Sensation and Perception
The ABCs of Sensation
Sensation
Activation of receptors in the various sense organs
allowing various forms of outside stimuli to become neural signals in the brain
transduction
process of converting outside stimuli, such as light, into neural activity
Sensory Receptors
specialized forms of neurons
Stimulated by different kinds of energy rather than neurotransmitters
turning outside stimuli into
neural activity
Sensory Thresholds
Absolute Threshold
Is the lowest level of stimulation that a person can consciously detect 50 percent of the time the stimulation is present.
HABITUATION AND SENSORY ADAPTATION
Synesthesia
Signals from various sensory organs are processed in wrong cortical areas
Result: sense information is interpreted as more
than one sensation
Examples
Grapheme-color: letters/numbers (colors)
Lexical-gustatory: words/sounds (tastes)
Habituation
the way the brain deals with unchanging information from the environment.
the tendency of the brain to stop
attending to constant, unchanging information
Sensory adaptation
another process by which constant, unchanging information from the sensory receptors is effectively ignored
the tendency of sensory receptor cells to become less responsive to a stimulus that is unchanging
Microsaccades prevent eyes from adapting
The Science of Seeing
Phantom Limbs
If there is an amputated limb the physical stimulation is not possible
brain responds as though stimulation occurred
Perceptual properties of light: CATCHING THE WAVES
With regard to its psychological properties, there are three aspects to our perception of light: brightness, color, and saturation.
Color
Saturation
Brightness
determined by the amplitude of the wave
-how high or how low the wave actually is
Largely determined by the length of the wave
purity of the color people perceive
THE STRUCTURE OF THE EYE
From front to back: The parts of the eye
Light enters the eye directly from a source (such as the sun) or indirectly by reflecting off of an object.
Light bends as it passes through substances of different densities, through a process known as re- fraction.
Pathway of light through the eye
Cornea -> Pupil -> Lens -> Retina
Cornea
surface of the eye is covered in a clear membrane
Aqueous humor
is the structure that focuses most of the light coming into the eye
watery fluid
continually replenished and supplies nourishment to the eye
Pupil
Hole where the light from the visual image then enters the interior of the eye
Iris
round muscle
the colored part of the eye
can change the size of the pupil, letting more or less light into the eye
helps focus the image; people try to do the same thing by squinting.
BEHIND -> lens
clear structure
The flexible lens finishes the focusing process begun by the cornea
visual accommodation
Process where the lens changes its shape from thick to thin, enabling it to focus on objects that are close or far away
presbyopia
myopia
the lens hardens through aging
visual accommodation may occur but the shape of the eye causes the focal point to fall short of the retina
Retina, Rods, and Cones
Rods
Cones
Retina
final stop for light within the eye
light-sensitive area at the back of the eye
Photoreceptors (rods and cones)
Bipolar cells
Ganglion cells
are found all over the retina except the fovea, but are concentrated in the periphery.
low levels of light, no color information
Fovea
the center of the retina, where cones are densely packed
are sensitive to changes in brightness but not to a variety of wavelengths, so they see only in black and white and shades of gray
high levels of light, color information
special receptor cells (photoreceptors) that respond to the various wavelengths of light
Optic nerve
bundle of ganglion cell axons that
exits the eye at the back of the retina
Carries information from retina to thalamus
Creates the blind spot
Light must travel past ganglion cells and bipolar
cells to get to photoreceptors
Neural signals travel in opposite direction
Photoreceptors -> Bipolar cells -> Ganglion cells
Perception of Sound: GOOD VIBRATIONS
Physical stimulus (sound waves)
Vibrations of molecules in the air
Pathway of sound waves through the ear
Outer ear ->middle ear -> inner ear
Components of sound waves
Amplitude
Frequency
number of peaks per second (Perceived as pitch)
height of peaks (Perceived as volume)
The Structure of the ear
Middle ear
Inner Ear
The outer ear
Auditory canal
Eardrum
Pinna
visible part of the ear (Collect sound waves)
short tunnel that runs from the pinna to the eardrum
tympanic membrane
Vibrates when hit by soundwaves
Three tiny bones (ossicles)
Anvil (incus)
Stirrup (stapes)
Hammer (malleus)
Ossicles amplify signal from sound waves
attached to eardrum
connects hammer and stirrup
attached to oval window
Oval window
Cochlea
Auditory nerve
membrane at the entrance of the inner ear
Vibrates when hit by stirrup
snail-shaped structure of the inner ear that is filled with fluid
Basilar membrane
membrane running through middle of cochlea, contains organ of Corti
Organ of Corti - contains receptor cells (hair cells)
bundle of axons from the hair cells in the inner ear
serves as a kind of concentrator, funneling the sound waves from the outside into the structure of the ear.
