Perception of StimuliStephen Taylor
Processing Visual Stimuli
httpwwwnaturecomnrnjournalv6n3fig_tabnrn1630_F4html
The lens focuses light onto the retina at the back of the eye where it stimulates photoreceptors (rods
sensitive in low light with low acuity and cones sensitive to colour in high light with high acuity)
Photoreceptors synapse with bipolar neurons These feed into ganglion cells carrying the impulse to the
visual cortex through the optic nerve
Some ganglia are sensitive to impulses from the edge of the receptive field where others are sensitive to
impulses from the centre
Edge enhancement (due to lateral inhibition of cells in the retina) results in greater
contrast around edges
Stimulus from the left visual field of each eye is processed in the right side of the brain
and vice versa This is due to contralateral processing via the optic chiasm
Uses the retina and the brain
Thanks to John Burrell amp David Mindorff
Rod Cells Cone Cells
Many rod cells feed into one ganglion all their action potentials are combined into a single impulse at the synapse This means
each ganglion has a large receptive field but low acuity (low ability to detect differences)
Rod cells are activated in low light conditions but lsquobleachedrsquo in high light intensities
They do not detect colour
Rods are distributed throughout the retina
Cone cells feed into their own ganglionThis gives a small receptive field for each ganglion leading to high visual acuity ndash small differences are easily detected
There are three types of cone cells receptive to different wavelengths (red green blue) These are only active in sufficient light
Cone cells are concentrated in the fovea
images adapted from httpwwwfujifilmusacomproductsdigital_camerasexreyespage_03html
images adapted from httpwwwfujifilmusacomproductsdigital_camerasexreyespage_03html
Receptive Fields and Processing Visual StimuliMany rod cells feed into one retinal ganglion This means that many impulse converge to form a single signal which is sent to the brain There is no distinction between stimuli which hit different sections of the same receptive field
Some ganglia are stimulated by impulses sent from rod cells from the edge of their receptive field and inhibited by signals from the middle
Other ganglia are inhibited by impulses sent from rod cells from the edge of their receptive field and stimulated by signals from the middle
This allows for greater perception of contrastEdge enhancement also plays a key role
Explaining Edge Enhancement Although each band is uniformly shaded regions around the edges are enhanced in your vision
appears darker
appearslighter
retina
Light hits the photoreceptorsMore light more stimulation
In these diagrams as the receptor cells get brighter is
shows a stronger signal
Stimulated photoreceptors pass the action potential to the bipolar neuron and ganglion
uniform signal
Explaining Edge Enhancement Although each band is uniformly shaded regions around the edges are enhanced in your vision
appears darker
appearslighter
retina
Light hits the photoreceptorsMore light more stimulation
Neighbouring cells will inhibit the neurons of each other
Greater stimulation of the receptor means greater
inhibition of the neighbours
This is called lateral inhibition
If all neighbouring cells receive the same stimulus (and
therefore inhibition) they will produce a uniform signal
Stimulated photoreceptors pass the action potential to the bipolar neuron and ganglion
uniform signal
Explaining Edge Enhancement Although each band is uniformly shaded regions around the edges are enhanced in your vision
uniform weak signal(dark colour perceived)
uniform strong signal(light colour perceived)
stronger signal brighter
weaker signal darker
If an edge falls within a visual field edge enhancement occurs
Receptors receiving a stronger stimulus will inhibit their neighbours more strongly and vice-versa
So a neuron that is more inhibited than its neighbours will result in a darker colour being perceived (on the dark side of the edge) and vice versa giving an enhanced contrast on the border between light and dark images
Explaining Edge Enhancement
A B C D
Why is B darker than AA receives the same weak stimulus as its
neighbours and so is inhibited equally by themB is next to C which recieves a stronger stimulus
and therefore inhibits C more As a result B is overall more inhibited than A so is darker
Why is C brighter than DD receives the same strong stimulus as its neighbours and so is inhibited equally by them C is next to B which recieves a weaker stimulus and therefore inhibits C less As a result C is overall less inhibited than D so is brighter
