Synesthesia: Mixing of the Senses
1. Synesthesia is a condition when perception in one sense is triggered by a sensation in a
2. Sounds as colours or tastes as touch. A stream of mixed up sensations.
Reasons: Proposals are crosswiring –activity in one part of brain evokes responses in
another dedicated to another sensory modality.
4. Lack of neural pruning that occurs in infancy.
5. Deficits in inhibitory processes that keep sensory information distinct.
I. Sensation and Perception
1. Data coming in
2. The process by which our sensory receptors and nervous system receive and
represent stimulus energies from our environment.
3. The brain receives input from the sensory organs.
4. The detection of environmental stimuli, such as sounds, objects and smells
1. How we make sense of the data
2. The process of organizing and interpreting sensory information, enabling us to
recognize meaningful objects and events.
3. The brain makes sense out of the input from sensory organs.
4. The experience of detecting those environmental stimuli—it refers to how our
brains organize and interpret sounds, objects and smells.
II. Sensory Processes
Overview of the process of sensation can be seen as three steps:
1. Receptionthe stimulation of sensory receptor cells by energy (sound, light, heat,
2. Transduction transforming this cell stimulation into neural impulses
3. Transmissiondelivering this neural information to the brain to be processed
Measuring the Senses
1. PsychophysicsField concerned the relationship between the actual physical
properties of a stimuli (e.g., decibel level) and our experience of these stimuli.
Stimulus Detection: The Absolute Threshold
How intense must a stimulus be before we can detect it?
1. The lowest intensity at which a stimulus can be detected 50% of the time.
2. The lower the threshold the greater the sensitivity.
B. Signal Detection Theory
1. Refers to whether or not we detect a stimulus, especially amidst background
2. People set their own standard of how certain they must be that a stimulus is
present before they will say they detect it.
3. This depends not just on intensity of the stimulus but on psychological factors such as the person’s experience, expectations, motivations, and alertness.
C. The Difference Threshold
1. Difference Threshold (Just Noticeable Difference or JND)
a) The smallest difference between two stimuli that people perceive 50% of the
b) Weber Law: The JND is proportional to the magnitude of the stimulus with
which it is being compared.
2. The “Just Noticeable Difference”
Difference threshold refers to the minimum difference (in color, pitch,
weight, temperature, etc.) for a person to be able to detect the difference half
b) Weber’s law refers to the principle that for two stimuli to be perceived as
different, they must differ by a constant minimum percentage and not a
constant amount (e.g. 1/100 of the weight, not 2 ounces).
D. Sensory Adaption
Diminishing sensitivity to an unchanging stimulus
1. Sensory neurons decrease activity when there is a constant stimulus (e.g., you no
longer hear cars go by).
2. Benefit—freedom to focus on informative changes without uninformative
III. The Sensory Systems
A. Vision: Energy, Sensation, and Perception
1. The Human Eye
a) Light from the candle passes through the cornea and behind that, the pupil.
The images gets focused and inverted by the lens. The light then lands on the
retina, where it begins the process of transduction into neural impulses to be
sent out through the optic nerve.
b) The lens is not rigid; it can perform modation by changing shape to
focus on near or far objects.
Accommodation: The lens changes shape to focus near or far objects on
c) Focusing Vision
In people with normal vision, both nearby and faraway objects are
focused on the retina at the back of the eye
In nearsighted people, faraway objects are focused in front of the retina
In farsighted people, nearby objects are focused beyond the retina
2. Photoreceptors: The Rods and Cones
a) Rods(120 million)
Rods in dim light, are primarily blackandwhite brightness receptors
120 million rod are about 500 times more sensitive to light than are the
cones, but they do not give rise to colour sensations.
b) Cones(6 million)
Colour receptors. Function in bright or day light
Detect fine detail c) The Retina
Light entering eye triggers photochemical reaction in rods and cones at
back of retina.
Chemical reaction in turn activates bipolar cells.
Bipolar cells then activate the ganglion cells, the axons of which
converge to form the optic nerve. This nerve transmits information to the
visual cortex (via the thalamus) in the brain.
When light reaches the back of the retina, it triggers chemical changes in
the receptor cells, cal and ones. The rods and cones in turn send
messages to ganglion and bipolar cells and on to the optic nerve.
Rods help us see the black and white actions in our peripheral view and
in the dark. Rods are about 20 times more common tha, which
help us see sharp colorful details in bright light.
e) The Blind Spot
There is an area of missing information in our field of vision known as
the lind sp. This occurs because the eye has no receptor cells at the
place where the optic nerve leaves the eye.
3. Visual Transduction: From Light to Nerve Impulses
4. Brightness Vision and Dark Adaptation
5. Colour Vision ( Additive)
a) Perceiving Color: Additive Color Mixing: Seeing Light
Adding primary colors of light creates other colours, such as yellow.
Where all the colours overlap, the color is white; this is the surface where
all colours reflected
b) YoungHelmholtz Trichromatic (ThreeColor) Theory
According to this theory, there are three types of color receptor cones
red, green, and blue.
All the colors we perceive are created by light waves stimulating
combinations of these cones.
c) Perceiving Color: Subtractive Colour Mixing: Seeing Objects
Mixing varying amounts of ee paint coloursred, blue, yellow to
create other colors
This removes light from the mix
The darker the colors mixed together the closer to black the resulting
Black surfaces reflect no light
Problem for YoungHelmholtz: Color Blindness
d) Opponent Process Theory
Opponentprocess theory: Each 3 cone types (red, blue, green)
responds to odifferent wavelengths: One red OR green, one blue OR
yellow, and a third, black OR white (opponents).
e) Dual process in colour transduction
Combines trichromatic and opponentprocess theory to account from colour transduction process.
YoungHelmholtz was correct: There are 3 cone types which are
sensitive to either red, green, blue. Different ratios of activity in these
cones produce a pattern of neural activity that corresponds to any hue in
Opponent Process Theory was correct, but Hering’s description of how
it works was wrong.
6. Analysis and Reconstruction of Visual Scenes
Once the transformation of light energy to nerve impulses occurs, messages
are sent from the retina via the optic nerve to the thalamus and then its routed
mainly to the visual cortex in the occipital lobe. Regions in the retina correspond
to specific groups of neurons in the visual cortex. These neurons receive and
integrate sensory nerve impulses. Some of these neurons are called feature
detectors—they fire in response to certain characteristics.
a) Feature detectors
Turning Neural Signals into Images
Some ganglion cells in the eye send signals directly to the visual cortex
in response to certain features such as visual patterns, certain edges,
lines, or movements.
In and around the visual cortex of the occipital lobe, feature detector
cells or super cells integrate these feature signals to recognize more
complex forms such as faces.
Constructing a Unified Image: Parallel Processing
Turning light into the mental act of seeing:
Light wavs chemical reactions neuralimpulss features objects
And one more step...allel Process: The brain processes colour,
movement, form, and depth simultaneously in different areas of the brain.
Then the brain integrates the separate, parallel dimensions of visual info.
Into a unified image.
b) Visual Processing
1. Hearing/Audition: Starting with Sound
Corresponds to our perception of pitch
Length of the sound wave; perceived as high and low sounds (pitch)
Corresponds to our perception of loudness Height or intensity of sound wave; perceived as loud and soft (volume)
Corresponds to our perception of timbre
Perceived as sound quality or resonance
2. Auditory Transduction: