A receptive field is understood as the area of sensory receptors that forwards information to a single downstream neuron.
Very often the term is used for areas on the retina of the eye. Many photoreceptors converge here on a few ganglion cells . A total of around 126 million receptors converge on one million retinal ganglion cells.
The convergence has four important factors:
- Reduction : The flood of incoming information is reduced so that the signals can be processed more easily.
- Visual acuity : About 120 million rods and six million cones converge on one million ganglion cells. The receptive fields for cones are much smaller and therefore their visual acuity is greater. The approximately 60,000 cones in the fovea play a special role here, as they do not converge but project directly onto their "own" ganglion cells. This is why the fovea is the place of sharpest vision, while the receptive fields are larger towards the periphery of the eye and visual acuity is lower.
- higher sensitivity : Since an incoming light signal can be amplified by convergence (a neuron is stimulated by several receptors), the sensitivity is greater at higher convergence (see spatial summation ). With the larger receptive fields in the periphery, the ability to perceive movements also increases.
- Specificity : Through convergence, downstream neurons are only activated if the signal stimulates a certain, activating area of the cells of the receptive field. If only too little or a different part of the cells of the receptive field is stimulated, the signal can remain subliminal.
Many receptive fields can be divided into a center and an environment. Usually these are connected in opposite directions, so that one speaks of the so-called center-environment antagonism . There are two main types of fields:
- On-center neurons have an exciting center and an inhibiting environment
- Off-center neurons have an inhibiting center and an exciting environment
For example, if the environment of the on-center neuron is illuminated, this causes an inhibition of the signal (the so-called lateral inhibition ). A receptive field responds optimally to a stimulus that only excites the center. The purpose of such interconnections lies in the higher contrast capability of the eye. As a result, for example, object edges can be better perceived.
Definition in Anglo-Saxon literature
Another fact of the same name, which is also related to neuronal stimulus processing, often leads to misunderstandings. Especially since this is the predominant definition of “receptive field” in Anglo-Saxon literature. Here, the receptive field of a neuron denotes the area in a (parameter) space in which a stimulus must lie so that the neuron reacts to this stimulus with action potentials. This applies to central neurons where the concept of “a single downstream” cell doesn't make sense.