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Striate Cortex Physiology - Coggle Diagram
Striate Cortex Physiology
How does the visual cortex structure relate to its function? What are the receptive field characteristics in and outside layer IVC?
Receptive fields
in layer IVC are similar to the magnocellular and parvocellular LGN neurons providing their input.
generally small monocular center-surround receptive fields.
In layer IVCα, the neurons are insensitive to the wavelength of light, whereas in layer IVCβ, the neurons exhibit center-surround color opponency.
Outside layer IVC (and somewhat within), new receptive field characteristics, not observed in the retina or LGN, are present.
Binocularity
most neurons in layers superficial to IVC are binocular, responding to light in either eye.
ocular dominance columns
We say that the neurons have
binocular receptive fields
they actually have two receptive fields, one in the ipsilateral eye and one in the contralateral eye.
the two receptive fields of a binocular neuron are precisely placed on the retina such that they are “looking” at the same point in in the contralateral visual field
Retinotopy is preserved
Orientation Selectivity
Most of the receptive fields in the retina, LGN, and layer IVC are circular
Outside layer IVC, we encounter cells that no longer follow this pattern.
many neurons in V1 respond best to an elongated
bar
of light moving across their receptive fields. But!
the
orientation
of the bar is critical.
bars perpendicular to the optimal orientation generally elicit much weaker responses
Neurons having this type of response are said to exhibit
orientation selectivity.
preferred orientation remains the same for all the selective neurons encountered from layer II down through layer VI.
this radial column of cells is called an
orientation column.
analysis of stimulus orientation appears to be one of the most important functions of the striate cortex
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Direction Selectivity
Many V1 receptive fields respond when a bar of light at the optimal orientation moves perpendicular to the orientation in one direction but not in the opposite direction.
subset of the cells that are orientation selective
hallmark of neurons receiving input from the magnocellular layers of the LGN.
thought to be specialized for the analysis of object motion.
Simple and Complex Receptive Fields
What do we know about the
inputs
to V1 neurons that might account for binocularity, orientation selectivity, and direction selectivity in their receptive fields?
Binocularity
binocular neurons receive afferents from both eyes.
Orientation selectivity
simple cells
linear arrangement of ON and OFF areas
receptive field elongated along a particular axis
complex cells
give both ON and OFF responses to stimuli throughout the receptive field
Different neurons show a range of sensitivities to color and direction of motion.