L07: Sensation & Perception Flashcards
Sensation
The ability to detect a stimulus. Features of the environment that are used to create understanding of the world.
Perception
The act of giving meaning to a detected stimulus. Combining of sensations arriving from the sensory system with prior knowledge.`
Transduction
Process where stimuli are converted to neural electrochemical energy.
Psychophysics
The science of defining quantitive relationships between physical & psychological events. Relates physical stimuli to the contents of consciousness.
Absolute Threshold
Level of stimulus intensity requires to create conscious experience.`
Signal Detection Theory
Accounts for individual biases
Just Noticeable Difference (JND)
the amount something must be changed in order for a difference to be noticeable, detectable at least half the time
Bottom-up processing
Processing the elementary messages from the environment
Top-down processing
Applying memory, knowledge, etc. to understand and create perception
Extromission theory of vision
Eyes send out vision beans, which seize objects. Plato & Galen
Intromission theory of vision
Visual perception comes from some representation of the object entering the eyes
What is light
Electromagnetic energy that exists as particles (photons) and waves
Wavelength
Perceived hue (shade)
Frequency
Cycle rate
Amplitude
Perceived intensity
Cornea
Transparent tissue which allows light rays to enter the eye and focus on objects
Iris
Coloured part of the eye consisting of muscular diaphragm which regulates light entering the eye
Pupil
Centre of the iris
Lens
Crystalline lens inside the eye that enables the changing of focus
Retina
Contains photoreceptors
Photoreceptors
Light sensitive neurons that transduce light into neural activity
Fovea
Smallest pit that contains the highest concentration of colour sensitive light receptors
Neuron Signal Pathway
- Photoreceptors
- Bipolar cells
- Ganglion cells
Rods- Function
- responsible for night vision
- dim light
- low resolution
Cones- Function
- responsible for daylight vision
- bright light
- sensitive to blue, red, and green
- high resolution
Blindspot
Where the optic nerve leaves the eye. no photoreceptors in this area, so the visual system usually fills in the area with info about the surroundings
3 types of cones
s- cones
m- cones
l- cones
s- cones
short wave cones
blue light
m- cones
medium wave length cones
yellow & green light
l- cones
long wave length
red light
Bipolar cells
Intermeditate cells that determine the info from photoreceptors to ganglion cells
Two types of bipolar cels
diffuse bipolar cells
midget bipolar cells
Diffuse bipolar cells
Convergence of info in the periphery.
1 diffuse bipolar cell = 50 rods
Midget bipolar cells
Found in the fovea.
1 midget bipolar cell= 1 cone
Ganglion cells
Final layer of the retina
M-cell
diffuse bipolar cells synapse onto m- cells
P-cell
midget bipolar cells -> p- cell
Retinal ganglion cell (RGC)
axons for the optic tract
Receptive field
the region on the retina in which the visual stimuli influence the neural firing rate
Retinal ganglia
receptive fields of individual retinal ganglion cells. conveys patterns of life
ON-centre, OFF-surround cell
A ganglion cell that increases firing in response to an increase in light intensity
OFF-centre, ON-surround cell
A ganglion cell that increases firing in response to a decrease in light intensity in its receptive field
Trichromatic Theory
Colour vision occurs by comparing the activation of 3 different cones
Opponent process theory
p-cells fire rapidly to one wavelength and reduce to another, forming pairs of colours (red-green, blue-yellow, black-white)
The visual pathway
- information from the retina leaves the eye via the optic nerve.
- information from the optic nerve travels to the optic chasm (cross-over)
- information reaches the lateral geniculate nucleus (LGN) of the thalamus
- information reaches the visual striate cortex then the occipital cortex to be processed
Feature detectors
receptive fields of individual neurons in the visual cortex
Simple cells
neurons fire vigorously when the line is orientated vertically but reduce firing horizontally
Complex cells
Fire most when lines are in certain motion
Ventral Pathway
What stream
Ventural -> temporal lobe -> object recognition
Dorsal Pathway
Where stream
Dorsal -> parietal lobe -> location of objects in space
Gesalt Psychology
Describes how people tend to organize visual elements into whole entities
- figure-ground law
- principle of proximity
- principle of similarity
- principle of closure
- principle of continuation
- principle of common fate
Figure-ground law
a form is naturally perceived as a figure while its surrounding area is perceived as ground
principle of proximity
elements placed close together are perceived as a group
principle of similarity
similar objects are perceived as a group
principle of closure
people perceive the whole by filling in missing info
principle of continuation
the eye is compelled to move through one object and continue to another object
principle of common fate
objects moving together are grouped together
biological motion
the pattern of movement of living beings
blindsight
damage to one of the visual cortexes leads to conscious blindness. typically only on one side. when patients are asked to identify visual stimuli in their blind field, they can do so with accuracy above change, suggesting conscious and unconscious vision
visual agnosia
inability to recognize visual objects. associated with issues in the ventral pathway
prosopagnosia
inability to recognize faces. associated with issues in the ventral pathway. shows emotional responses to very close relatives, suggesting unconscious vision
akinetopsia
inability to detect motion, associated with issues in the dorsal pathway. patients see life in a series of snapshots.
