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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,
○ 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
○ 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
●1. Magnitude: Measure size or quantity.
○ Example: Rate how bright the light is, how loud the tone is, how large or
●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
●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
○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
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.
○ 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
● Example: You no longer hear cars go by. Sensory neurons
● 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
●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
○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
○Get distracted again in phase 3
○Process is sequential.
○Disengagement takes 1/10 of a second
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
● 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.