Receptor A receives the same light stimulus as B
Receptor D receives the same light stimulus as C
Itrsquos more like a gradienthellip see if you can explain why by annotating the diagram
images adapted from httpwwwfujifilmusacomproductsdigital_camerasexreyespage_03html
This is a Creative Commons presentation It may be linked and embedded but not sold or re-hosted
Please consider a donation to charity via Biology4GoodClick here for more information about Biology4Good charity donations
IBiologyStephen
Wheels turning illusion fromhttpwwwnewopticalillusionscommoving-optical-illusionstwo-wheels-new-optical-illusion
Processing Visual Stimuli
httpwwwnaturecomnrnjournalv6n3fig_tabnrn1630_F4html
The lens focuses light onto the retina at the back of the eye where it stimulates photoreceptors (rods
sensitive in low light with low acuity and cones sensitive to colour in high light with high acuity)
Photoreceptors synapse with bipolar neurons These feed into ganglion cells carrying the impulse to the
visual cortex through the optic nerve
Some ganglia are sensitive to impulses from the edge of the receptive field where others are sensitive to
impulses from the centre
Edge enhancement (due to lateral inhibition of cells in the retina) results in greater
contrast around edges
Stimulus from the left visual field of each eye is processed in the right side of the brain
and vice versa This is due to contralateral processing via the optic chiasm
Uses the retina and the brain
Thanks to John Burrell amp David Mindorff
Rod Cells Cone Cells
Many rod cells feed into one ganglion all their action potentials are combined into a single impulse at the synapse This means
each ganglion has a large receptive field but low acuity (low ability to detect differences)
Rod cells are activated in low light conditions but lsquobleachedrsquo in high light intensities
They do not detect colour
Rods are distributed throughout the retina
Cone cells feed into their own ganglionThis gives a small receptive field for each ganglion leading to high visual acuity ndash small differences are easily detected
There are three types of cone cells receptive to different wavelengths (red green blue) These are only active in sufficient light
Cone cells are concentrated in the fovea
images adapted from httpwwwfujifilmusacomproductsdigital_camerasexreyespage_03html
images adapted from httpwwwfujifilmusacomproductsdigital_camerasexreyespage_03html
Receptive Fields and Processing Visual StimuliMany rod cells feed into one retinal ganglion This means that many impulse converge to form a single signal which is sent to the brain There is no distinction between stimuli which hit different sections of the same receptive field
Some ganglia are stimulated by impulses sent from rod cells from the edge of their receptive field and inhibited by signals from the middle
Other ganglia are inhibited by impulses sent from rod cells from the edge of their receptive field and stimulated by signals from the middle
This allows for greater perception of contrastEdge enhancement also plays a key role
Explaining Edge Enhancement Although each band is uniformly shaded regions around the edges are enhanced in your vision
appears darker
appearslighter
retina
Light hits the photoreceptorsMore light more stimulation
In these diagrams as the receptor cells get brighter is
shows a stronger signal
Stimulated photoreceptors pass the action potential to the bipolar neuron and ganglion
uniform signal
Explaining Edge Enhancement Although each band is uniformly shaded regions around the edges are enhanced in your vision
appears darker
appearslighter
retina
Light hits the photoreceptorsMore light more stimulation
Neighbouring cells will inhibit the neurons of each other
Greater stimulation of the receptor means greater
inhibition of the neighbours
This is called lateral inhibition
If all neighbouring cells receive the same stimulus (and
therefore inhibition) they will produce a uniform signal
Stimulated photoreceptors pass the action potential to the bipolar neuron and ganglion
uniform signal
Explaining Edge Enhancement Although each band is uniformly shaded regions around the edges are enhanced in your vision
uniform weak signal(dark colour perceived)
uniform strong signal(light colour perceived)
stronger signal brighter
weaker signal darker
If an edge falls within a visual field edge enhancement occurs
Receptors receiving a stronger stimulus will inhibit their neighbours more strongly and vice-versa
So a neuron that is more inhibited than its neighbours will result in a darker colour being perceived (on the dark side of the edge) and vice versa giving an enhanced contrast on the border between light and dark images
