Chapter 2: Beginning Of The Perceptual Process Flashcards
FIrst step of the process
Light reflected from an object into the eye
Virtual Process first four steps
1) The distal stimulus (aika the tree)
2) Light is reflected from the tree and enters the eye to create the proximal stimulus on the vision receptor
3) Receptors transform light into electrical signals
4) Electrical signals are ‘processed” as they travel through a network of neurons
Visible light
The energy within the electromagnetic spectrum that humans can perceive, has wavelength from 400nm-700nm
Electromagnetic spectrum
A continuum of electromagnetic energy that is produced by electric charges and is radiated as waves
Wavelength
The distance between the peaks of the electromagnetic waves
The eye (how it works)
Light reflected from objects in the environment enters the eye through the pupil and is focussed by the cornea and lens to form sharp images of the objects on the retina, the network of neurons that covers the back of the eye and that contains the receptors for vision
2 types of visual receptors
Rods
Cones
Outer segments
Part of the receptor that contains light-sensitive chemicals called visual pigments that react to light and trigger electrical signals
Fovea
Only contains cones (when we look at an object, the objects image falls on the fovea)
Peripheral retina
Includes all of the retina outside of the fovea, contains both rods and cones
Macular degeneration
Common in older people
Destroys the cone rich fovea and a small area surrounding it, which creates a blind spot when seeing an object (loses sight of the object)
Retina pigmentosa
Degeneration of the retina that is passed from one generation to the next, attacks peripheral rod receptors and results in poor vision in the peripheral vision field
Blind spot
A spot where there is an absence of receptors where the nerve fibers leave the eye
2-element optical system
cornea and lens
Cornea
Transparent covering of the front of the eye
-accounts for 80 percent of the eye’s focussing power
Lens
supplies remaining 20% of focussing power
-can change it shapes to adjust focus for objects at various distances
Accommodation
Change in the len’s shape that occurs when the ciliary muscles at the front of the eye tighten and increase the curvature of the lens so it gets thicker
Presbyopia
Unable to accommodate enough to see objects (due to hardening of lens and weakening of muscles)
myopia (nearsightnedness)
an inability to see distant objects clearly (light rays come to focus in front of the retina)
Refractive myopia
the cornea and or the lns bends the light too much
Axial myopia
In which the eyeball is too long
Hyperopia (farsightedness)
Can see distant objects clearly but have trouble seeing nearby objects because the focus point for parallel rays of light is located behind the retina, usually due to too small of an eyeball
Transduction
The transformation of one form of energy into another form of energy
Visual pigments have two parts
Long protein called Opsin
Small light sensitive component called retinal
Isomerization
The retinal changing shape due to the pigment molecule absorbing light
Dark Adaption
The process of increasing sensitivity in the dark
Dark adaption is measured by
Determining a dark adaptation curve
Rod monochromats
People who have no cones
As soon as lights are extinguished…
Rods and cones begin to get more sensitive, but as cones are much more sensitive than rods at the beginning of dark adaptation, we see with our cones right after lights are turned off
After 3-5 minutes the cones have reached maximum sensitivity (but rods are still adjusting and take about 7 minutes, reach maximum at about 20-30 mins)
Rod-Cone break
The place where the rods begin to determine the dark adaption curve
Visual pigment bleaching
The change in shape and separation from the opsin causes the molecule to become lighter in colour (process is called card name)
2 important connections between perception and physiology
1) Our sensitivity to light depends on the concentration a chemical-the visual pigment
2) The speed at which our sensitivity increase in the dark depends on a chemical reaction - the regeneration of the visual pigment
Electrical signals occur in structures called
neurons
Components of a neuron
Cell Body: contains mechanisms to keep the cell alive
Dendrites: Branch out from the cell body to receive electrical signals from other neurons
Axon or nerve fiber: full of fluid that conducts electrical signals
Sensory receptors
Neurons specialized to respond to environmental stimuli
When the axon or nerve fiber is at rest, the difference in electrical potential between the tips of the two electrodes is:
- 70 millivolts (mV)
- this means that the inside of the axon is 70mV more negative than the outside
Resting potential
As long as there are no signals in the neuron (refer to card above #36)
Action potential
Neurons receptors are stimulated so that a signal is transmitted down the axon. As the signal passes the recording electrode, the charge inside the axon rises to +40mV compared to the outside
-as the signal passes through the charge inside the fiber reverses course and starts becoming negative again
Propagated response
Once the response is triggered, it travels all the way down the axon without decreasing in size
(would be the same size even if moved, increasing from -70mV to +40mV)
Changing the stimulus intensity does not affect the size of the action potentials but does affect the ___ of firing
rate
Refractory period
The interval between the time one nerve impulse occurs and the next one can be generated in the axon
-Refractory period is typically 1ms, so 500-800 impulses per second
Spontaneous activity
Action potentials that occur in the absence of stimuli from the environment
ions
molecules that carry an electrical charge
The solution outside the axon of a neuron is rich in positively charged _____ (Na+) ions, whereas the solution inside the axon is rich in positively charged _________ (K+) ions
sodium
potassium
Permeability
The ease with which a molecule can pass through the membrane
The opening of sodium channels in the membrane represents an increase in the permeability
Rising phase of the action potential
The increase in potential from -70mV to +40mV (polarized)
Once the neuron reaches +40mV the sodium cannels close (membrane becomes impermeable to sodium) and the potassium channels open up
CRAZZZZY #BIO11
Falling phase of the action potential
Going from +40mV to -70mV (repolarization)
Synapse
The spaces between neurons
Neurotransmitters
Flow into the synapse to small areas on the receiving neuron receptor sites that are sensitive to specific neurotransmitters
Two types of responses at the receptor sites
Excitatory
Inhibitory
Excitatory response
occurs when the inside of the neuron becomes more positive
Depolarization
Process when the inside of the neuron becomes more positive
Depolarization is an excitatory response
Inhibitory response
occurs when the inside of the neuron becomes more negative, a process called hyperpolarization
Hyperpolarization is a _____ response
inhibitory (as it causes the charge inside the axon to move away from the level of depolarization)
Neural Circuits
interconnected groups of neurons - within the retina
Two types of neurons that connect neurons across the retina (asides from bipolar cells and ganglion cells
Horizontal cells
Amacrine cells
Neural convergence
Occurs when a number of neurons synapse onto a single neuron
The greater convergence of the rods compared to the cones translate into two differences in perception
1) the rods result in better sensitivity than the cones
2) The cones result in better detail vision than the rods
Visual acuity
Referrers to the ability to see details (seeing small letters at eye doctor equals high acuity)
High convergence results in high sensitivity but poor acuity (the rods)
WOW
Low convergence results in low sensitivity but high acuity (Cones)
WOW
Preferential lookin technique
Two stimuli are presented and the observer sees what one the child looks at longer
Node of ranvier
Little gaps in myelin sheath used to facilitate speed
