Properties of the visual cortical cells

Properties of the visual cortical cells
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Properties of the Visual Cortical Cells
The critical functional properties of the visual cortical cells include the receptive field (RF) and the area visual magnification factor (ACMF) (Stevens, 2002). The values of the two systematically vary at different locations of the cortical surface. The population density of the neurons on the cortical surface determines the ACMF. For the eye, unlike a camera which is made to analyze the field of view uniformly, it has a sampling mechanism which limits its detailed analysis to the center of the field of view with the focus reducing towards the periphery of the field of view. The neuron density is highest in the middle of the retina (Stevens, 2002) hence more stimuli are sent to the brain in from the center.
The RF of a neuron is defined by the area of the field of view it receives stimuli from (Ringach, 2004). From the definition and the sampling mechanism of the eye, neurons at the periphery have a larger RF than those at the middle. This allocation of RF explains why the peripheral view is not as much detailed as the central view since the brain receives fewer stimuli per area covered.
Increase in age has an adverse effect on the ACMF. Detoriation of the neurons reduces their density at across the whole cortical surface hence reducing the overall ability to focus sharply on objects (Mendelson & Wells, 2002). For instance, this explains why extremely aged people are likely to lose their sight or have it significantly reduced.

The speed of an object affects the RF of each neuron since as the object moves, the RF of a neuron is shifted to a different part of the object hence obtained the detailed vision of the object is impaired (Mendelson & Wells, 2002). This phenomenon can be illustrated with the inability to tell the pattern of a vehicle’s rims while its moving fast yet the same is very clear when it’s not in motion.
Under situations of flight, the adrenaline released leads to enlargement of the pupil (“Adrenaline | You and Your Hormones from the Society for Endocrinology”, 2018). The expansion of the pupil translates to more light entering the eye triggering more neurons hence the visual clarity. Situations of flight, therefore, increase the effective ACMF. It can be illustrated with the ability to drive fast in dim light in cases of danger.
References
Adrenaline | You and Your Hormones from the Society for Endocrinology. (2018). Yourhormones.info. Retrieved 23 April 2018, from http://www.yourhormones.info/Hormones/Adrenaline.aspx
Mendelson, J., & Wells, E. (2002). Age-related changes in the visual cortex. Vision Research, 42(6), 695-703. http://dx.doi.org/10.1016/s0042-6989(01)00307-8Ringach, D. (2004). Mapping receptive fields in the primary visual cortex. The Journal Of Physiology, 558(3), 717-728. http://dx.doi.org/10.1113/jphysiol.2004.065771Stevens, C. (2002). Predicting Functional Properties of Visual Cortex from an Evolutionary Scaling Law. Neuron, 36(1), 139-142. http://dx.doi.org/10.1016/s0896-6273(02)00902-9