Field Periphery Research Articles

The summation of excitation in the receptive fields of movement-sensitive neurons of the frog's retina

The receptive field of movement detecting class-2 neurons of the frog's retina is composed of an excitatory receptive field center (ERF) and an inhibitory receptive field periphery (IRF). The summation of activation elicited by two black stimuli moving against a white background through the ERF was measured. The action potentials of optic nerve fibers in the superficial layers were recorded by means of microelectrodes. The average impulse frequency during the ERF-transverse was varied by changing stimulus velocities. The average impulse frequencies elicited by movement of each stimulus alone did not summate algebraically, if two stimuli were moved simultaneously through the ERF. The results indicate that for the summation of neuronal signals within the ERF a superimposition of lateral excitatory processes and lateral inhibition occurs.

Receptive fields of single cells in the cat's superior colliculus.

Receptive field analysis of single units in the superior colliculus of the mid-pontine, pretrigeminal cat has confirmed previous reports of directionally selective units in the tectum. The directional property was based principally upon a unilateral inhibitory mechanism, although some directional responses to small moving objects depended equally upon summation of excitation. Receptive field size varied greatly, with field diameters not uncommonly exceeding 30 degrees. Fields near the area centralis and along the horizontal meridian tended to be smaller than those elsewhere. An inhibitory influence from the field periphery was demonstrated.

The conduction velocity of lateral inhibition in the cat's retina.

By means of microelectrodes action potentials of single optic nerve fibers from on-center neurons of the cat's retina were recorded. The latency of the inhibition of the neuronal activity elicited by light stimuli in the inhibitory receptive field periphery was measured. The inhibiting light stimuli (rings or bars) were projected into different parts of the receptive field periphery. From the spatial separations of the inhibiting light stimuli and the differences of the corresponding inhibition latencies the conduction velocity of lateral inhibition within the receptive field was measured. A value of 90–110 mm · sec−1 in the retina was found, which corresponds to about 400–480 degrees · sec−1 in the visual field.

FUNCTIONAL ORGANIZATION OF RECEPTIVE FIELDS OF MOVEMENT DETECTING NEURONS IN THE FROG'S RETINA.

The name “receptive field” (RF) was defined by Hartline 4 as that part of the retina from which stimulation with small light spots elicits an activation of the recorded retinal neuron. Kuffler 5 enlarged this definition by the experimental observation that the on-neurons in the cat’s retina have field centers from which stimulation with light spots elicits an on-activation and off-inhibition, whereas light spots in the annular RF periphery cause an on-inhibition and an off-activation. The off-activation may be explained by a rebound effect or by the assumption that the functional connection of the receptors through the bipolar cells with the retinal ganglion cells is such that an increase of the receptor-potential activates on-neurons and inhibits the off-neurons from the field center, while a decrease of the receptor potential elicits the reverse effect1a. For the field periphery the relations are reversed in toto. An “adequate” stimulus to the cat’s retina activates a neuron from all parts of the RF either at on or off; the RF may be called therefore “excitatory receptive field” (ERF). If there are zones in the retina where any effective stimulation causes only inhibition on a recorded neuron, they may be called “inhibitory receptive fields” (IRF). With this definition the RF of the on- and off-neurons in the cat’s retina would be an ERF, having on- and off-“zones”. The following report demonstrates that a distinction between ERF and IRF must be made to describe adequately the functional organization of the total field of the “movement detecting” neurons in the ganglion cell layer of the frog’s retina. Barlow 1 reported a large inhibiory field in another class of units.