L7 Flashcards
the visual cortex ….
• Multiple representations of the visual world exist in visual cortex.
• Beyond the striate cortex lie the extrastriate areas, which are higher-order visual areas that also contain
representations of the retina.
how can neurophysiologists can identify the representational characteristics
of neurons in different visual areas.
With the use of single cell recording
• Remember that visually sensitive cells respond to stimuli within a limited region of space (i.e., their
receptive field).
• Thus, before you can test which type of stimuli cause a neuron to fire, you need to map the neuron’s
receptive field so that you know where to present the stimuli.
MT = to what
visual cortex (in non humans)
Single Cell Recording in Area MT of Macaque monkeys
had The activity of a single neuron in
area MT recorded while a white bar
passed through the neuron’s receptive field in varying directions.
what did this show
The neuron fired vigorously when
the bar moved downward toward the left, and opposite movement elicited the least
activity
• Conclusion: Neurons in area MT are selective for the direction of motion.
they did the MT single cell recording again but this time the motion of the white bar was
always in the optimal direction, but the
speed varied.
what did this show
This neuron fired most vigorously
to movement at 64 degrees/second.
• Conclusion: Neurons in area MT are selective for the speed of motion.
single cells recordings of MT show that
Neurons in area MT are selective for the speed and dirrection of motion.
what do – Positron Emission Tomography (PET) detect
– PET scanners detect radioactive material. meaning that
how do PET scans work
participants either inhale or are injected with a radioactive material.
– When the radioactive material gets into the bloodstream, it goes to areas of the brain that are
metabolically active.
– PET provides a functional view of the brain by measuring regional cerebral blood flow.
in order to know what structures are metabolically active (to get a structural view of the brain) PET data is overlaid on a structural image.
this is how you get a functional AND structural view using PET
As with event-related potentials (ERPs), the background noise must be removed from the data in order to observe the event-related signal in a PET scan
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Specialization of function in human visual cortex was investigated using positron emission tomography.
the study included nine neurologically-healthy adults and PET was used to measure regional cerebral blood flow in order to
identify which parts of the brain are involved in the perception of different types of visual stimuli.
Participants viewed either coloured stimuli or moving stimuli
what did they do to make sure the results were accurate
In order to remove activity that is associated with vision but is not specific to colour perception, activity elicited by the abstract scene when shown in greys (not colour) was subtracted from the activity elicited by the
abstract scene when shown in colour.
(no colour vs colour)
In order to remove activity that is associated with vision but is not specific to motion perception,
activity elicited by the display when it was stationary (not moving) was subtracted from the activity elicited by the
display when it was moving.
(not moving/moving)
Specialization of function in human visual cortex was investigated using positron emission tomography.
the study included nine neurologically-healthy adults and PET was used to measure regional cerebral blood flow in order to
identify which parts of the brain are involved in the perception of different types of visual stimuli.
Participants viewed either coloured stimuli or moving stimuli
what did they find
This data shows that, as in macaque monkeys, different areas of human extrastriate visual
cortex are involved in processing different attributes of vision.
there are 2 Cortical Visual Pathways
what does this mean
There are two main projection routes from primary visual cortex (V1) to extrastriate visual cortex
There are two main projection routes from primary visual cortex (V1) to extrastriate visual cortex
what are they
– The dorsal stream codes motion and location.
– The ventral stream processes detailed stimulus features and object identity.
the interconnectivity of the different areas of visual cortex is complex but not random. Not every area is connected with every other.
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• The numbering scheme should not be taken to mean
that the synapses proceed sequentially from one area
to the next. eg V1 -> V2 -> v3 ect
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