A simple cell in the

primary 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 ...

is a cell that responds primarily to oriented edges and gratings (bars of particular orientations). These cells were discovered by

Torsten Wiesel Torsten Nils Wiesel (born 3 June 1924) is a Swedish neurophysiologist. With David H. Hubel, he received the 1981 Nobel Prize in Physiology or Medicine, for their discoveries concerning information processing in the visual system; the prize was s ...

and

David Hubel David Hunter Hubel (February 27, 1926 – September 22, 2013) was a Canadian American neurophysiologist noted for his studies of the structure and function of the visual cortex. He was co-recipient with Torsten Wiesel of the 1981 Nobel Priz ...

in the late 1950s. Such cells are tuned to different frequencies and orientations, even with different phase relationships, possibly for extracting disparity (depth) information and to attribute depth to detected lines and edges. This may result in a 3D 'wire-frame' representation as used in computer graphics. The fact that input from the left and right eyes is very close in the so-called cortical hypercolumns is an indication that depth processing occurs at a very early stage, aiding recognition of 3D objects. Later, many other cells with specific functions have been discovered: (a) end-stopped cells which are thought to detect singularities like line and edge crossings, vertices and line endings; (b) bar and grating cells. The latter are not linear operators because a bar cell does not respond when seeing a bar which is part of a periodic grating, and a grating cell does not respond when seeing an isolated bar. Using the mathematical Gabor model with sine and cosine components (phases),

complex cell Complex cells can be found in the primary visual cortex (V1), the secondary visual cortex (V2), and Brodmann area 19 ( V3). Like a simple cell, a complex cell will respond primarily to oriented edges and gratings, however it has a degree of spa ...

s are then modeled by computing the modulus of complex Gabor responses. Both simple and complex cells are linear operators and are seen as filters because they respond selectively to a large number of patterns. However, it has been claimed that the Gabor model does not conform to the anatomical structure of the visual system as it short-cuts the

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 uses the 2D image as it is projected on the

retina The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which then ...

. Azzopardi and PetkovG. Azzopardi and N. Petko
''A CORF computational model that relies on LGN input outperforms the Gabor function model''
Biological Cybernetics, vol. 106(3), pp. 177-189, DOI: 10.1007/s00422-012-0486-6, 2012 have proposed a computational model of a simple cell, which combines the responses of model

cells with center-surround

receptive field The receptive field, or sensory space, is a delimited medium where some physiological stimuli can evoke a sensory neuronal response in specific organisms. Complexity of the receptive field ranges from the unidimensional chemical structure of od ...

s (RFs). They call it Combination of RFs (CORF) model. Besides orientation selectivity, it exhibits cross orientation suppression, contrast invariant orientation tuning and response saturation. These properties are observed in real simple cells but are not possessed by the Gabor model. Using simulated reverse correlation they also demonstrate that the RF map of the CORF model can be divided into elongated excitatory and inhibitory regions typical of simple cells. Lindeberg T. Lindeberg "A computational theory of visual receptive fields", Biological Cybernetics 107(6): 589-635, 2013
/ref>T. Lindeberg "Normative theory of visual receptive fields", Heliyon 7(1):e05897, 2021.
/ref> has derived axiomatically determined models of simple cells in terms of directional derivatives of affine Gaussian kernels over the spatial domain in combination with temporal derivatives of either non-causal or time-causal scale-space kernels over the temporal domain and shown that this theory both leads to predictions about receptive fields with good qualitative agreement with the biological receptive field measurements performed by DeAngelis et al. and guarantees good theoretical properties of the mathematical receptive field model, including covariance and invariance properties under natural image transformations.T. Lindeberg "Invariance of visual operations at the level of receptive fields", PLOS ONE 8(7): e66990, pages 1-33, 2013
/ref>

History

These cells were discovered by

and

in the late 1950s. Hubel and Wiesel named these cells "simple," as opposed to "

", because they shared the following properties:D. H. Hubel and T. N. Wiesel ''Receptive Fields, Binocular Interaction and Functional Architecture in the Cat's Visual Cortex'' J. Physiol. 160 pp. 106-154 1962 # They have distinct excitatory and inhibitory regions. # These regions follow the summation property. # These regions have mutual antagonism - excitatory and inhibitory regions balance themselves out in diffuse lighting. # It is possible to predict responses of moving stimuli given the map of excitatory and inhibitory regions. Some other researchers such as Peter Bishop and Peter Schiller used different definitions for simple and complex cells.''Brain and Visual Perception: The Story of a 25-Year Collaboration'' D. H. Hubel and T. N. Wiesel Oxford 2005

History

References

See also