Explaining Edge Enhancement
A B C D
Why is B darker than AA receives the same weak stimulus as its
neighbours and so is inhibited equally by themB is next to C which recieves a stronger stimulus
and therefore inhibits C more As a result B is overall more inhibited than A so is darker
Why is C brighter than DD receives the same strong stimulus as its neighbours and so is inhibited equally by them C is next to B which recieves a weaker stimulus and therefore inhibits C less As a result C is overall less inhibited than D so is brighter
Receptor A receives the same light stimulus as B
Receptor D receives the same light stimulus as C
Itrsquos more like a gradienthellip see if you can explain why by annotating the diagram
images adapted from httpwwwfujifilmusacomproductsdigital_camerasexreyespage_03html
This is a Creative Commons presentation It may be linked and embedded but not sold or re-hosted
Please consider a donation to charity via Biology4GoodClick here for more information about Biology4Good charity donations
IBiologyStephen
Wheels turning illusion fromhttpwwwnewopticalillusionscommoving-optical-illusionstwo-wheels-new-optical-illusion
Rod Cells Cone Cells
Many rod cells feed into one ganglion all their action potentials are combined into a single impulse at the synapse This means
each ganglion has a large receptive field but low acuity (low ability to detect differences)
Rod cells are activated in low light conditions but lsquobleachedrsquo in high light intensities
They do not detect colour
Rods are distributed throughout the retina
Cone cells feed into their own ganglionThis gives a small receptive field for each ganglion leading to high visual acuity ndash small differences are easily detected
There are three types of cone cells receptive to different wavelengths (red green blue) These are only active in sufficient light
Cone cells are concentrated in the fovea
images adapted from httpwwwfujifilmusacomproductsdigital_camerasexreyespage_03html
images adapted from httpwwwfujifilmusacomproductsdigital_camerasexreyespage_03html
Receptive Fields and Processing Visual StimuliMany rod cells feed into one retinal ganglion This means that many impulse converge to form a single signal which is sent to the brain There is no distinction between stimuli which hit different sections of the same receptive field
Some ganglia are stimulated by impulses sent from rod cells from the edge of their receptive field and inhibited by signals from the middle
Other ganglia are inhibited by impulses sent from rod cells from the edge of their receptive field and stimulated by signals from the middle
This allows for greater perception of contrastEdge enhancement also plays a key role
Explaining Edge Enhancement Although each band is uniformly shaded regions around the edges are enhanced in your vision
appears darker
appearslighter
retina
Light hits the photoreceptorsMore light more stimulation
In these diagrams as the receptor cells get brighter is
shows a stronger signal
Stimulated photoreceptors pass the action potential to the bipolar neuron and ganglion
uniform signal
Explaining Edge Enhancement Although each band is uniformly shaded regions around the edges are enhanced in your vision
appears darker
appearslighter
retina
Light hits the photoreceptorsMore light more stimulation
Neighbouring cells will inhibit the neurons of each other
Greater stimulation of the receptor means greater
inhibition of the neighbours
This is called lateral inhibition
If all neighbouring cells receive the same stimulus (and
therefore inhibition) they will produce a uniform signal
Stimulated photoreceptors pass the action potential to the bipolar neuron and ganglion
uniform signal
Explaining Edge Enhancement Although each band is uniformly shaded regions around the edges are enhanced in your vision
uniform weak signal(dark colour perceived)
uniform strong signal(light colour perceived)
stronger signal brighter
weaker signal darker
If an edge falls within a visual field edge enhancement occurs
Receptors receiving a stronger stimulus will inhibit their neighbours more strongly and vice-versa
So a neuron that is more inhibited than its neighbours will result in a darker colour being perceived (on the dark side of the edge) and vice versa giving an enhanced contrast on the border between light and dark images
Explaining Edge Enhancement
A B C D
Why is B darker than AA receives the same weak stimulus as its
neighbours and so is inhibited equally by themB is next to C which recieves a stronger stimulus
