Orientation selectivity is expressed by cells within the

visual cortex The visual cortex of the brain is the area of the cerebral cortex that processes visual information. It is located in the occipital lobe. Sensory input originating from the eyes travels through the lateral geniculate nucleus in the thalamus and ...

, when such cells increase impulse or signal activity for specific oriented degree of shape presented within the visual field. Orientation selectivity can also be expressed by simple cells if the orientation of a stimulus is orthogonal to the preferred degree of orientation, which results in the inhibition of impulse activity.

Orientation testing

Single receptive field cells across the retina,

LGN In neuroanatomy, the lateral geniculate nucleus (LGN; also called the lateral geniculate body or lateral geniculate complex) is a structure in the thalamus and a key component of the mammalian visual pathway. It is a small, ovoid, Anatomical term ...

, and primary visual cortex are in a state of continuous

neurotransmission Neurotransmission (Latin: ''transmissio'' "passage, crossing" from ''transmittere'' "send, let through") is the process by which signaling molecules called neurotransmitters are released by the axon terminal of a neuron (the presynaptic neuron), ...

. Impulse activity is the continuous state of regular and constant

between neurons. Tests conducted by David H. Hubel and Torsten N. Wiesel (1968) utilized a single light dot presented within the visual field of a house cat to map out the location of a cell's receptive field within the cat's

visual field The visual field is the "spatial array of visual sensations available to observation in introspectionist psychological experiments". Or simply, visual field can be defined as the entire area that can be seen when an eye is fixed straight at a point ...

Once the receptive field of a cell had been completely mapped out, it was found that some of the

simple cell A simple cell in the visual cortex, primary visual cortex is a cell that responds primarily to oriented edges and gratings (bars of particular orientations). These cells were discovered by Torsten Wiesel and David Hubel in the late 1950s. Such ...

receptive fields mapped out had a region which excited for a stimulus sandwiched between two inhibitory regions. These inhibitory and excitatory regions together formed a single receptive field selective for stimulus shape fitting within the excitatory region. Only a bar of light stimulus oriented at the correct angle and position within the receptive field covering only the excitatory region excluding the two inhibitory regions would express the greatest increase in the rate of impulse activity for that cell. Some layers of the striate cortex were found to contain orientation and direction selective cells. These cells were referred to as complex cells, and consisted of several orientation selective simple cells inputting into a single Complex cell. This was believed to result in a cell selective for direction and motion input. These receptive fields were called

receptive fields, and were believed consist of single center-surround

input.

References

Visual cortex {{eye-stub