PSYC 100 Lecture Notes - Lecture 4: Interposition, Eye Tracking, Two-Streams Hypothesis

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Sensation: The detection of environmental stimuli, such as sounds, objects and smells.
Simple stimulation of sense organ.
Process of Sensation
○ Reception: The stimulation of sensory receptor cells by energy (sound, light,
heat)
○ Transduction: Transforming this cell stimulation into neural impulses
When many sensors in the body convert to physical signals from the
environment into encoded signals sent to the CNS
You can enjoy ice cream even if you don’t that it’s the process
of transduction
Transmission: Delivering this neural information to the brain to be processed
Perception: The organization, identification and interpretation of that sensation in order to
form a mental picture.
Synesthesia: Perceptual experience of one’s senses that is evoked by another scent
Psychophysicists: Often measure the minimum amount of a stimulus needed for detection
Psychophysics: Methods that measure the strength of a stimulus and the observer’s
sensitivity to that stimulus
4 Methods:
1. Magnitude: Measure size or quantity.
○ Example: Rate how bright the light is, how loud the tone is, how large or
small.
2. Matching: Adjust one of two stimuli so they look or sound the same.
Turn down volume of one source to match the other or adjust the colour so
they match.
3. Detection: Detect small differences between stimuli.
Measuring sensitivity (for example, Just Noticeable Difference)
4. Adjustment: Adjust the intensity of the light until you judge it to be just barely
detectable.
Measuring minimum amounts.
Threshold: A boundary
Absolute threshold: Minimal intensity needed to just barely detect a stimulus
(usually idefincation on 50% of trials)
As intensity gradually increases, we detect stimulation more frequently
Difference threshold: The smallest difference (in color, pitch, weight, temperature.
etc) between two stimuli for a person to be able to detect the difference half the time.
(Example: Music (I’m a bit flat)
Weber’s Law: The minimum amount of stimulation required to tell the
difference between 2 stimuli
They must differ by a constant minimum percentage and not a
constant amount (e.g. 1/100th of the weight, not 2 ounces)
JND of a stimulus is a constant proportion despite variation in intensity
Just Noticeable DIfference: Minimal change in a stimulus that can barely be
detected
Psychophysics: Signal Detection of Absolute Threshold
The lowest intensity at which a stimulus can be detected 50% of the time.
The lower the threshold the greater the sensitivity.
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Example: The feather may be in fact touching grandfather’s face but he
doesn’t detect it reliably.
Signal Detection Theory: Whether or not we detect a stimulus reliably, especially
amidst background noise.
People set their own standard of how certain they must be that a stimulus is
present before they will say they detect it.
Detection depends not just on intensity of the stimulus but on psychological
factors such as the person’s experience, expectations, motivations, and
alertness. (Grandfather is sleepy)
Sensory signals: Perceived among environmental “noise.”
Sensory adaptation: Sensitivity to prolonged stimulation tends to decline
over time as an organism adapts to current conditions
Diminishing sensitivity to an unchanging stimulus
Sensory neurons decrease their activity when there is a constant
stimulus
Example: You no longer hear cars go by. Sensory neurons
stop firing)
● Benefit: Freedom to focus on informative changes without
uninformative background stimulation
Multitasking: Perception is active and resources are limited
We use selective attention to focus in on chosen stimuli in our environment
Multitasking involves paying attention to more than one stimulus at a time
Example: Using your phone while driving increases chance of a crash 4
times
IMRI studies show decreases in brain activity during multitasking
People who frequently multitask often may have trouble focusing on one task
Multitasking makes our work 59% less valuable and takes 50% longer to finish.
Phase 1: Blood Rush Alert: Decide to write essay and blood goes to anterior
prefrontal cortex, a switchboard that tells the brain you are going to concentrate
Phase 2: Find and Execute: The alert carries an electrical charge
1) Search query to identify the correct neurons to fire to complete a specific
task
2) A command which tells the neurons what to do. Put one into the correct
mental state for the task.
Phase 3: Disengagement: When distracted you mind disengages from mental state
of doing your paper and then blood flows back to anterior prefrontal cortex and begin
over.
Get distracted again in phase 3
Process is sequential.
Disengagement takes 1/10 of a second
Visual Activity:
Visual Acuity: Ability to see fine detail
Visible Light: Portion of electromagnetic spectrum seen
Color Mixing: The millions of shades of color that humans can perceive are products not
only of a light’s wavelength, but also of the mixture of wavelengths a stimulus absorbs
or reflects.
Colored spotlights work by causing the surface to reflect light of a particular
wavelength, which stimulates the red, blue, or green photopigments the cones.
When all visible wavelengths are present, we see white.
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