Optic Nerve
a paired cranial nerve that transmits visual information from the retina to the brain
Rods- Distribution
- found in the periphery
- around 100 million in each eye
- one photopigment
Cones- Distribution
- multiple photopigments
- around 5 million in each eye
- spike in the number of cones by the fovea
Visible light spectrum
We only detect b/n 400-700nm of light
400- ultraviolet, 700- infrared
Optic Chiasm
X-shaped structure formed by the crossing of the optic nerves in the brain
Lateral geniculate nucleus
a relay center in the thalamus for the visual pathway
Visual Striate Cortex
The part of the visual cortex that is involved in processing visual information and first receives info from the lateral geniculate nucleus.
Occipital Cortex
primarily responsible for visual processing. It contains the primary and association visual cortex
Sound
Vibrations in a medium that cause pressure changes or waves
Frequency
The number of times per second that a pattern of pressure change repeats. Perceived as pitch
Amplitude
The magnitude of displacement of a sound pressure wave. Perceived as loudness
Outer ear
Contains the pinna and tympanic membrane
Pinna
the outer segment of the ear, shaped to collect and funnel sound toward the tympanic membrane
Tympanic Membrane
also known as the eardrum. Transfers sound energy from air to the ossicle
Hair Cells
Transduce mechanical movement from sound waves into neural activity
Place Theory
The brain uses the location of neural firing to understand sound
Frequency Theory
the more rapidly the cells fire, the higher the perception of the pitch
Interpreting sound
2 theories: place & frequency theory
Thermoreceptors
Signals info about changes in skin temp. Also responds to chemical stimuli. 2 distinct populations: warm and cold fibers
Nociceptors
Transmit info about painful stimulation that causes damage to the skin. Mix of signals transduced: mechanical, thermal, and chemical
Middle Ear
Contains 3 ossicles, tiny bones responsible for amplifying sound arriving at the eardrum to the oval window (small membrane) of the cochlea
Ossicles
Malleus
Incus
Stapes
Inner ear
Helps you hear and maintain your balance. Contains the cochlea
Cochlea
Fluid-filled, coiled structure with two membranes, creating 3 canals
Basilar Membrane
Where the hair cells (sound transduction) are located
Tectorial Membrane
Floats above and connects to hair cells
Sound localization
Detecting objects’ location in space requires binaural cues
Binaural cues (def)
Auditory cues that require comparison from both ears
Interaural time differences
differences in arrival times at each ear
Interaural level differences
differences in the intensity of sounds that reach each ear
Phantom words
Although everyone hears the same stimulus, perceptions differ based on our prior knowledge.
Tonotopic organisation:
The spatial organization of the basilar membrane is maintained through the auditory pathway
The auditory pathway
- Auditory information travels to the medial geniculate nucleus of the thalamus.
- Info then travels to the auditory cortex in temporal lobes.
Mechanoreceptors (def)
transduce mechanical stimulation (pressure) into touch sensation
Mechanoreceptors (types)
Merkel receptor, Meissner Corpuscle, Ruffini cylinder, Pacinian corpuscle
Merkel receptor
Application and removal of pressure (constant firing while pressure applied)
Meissner Corpuscle
Application and removal of pressure (fire only during the application and removal –changes in pressure)
Ruffini cylinder
Interpret stretch of skin
Pacinian corpuscle
Vibration and texture
Somatosensory Pathway
Info is relayed via the thalamus to the contralateral parietal lobe.
Somatotopic homunculus
- Spatial mapping of the somatosensory cortex in correspondence to spatial events on the skin
- Adjacent points on your skin are represented by adjacent points on the somatosensory cortex
Body Schema Modifications
visual input integrates with and even overrides our conscious body image
Split Brain Patients
Corpus callosum is severed –communication between the left and right hemisphere is impaired
If a split-brain patient sees an object in the right visual field, this is projected to the left hemisphere and they are able to name the object. When a patient sees an object with their left visual field (which projects to the right hemisphere) they cannot name the object (no access to language system on left hemisphere)
What hemisphere is the language center located in
Left
The interpreter
The neuro-psychological concept proposed by Michael Gazzaniga to explain narrative. Causal explanations (narrative) are generated by the left-hemisphere