and therefore inhibits C more As a result B is overall more inhibited than A so is darker
Why is C brighter than DD receives the same strong stimulus as its neighbours and so is inhibited equally by them C is next to B which recieves a weaker stimulus and therefore inhibits C less As a result C is overall less inhibited than D so is brighter
Receptor A receives the same light stimulus as B
Receptor D receives the same light stimulus as C
Itrsquos more like a gradienthellip see if you can explain why by annotating the diagram
images adapted from httpwwwfujifilmusacomproductsdigital_camerasexreyespage_03html
This is a Creative Commons presentation It may be linked and embedded but not sold or re-hosted
Please consider a donation to charity via Biology4GoodClick here for more information about Biology4Good charity donations
IBiologyStephen
Wheels turning illusion fromhttpwwwnewopticalillusionscommoving-optical-illusionstwo-wheels-new-optical-illusion
images adapted from httpwwwfujifilmusacomproductsdigital_camerasexreyespage_03html
Receptive Fields and Processing Visual StimuliMany rod cells feed into one retinal ganglion This means that many impulse converge to form a single signal which is sent to the brain There is no distinction between stimuli which hit different sections of the same receptive field
Some ganglia are stimulated by impulses sent from rod cells from the edge of their receptive field and inhibited by signals from the middle
Other ganglia are inhibited by impulses sent from rod cells from the edge of their receptive field and stimulated by signals from the middle
This allows for greater perception of contrastEdge enhancement also plays a key role
Explaining Edge Enhancement Although each band is uniformly shaded regions around the edges are enhanced in your vision
appears darker
appearslighter
retina
Light hits the photoreceptorsMore light more stimulation
In these diagrams as the receptor cells get brighter is
shows a stronger signal
Stimulated photoreceptors pass the action potential to the bipolar neuron and ganglion
uniform signal
Explaining Edge Enhancement Although each band is uniformly shaded regions around the edges are enhanced in your vision
appears darker
appearslighter
retina
Light hits the photoreceptorsMore light more stimulation
Neighbouring cells will inhibit the neurons of each other
Greater stimulation of the receptor means greater
inhibition of the neighbours
This is called lateral inhibition
If all neighbouring cells receive the same stimulus (and
therefore inhibition) they will produce a uniform signal
Stimulated photoreceptors pass the action potential to the bipolar neuron and ganglion
uniform signal
Explaining Edge Enhancement Although each band is uniformly shaded regions around the edges are enhanced in your vision
uniform weak signal(dark colour perceived)
uniform strong signal(light colour perceived)
stronger signal brighter
weaker signal darker
If an edge falls within a visual field edge enhancement occurs
Receptors receiving a stronger stimulus will inhibit their neighbours more strongly and vice-versa
So a neuron that is more inhibited than its neighbours will result in a darker colour being perceived (on the dark side of the edge) and vice versa giving an enhanced contrast on the border between light and dark images
Explaining Edge Enhancement
A B C D
Why is B darker than AA receives the same weak stimulus as its
neighbours and so is inhibited equally by themB is next to C which recieves a stronger stimulus
and therefore inhibits C more As a result B is overall more inhibited than A so is darker
Why is C brighter than DD receives the same strong stimulus as its neighbours and so is inhibited equally by them C is next to B which recieves a weaker stimulus and therefore inhibits C less As a result C is overall less inhibited than D so is brighter
Receptor A receives the same light stimulus as B
Receptor D receives the same light stimulus as C
Itrsquos more like a gradienthellip see if you can explain why by annotating the diagram
images adapted from httpwwwfujifilmusacomproductsdigital_camerasexreyespage_03html
This is a Creative Commons presentation It may be linked and embedded but not sold or re-hosted
Please consider a donation to charity via Biology4GoodClick here for more information about Biology4Good charity donations
IBiologyStephen
Wheels turning illusion fromhttpwwwnewopticalillusionscommoving-optical-illusionstwo-wheels-new-optical-illusion
Explaining Edge Enhancement Although each band is uniformly shaded regions around the edges are enhanced in your vision
appears darker
appearslighter
retina
