Stages of the Perceptual Process
(contd.)
Stages of the Perceptual Process
1) Distal stimulus: our environment
2) Proximal stimulus: information that
stimulates the receptors (i.e., light striking
the retina)
3) Transduction: transforming proximal
stimulus into another form of energy (i.e.,
our brains process electrochemical not
“light” energy)
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4) Neural processing: computations
5) Perception: organization of computations
6) Recognition: meaningfulness of perception
7) Action: response to meaning
– Another view: Direct Perception – we act to
create lawful changes in our environment that
we perceive and that tell us about the structure
of our environment
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Overview of Relationships
Neurons …….
(for studying perceptual processes)
• Four major parts to neurons….
– Dendrites
• Stimulus-perceptual: change the physical
stimulation and “ask” how perception changes
(behavioral)
• Stimulus-physiological: measure brain/neuron
activity in response to stimulation
• Physiological-perceptual: measure how
physiological capabilities correlate with
perception
• “receiving” part – electrical activity from coming from other neurons
“stimulate” these parts
– Soma (body)
• Contains structures to keep the cell alive
– Axon
• “Sending” part – the electrical signal generated by the neuron travels
down the axon in order to “stimulate” a nearby neighboring neuron.
– Synapse
• Very end of the axon where chemicals are released to stimulate the
next neighboring neuron located nearby
• Sensory systems have “specialized” neurons called
“receptors”
– Specialized to detect and react to external stimulus energy
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Parts of a Neuron……
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Neuronal Communication….
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Synapse….
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Action potential….
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Basic structure of the brain….
Patterns of neural firing …
• The brain can be divided into different parts and
regions
•Each “tick” seen in the figures below represent an action potential being
generated in a neuron
•The brain assigns different “meaning” to different patterns or rates of
firing
– This is known as “modular organization”
• Different parts or regions are responsible for
processing different things
• Certain parts of the brain are known to be
primarily responsible for processing incoming
information from the sensory systems and are
located I the very outer layering called the cerebral
cortex
Stimulation Causes
FAST firing
Time
Stimulation Causes
SLOW firing
Time
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Basic structure of the brain….
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Structure of the brain…..
– The cortex has four primary “lobes”
• Occipital lobe – primary receiving lobe for
vision
• Temporal lobe - primary receiving lobe for
audition
• Parietal lobe - primary receiving lobe for
skin senses; handles spatial location and
attentional allocation
• Frontal Lobe - responsible for executive
control; also primary receiving lobe for
chemical senses (e.g., smell)
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The “physical” properties of the
visual stimulus
• electromagnetic energy
Visual System:
– Measured in “photons”
– portion of electromagnetic
spectrum between 400 nm and
700 nm
The Stimulus
• nm is a nanometer (1 billionth of a
meter)
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A Little Light Physics
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Visible Spectrum…...
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A Little Light Physics (cont’d)
• Light can be absorbed, diffracted, reflected,
transmitted, or refracted
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A Little Light Physics (cont’d)
A Little Light Physics (cont’d)
• Absorbed: Energy (e.g., light) that is taken
up, and is not transmitted at all
• Diffracted: Bent, or having waves that are
spread out, (e.g., waves of sound or light, as
they pass through a narrow aperture)
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A Little Light Physics (cont’d)
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A Little Light Physics (cont’d)
• Reflected: Energy that is redirected when it
strikes a surface, usually back to its point of
origin
• Transmitted: Energy that is passed on
through a surface (when it is neither
reflected nor absorbed by the surface)
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The “psychological” properties of
the visual stimulus as related to
the “physical” properties
A Little Light Physics (cont’d)
• Refracted: Energy that is altered as it
passes into another medium, (e.g., light
entering water from the air)
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Physical
Psychological
Wavelength
Amplitude
Purity
Hue
Brightness
Saturation
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In this discussion…
• Much of our time will be spent describing
perceptual systems and how they interact with one
another and the environment
• Species-specificity
– e.g., there are some tacit assumptions at work in
research on human perception
– In the case of the visual system, for example, different
species are sensitive to different ranges of wavelengths
(within a broader, but still constrained, range of the
electromagnetic spectrum)
– Humans are sensitive to a specific range (350 or 400
nm to 700nm)
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Biologically Relevant
Perturbations of Environment
• Consider the “human sensitive” range of the
electro-magnetic (EM) spectrum…
• This narrow band is called “visible light”
(wavelengths b/t 350 and 700
nanometers…where nm = 9 decimal places,
e.g., .000000350m)
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Is it really “visible?”
Why so constrained?
• It’s not the case that it’s “visible, therefore
we see it” but “we see it, therefore we call it
‘visible’”
• e.g., this labeling is very species-specific;
for bees, “visible light” is a different band,
shifted to include ultraviolet (UV)
wavelengths
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• Theoretically, all that would be required for
Radar to be included in a species’ “visible
light” is their having a perceptual system
that would interact with those wavelengths
• But there’s a good reason most eyes on the
planet only interact with wavelengths b/t
UV and Infra-red…
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These wavelengths are of a size
most likely to interact with
creature-sized objects!
• Gamma rays:
– wavelengths so short (12+ decimal places), they
pass through most matter
• Radio waves:
– wavelengths so long (10 meters) they pass
around biological objects (though not always
mountains)
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