Sensation and Perception Flashcards
What are receptors?
Receptors are specialised cells that convert environmental energies into signals for the nervous system.
What are the different parts of the eye?
- pupil - controls amount of light entering the eye
- iris - muscles in the iris control the pupil’s size
- retina - a layer of visual receptors covering the back surface of the eyeball
- cornea - a rigid transparent structure on the surface of the eyeball
- lens - flexible structure that varies its thickness (thinner: distant objects, thicker: nearby objects)
- fovea - central area of the human retina where vision is the clearest
- vitreous humor
How are we able to see?
- Light waves enter the eye through the cornea.
- The pupil adjusts to control the amount of light that enters the eye, and light travels through the vitreous humor to strike the retina.
- The cornea and lens focus the image onto the retina, reversing the image from right to left and from top to bottom, and the brain reconstructs it into the image we perceive.
What are some common disorders of vision?
- Myopia - impaired ability to focus on distant objects bc of shape of the eyeball
- Presbyopia - impaired ability to focus on nearby objects bc of decreased flexibility of lens
- Hyperopia - impaired ability to focus on nearby objects bc of shape of the eyeball
- Glaucoma - damage to the optic nerve
- Cataract - lens becomes cloudy
What are the two types of visual receptors in the retina?
Cones - for perceiving colour and detail in bright light, serve as colour receptors
Rods - vision in dim light, primarily b&w brightness receptors, more sensitive to light than cones, no colour sensation
What is dark adaptation?
Dark adaptation is the gradual improvement in the ability to see in dim light.
How does dark adaptation work?
- Exposure to light chemically alters retinaldehydes and stimulates the visual receptors.
- Under moderate light, the rate at which receptors regenerate molecules and light breaks them down is the same.
- In dim light, receptors regenerate their molecules without competition, thus improving detection of faint light.
Cones regenerate their retinaldehydes first but because rods are more sensitive to faint light, you see mostly with rods in faint light.
Explain the visual pathway from the eye to the brain.
- Visual receptors send impulses away from the brain towards the centre of the eye.
- They contact bipolar cells, which contact ganglion cells.
- Axons from the ganglion cells join to form the optic nerve, which turns around and exits the eye.
- Half of each optic nerve crosses to the opposite side of the brain at the optic chiasm.
- Most of the optic nerve goes to the thalamus, which sends info to the primary visual cortex in the occipital lobe.
What is the blind spot?
The blind spot is where the optic nerve exits, creating a hole in the retina known as the optic disc.
Our eyes compensate for the blind spot with the other eye.
What is the trichromatic theory?
The trichromatic theory suggests that colour vision depends on the relative responses of three types of cones, each cone is most sensitive to short (blue), medium (green), or long (red) wavelengths.
What is the opponent-process theory or color-opponent system?
The opponent-process theory suggests that we perceive colour in terms of paired opposites, and that each type of cone responds to two different wavelengths (red/green, blue/yellow, etc)
What are negative afterimages?
Negative afterimages are experiences of one colour after the removal of another.
What is colour constancy?
Colour constancy is the tendency of an object to appear nearly the same colour under a variety of lighting conditions.
What is the retinex theory?
The retinex theory suggests that the cerebral cortex compares the patterns of light coming from different parts of the retina and synthesises a colour perception for each area.
What is the cochlea?
The cochlea are fluid-filled canals in the ear which contains receptors for hearing.
Explain the mechanisms of hearing.
- Sound waves travel into the auditory canal and strike the eardrum, causing it to vibrate.
- Weak vibrations of the large eardrum travel through the hammer, anvil, and stirrup, and transform into stronger vibrations of the smaller stirrup, amplifying the sound waves.
- The stirrup transmits the vibrations to the cochlea, where vibrations displace cilia along the basilar membrane.
- The cilia, which are connected to neurons whose axons form the auditory nerve, move in different directions, thus triggering the sensory neurons and an action potential.
- The auditory nerve transmits impulses to the brain areas responsible for hearing.
What is conduction deafness?
Conduction deafness is when the bones connected to the eardrum fail to transmit sound waves properly to the cochlea.
What is nerve deafness?
Nerve deafness is deafness caused by damage to the cochlea, hair cells, or auditory nerve, and can be due to disease, heredity, and exposure to loud noises.
Why do some people still have hearing difficulties even with hearing aids?
- The brain areas for language comprehension started deteriorating due to inadequate input.
- Impaired attention due to difficulty filtering out irrelevant sounds.
Explain the frequency principle.
The frequency principle states that a sound wave through the fluid of the cochlea vibrates all the hair cells, which produces action potentials in synchrony with sound waves.
Explain the volley principle.
The volley principle suggests that each sound wave excites a group of hair cells, which respond to each vibration with an action potential.
What does the vestibular sense detect?
The vestibular sense detects the tilt and acceleration of the head and the orientation of the head with respect to gravity, and thus helps with balance.
What are the parts of the vestibular system?
The vestibular system consists of three semicircular canals oriented in different directions and two otolith organs.
How do the semicircular canals and otolith organs help with our orientation?
When the body accelerates in any direction, the jellylike substance in the corresponding semicircular canal pushes against the hair cells, which sends messages to the brain.
The otolith organs report the direction of gravity depending on which sets of hair cells are excited when our head tilts.
What is the gate theory of pain?
The gate theory of pain suggests that pain messages must pass through a gate, presumably in the spinal cord, that can block the messages.
When other inputs close the gate, pain messages are prevented from reaching the brain.