Light hits the photoreceptorsMore light more stimulation
In these diagrams as the receptor cells get brighter is
shows a stronger signal
Stimulated photoreceptors pass the action potential to the bipolar neuron and ganglion
uniform signal
Explaining Edge Enhancement Although each band is uniformly shaded regions around the edges are enhanced in your vision
appears darker
appearslighter
retina
Light hits the photoreceptorsMore light more stimulation
Neighbouring cells will inhibit the neurons of each other
Greater stimulation of the receptor means greater
inhibition of the neighbours
This is called lateral inhibition
If all neighbouring cells receive the same stimulus (and
therefore inhibition) they will produce a uniform signal
Stimulated photoreceptors pass the action potential to the bipolar neuron and ganglion
uniform signal
Explaining Edge Enhancement Although each band is uniformly shaded regions around the edges are enhanced in your vision
uniform weak signal(dark colour perceived)
uniform strong signal(light colour perceived)
stronger signal brighter
weaker signal darker
If an edge falls within a visual field edge enhancement occurs
Receptors receiving a stronger stimulus will inhibit their neighbours more strongly and vice-versa
So a neuron that is more inhibited than its neighbours will result in a darker colour being perceived (on the dark side of the edge) and vice versa giving an enhanced contrast on the border between light and dark images
Explaining Edge Enhancement
A B C D
Why is B darker than AA receives the same weak stimulus as its
neighbours and so is inhibited equally by themB is next to C which recieves a stronger stimulus
and therefore inhibits C more As a result B is overall more inhibited than A so is darker
Why is C brighter than DD receives the same strong stimulus as its neighbours and so is inhibited equally by them C is next to B which recieves a weaker stimulus and therefore inhibits C less As a result C is overall less inhibited than D so is brighter
Receptor A receives the same light stimulus as B
Receptor D receives the same light stimulus as C
Itrsquos more like a gradienthellip see if you can explain why by annotating the diagram
images adapted from httpwwwfujifilmusacomproductsdigital_camerasexreyespage_03html
This is a Creative Commons presentation It may be linked and embedded but not sold or re-hosted
Please consider a donation to charity via Biology4GoodClick here for more information about Biology4Good charity donations
IBiologyStephen
Wheels turning illusion fromhttpwwwnewopticalillusionscommoving-optical-illusionstwo-wheels-new-optical-illusion
Explaining Edge Enhancement Although each band is uniformly shaded regions around the edges are enhanced in your vision
appears darker
appearslighter
retina
Light hits the photoreceptorsMore light more stimulation
Neighbouring cells will inhibit the neurons of each other
Greater stimulation of the receptor means greater
inhibition of the neighbours
This is called lateral inhibition
If all neighbouring cells receive the same stimulus (and
therefore inhibition) they will produce a uniform signal
Stimulated photoreceptors pass the action potential to the bipolar neuron and ganglion
uniform signal
Explaining Edge Enhancement Although each band is uniformly shaded regions around the edges are enhanced in your vision
uniform weak signal(dark colour perceived)
uniform strong signal(light colour perceived)
stronger signal brighter
weaker signal darker
If an edge falls within a visual field edge enhancement occurs
Receptors receiving a stronger stimulus will inhibit their neighbours more strongly and vice-versa
So a neuron that is more inhibited than its neighbours will result in a darker colour being perceived (on the dark side of the edge) and vice versa giving an enhanced contrast on the border between light and dark images
Explaining Edge Enhancement
A B C D
Why is B darker than AA receives the same weak stimulus as its
neighbours and so is inhibited equally by themB is next to C which recieves a stronger stimulus
and therefore inhibits C more As a result B is overall more inhibited than A so is darker
Why is C brighter than DD receives the same strong stimulus as its neighbours and so is inhibited equally by them C is next to B which recieves a weaker stimulus and therefore inhibits C less As a result C is overall less inhibited than D so is brighter
Receptor A receives the same light stimulus as B
Receptor D receives the same light stimulus as C
Itrsquos more like a gradienthellip see if you can explain why by annotating the diagram
images adapted from httpwwwfujifilmusacomproductsdigital_camerasexreyespage_03html