contains the axons of all the receptor neurons
Perceiving Pitch
Pitch
psychological experience of sound that corresponds to the frequency of the sound waves
Higher frequencies -> higher pitches
how high or low a sound is
Place theory
Frequency theory
location of neural (hair cell) firing on organ of Corti determines perceived pitch
Explains perception of moderate/high pitches
states that pitch is related to how fast the basilar membrane vibrates
frequency of neural (hair cell)
firing determines perceived pitch
Explains perception of lower pitches (< 1,000 Hz)v
Types of hearing Impairments
difficulties in hearing.
Conduction hearing impairment (Conductive hearing loss)
nerve hearing impairment (sensorineural hearing loss)
problems with the mechanics of the outer or middle ear and means that sound vibrations cannot be passed from the eardrum to the cochlea.
In this kind of impairment the causes can often be treated
the problem lies either in the inner ear or in the auditory pathways and cortical areas of the brain
This is the most common type of permanent hearing loss
The ABCs of Perception
Perception
method by which the brain takes all the sensations a person experiences at any given moment and allows them to be interpreted in some meaningful fashion
Constructive
Can vary from person to person
The constancies: Size, Shape, and Brightness
Shape constancy
Brightness constancy
Size constancy
tendency to interpret an object as always being the same actual size,regardless of its distance
tendency to interpret the shape on an object as being constant, even when its shape changes on the retina
tendency to perceive the apparent brightness of an object as the same, even when the light conditions change
Gestalt principles
tendency to group objects and perceive whole shapes
Figure-ground relationship
tendency to perceive objects,
or figures, as existing on a background
Reversible figures
visual illusions in which the figure and ground can be reversed
Proximity
tendency to perceive objects that are close to one another as part of the same grouping
Group nearby items
Similarity
tendency to perceive things that look similar as being part of the same group
Group similar items
Closure
Continuity
tendency to complete figures that are incomplete
Fill in missing parts
tendency to perceive things as simply as possible with a continuous pattern rather than with a complex, broken-up pattern
Simple, continuous patterns
Common region
Group items in same area
tendency is to perceive object by different groups
Depth Perception
capability to see the world in three dimensions
Monocular Cues
Binocular Cues
Overlap
Aerial (atmospheric) perspective
Relative size
Texture gradient
Motion parallax
Linear perspective
Accommodation
When looking down a long interstate highway, the two sides of the highway appear to merge together in the distance
when objects that people expect to be of a certain size appear to be small and are, therefore, assumed to be much farther away
If one object seems to be blocking another object, people assume that the blocked object is behind the first one and, therefore, farther away.
The farther away an object is, the hazier the object will appear to be due to tiny particles of dust, dirt, and other pollutants in the air
If there are any large expanses of pebbles, rocks, or patterned roads (such as a cobblestone street) nearby, go take a look at them one day.
objects outside the car window seem to zip by very fast when they are close to the car, and objects in the distance, such as mountains, seem to move more slowly
makes use of something that happens inside the eye.
The lens of the human eye is flexible and held in place by a series of muscles
Convergence
Binocular disparity
muscular cue
rotation of the two eyes in their sockets to focus on a single object
the eyes are a few inches apart, they don’t see exactly the same image
Greater disparity for closer objects
Muscular cue
Smaller disparity distant objects
More convergence for closer objects
Less convergence for distant objects
Perceptual Illusions
perception that does not
correspond to reality
Visual stimuli that fool the eye
Show vision is constructive
The Hermann Grid
responses of neurons in the primary visual cortex that respond best to bars of light of a specific orientation
Müller-Lyer illusion
The moon illusion
the moon on the horizon* appears to be much larger than the moon in the sky
Motion Illusions
Stroboscopic motion
Phi phenomenon
Autokinetic effect
a small, stationary light in a darkened room will appear to move or drift
Because there are no surrounding cues to indicate that the light is not moving
a rapid series of still pictures will appear to be in motion
Motion pictures
lights turned on in a sequence appear to move
Static images can produce apparent motion as well
Types of Processing
Top-down processing
Bottom-up processing
the use of preexisting knowledge to organize individual features into a unified whole
the analysis of the smaller features to build up to a complete perception