Light and Eyeballs

84 Lateral Inhibition

Learning Objectives

Be able to describe what lateral inhibition is.

Be able to give at least one example of lateral inhibition or an illusion caused by it.

Lateral inhibition is a secondary signal sent by a neuron to reduce the responses of neighboring neurons when firing information. In vision, this can be observed through a neuron that is responding to differences in light, which will fire one signal of information about light to the next level in vision while a second signal is sent to neighboring neurons to suppress their firing rate. This suppression of response in neighboring neurons helps to pinpoint visual information by exaggerating differences in light.

There are four basic types of lateral inhibition:

  1. Transient response with an excitatory center and inhibitory surrounding, or a shorter response in the retinal ganglion cells (RGC) with a receptive field that has a high firing rate in the center and low firing rate in the surrounding part of the receptive field.
  2. Transient response with an inhibitory center and excitatory surrounding, or a shorter response in the RGC with a receptive field that has a low firing rate in the center and high firing rate in the surrounding part of the receptive field.
  3. Sustained response with an excitatory center and inhibitory surrounding, or a longer response in the RGC with a receptive field that has a high firing rate in the center and low firing rate in the surrounding part of the receptive field.
  4. Sustained response with an inhibitory center and excitatory surrounding, or a longer response in the RGC with a receptive field that has a low firing rate in the center and high firing rate in the surrounding part of the receptive field.

Lateral inhibition can explain Mach bands, or the illusion that light and dark lines exist adjacent to sudden changes in brightness, and the gray dots that appear between intersections in the Hermann grid illusion (Fig.8.11.1).

 

Fig. 8.11.1. Hermann Grid Illusion. The Hermann grid illusion is the perception of gray dots at each intersection of white lines when not directly looking at the intersection. The bottom circle shows that when looking at lines between intersections, the inhibitory surround is mostly picking up black, making the white line appear brighter due to the contrast in light. The top circle also has black in the inhibitory surround which causes the intersection to appear brighter. However, since there is less black in the top circle than the bottom, there is more emphasis on the brightness between intersections, causing the illusion of gray dots.  (Provided by: Wikimedia Commons. License: CC-BY-SA 4.0)

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Introduction to Sensation and Perception by Students of PSY 3031 and Edited by Dr. Cheryl Olman is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

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