This is a Creative Commons presentation It may be linked and embedded but not sold or re-hosted
Please consider a donation to charity via Biology4GoodClick here for more information about Biology4Good charity donations
IBiologyStephen
Wheels turning illusion fromhttpwwwnewopticalillusionscommoving-optical-illusionstwo-wheels-new-optical-illusion
Explaining Edge Enhancement Although each band is uniformly shaded regions around the edges are enhanced in your vision
uniform weak signal(dark colour perceived)
uniform strong signal(light colour perceived)
stronger signal brighter
weaker signal darker
If an edge falls within a visual field edge enhancement occurs
Receptors receiving a stronger stimulus will inhibit their neighbours more strongly and vice-versa
So a neuron that is more inhibited than its neighbours will result in a darker colour being perceived (on the dark side of the edge) and vice versa giving an enhanced contrast on the border between light and dark images
Explaining Edge Enhancement
A B C D
Why is B darker than AA receives the same weak stimulus as its
neighbours and so is inhibited equally by themB is next to C which recieves a stronger stimulus
and therefore inhibits C more As a result B is overall more inhibited than A so is darker
Why is C brighter than DD receives the same strong stimulus as its neighbours and so is inhibited equally by them C is next to B which recieves a weaker stimulus and therefore inhibits C less As a result C is overall less inhibited than D so is brighter
Receptor A receives the same light stimulus as B
Receptor D receives the same light stimulus as C
Itrsquos more like a gradienthellip see if you can explain why by annotating the diagram
images adapted from httpwwwfujifilmusacomproductsdigital_camerasexreyespage_03html
This is a Creative Commons presentation It may be linked and embedded but not sold or re-hosted
Please consider a donation to charity via Biology4GoodClick here for more information about Biology4Good charity donations
IBiologyStephen
Wheels turning illusion fromhttpwwwnewopticalillusionscommoving-optical-illusionstwo-wheels-new-optical-illusion
Explaining Edge Enhancement
A B C D
Why is B darker than AA receives the same weak stimulus as its
neighbours and so is inhibited equally by themB is next to C which recieves a stronger stimulus
and therefore inhibits C more As a result B is overall more inhibited than A so is darker
Why is C brighter than DD receives the same strong stimulus as its neighbours and so is inhibited equally by them C is next to B which recieves a weaker stimulus and therefore inhibits C less As a result C is overall less inhibited than D so is brighter
Receptor A receives the same light stimulus as B
Receptor D receives the same light stimulus as C
Itrsquos more like a gradienthellip see if you can explain why by annotating the diagram
images adapted from httpwwwfujifilmusacomproductsdigital_camerasexreyespage_03html
This is a Creative Commons presentation It may be linked and embedded but not sold or re-hosted
Please consider a donation to charity via Biology4GoodClick here for more information about Biology4Good charity donations
IBiologyStephen
Wheels turning illusion fromhttpwwwnewopticalillusionscommoving-optical-illusionstwo-wheels-new-optical-illusion
Itrsquos more like a gradienthellip see if you can explain why by annotating the diagram
images adapted from httpwwwfujifilmusacomproductsdigital_camerasexreyespage_03html
This is a Creative Commons presentation It may be linked and embedded but not sold or re-hosted
Please consider a donation to charity via Biology4GoodClick here for more information about Biology4Good charity donations
IBiologyStephen
Wheels turning illusion fromhttpwwwnewopticalillusionscommoving-optical-illusionstwo-wheels-new-optical-illusion
images adapted from httpwwwfujifilmusacomproductsdigital_camerasexreyespage_03html
This is a Creative Commons presentation It may be linked and embedded but not sold or re-hosted
Please consider a donation to charity via Biology4GoodClick here for more information about Biology4Good charity donations
IBiologyStephen
Wheels turning illusion fromhttpwwwnewopticalillusionscommoving-optical-illusionstwo-wheels-new-optical-illusion
This is a Creative Commons presentation It may be linked and embedded but not sold or re-hosted
Please consider a donation to charity via Biology4GoodClick here for more information about Biology4Good charity donations
IBiologyStephen
Wheels turning illusion fromhttpwwwnewopticalillusionscommoving-optical-illusionstwo-wheels-new-optical-illusion