the sound volume
• Vibrato: periodic change in pitch of the tone
• Harmonic content: the complexity of the tone
combinations
Other Major Senses
• Motion and position in space:
– Vestibular sensation based on cilia (tiny hairs) in the inner ear;
• As our head moves, fluid in the semicircular canals stimulate the
cilia and stimulate nerve cells that give us the sensation of motion
• Conflicts between vestibular sensation and other motion cues
coming from vision can bring about motion sickness
• Inner ear infections can lead to similar experiences
– Kinesthetic sensation based on feedback from muscles
• Allow us to position our extremities in space
• With vestibular sense we are aware of our spatial position
– Vestibular and Kinesthetic sensations are processed in the
parietal lobe and lead to awareness of our spatial position
Making Sense of our Senses:
Perception
• Once the sensation is detected (signal detection theory)
the mind begins to “make sense” of the sensory
experience. This involves:
– Interpreting (naming, recognizing)
– Organizing (creating structures based on existing mental
structures or creating new structures)
– Perceptual experiences typically involve higher cognitive
functions and rely on top-down and bottom-up processes
Perception
• Bottom-up Processes:
– These processes are “driven” by the sensory experiences
created from the stimulus from the environment;
– Distinctive features of the stimulus control our representation of
that stimulus (e.g. color, motion, texture)
• Top-down Processes:
– Processes driven by the individual’s biases, expectations,
motives, and existing knowledge
– Features of the stimulus can be interpreted in a number of ways
depending on the state of the organism
– The organism “constructs” unique precepts from the sensory
experiences
– Frequently the perceptual experience is at odds with the “reality”
of the stimulus
Perception
• Perceptual constancy:
– Stability of members of a category of objects or
events;
– Based on shared attributes
– Identification of objects/events is constant even with
highly different sensory experiences
– Top-down driven based on experience and
expectations about the objects or experiences
• Shape constancy
• Color constancy
• Etc.,
Perception
• Bridging the top-down and bottom-up process:
– Sense organs are “wired” to detect particular features of the
environmental stimuli
– Once detected, the sensory experience and the expectations,
motives, and mental set of the organism bring to the experience
a set of plausible interpretations.
• Therefore, perception is a hybrid of top-down and bottom-up
processes.
Perceptual Theories
• Gestalt Theory:
– Human beings evidence a tendency to aggregate
elements of a stimulus array into an organized pattern
or array;
– This pattern or array is the basis from which we
interpret sensory information into perceptions.
– Such interpretations are always based on incomplete
sensory information and reflect individual experience
Perceptual Organization
Figure Ground
Perceptual Organization
Closure
Perceptual Grouping
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Law of Similarity
Perceptual Grouping
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Law of Proximity
Depth Perception
• Binocular Cues (both eyes)
– Binocular Convergence: degree to which the two eyes
must converge to focus on the object
– Retinal Disparity: difference in perspective of the two
images on the retina
Depth Perception
• Monocular Cues (single eye depth perception)
– Relative Size: for objects known to be similar in size,
the one seen to be larger is perceived to be closer
– Interposition: if one object hides part of another, the
one hiding the other is perceived to be closer
– Relative Motion: objects at different depths from the
eye appear to move at different rates when the
individual is in motion (closer objects appear to
“move” more quickly)
Perceptual Set: Seeing what we expect
• Expectations can influence what we are “ready” to
perceive
• Contextual “set-ups” can prepare us to one interpretation
vs. another
• Perception is NOT reality; it is OUR reality